Prof. Dr. Thomas Hobiger

Bibliography

Peer-reviewed papers

H. Gutsche, T. Hobiger, and S. Winkler, "Addressing Inaccurate Phase Center Offsets in Precise Orbit Determination for Agile Satellite Missions," NAVIGATION, vol. 71, iss. 4, pp. 1-22, 2024.

@ARTICLE{Gutsche24Nav, author={Gutsche, He and Hobiger, Thomas and Winkler, Stefan}, title = {Addressing Inaccurate Phase Center Offsets in Precise Orbit Determination for Agile Satellite Missions}, journal = {NAVIGATION}, year = {2024}, volume={71}, number={4}, pages={1-22}, abstract = {Incorrect offsets between a satellite’s center of mass and its global navigation satellite system antenna phase center pose challenges to the precise orbit determination (POD) of many current Earth observation missions. Based on hardware-in-the-loop simulations, this paper demonstrates the more adverse effects on agile satellites, which perform frequent attitude maneuvers around all spacecraft axes. However, findings obtained from an observability analysis and Monte Carlo simulations indicate that rapid attitude changes enable the direct estimation of otherwise unobservable offsets. Application to the POD of agile satellites leads to a consistent and significant performance improvement in the presence of incorrect phase center offsets. Directly estimated corrections for the phase center offset of Sentinel-6A, which performs slews on several occasions, are consistent with values obtained from other studies via independent methods. These results underscore the possibility of estimating the lever arm for both agile and non-agile satellites in dedicated calibration maneuvers.}, doi = {10.33012/navi.671}, url = {https://navi.ion.org/content/71/4/navi.671} }

bibtex
R. Wang, G. Marut, T. Hadas, and T. Hobiger, "Improving GNSS Meteorology by Fusing Measurements of Several Colocated Receivers on the Observation Level," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 17, pp. 7841-7851, 2024.

@ARTICLE{Wang24, author={Wang, Rui and Marut, Grzegorz and Hadas, Tomasz and Hobiger, Thomas}, title = {Improving GNSS Meteorology by Fusing Measurements of Several Colocated Receivers on the Observation Level}, journal = {IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing}, year = {2024}, volume={17}, number={}, pages={7841-7851}, abstract = {Zenith wet delay (ZWD) estimation is a key component for the global navigation satellite system (GNSS) meteorology. At present, the zenith hydrostatic delay can be computed with sufficient accuracy by means of empirical models, while the ZWD, which is induced by water vapor with the nature of highly spatio-temporal variability, is typically estimated as an unknown parameter in precise point positioning (PPP). Due to GNSS receiver noise and the system biases of GNSS receivers, the accuracy as well as the precision of ZWD estimates is limited. In this study, we propose a novel fusion model based on undifferenced GNSS pseudorange and carrier-phase observations for sites, which have several receivers connected to a single antenna or which are separated horizontally by only a few meters. By fusing GNSS measurements collected by multiple receivers on the observation level, our model can provide common ZWD estimates with a high temporal resolution, which can then be used for more accurate and reliable meteorologic applications on a local scale. According to results with simulated and real data, it is revealed that such combined ZWD estimates are superior to single receiver estimates in terms of precision and accuracy. On the other hand, it is confirmed that the estimation of a common ZWD parameter leads to an improvement in positioning accuracy and precision, especially in the vertical component.}, doi = {10.1109/JSTARS.2024.3381792}, url = {https://ieeexplore.ieee.org/abstract/document/10480123} }

bibtex
S. He, T. Hobiger, and D. Becker, "Improving PPP positioning and troposphere estimates using an azimuth-dependent weighting scheme," GPS Solutions, vol. 24, iss. 212, pp. 1-14, 2024.

@ARTICLE{He24GPSSol, author={He, Shengping and Hobiger, Thomas and Becker, Doris}, title = {Improving PPP positioning and troposphere estimates using an azimuth-dependent weighting scheme}, journal = {GPS Solutions }, year = {2024}, volume={24}, number={212}, pages={1-14}, abstract = {Asymmetric troposphere modeling is crucial in Precise Point Positioning (PPP). The functional model of the asymmetric troposphere has been thoroughly studied, while the stochastic model lacks discussion. Currently, there is no suitable stochastic model for asymmetric tropospheric conditions, potentially degrading the positioning accuracy and the reliability of Zenith Total/Wet Delay (ZTD/ZWD) estimates. This paper introduces an Azimuth-Dependent Weighting (ADW) scheme that utilizes information from asymmetric mapping functions to adaptively weight Global Navigation Satellite System (GNSS) observations affected by azimuth-dependent errors. The concept of ADW has been validated using Numerical Weather Prediction data and International GNSS Service data. The results indicate that ADW effectively improves the coordinate repeatability of the PPP solution by approximately 10% in the horizontal and 20% in the vertical direction. Additionally, ADW appears to be capable to improve the ZWD estimates during the PPP convergence period and yields smoother ZWD estimates. Consequently, it is recommended to adopt this new weighting scheme in PPP applications when an asymmetric mapping functions is employed.}, doi = {10.1007/s10291-024-01754-z}, url = {https://link.springer.com/article/10.1007/s10291-024-01754-z} }

bibtex
S. He, T. Hobiger, and D. Becker, "The B-spline mapping function (BMF): representing anisotropic troposphere delays by a single self-consistent functional model," Journal of Geodesy, vol. 98, iss. 6, pp. 1432-1394, 2024.

@ARTICLE{He24JoG, author={He, Shengping and Hobiger, Thomas and Becker, Doris}, title = {The B-spline mapping function (BMF): representing anisotropic troposphere delays by a single self-consistent functional model}, journal = {Journal of Geodesy}, year = {2024}, volume={98}, number={6}, pages={1432-1394}, abstract = {Troposphere’s asymmetry can introduce errors ranging from centimeters to decimeters at low elevation angles, which cannot be ignored in high-precision positioning technology and meteorological research. The traditional two-axis gradient model, which strongly relies on an open-sky environment of the receiver, exhibits misfits at low elevation angles due to their simplistic nature. In response, we propose a directional mapping function based on cyclic B-splines named B-spline mapping function (BMF). This model replaces the conventional approach, which is based on estimating Zenith Wet Delay and gradient parameters, by estimating only four parameters which enable a continuous characterization of the troposphere delay across any directions. A simulation test, based on a numerical weather model, was conducted to validate the superiority of cyclic B-spline functions in representing tropospheric asymmetry. Based on an extensive analysis, the performance of BMF was assessed within precise point positioning using data from 45 International GNSS Service stations across Europe and Africa. It is revealed that BMF improves the coordinate repeatability by approximately 10% horizontally and about 5% vertically. Such improvements are particularly pronounced under heavy rainfall conditions, where the improvement of 3-dimensional root mean square error reaches up to 13%}, doi = {10.1007/s00190-024-01864-z}, url = {https://doi.org/10.1007/s00190-024-01864-z} }

bibtex
R. Wang, D. Becker, and T. Hobiger, "Stochastic modeling with robust Kalman filter for real-time kinematic GPS single-frequency positioning," GPS Solutions, vol. 13, iss. 3, p. 153, 2023.

@ARTICLE{Wang23, author={Wang, Rui and Becker, Doris and Hobiger, Thomas}, title = {Stochastic modeling with robust {Kalman} filter for real-time kinematic {GPS} single-frequency positioning}, journal = {GPS Solutions}, year = {2023}, volume={13}, number={3}, pages={153}, abstract = {The centimeter-level positioning accuracy of real-time kinematic (RTK) depends on correctly resolving integer carrier-phase ambiguities. To improve the success rate of ambiguity resolution and obtain reliable positioning results, an enhanced Kalman filtering procedure has been developed. Based on a posteriori residuals of measurements and state predictions, the measurement noise variance–covariance matrix for double-differenced measurements is adaptively estimated, rather than approximated by an empirical function which uses satellite elevation angle as input. Since, in real-world situations, unexpected outliers and carrier-phase outages can degrade the filter performance, a stochastic model based on robust Kalman filtering is proposed, for which the double-differenced measurement noise variance–covariance matrix is computed empirically with a modified version of the IGG (Institute of Geodesy and Geophysics) III method in order to detect and identify outliers. The performance of the proposed method is assessed by two tests, one with simulated data and one with real data. In addition, the performance of F-ratio and W-ratio tests as proxies for the success of ambiguity fixing is investigated. Experimental results reveal that the proposed method can improve the reliability and robustness of relative kinematic positioning for simulation scenarios as well as in a real urban test.}, doi = {10.1007/s10291-023-01479-5}, url = {https://link.springer.com/10.1007/s10291-023-01479-5} }

bibtex
F. Nievinski, T. Hobiger, R. Haas, W. Liu, J. Strandberg, S. Tabibi, S. Vey, S. Williams, and J. Wickert, "SNR-based GNSS reflectometry for coastal sea-level altimetry – Results from the first IAG inter-comparison campaign," Journal of Geodesy, vol. 94, iss. 70, 2020.

@ARTICLE{JoG-Nievinski19, author = {Nievinski,Felipe and Hobiger,Thomas and Haas,R{\"u}diger and Liu,Wei and Strandberg,Joakim and Tabibi,Sajad and Vey,Sibylle and Williams,Simon and Wickert,Jens}, title = {SNR-based GNSS reflectometry for coastal sea-level altimetry – Results from the first IAG inter-comparison campaign}, journal = {Journal of Geodesy}, year = {2020}, volume={94}, number={70}, pages={}, abstract = {Ground-based Global Navigation Satellite System Reflectometry (GNSS-R) is quickly maturing as a viable alternative for operational coastal sea-level (SL) altimetry in a geocentric reference frame. SL has immense societal implications related to climate change, both in its mean and extreme values. Of particular interest is the exploitation of existing GNSS networks for reflectometry by means of signal-to-noise ratio (SNR) observables. We report results from the first inter-comparison campaign on SNR-based GNSS-R. The goal was to cross-validate retrieval solutions from independent research groups under comparable conditions. This action was an initiative of the International Association of Geodesy working group 4.3.9 (2015-2019 term). Data collected at the Onsala Space Observatory for a one-year period (2015-2016) were compared to a co-located tide gauge (TG). SNR data for the GPS L1-C/A signal were processed by four groups, in Sweden, Luxembourg/Brazil, Germany, and the UK. Semi-diurnal tidal constituents showed good agreement between TG and all GNSS-R groups. Diurnal and lower-frequency components were also well captured by all series. Most solutions exhibited spurious tones at integer fractions of the GPS satellite revisit period (one sidereal day). Band-pass filtering between 3- and 30-hours confirmed that the dominant tidal components were well captured by most GNSS-R solutions. The higher-frequency band (< 3 h) is poorly represented by GNSS-R. The most discrepant solution neglects a correction associated with the rate of change in sea level and satellite elevation. Overall there was excellent performance, with correlation coefficients exceeding 0.9 and RMSE at a few centimeters.}, doi = {}, url = {https://doi.org/10.1007/s00190-020-01387-3} }

bibtex
G. Klopotek, T. Hobiger, R. Haas, and T. Otsubo, "Geodetic VLBI for precise orbit determination of Earth satellites: a simulation study," Journal of Geodesy, vol. 91, iss. 52, 2020.

@ARTICLE{JoG-KLopotek20, author = {Klopotek,Grzegorz and Hobiger,Thomas and Haas,Ruediger and Otsubo,Toshimichi}, title = {Geodetic VLBI for precise orbit determination of Earth satellites: a simulation study}, journal = {Journal of Geodesy}, year = {2020}, volume={91}, number={52}, pages={}, abstract = {Recent efforts of tracking low Earth orbit and medium Earth orbit (MEO) satellites using geodetic very long baseline interferometry (VLBI) raise questions on the potential of this novel observation concept for space geodesy. Therefore, we carry out extensive Monte Carlo simulations in order to investigate the feasibility of geodetic VLBI for precise orbit determination (POD) of MEO satellites and assess the impact of quality and quantity of satellite observations on the derived geodetic parameters. The MEO satellites are represented in our study by LAGEOS-1/-2 and a set of Galileo satellites. The concept is studied on the basis of 3-day solutions in which satellite observations are included into real schedules of the continuous geodetic VLBI campaign 2017 (CONT17) as well as simulated schedules concerning the next-generation VLBI system, known as the VLBI Global Observing System (VGOS). Our results indicate that geodetic VLBI can perform on a comparable level as other space-geodetic techniques concerning POD of MEO satellites. For an assumed satellite observation precision better than 14.1 mm (47 ps), an average 3D orbit precision of 2.0 cm and 6.3 cm is found for schedules including LAGEOS-1/-2 and Galileo satellites, respectively. Moreover, geocenter offsets, which were so far out of scope for the geodetic VLBI analysis, are close to the detection limit for the simulations concerning VGOS observations of Galileo satellites, with the potential to further enhance the results. Concerning the estimated satellite orbits, VGOS leads to an average precision improvement of 80% with respect to legacy VLBI. In absolute terms and for satellite observation precision of 14.1 mm (47 ps), this corresponds to an average value of 17 mm and 7 mm concerning the 3D orbit scatter and precision of geocenter components, respectively. As shown in this study, a poor satellite geometry can degrade the derived Earth rotation parameters and VLBI station positions, compared to the quasar-only reference schedules. Therefore, careful scheduling of both quasar and satellite observations should be performed in order to fully benefit from this novel observation concept.}, doi = {10.1007/s00190-020-01381-9}, url = {https://doi.org/10.1007/s00190-020-01381-9} }

bibtex
T. Hadas, T. Hobiger, and P. Hordyniec, "Considering different recent advancements in GNSS on real-time zenith troposphere," GPS Solutions, vol. 24, iss. 4, 2020.

@ARTICLE{GPSSol-Hadas20, author = {Hadas,Tomasz and Hobiger,Thomas and Hordyniec, Pawel}, title = {Considering different recent advancements in GNSS on real-time zenith troposphere }, journal = {GPS Solutions}, year = {2020}, volume={24}, number={4}, pages={}, abstract = {Global navigation satellite system (GNSS) remote sensing of the troposphere, called GNSS meteorology, is already a well-established tool in post-processing applications. Real-time GNSS meteorology has been possible since 2013, when the International GNSS Service (IGS) established its real-time service. The reported accuracy of the real-time zenith total delay (ZTD) has not improved significantly over time and usually remains at the level of 5–18 mm, depending on the station and test period studied. Millimeter-level improvements are noticed due to GPS ambiguity resolution, gradient estimation, or multi-GNSS processing. However, neither are these achievements combined in a single processing strategy, nor is the impact of other processing parameters on ZTD accuracy analyzed. Therefore, we discuss these shortcomings in detail and present a comprehensive analysis of the sensitivity of real-time ZTD on processing parameters. First, we identify a so-called common strategy, which combines processing parameters that are identified to be the most popular among published papers on the topic. We question the popular elevation-dependent weighting function and introduce an alternative one. We investigate the impact of selected processing parameters, i.e., PPP functional model, GNSS selection and combination, inter-system weighting, elevation-dependent weighting function, and gradient estimation. We define an advanced strategy dedicated to real-time GNSS meteorology, which is superior to the common one. The a posteriori error of estimated ZTD is reduced by 41%. The accuracy of ZTD estimates with the proposed strategy is improved by 17% with respect to the IGS final products and varies over stations from 5.4 to 10.1 mm. Finally, we confirm the latitude dependency of ZTD accuracy, but also detect its seasonality.}, doi = {10.1007/s10291-020-01014-w}, url = {https://doi.org/10.1007/s10291-020-01014-w} }

bibtex
T. Hadas and T. Hobiger, "Benefits of using Galileo for Real-Time GNSS Meteorology," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2020.

@ARTICLE{JSTARS-Hadas20, author = {Hadas,Tomasz and Hobiger,Thomas}, title = {Benefits of using Galileo for Real-Time GNSS Meteorology}, journal = {IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing}, year = {2020}, volume={}, number={}, pages={}, abstract = {Remote sensing of water vapor using Global Navigation Satellite Systems (GNSS) is a well-established tool for weather and climate monitoring. Current challenges of GNSS meteorology are real-time performance and the inclusion of emerging GNSS, such as Galileo. We demonstrate that real-time GPS-only, Galileo-only and GPS+Galileo solutions are consistent among each other. However, our results show that Galileo-only solutions tend to underestimate Zenith Total Delay (ZTD) with respect to GPS. The Galileo-only real-time ZTD is less accurate as the one from GPS. The combination of both GNSS leads to a superior product. The daily solution availability increases by up to 50%, and the overall gain is 0.7% over entire year. The accuracy improves by 3.7% to 8.5% and uncertainty is reduced by a factor of 1.5 to 2. A combined GPS and Galileo solution suppresses artifacts in a real-time ZTD product which otherwise would be attributed to high frequencies orbital effects.}, doi = {10.1109/LGRS.2020.3007138.}, url = {https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=9141353} }

bibtex
D. Purnell, N. Gomez, N. H. Chan, J. Strandberg, D. M. Holland, and T. Hobiger, "Quantifying the Uncertainty in Ground-Based GNSS-Reflectometry Sea Level Measurements," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 13, pp. 4419-4428, 2020.

@ARTICLE{Purnell20, author={Purnell, David and Gomez, Natalya and Chan, Ngai Ham and Strandberg, Joakim and Holland, David M. and Hobiger, Thomas}, title = {Quantifying the Uncertainty in Ground-Based GNSS-Reflectometry Sea Level Measurements}, journal = {IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing}, year = {2020}, volume={13}, number={}, pages={4419-4428}, abstract = {Global Navigation Satellite System reflectometry (GNSS-R) tide gauges are a promising alternative to traditional tide gauges. However, the precision of GNSS-R sea-level measurements when compared to measurements from a colocated tide gauge is highly variable, with no clear indication of what causes the variability. Here, we present a modeling technique to estimate the precision of GNSS-R sea-level measurements that relies on creating and analyzing synthetic signal-to-noise-ratio (SNR) data. The modeled value obtained from the synthetic SNR data is compared to observed root mean square error between GNSS-R measurements and a colocated tide gauge at five sites and using two retrieval methods: spectral analysis and inverse modeling. We find that the inverse method is more precise than the spectral analysis method by up to 60% for individual measurements but the two methods perform similarly for daily and monthly means. We quantify the contribution of dominant effects to the variations in precision and find that noise is the dominant source of uncertainty for spectral analysis whereas the effect of the dynamic sea surface is the dominant source of uncertainty for the inverse method. Additionally, we test the sensitivity of sea-level measurements to the choice of elevation angle interval and find that the spectral analysis method is more sensitive to the choice of elevation angle interval than the inverse method due to the effect of noise, which is greater at larger elevation angle intervals. Conversely, the effect of tropospheric delay increases for lower elevation angle intervals but is generally a minor contribution.}, doi = {10.1109/JSTARS.2020.3010413}, url = {https://ieeexplore.ieee.org/abstract/document/9144372} }

bibtex
J. Strandberg, T. Hobiger, and R. Haas, "Real-time sea-level monitoring using Kalman filtering of GNSS-R data," GPS Solutions, vol. 23, iss. 61, p. 1, 2019.

@ARTICLE{GPSSol-Strandberg19, author = {Strandberg, Joakim and Hobiger, Thomas and Haas,R{\"u}diger}, title = {Real-time sea-level monitoring using Kalman filtering of GNSS-R data}, journal = {GPS Solutions}, year = {2019}, volume={23}, number={61}, pages={1}, abstract = {Current GNSS-R (GNSS reflectometry) techniques for sea surface measurements require data collection over longer periods, limiting their usability for real-time applications. In this work, we present a new, alternative GNSS-R approach based on the unscented Kalman filter and the so-called inverse modeling approach. The new method makes use of a mathematical description that relates SNR (signal-to-noise ratio) variations to multipath effects and uses a B-spline formalism to obtain time series of reflector height. The presented algorithm can provide results in real time with a precision that is significantly better than spectral inversion methods and almost comparable to results from inverse modeling in post-processing mode. To verify the performance, the method has been tested at station GTGU at the Onsala Space Observatory, Sweden, and at the station SPBY in Spring Bay, Australia. The RMS (root mean square) error with respect to nearby tide gauge data was found to be 2.0 cm at GTGU and 4.8 cm at SPBY when evaluating the output corresponding to real-time analysis. The method can also be applied in post-processing, resulting in RMS errors of 1.5 cm and 3.3 cm for GTGU and SPBY, respectively. Finally, based on SNR data from GTGU, it is also shown that the Kalman filter approach is able to detect the presence of sea ice with a higher temporal resolution than the previous methods and traditional remote sensing techniques which monitor ice in coastal regions.}, doi = {10.1007/s10291-019-0851-1}, url = {https://doi.org/10.1007/s10291-019-0851-1} }

bibtex
G. Klopotek, T. Hobiger, R. Haas, Z. Zhang, S. Han, A. Nothnagel, L. La Porta, F. Jaron, A. Neidhardt, and C. Plötz, "Position determination of the Chang’e 3 lander with geodetic VLBI," Earth, Planets and Space, vol. 71, iss. 1, p. 23, 2019.

@ARTICLE{EPS-Klopotek19, author = {Klopotek, Grzegorz and Hobiger, Thomas and Haas,R{\"u}diger and Zhang, Zhongkai and Han,Songtao and Nothnagel,Axel and La Porta, Laura and Jaron, Frederic and Neidhardt,Alexander and Pl{\"o}tz, Christian}, title = {Position determination of the Chang’e 3 lander with geodetic VLBI}, journal = {Earth, Planets and Space}, year = {2019}, volume={71}, number={1}, pages={23}, abstract = {We present results from the analysis of observations of the Chang'e 3 lander using geodetic Very Long Baseline Interferometry. The applied processing strategy as well as the limiting factors to our approach is discussed. We highlight the current precision of such observations and the accuracy of the estimated lunar-based parameters, i.e., the lunar lander's Moon-fixed coordinates. Our result for the position of the lander is {\$}{\$}44.1219{\{}3{\}}^{\backslash}circ {\backslash}hbox {\{}N{\}}{\$}{\$}44.12193∘N, {\$}{\$}-{\backslash}, 19.511{\{}59{\}}^{\backslash}circ {\backslash}hbox {\{}E{\}}{\$}{\$}-19.51159∘Eand {\$}{\$}-{\backslash}, 263{\{}7.3{\}}{\$}{\$}-2637.3 m, with horizontal position uncertainties on the lunar surface of 8.9 m and 4.5 m in latitude and longitude, respectively. This result is in good agreement with the position derived from images taken by the Narrow Angle Camera of the Lunar Reconnaissance Orbiter. Finally, we discuss potential improvements to our approach, which could be used to apply the presented concept to high-precision lunar positioning and studies of the Moon."}, doi = {10.1186/s40623-019-1001-2}, url = {https://doi.org/10.1186/s40623-019-1001-2} }

bibtex
G. Klopotek, T. Hobiger, and R. Haas, "Geodetic VLBI with an artificial radio source on the Moon – A simulation study," Journal of Geodesy, vol. 92, iss. 5, p. 457—469, 2018.

@ARTICLE{JOG-Klopotek17, author = {Klopotek, Grzegorz and Hobiger, Thomas and Haas,R{\"u}diger}, title = {Geodetic VLBI with an artificial radio source on the Moon - A simulation study}, journal = {Journal of Geodesy}, year = {2018}, volume={92}, number={5}, pages={457–-469}, abstract = {We perform extensive simulations in order to assess the accuracy with which the position of a radio transmitter on the surface of the Moon can be determined by geodetic VLBI. We study how the quality and quantity of geodetic VLBI observations influence these position estimates and investigate how observations of such near-field objects affect classical geodetic parameters like VLBI station coordinates and Earth rotation parameters. Our studies are based on today’s global geodetic VLBI schedules as well as on those designed for the next-generation geodetic VLBI system. We use Monte Carlo simulations including realistic stochastic models of troposphere, station clocks, and observational noise. Our results indicate that it is possible to position a radio transmitter on the Moon using today’s geodetic VLBI with a two-dimensional horizontal accuracy of better than one meter. Moreover, we show that the next-generation geodetic VLBI has the potential to improve the two-dimensional accuracy to better than 5 cm. Thus, our results lay the base for novel observing concepts to improve both lunar research and geodetic VLBI.}, doi = {10.1007/s00190-017-1072-4}, url = {https://doi.org/10.1007/s00190-017-1072-4} }

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R. Haas, T. Hobiger, S. Kurihara, and T. Hara, "Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14," Journal of Geodesy, vol. 91, iss. 7, pp. 831-837, 2017.

@ARTICLE{JOG-Haas16, author = {Haas, R{\"u}diger and Hobiger,Thomas and Kurihara,Shinobu and Hara,Tetsuya}, title = {Ultra-rapid earth rotation determination with VLBI during CONT11 and CONT14}, journal = {Journal of Geodesy}, year = {2017}, volume={91}, number={7}, pages={831--837}, abstract = {We present earth rotation results from the ultra-rapid operations during the continuous VLBI campaigns CONT11 and CONT14. The baseline Onsala–Tsukuba, i.e., using two out of the 13 and 17 stations contributing to CONT11 and CONT14, respectively, was used to derive UT1-UTC in ultra-rapid mode during the ongoing campaigns. The latency between a new observation and a new UT1-UTC result was less than 10 min for more than 95% of the observations. The accuracy of the derived ultra-rapid UT1-UTC results is approximately a factor of three worse than results from optimized one-baseline sessions and/or complete analysis of large VLBI networks. This is, however, due to that the one-baseline picked from the CONT campaigns is not optimized for earth rotation determination. Our results prove that the 24/7 operation mode planned for VGOS, the next-generation VLBI system, is possible already today. However, further improvements in data connectivity of stations and correlators as well in the automated analysis are necessary to realize the ambitious VGOS plans.}, doi = {10.1007/s00190-016-0974-x}, url = {http://link.springer.com/article/10.1007/s00190-016-0974-x} }

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N. Kareinen, G. Klopotek, T. Hobiger, and R. Haas, "Identifying optimal tag-along station locations for improving VLBI Intensive sessions," Earth, Planets and Space, vol. 69, iss. 16, pp. 1-9, 2017.

@ARTICLE{EPS-Kareinen17, author = {Kareinen, Niko and Klopotek,Grzegorz and Hobiger,Thomas and Haas,R{\"u}diger}, title = {Identifying optimal tag-along station locations for improving VLBI Intensive sessions}, journal = {Earth, Planets and Space}, year = {2017}, volume={69}, number={16}, pages={1--9}, abstract = {Very Long Baseline Interferometry (VLBI) is a unique space-geodetic technique capable of direct observation of the Earth's phase of rotation, namely Universal Time (UT1). The International VLBI Service for Geodesy and Astrometry(IVS) conducts daily 1-h Intensive VLBI sessions to determine rapid variations in the difference between UT1 and Coordinated Universal Time (UTC). The mainobjective of the Intensive sessions is to provide timely UT1-UTC estimates.These estimates are especially crucial for Global Navigation Satellite Systems (GNSS). The monitoring of rapid variations in Earth rotation also provide insight into various geophysical phenomena. There is an ongoing effort to improve the quality of the UT1-UTC estimates from single-baseline Intensive sessions to realise the expected accuracy and to bring them to a better agreement with the 24-hour VLBI sessions. In this paper, we investigate the possibility to improve the Intensives by including a third station in tag-along mode to these regularly observed sessions. The impact of the additional station is studied via extensive simulations using the c5++ analysis software. The location of the station is varied within a pre-determined grid. Based on actual Intensive session schedules a set of simulated observations are generated for the two original stations and each grid point. These simulated data are used to estimate UT1-UTC for every Intensive session scheduled during the year 2014 on the Kokee--Wettzell and Tsukuba-Wettzell baselines, with the addition of a third station. We find that in tag-along mode when a third station is added to the schedule we can identify areas where the UT1-UTC estimates are improved up to 67 % w.r.t. the original single-baseline network. There are multiple operational VLBI stations in these areas, which could with little effort be included in a tag-along mode to the currently scheduled Intensive sessions, thus providing the possibility to improve the UT1-UTC estimates by extending the observation network.}, doi = {10.1186/s40623-017-0601-y}, url = {http://earth-planets-space.springeropen.com/articles/10.1186/s40623-017-0601-y} }

bibtex
W. Liu, J. Beckheinrich, M. Semmling, M. Ramatschi, S. Vey, J. Wickert, T. Hobiger, and R. Haas, "Coastal Sea Level Measurements Based on GNSS-R Phase Altimetry: A case study at the Onsala Space Observatory, Sweden," IEEE Transactions on Geoscience and Remote Sensing, vol. 55, iss. 10, pp. 5625-5636, 2017.

@ARTICLE{TGRS-Liu17, author = {Liu, Wei and Beckheinrich,Jamila and Semmling,Maximilian and Ramatschi,Markus and Vey,Sibylle and Wickert,Jens and Hobiger,Thomas and Haas,R{\"u}diger}, title = {Coastal Sea Level Measurements Based on GNSS-R Phase Altimetry: A case study at the Onsala Space Observatory, Sweden}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, year = {2017}, volume={55}, number={10}, pages={5625--5636}, abstract = {The characterization of global mean sea level is important to predict floods and to quantify water resources for human use and irrigation, especially in coastal regions. Recently, the application of Global Navigation Satellite System Reflectometry (GNSS-R) for water level monitoring has been successfully demonstrated. This paper focuses on the retrieval of sea surface height within a field experiment, that was conducted at the Onsala Space Observatory (OSO) using the phase-based altimetry method. A continuous phase tracking algorithm, which relies on the GNSS amplitude and phase observations is proposed and works even under rough sea conditions at OSO’s coast. Factors, impacting the phase-based altimetry model, i.e. atmospheric propagation effects of the GNSS signals and influence of the GNSS-R observation instrument, are discussed. The relationship between the yield of coherent GNSS-R compared to the overall recorded events and the wind speed is investigated in detail. Ground-based sea level measurements from June 10 to July 3, 2015 demonstrate, that altimetric information about the reflecting water surface can be obtained with a Root Mean Square Error (RMSE) of 4.37 cm with respect to a reference tide gauge dataset. The sea surface changes, derived from our field experiment and the reference tide gauge, are highly correlated with a correlation coefficient of 0.93. The altimetric information can be retrieved even when the sea surface is very rough, corresponding to wind speeds up to 13 m/s. Moreover, the use of inexpensive conventional GNSS antennas shows that the system is useful for future large-scale sea level monitoring applications including numerous low-cost coastal ground stations.}, doi = {10.1109/TGRS.2017.2711012}, url = {https://doi.org/10.1109/TGRS.2017.2711012} }

bibtex
J. Strandberg, T. Hobiger, and R. Haas, "Coastal sea ice detection using ground-based GNSS-R," IEEE Geoscience and Remote Sensing Letters, vol. 14, iss. 9, pp. 1552-1556, 2017.

@ARTICLE{GRSL-Strandberg17, author = {Strandberg, Joakim and Hobiger, Thomas and Haas,R{\"u}diger}, title = {Coastal sea ice detection using ground-based GNSS-R}, journal = {IEEE Geoscience and Remote Sensing Letters}, year = {2017}, volume={14}, number={9}, pages={1552 -- 1556}, abstract = {Determination of sea ice extent is important both for climate modeling and transportation planning. Detection and monitoring of ice is often done by SAR imagery, but mostly without any ground truth. For the latter purpose, robust and continuously operating sensors are required. We demonstrate that signals recorded by ground-based GNSS receivers can detect coastal ice coverage on nearby water surfaces. Beside a description of the retrieval approach, we discuss why GNSS reflectometry is sensitive to the presence of sea ice. It is shown that during winter seasons with freezing periods, GNSS-R analysis of data recorded with a coastal GNSS installation clearly shows the occurrence of ice in the bay where this installation is located. Thus, coastal GNSS installations could be promising sources of ground truth for sea ice extent measurements.}, doi = {10.1109/LGRS.2017.2722041}, url = {http://ieeexplore.ieee.org/document/7993065/} }

bibtex
T. Otsubo, K. Matsuo, Y. Aoyama, K. Yamamoto, T. Hobiger, T. Kubo-oka, and M. Sekido, "Effective expansion of satellite laser ranging network to improve global geodetic parameters," Earth, Planets and Space, vol. 68, iss. 1, pp. 1-7, 2016.

@ARTICLE{EPS-Otsubo16, author = {Otsubo, Toshimichi and Matsuo, Koji and Aoyama, Yuichi and Yamamoto, Keiko and Hobiger, Thomas and Kubo-oka, Toshihiro and Sekido, Mamoru}, title = {Effective expansion of satellite laser ranging network to improve global geodetic parameters}, journal = {Earth, Planets and Space}, year = {2016}, volume={68}, number={1}, pages={1--7}, abstract = {The aim of this study is to find an effective way to expand the ground tracking network of satellite laser ranging on the assumption that a new station is added to the existing network. Realistic numbers of observations for a new station are numerically simulated, based on the actual data acquisition statistics of the existing stations. The estimated errors are compared between the cases with and without a new station after the covariance matrices are created from a simulation run that contains six-satellite-combined orbit determination. While a station placed in the southern hemisphere is found to be useful in general, it is revealed that the most effective place differs according to the geodetic parameter. The X and Y components of the geocenter and the sectoral terms of the Earth's gravity field are largely improved by a station in the polar regions. A middle latitude station best contributes to the tesseral gravity terms, and, to a lesser extent, a low latitude station best performs for the Z component of the geocenter and the zonal gravity terms.}, doi = {10.1186/s40623-016-0447-8}, url = {http://dx.doi.org/10.1186/s40623-016-0447-8} }

bibtex
T. Hobiger, R. Haas, and J. Löfgren, "Software defined radio direct correlation GNSS reflectometry by means of GLONASS," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, vol. 9, iss. 10, pp. 4834-4842, 2016.

@ARTICLE{JSTARS-Hobiger16, author = {Hobiger, Thomas and Haas,R{\"u}diger and L{\"o}fgren, Johan}, title = {Software defined radio direct correlation GNSS reflectometry by means of GLONASS}, journal = {IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing}, year = {2016}, volume={9}, number={10}, pages={4834--4842}, abstract = {Ground-based GNSS reflectometry systems can be realized by different means. The concept of correlation between direct and reflected GNSS signals is basically possible with all GNSS systems. However, using signals from the Russian GLONASS system simplifies the signal processing so that software defined radio components can be used at replace expensive hardware solutions. This paper discusses how such a solution, called GLONASS-R, can be realized by using entirely off-the-shelf components. Field tests with such a system demonstrate the capability to monitor sea surface heights with a precision of 3~cm or better even with a sampling rate of 1.5~Hz. The flexibility of a software defined radio and the simple concept of GLONASS-R allows to build such a system with low costs and adapt it to the needs of any ground-based GNSS-R problem.}, doi = {10.1109/JSTARS.2016.2529683}, url = {http://ieeexplore.ieee.org/document/7425137/} }

bibtex
N. Kareinen, T. Hobiger, and R. Haas, "Automated ambiguity estimation for VLBI Intensive sessions using L1-norm," Journal of Geodynamics, vol. 102, pp. 39-46, 2016.

@ARTICLE{JGD-Kareinen16, author = {Kareinen, Niko and Hobiger, Thomas and Haas,R{\"u}diger}, title = {Automated ambiguity estimation for VLBI Intensive sessions using L1-norm}, journal = {Journal of Geodynamics}, year = {2016}, volume={102}, pages={39--46}, abstract = {Very Long Baseline Interferometry (VLBI) is a space-geodetic technique that is uniquely capable of direct observation of the angle of the Earth's rotation about the Celestial Intermediate Pole (CIP) axis, namely UT1. The daily estimates of the difference between UT1 and Coordinated Universal Time (UTC) provided by the 1-hour long VLBI Intensive sessions are essential in providing timely UT1 estimates for satellite navigation systems and orbit determination. In order to produce timely UT1 estimates, efforts have been made to completely automate the analysis of VLBI Intensive sessions. This involves the automatic processing of X- and S-band group delays. These data contain an unknown number of integer ambiguities in the observed group delays. They are introduced as a side-effect of the bandwidth synthesis technique, which is used to combine correlator results from the narrow channels that span the individual bands. In an automated analysis with the c5++ software the standard approach in resolving the ambiguities is to perform a simplified parameter estimation using a least-squares adjustment (L2-norm minimisation). We implement L1-norm as an alternative estimation method in c5++. The implemented method is used to automatically estimate the ambiguities in VLBI Intensive sessions on the Kokee-Wettzell baseline. The results are compared to an analysis setup where the ambiguity estimation is computed using the L2-norm. For both methods three different weighting strategies for the ambiguity estimation are assessed. The results show that the L1-norm is better at automatically resolving the ambiguities than the L2-norm. The use of the L1-norm leads to a significantly higher number of good quality UT1-UTC estimates with each of the three weighting strategies. The increase in the number of sessions is approximately 5 % for each weighting strategy. This is accompanied by smaller post-fit residuals in the final UT1-UTC estimation step.}, doi = {10.1016/j.jog.2016.07.003}, url = {http://www.sciencedirect.com/science/article/pii/S0264370716300679} }

bibtex
J. Strandberg, T. Hobiger, and R. Haas, "Improving GNSS-R sea level determination through inverse modeling of SNR data," Radio Science, vol. 51, iss. 8, p. 1286—1296, 2016.

@ARTICLE{RS-Strandberg16, author = {Strandberg, Joakim and Hobiger, Thomas and Haas,R{\"u}diger}, title = {Improving GNSS-R sea level determination through inverse modeling of SNR data}, journal = {Radio Science}, year = {2016}, volume={51}, number={8}, pages={1286–-1296}, abstract = {This paper presents a new method for retrieving sea-surface heights from GNSS-R data by inverse modeling of SNR observations from a single geodetic receiver. The method relies on a B-spline representation of the temporal sea-level variations in order to account for its continuity. The corresponding B-spline coefficients are determined through a non-linear least-squares fit to the SNR data and a consistent choice of model parameters enables the combination of multiple GNSS in a single inversion process. This leads to a clear increase in precision of the sea-level retrievals which can be attributed to a better spatial and temporal sampling of the reflecting surface. Tests with data from two different coastal GNSS sites and comparison with co-located tide gauges show a significant increase in precision when compared to previously used methods, reaching standard deviations of 1.4 cm at Onsala, Sweden, and 3.1 cm at Spring Bay, Tasmania.}, doi = {10.1002/2016RS006057}, url = {http://onlinelibrary.wiley.com/doi/10.1002/2016RS006057/abstract} }

bibtex
N. Kareinen, T. Hobiger, and R. Haas, "Automated analysis of Kokee–Wettzell Intensive VLBI sessions – algorithms, results, and recommendations," Earth, Planets and Space, vol. 67, iss. 1, p. 181, 2015.

@ARTICLE{EPS-Kareinen15, author = {Kareinen, Niko and Hobiger, Thomas and Haas,R{\"u}diger}, title = {Automated analysis of Kokee–Wettzell Intensive VLBI sessions - algorithms, results, and recommendations}, journal = {Earth, Planets and Space}, year = {2015}, volume={67}, number={1}, pages={181}, abstract = {The time-dependent variations in the rotation and orientation of the Earth are represented by a set of Earth Orientation Parameters (EOP). Currently, Very Long Baseline Interferometry (VLBI) is the only technique able to measure all EOP simultaneously and to provide direct observation of universal time, usually expressed as UT1-UTC. To produce estimates for UT1-UTC on a daily basis, 1-h VLBI experiments involving two or three stations are organised by the International VLBI Service for Geodesy and Astrometry (IVS), the IVS Intensive (INT) series. There is an ongoing effort to minimise the turn-around time for the INT sessions in order to achieve near real-time and high quality UT1-UTC estimates. As a step further towards true fully automated real-time analysis of UT1-UTC, we carry out an extensive investigation with INT sessions on the Kokee-Wettzell baseline. Our analysis starts with the first versions of the observational files in S- and X-band and includes an automatic group delay ambiguity resolution and ionospheric calibration. Several different analysis strategies are investigated. In particular, we focus on the impact of external information, such as meteorological and cable delay data provided in the station log-files, and a priori EOP information. The latter is studied by extensive Monte Carlo simulations.Our main findings are that it is easily possible to analyse the INT sessions in a fully automated mode to provide UT1-UTC with very low latency. The information found in the station log-files is important for the accuracy of the UT1-UTC results, provided that the data in the station log-files are reliable. Furthermore, to guarantee UT1-UTC with an accuracy of less than 20 mus, it is necessary to use predicted a priori polar motion data in the analysis that are not older than 12 h.}, doi = {10.1186/s40623-015-0340-x}, url = {http://www.earth-planets-space.com/content/67/1/181} }

bibtex
T. Hobiger, C. Rieck, R. Haas, and Y. Koyama, "Combining GPS and VLBI for inter-continental frequency transfer," Metrologia, vol. 52, iss. 2, pp. 251-261, 2015.

@ARTICLE{MET-HOBIGER15, author = {Hobiger, Thomas and Rieck,Carsten and Haas,R{\"u}diger and Koyama,Yasuhiro}, title = {Combining GPS and VLBI for inter-continental frequency transfer}, journal = {Metrologia}, year = {2015}, volume={52}, number={2}, pages={251--261}, abstract = {For decades the Global Positioning System (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past Very Long Baseline Interferometry (VLBI) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining GPS and VLBI on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses, both with individual software packages and with the multi-technique software c5++. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 1e-14 to 1e-15 (MDEV) on inter-continental baselines for averaging times of one day. Then we use the c5++ software for a combined analysis of GPS and VLBI data on the observation level. We demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10~\%, in particular for averaging periods longer than 3000 s.}, doi = {10.1088/0026-1394/52/2/251} }

bibtex
T. Hobiger and T. Otsubo, "Combination of GPS and VLBI on the observation level during CONT11 – common parameters, ties and inter-technique biases," Journal of Geodesy, vol. 88, iss. 11, pp. 1017-1028, 2014.

@ARTICLE{JOG-HOBIGER14, author = {Hobiger, Thomas and Otsubo, Toshimichi}, title = {Combination of GPS and VLBI on the observation level during CONT11 - common parameters, ties and inter-technique biases}, journal = {Journal of Geodesy}, year = {2014}, volume={88}, number={11}, pages={1017--1028}, abstract = {Multi-technique space geodetic analysis software has been developed which allows to combine data on the observation level. In addition to local tie information, site-wise common parameters, i.e. troposphere and clocks, can be estimated with this software. Thus, it will be discussed how common parameters have to be estimated and where biases/offsets need to be taken into account. In order to test such a novel concept, Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) data from the CONT11 campaign are being utilized. Since the VLBI baselines of this campaign extend over several thousands of kilometers, GPS data is processed in precise point positioning (PPP) mode and satellite orbits and clocks are kept fixed to the IGS final products. From the obtained results it can be shown that the combination of space geodetic data on the observation level leads to a consistent improvement of station position repeatability as well as nuisance parameters like troposphere estimates. Furthermore, estimation of common parameters (troposphere or clocks) at co-located sites helps to improve the solution further and derive an utmost physically consistent model of the concerned parameters.}, doi = {10.1007/s00190-014-0740-x} }

bibtex
T. Hobiger, R. Haas, and J. Löfgren, "GLONASS-R: GNSS reflectometry with a Frequency Division Multiple Access-based satellite navigation system," Radio Science, vol. 49, iss. 4, pp. 271-282, 2014.

@ARTICLE{RS-HOBIGER14, author = {Hobiger, Thomas and Haas,R{\"u}diger and L{\"o}fgren, Johan}, title = {GLONASS-R: GNSS reflectometry with a Frequency Division Multiple Access-based satellite navigation system}, journal = {Radio Science}, year = {2014}, volume={49}, number={4}, pages={271-282}, abstract = {The information from reflected Global Navigation Satellite System (GNSS) signals can become a valuable data source, from which geophysical properties can be deduced. This approach, called GNSS Reflectometry (GNSS-R), can be used to develop instruments that act like an altimeter when arrival times of direct and reflected signals are compared. Current GNSS-R systems usually entirely rely on signals from the Global Positioning Service (GPS), and field experiments could demonstrate that information from such systems can measure sea level with an accuracy of a few centimeters. However, the usage of the Russian GLONASS system has the potential to simplify the processing scheme and to allow handling of direct and reflected signals like a bistatic radar. Thus, such a system has been developed and deployed for test purposes at the Onsala Space Observatory, Sweden, that has an operational GPS-based GNSS-R system. Over a period of 2 weeks in October 2013, GPS-based GNSS-R sea level monitoring and measurements with the newly developed GLONASS-R system were carried out in parallel. In addition, data from colocated tide gauge measurements were available for comparison. It can be shown that precision and accuracy of the GLONASS-based GNSS-R system is comparable to, or even better than, conventional GPS-based GNSS-R solutions. Moreover, the simplicity of the newly developed GLONASS-R system allows to make it a cheap and valuable tool for various remote sensing applications.}, doi = {10.1002/2013RS005359} }

bibtex
T. Hobiger, T. Otsubo, and M. Sekido, "Observation Level Combination of SLR and VLBI with c5++: a case study for TIGO," Advances in Space Research, vol. 53, iss. 1, pp. 119-129, 2014.

@ARTICLE{JASR-HOBIGER14, author = {Hobiger, Thomas and Otsubo, Toshimichi and Sekido,Mamoru}, title = {Observation Level Combination of SLR and VLBI with c5++: a case study for TIGO}, journal = {Advances in Space Research}, year = {2014}, volume={53}, number={1}, pages={119-129}, abstract = {A multi-technique space geodetic analysis software named c5++ has been developed and allows one to combine data on the observation level. With SLR and VLBI modules being ready and tested, this software has been used to compute coordinate time series of the geodetic fundamental station TIGO, located near Concepción, Chile. It can be shown that the combination of space geodetic data on the observation level leads to a significant improvement of station position repeatability, which is an important measure for the stability of a station in the terrestrial reference frame. Moreover, it could be demonstrated that the geophysical signal of the post-seismic tectonic plate movement is usually more complete than detected by any of the two single-technique solutions. In addition, it has been confirmed that so-called nuisance parameters, which are relying on data from a single technique, are not biased when combing observations from different space geodetic techniques.}, doi = {10.1016/j.asr.2013.10.004} }

bibtex
T. Gotoh, T. Hobiger, J. Amagai, and H. Li, "Development of a Software Based GPS Time Transfer Receiver (in Japanese)," 電子情報通信学会論文誌 B, vol. J97-B, iss. 4, pp. 363-370, 2014.

@ARTICLE{IEICE-GOTOH14, author = {Gotoh, Tadahiro and Hobiger, Thomas and Amagai,Jun and Li, Huan-Bang}, title = {Development of a Software Based GPS Time Transfer Receiver (in Japanese)}, journal = {電子情報通信学会論文誌 B}, year = {2014}, volume={J97-B}, number={4}, pages={363-370}, abstract = {GPSやGlonassなどに代表される衛星測位システムは，国際原子時決定の手段としても重要な役割を担っている．しかし，市販の受信機の多くは測量目的のため，時刻比較に使用できる受信機の種類は限られており，価格も測量のみを目的としたものに比べると高価である．筆者らは，汎用のA/D変換器とソフトウェア無線技術を使用することで，時刻比較目的に使用できるGPS受信機の開発を行った．開発した受信機は，新しい測距信号であるL2C信号を受信することで電離層の影響を相殺した高精度な時刻比較を可能とする．ソフトウェア受信機と市販受信機の組合せによる，国内基線での時刻比較結果では10-13乗台の比較が行えることを実証した．また，衛星双方向方式との比較により2 ns以内の一致を得た．}, url = {http://search.ieice.org/bin/pdf_link.php?category=B&lang=J&year=2014&fname=j97-b_4_363&abst=} }

bibtex
T. Hobiger, D. Piester, and P. Baron, "A correction model of dispersive troposphere delays for the ACES microwave link," Radio Science, vol. 48, iss. 2, pp. 131-142, 2013.

@ARTICLE{RS-HOBIGER13, author = {Hobiger, Thomas and Piester,Dirk and Baron, Phillipe}, title = {A correction model of dispersive troposphere delays for the ACES microwave link}, journal = {Radio Science}, year = {2013}, volume={48}, number={2}, pages={131-142}, abstract = {The Atomic Clock Ensemble in Space (ACES) will be a future ESA experiment which utilizes ultra-stable clocks on-board the International Space Station (ISS). This mission is expected to perform tests of fundamental physics (relativity, possible drift of fundamental constants with time) and at the same time allows to compare the ACES time reference with respect to ground stations by using a novel microwave link concept. However, uncorrected dispersive troposphere delays pose the risk of degrading the performance of this microwave link over longer integration periods. Thus, a semi-empirical correction model has been developed which is only based on input from meteorologic sensors at the ground stations. The proposed model has been tested with simulated ISS overflights at different potential ACES ground station sites and it could be demonstrated that this model is capable to remove biases and elevation dependent features caused by the dispersive troposphere delay difference between the up-link and down-link. The model performs well at all sites by reducing the impact on all reasonable averaging time scales by at least one order of magnitude. Similar studies like this might be of importance for other time and frequency transfer instruments or future space geodetic instruments.}, doi = {10.1002/rds.20016} }

bibtex
K. Teke, T. Nilsson, J. Boehm, T. Hobiger, P. Steigenberger, S. Garcia-Espada, R. Haas, and P. Willis, "Troposphere delays from space geodetic techniques, water vapor radiometers, and numerical weather models over a series of continuous VLBI campaigns," Journal of Geodesy, vol. 87, iss. 10-12, pp. 981-1001, 2013.

@ARTICLE{JOG-TEKE13, author = {Teke,Kamil and Nilsson,Tobias and Boehm,Johannes and Hobiger,Thomas and Steigenberger,Peter and Garcia-Espada,Susana and Haas,R{\"u}diger and Willis,Pascal}, title = {Troposphere delays from space geodetic techniques, water vapor radiometers, and numerical weather models over a series of continuous VLBI campaigns}, journal = {Journal of Geodesy}, year = {2013}, volume={87}, number={10-12}, pages={981-1001}, abstract = {Continuous VLBI (Very Long Baseline Interferometry) campaigns over two weeks have been carried out repeatedly, i.e. CONT02 in October 2002, CONT05 in September 2005, CONT08 in August 2008, and CONT11 in September 2011, to demonstrate the highest accuracy the current VLBI is capable at that time. In this study, we have compared zenith total delays (ZTD) and troposphere gradients as consistently estimated from the observations of VLBI, Global Navigation Satellite Systems (GNSS), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) at VLBI sites participating in the CONT campaigns. We analyzed the CONT campaigns using the state of the art software following common processing strategies as closely as possible. In parallel, ZTD and gradients were derived from numerical weather models, i.e. from the global European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields, the High Resolution Limited Area Model (HIRLAM, European sites), the Japan Meteorological Agency (JMA) - Operational Meso-Analysis Field (MANAL, over Japan), and the Cloud Resolving Storm Simulator (CReSS, Tsukuba, Japan). Finally, zenith wet delays were estimated from the observations of water vapor radiometers (WVR) at sites where the WVR observables are available during the CONT sessions. The best ZTD agreement, interpreted as the smallest standard deviation, was found between GNSS and VLBI techniques being about 5 to 6 millimeters at most of the co-located sites and CONT campaigns. We did not detect any significant improvement on the ZTD agreement between various techniques over time, except for DORIS and MANAL. On the other hand, the agreement and thus the accuracy of the troposphere parameters mainly depend on the amount of humidity in the atmosphere.}, doi = {10.1007/s00190-013-0662-z} }

bibtex
Y. Kinoshita, M. Furuya, T. Hobiger, and R. Ichikawa, "Are numerical weather model outputs helpful to reduce tropospheric delay signals in InSAR data?," Journal of Geodesy, vol. 87, iss. 3, pp. 267-277, 2013.

@ARTICLE{JOG-Kinoshita13, author = {Kinoshita,Youhei and Furuya,Masato and Hobiger, Thomas and Ichikawa,Ryuichi}, title = {Are numerical weather model outputs helpful to reduce tropospheric delay signals in InSAR data?}, journal = {Journal of Geodesy}, year = {2013}, volume={87}, number={3}, pages={267-277}, abstract = {Interferometric Synthetic Aperture Radar (InSAR) phase data include not only signals due to crustal movements but also those associated with microwave propagation delay through the atmosphere. In particular, the effect of water vapor can generate apparent signals on the order of a few centimeters or more, and prevent us from detecting such geophysical signals as those due to secular crustal deformation. In order to examine if and to what extent numerical weather model (NWM) outputs are helpful to reduce the tropospheric delay signals at spatial scales of 5 to 50 km wavelengths, we compared three approaches of tropospheric signal reduction, using 54 interferograms in central Hokkaido, Japan. The first approach is the conventional topography-correlated delay correction that is based on the regional digital elevation model (DEM). The second approach is based on the Japan Meteorological Agency's operational meso-scale analysis model (MSM) data, where we compute tropospheric delays and subtract them from the interferogram. However, the MSM data are available at predefined epochs, and their spatial resolution is about 10 km, and therefore we need to interpolate both temporally and spatially to match with interferograms. Expecting to obtain a more physically plausible reduction of the tropospheric effects, we ran a 1-km mesh high-resolution numerical weather model WRF (Weather Research and Forecasting model) by ourselves, using the MSM data as the initial and boundary conditions. The third approach is similar to the second approach except that we make use of the WRF-based tropospheric data. } }

bibtex
T. Hobiger, Y. Takahashi, M. Nakamura, T. Gotoh, S. Hama, T. Maruyama, T. Nagatsuma, H. Noda, M. Kishimoto, M. Nakayama, and Y. Ohki, "Dissemination of UTC(NICT) by means of QZSS," IEEE Transactions on Instrumentation and Measurement, vol. 62, iss. 2, pp. 1537-1544, 2013.

@ARTICLE{IEEE-TIM13, author = {Hobiger, Thomas and Takahashi,Yasuhiro and Nakamura,Maho and Gotoh,Tadahiro and Hama,Shinichi and Maruyama,Takashi and Nagatsuma,Tsutomu and Noda,Hiroyuki and Kishimoto,Motohisa and Nakayama,Motohisa and Ohki,Yasuhiro}, title = {Dissemination of UTC(NICT) by means of QZSS}, journal = {IEEE Transactions on Instrumentation and Measurement}, year = {2013}, volume={62}, number={2}, pages={1537-1544}, abstract = {The Japanese Quasi-Zenith Satellite System (QZSS) offers the possibility to transmit information with an unprecedented bit rate of 2000 bps via the L-band experimental (LEX) signal. This feature can be used to disseminate Japan Standard Time, i.e. UTC(NICT) to any user capable of receiving the new QZSS signal. Various timing transmission modes as well as a dedicated ionosphere correction model allow users to instantaneously realize UTC(NICT) across Japan with an uncertainty of a few ns. However, a sophisticated real-time ionosphere correction model also needs to be transmitted to the user to compensate for dispersive ionosphere delays which are the largest contributor to the total error budget of the system.}, doi = {10.1109/TIM.2012.2225920 } }

bibtex
V. Nafisi, L. Urquhart, M. Santos, F. Nievinski, J. Boehm, D. Wijaya, H. Schuh, A. Ardalan, T. Hobiger, R. Ichikawa, F. Zus, J. Wickert, and P. Gegout, "Comparison of ray-tracing packages for troposphere delays," IEEE Transactions on Geoscience and Remote Sensing, vol. 50, iss. 2, pp. 469-481, 2012.

@ARTICLE{IEEE2012, author = {Nafisi, Vahab and Urquhart, Landon and Santos, Marcelo and Nievinski, Felipe and Boehm, Johannes and Wijaya, Dudy and Schuh, Harald and Ardalan, Alireza and Hobiger, Thomas and Ichikawa, Ryuichi and Zus, Florian and Wickert, Jens and Gegout, Pascal}, title = {Comparison of ray-tracing packages for troposphere delays}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, year = {2012}, volume = {50}, pages = {469-481}, number = {2}, abstract = {A comparison campaign to evaluate and compare troposphere delays from different ray-tracing software was carried out under the umbrella of the International Association of Geodesy (IAG) Working Group 4.3.3 in the first half of 2010 with five institutions participating: the German Research Centre for Geosciences (GFZ), the Groupe de Recherche de Geodesie Spatiale (GRGS), the National Institute of Information and Communication Technology (NICT), the University of New Brunswick (UNB), and the Institute of Geodesy and Geophysics (IGG) of the Vienna University of Technology. High-resolution data from the operational analysis of the European Centre for Medium-Range Weather Forecasts (ECMWF) was provided to the participants of the comparison campaign for the stations Tsukuba (Japan) and Wettzell (Germany). The data consisted of geopotential differences with respect to mean sea level, temperature, and specific humidity, all at isobaric levels. Additionally, information about the geoid undulations was provided and the participants computed the ray-traced total delays for 5o elevation angle and every degree in azimuth. In general, we find good agreement, with standard deviations and biases at the 1 cm level (or significantly better for some combinations) between the ray-traced slant factors from the different solutions at 5 degrees elevation if determined from the same pressure level data of the ECMWF. Some of these discrepancies are due to differences in the algorithms and the interpolation approaches. If compared to slant factors determined from ECMWF native model level data, the biases can be significantly larger, and when employing different atmospheric models provided by different weather agencies, discrepancies as large as 20 cm show up, indicating the accuracy that could be expected for ray-traced delays.}, doi = {doi:10.1109/TGRS.2011.2160952}, domains = {troposphere} }

bibtex
W. Tseng, Y. Huang, T. Gotoh, J. Amagai, T. Hobiger, M. Fujieda, S. Lin, H. Lin, and K. Feng, "First International TWSTFT Experiment by Employing Dual Pseudo-random Noise Codes," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 59, iss. 3, pp. 531-538, 2012.

@ARTICLE{Tseng2012, author = {Wen-Hung Tseng and Yi-Jiun Huang and Tadahiro Gotoh and Jun Amagai and Thomas Hobiger and Miho Fujieda and Shinn-Yan Lin and Huang-Tien Lin and Kai-Ming Feng}, title = {First International TWSTFT Experiment by Employing Dual Pseudo-random Noise Codes}, journal = {IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control}, year = {2012}, volume={59}, number={3}, pages={531 -538}, abstract = {Two-way satellite time and frequency transfer (TWSTFT) is one of the major techniques to compare atomic time scales over long distances. In order to both improve the precision of TWSTFT and decrease the satellite link fee, a new software-defined modem with dual pseudo-random noise (DPN) codes has been developed. In this paper, we demonstrate the first international DPN-based TWSTFT experiment over a period of 6 months. The results of DPN exhibit an excellent performance, which is competitive with the GPS precise point positioning (PPP) technique in the short term and consistent with the conventional TWSTFT in the long term. The time deviations of below 75 ps are achieved for averaging times from 1 s to 1 day. Moreover, the DPN data has less diurnal variations than that of the conventional TWSTFT. Since the DPN-based system has advantages of higher precision and lower bandwidth cost, it is one of the most promising methods to improve the international time transfer links.}, doi={10.1109/TUFFC.2012.2224} }

bibtex
T. Hobiger, J. Amagai, M. Aida, and H. Narita, "A real-time GNSS-R system based on software-defined radio and graphics processing units," Advances in Space Research, vol. 49, iss. 7, pp. 1180-1190, 2012.

@ARTICLE{ASR-Hobiger2012, author = {Hobiger, Thomas and Amagai, Jun and Aida,Masanori and Narita, Hideki}, title = {A real-time GNSS-R system based on software-defined radio and graphics processing units}, journal = {Advances in Space Research}, year = {2012}, volume={49}, number={7}, pages={1180-1190}, abstract = {Reflected signals of the Global Navigation Satellite System (GNSS) from the sea or land surface can be utilized to deduce and monitor physical and geophysical parameters of the reflecting area. Unlike most other remote sensing techniques, GNSS-Reflectometry (GNSS-R) operates as a passive radar that takes advantage from the increasing number of navigation satellites that broadcast their L-band signals. Thereby, most of the GNSS-R receiver architectures are based on dedicated hardware solutions. Software-defined radio (SDR) technology has advanced in the recent years and enabled signal processing in real-time, which makes it an ideal candidate for the realization of a flexible GNSS-R system. Additionally, modern commodity graphic cards, which offer massive parallel computing performances, allow to handle the whole signal processing chain without interfering with the PC’s CPU. Thus, this paper describes a GNSS-R system which has been developed on the principles of software-defined radio supported by General Purpose Graphics Processing Units (GPGPUs), and presents results from initial field tests which confirm the anticipated capability of the system.}, doi = {10.1016/j.asr.2012.01.009} }

bibtex
T. Hobiger, "宇宙測地技術における大気電波伝播遅延の高精度補正," 測地学会誌, vol. 58, iss. 1, pp. 1-8, 2012.

@ARTICLE{JGS2012, author = {Hobiger, Thomas }, title = {宇宙測地技術における大気電波伝播遅延の高精度補正}, journal = {測地学会誌}, year = {2012}, volume={58}, number={1}, pages={1-8}, abstract = {The atmospheric excess path delay is a major contributor to the error budget of space geodetic applications and should therefore be reduced to the maximum possible extent. Numerical weather models are undergoing improvements with regard to their spatial resolution, which enables compensation of troposphere propagation errors by applying corrections obtained from ray-tracing through three-dimensional meteorologic fields. Such correction can be applied utilized for GNSS positioning, removal of troposphere artifacts in InSAR images or even help to improve Earth orientation parameters determined from VLBI measurements.}, url = {https://www.jstage.jst.go.jp/browse/sokuchi/-char/ja/} }

bibtex
T. Gotoh, J. Amagai, T. Hobiger, M. Fujieda, and M. Aida, "Development of a GPU-Based Two-Way Time Transfer Modem," IEEE Transactions on Instrumentation and Measurement, vol. 60, iss. 7, pp. 2495-2499, 2011.

@ARTICLE{IEEEIM11, author = {Gotoh, Tadahiro and Amagai, Jun and Hobiger, Thomas and Fujieda, Miho and Aida, Masanori}, title = {Development of a GPU-Based Two-Way Time Transfer Modem}, journal = {IEEE Transactions on Instrumentation and Measurement}, year = {2011}, volume = {60}, pages = {2495-2499}, number = {7}, abstract = {We have developed a new two-way time transfer modem to improve the time transfer precision of remote clock comparison. As a timing signal, we apply a binary offset carrier, which is similar to those signals used for the next-generation Global Navigation Satellite Systems. We took advantage of versatile A/D and D/A converters, and most of the digital signal processing stages were realized by software, running on an off-the-shelf PC. This enabled us to realize the complete system with cheaper equipment, leading to an affordable low-cost modem. For the real-time digital signal processing stages implemented in software, we relied on a graphics processing unit (GPU) developed for computer game enthusiast. The developed modem can receive four channels at the same time with a single GPU card. We performed two-way satellite time transfer experiments using these modems between Japan and Taiwan. The obtained results are consistent within 200 ps with respect to the results of GPS carrier phase time transfer. As a consequence, we improved the time transfer precision by nearly one order of magnitude as compared to a conventional two-way modem without increasing the connection fees caused by commercial communication satellites.}, doi = {10.1109/TIM.2010.2091313}, domains = {time transfer} }

bibtex
K. Teke, J. Boehm, T. Nilsson, H. Schuh, P. Steigenberger, R. Dach, R. Heinkelmann, P. Willis, R. Haas, S. Garcia-Espada, T. Hobiger, R. Ichikawa, and S. Shimizu, "Multi-technique comparison of troposphere zenith delays and gradients during CONT08," Journal of Geodesy, vol. 85, iss. 7, pp. 395-413, 2011.

@ARTICLE{JOG2011, author = {Teke, Kamil and Boehm, Johannes and Nilsson, Tobias and Schuh, Harald and Steigenberger, Peter and Dach, Rolf and Heinkelmann, Robert and Willis, Pascal and Haas, R{\"u}diger and Garcia-Espada, Susana and Hobiger, Thomas and Ichikawa, Ryuichi and Shimizu, Shingo}, title = {Multi-technique comparison of troposphere zenith delays and gradients during CONT08}, journal = {Journal of Geodesy}, year = {2011}, volume = {85}, pages = {395-413}, number = {7}, abstract = {CONT08 was a 15 days campaign of continuous Very Long Baseline Interferometry (VLBI) sessions during the second half of August 2008 carried out by the International VLBI Service for Geodesy and Astrometry (IVS). In this study, VLBI estimates of troposphere zenith total delays (ZTD) and gradients during CONT08 were compared with those derived from observations with the Global Positioning System (GPS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and water vapor radiometers (WVR) co-located with the VLBI radio telescopes. Similar geophysical models were used for the analysis of the space geodetic data, whereas the parameterization for the least-squares adjustment of the space geodetic techniques was optimized for each technique. In addition to space geodetic techniques and WVR, ZTD and gradients from numerical weather models (NWM) were used from the European Centre for Medium-Range Weather Forecasts (ECMWF) (all sites), the Japan Meteorological Agency (JMA) and Cloud Resolving Storm Simulator (CReSS) (Tsukuba), and the High Resolution Limited Area Model (HIRLAM) (European sites). Biases, standard deviations, and correlation coefficients were computed between the troposphere estimates of the various techniques for all eleven CONT08 co-located sites. ZTD from space geodetic techniques generally agree at the sub-centimetre level during CONT08, and—as expected—the best agreement is found for intra-technique comparisons: between the Vienna VLBI Software and the combined IVS solutions as well as between the Center for Orbit Determination (CODE) solution and an IGS PPP time series; both intra-technique comparisons are with standard deviations of about 3–6 mm. The best inter space geodetic technique agreement of ZTD during CONT08 is found between the combined IVS and the IGS solutions with a mean standard deviation of about 6 mm over all sites, whereas the agreement with numerical weather models is between 6 and 20 mm. The standard deviations are generally larger at low latitude sites because of higher humidity, and the latter is also the reason why the standard deviations are larger at northern hemisphere stations during CONT08 in comparison to CONT02 which was observed in October 2002. The assessment of the troposphere gradients from the different techniques is not as clear because of different time intervals, different estimation properties, or different observables. However, the best inter-technique agreement is found between the IVS combined gradients and the GPS solutions with standard deviations between 0.2 and 0.7 mm.}, doi = {doi:10.1007/s00190-010-0434-y}, domains = {VLBI:troposphere}, issn = {0949-7714} }

bibtex
T. Hobiger, T. Otsubo, M. Sekido, T. Gotoh, T. Kubooka, and H. Takiguchi, "Fully automated VLBI analysis with c5++ for ultra-rapid determination of UT1," Earth Planets Space, vol. 45, iss. 2, pp. 75-79, 2010.

@ARTICLE{EPS10, author = {Hobiger, Thomas and Otsubo, Toshimichi and Sekido, Mamoru and Gotoh, Tadahiro and Kubooka, Toshihiro and Takiguchi, Hiroshi}, title = {Fully automated VLBI analysis with c5++ for ultra-rapid determination of UT1}, journal = {Earth Planets Space}, year = {2010}, volume = {45}, pages = {75-79}, number = {2}, abstract = {VLBI is the only space-geodetic technique which gives direct access to the Earth's phase of rotation, i.e. universal time UT1. Beside multi-baseline sessions, regular single baseline VLBI experiments are scheduled in order to provide estimates of UT1 for the international space community. Although the turn-around time of such sessions is usually much shorter and results are available within one day after the data were recorded, lower latency of UT1 results is still requested. Based on the experience gained over the last two years, an automated analysis procedure was established. The main goal was to realize fully unattended operation and robust estimation of UT1. Our new analysis software, named c5++, is capable of interfacing directly with the correlator output, carry out all processing stages without human interaction and provide the results for the scientific community or dedicated space applications. Moreover, the concept of ultra-rapid VLBI sessions can be extended to include further well-distributed stations, in order to obtain the polar motion parameters with the same latency and provide an up-to-date complete set of Earth orientation parameters for navigation of space and satellite missions.}, domains = {VLBI, c5++}, url = {http://www.terrapub.co.jp/journals/EPS/abstract/6212/62120933.html} }

bibtex
R. Haas, M. Sekido, T. Hobiger, T. Kondo, S. Kurihara, D. Tanimoto, K. Kokado, J. Wagner, J. Ritakari, and M. A., "Ultra-Rapid dUT1-Observations with e-VLBI," Artificial Satellites, vol. 45, iss. 2, pp. 75-79, 2010.

@ARTICLE{AI10, author = {Haas, R{\"u}diger and Sekido, Mamoru and Hobiger, Thomas and Kondo, Tetsuro and Kurihara, Shinobu and Tanimoto, D. and Kokado, Kensuke and Wagner, Jan and Ritakari, J. and Mujunen A.}, title = {Ultra-Rapid dUT1-Observations with e-VLBI}, journal = {Artificial Satellites}, year = {2010}, volume = {45}, pages = {75-79}, number = {2}, abstract = {We give a short overview about the achievements of the Fennoscandian-Japanese ultra-rapid dUT1-project that was initiated in early 2007. The combination of real-time data transfer, near real-time data conversion and correlation, together with near-real time data analysis allows to determine dUT1 with a very low latency of less than 5 minutes after the end of a VLBI-session. The accuracy of these ultra-rapid dUT1-results is on the same order than the results of the standard rapid-service of the International Earth Rotation and Reference Frame Service (IERS). The ultra-rapid approach is currently extended to 24 hour sessions and is expected to become an important contribution for the future next generation VLBI system called VLBI2010.}, doi = {10.2478/v10018-010-0007-6}, domains = {VLBI} }

bibtex
J. Boehm, T. Hobiger, R. Ichikawa, T. Kondo, Y. Koyama, A. Pany, H. Schuh, and K. Teke, "Asymmetric tropospheric delays from numerical weather models for UT1 determination from VLBI Intensive sessions on the baseline Wettzell-Tsukuba," Journal of Geodesy, vol. 84, iss. 5, pp. 319-325, 2010.

@ARTICLE{JOG10a, author = {Boehm, Johannes and Hobiger, Thomas and Ichikawa, Ryuichi and Kondo, Tetsuro and Koyama, Yasuhiro and Pany, Andrea and Schuh, Harald and Teke, Kamil}, title = {Asymmetric tropospheric delays from numerical weather models for UT1 determination from VLBI Intensive sessions on the baseline Wettzell-Tsukuba}, journal = {Journal of Geodesy}, year = {2010}, volume = {84}, pages = {319-325}, number = {5}, abstract = {One-baseline 1-h Very Long Baseline Interferometry (VLBI) Intensive sessions are carried out every day to determine Universal Time (UT1). Azimuthal asymmetry of tropospheric delays around the stations is usually ignored and not estimated because of the small number of observations. In this study we use external information about the asymmetry for the Intensive sessions between Tsukuba (Japan) and Wettzell (Germany), which are carried out on Saturdays and Sundays (1) from direct ray-tracing for each observation at Tsukuba and (2) in the form of linear horizontal north and east gradients every 6 h at both stations. The change of the UT1 estimates is at the 10 mu s level with maximum differences of up to 50 mu s, which is clearly above the formal uncertainties of the UT1 estimates (between 5 and 20 mu s). Spectral analysis reveals that delays from direct ray-tracing for the station Tsukuba add significant power at short periods (1-2 weeks) w.r.t. the state-of-the-art approach, and comparisons with length-of-day (LOD) estimates from Global Positioning System (GPS) indicate that these ray-traced delays slightly improve the UT1 estimates from Intensive sessions.}, doi = {doi:10.1007/s00190-010-0370-x}, domains = {VLBI, troposphere} }

bibtex
T. Hobiger, T. Gotoh, J. Amagai, Y. Koyama, and T. Kondo, "A GPU based real-time GPS software receiver," GPS Solutions, vol. 14, iss. 2, pp. 207-216, 2010.

@ARTICLE{GPSSOL10, author = {Hobiger, Thomas and Gotoh, Tadahiro and Amagai, Jun and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {A GPU based real-time GPS software receiver }, journal = {GPS Solutions}, year = {2010}, volume = {14}, pages = {207-216}, number = {2}, abstract = {Off-the-shelf graphics processing units provide low-cost massive parallel computing performance, which can be utilized for the implementation of a GPS software receiver. In order to realize a real-time capable system the crucial stages of the receiver should be optimized to suit the requirements of a parallel processor. Moreover, the receiver should be capable to provide wider correlation functions and provide easy access to the spectral domain of the signals. Thus, the most suitable correlation algorithm, which forms the core part of each receivers should be chosen and implemented on the graphics processor. Since the sampling rate of the received signal limits the real-time capabilities of the software radio it is necessary to determine an optimum value, considering that the precision of the observable varies with sampling bandwidth. We are going to discuss details and present our single frequency multi-channel implementation, which is capable of operating in real-time mode. Our implementation differs from other solutions by the wideness of the correlation function and allows simple handling of data in the spectral domain. Comparison with output from a commercial hardware receiver, which shares the antenna with the software radio, confirms the consistency and accuracy of our development.}, doi = {10.1007/s10291-009-0135-2}, domains = {GPS, GPU} }

bibtex
T. Hobiger, S. Shimada, S. Shimizu, R. Ichikawa, Y. Koyama, and T. Kondo, "Improving GPS positioning estimates during extreme weather situations by the help of fine-mesh numerical weather models," Journal of Atmospheric and Solar-Terrestrial Physics, vol. 72, iss. 2-3, pp. 262-270, 2010.

@ARTICLE{JASTP10, author = {Hobiger, Thomas and Shimada, Seiji and Shimizu, Shingo and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Improving GPS positioning estimates during extreme weather situations by the help of fine-mesh numerical weather models }, journal = {Journal of Atmospheric and Solar-Terrestrial Physics}, year = {2010}, volume = {72}, pages = {262-270}, number = {2-3}, abstract = {Space geodetic applications require to model troposphere delays as good as possible in order to achieve highly accurate positioning estimates. However, these models are not capable to consider complex refractivity fields which are likely to occur during extreme weather situations like typhoons, storms, heavy rain-fall, etc. Thus it has been investigated how positioning results can be improved if information from numerical weather models is taken into account. It will be demonstrated that positioning errors can be significantly reduced by the usage of ray-traced slant delays. Therefore, meso-scale and fine-mesh numerical weather models are utilized and their impact on the positioning results will be measured. The approach has been evaluated during a typhoon passage using global positioning service (GPS) observations of 72 receivers located around Tokyo, proving the usefulness of ray-traced slant delays for positioning applications. Thereby, it is possible reduce virtual station movements as well as improve station height repeatabilities by up to 30% w.r.t. standard processing techniques. Additionally the advantages and caveats of numerical weather models will be discussed and it will be shown how fine-mesh numerical weather models, which are restricted in their spatial extent, have to be handled in order to provide useful corrections.}, doi = {doi:10.1016/j.jastp.2009.11.018}, domains = {GPS, troposphere} }

bibtex
T. Hobiger, Y. Kinoshita, S. Shimizu, R. Ichikawa, M. Furuya, T. Kondo, and Y. Koyama, "On the importance of accurately ray-traced troposphere corrections for Interferometric SAR data," Journal of Geodesy, vol. 84, iss. 9, pp. 537-546, 2010.

@ARTICLE{JOG10b, author = {Hobiger, Thomas and Kinoshita, Youhei and Shimizu, Shingo and Ichikawa, Ryuichi and Furuya, Masato and Kondo, Tetsuro and Koyama, Yasuhiro}, title = {On the importance of accurately ray-traced troposphere corrections for Interferometric SAR data }, journal = {Journal of Geodesy}, year = {2010}, volume = {84}, pages = {537-546}, number = {9}, abstract = {Numerical weather models offer the possibility to compute corrections for a variety of space geodetic applications, including remote sensing techniques like interferometric SAR. Due to the computational complexity, exact ray-tracing is avoided in many cases and mapping approaches are applied to transform vertically integrated delay corrections into slant direction. Such an approach works well as long as lateral atmospheric gradients are small enough to be neglected. But since such an approximation holds only for very rare cases it is investigated how horizontal gradients of different atmospheric constituents can evoke errors caused by the mapping strategy. Moreover, it is discussed how sudden changes of wet refractivity can easily lead to millimeter order biases when simplified methods are applied instead of ray-tracing. By an example, based on real InSAR data, the differences of the various troposphere correction schemes are evaluated and it is shown how the interpretation of the geophysical signals can be affected. In addition, it is studied to which extend troposphere noise can be reduced by applying the exact ray-tracing solution.}, doi = {doi:10.1007/s00190-010-0393-3}, domains = {SAR, troposphere} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Computation of Troposphere Slant Delays on a GPU," IEEE Transactions on Geoscience and Remote Sensing, vol. 47, iss. 10, pp. 3313-3318, 2009.

@ARTICLE{IEEE2009, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Computation of Troposphere Slant Delays on a GPU}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, year = {2009}, volume = {47}, pages = {3313-3318 }, number = {10}, abstract = {The computation of ray-traced troposphere delays which can be utilized for space geodetic applications is a time-consuming effort when a large number of rays has to be calculated. On the other hand, computation time can be tremendously reduced when algorithms are capable of supporting parallel processing architectures. Thus, by the use of an off-the-shelf graphics processing unit (GPU), it is demonstrated that troposphere slant delays can be computed very efficiently, without loss of accuracy. An adopted ray-tracing algorithm is presented, and results from GPU computations are compared with those obtained from calculations on a standard personal computer's CPU.}, doi = {doi:10.1109/TGRS.2009.2022168}, domains = {GPU, GPS, troposphere} }

bibtex
T. Hobiger, M. Sekido, Y. Koyama, and T. Kondo, "Integer phase ambiguity estimation in next-generation geodetic Very Long Baseline Interferometry," Advances in Space Research, vol. 43, iss. 1, pp. 187-192, 2009.

@ARTICLE{JASR2009a, author = {Hobiger, Thomas and Sekido, Mamoru and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Integer phase ambiguity estimation in next-generation geodetic Very Long Baseline Interferometry}, journal = {Advances in Space Research}, year = {2009}, volume = {43}, pages = {187-192}, number = {1}, abstract = {Next-generation Very Long Baseline Interferometry (VLBI) system designs are aiming at 1 mm global position accuracy. In order to achieve this, it is not only necessary to deploy improved VLBI systems, but also to develop analysis strategies that take full advantage of the observations taken. Since the new systems are expected to incorporate four independent radio frequency bands, it should be feasible to resolve phase ambiguities directly from post-correlation data, providing roughly an order of magnitude improvement in precision of the delay observable. As the unknown ambiguities are of integer nature, it is discussed here how they the can be resolved analytically using algorithms which have been developed for Global Navigation Satellite System (GNSS) applications. Furthermore, it will be shown that ionosphere contribution and source structure effects, so-called core-shifts, can be solved simultaneously with the delay, which is the main geodetic observable for follow-on analysis. In order to verify the proposed algorithm, simulated observations were created using parameters from actual design studies. It is shown that, even in the case of low signal-to-noise ratio observations, reliable phase ambiguity resolution can be achieved and it is discussed how the integer ambiguity recovery depends on the number of observations and signal-to-noise ratio.}, doi = {doi:10.1016/j.asr.2008.06.004}, domains = {VLBI} }

bibtex
T. Kondo, T. Hobiger, M. Sekido, R. Ichikawa, Y. Koyama, and H. Takaba, "Estimation of scan-gap limits on phase delay connections in Delta VLBI observations based on the phase structure function at a short time period," Earth, Planets and Space, vol. 61, iss. 3, pp. 357-371, 2009.

@ARTICLE{EPS2009a, author = {Kondo, Tetsuro and Hobiger, Thomas and Sekido, Mamoru and Ichikawa, Ryuichi and Koyama, Yasuhiro and Takaba, Hiroshi}, title = {Estimation of scan-gap limits on phase delay connections in Delta VLBI observations based on the phase structure function at a short time period}, journal = {Earth, Planets and Space}, year = {2009}, volume = {61}, pages = {357-371}, number = {3}, abstract = {The maximum scan-gap length which connects phase delays from scan to scan over a gap is an important issue in Delta Very Long Baseline Interferometry (D-VLBI), and it is affected by delay fluctuations caused by the wet troposphere. It has recently become possible to obtain near real-time fringe phases by using an e-VLBI technique that realizes real-time VLBI by connecting stations through high-speed Internet. Such real-time VLBI raises the possibility of dynamic D-VLBI scheduling, which changes scan and gap length dynamically according to the weather condition of the date. We have investigated this possibility by using phase structure functions obtained from continuous VLBI observations at S- and X-bands for 1–2 h at the Kashima, Gifu, and Koganei stations (not real-time ones). Five VLBI sessions were conducted during this study between March and July 2006 under different weather conditions. At first a simple method was developed to evaluate phase connectivity from a phase structure function. A model was also proposed to estimate a phase-structure function at longer time periods from a short time period. Finally, an available gap length was estimated using the model. Our results show that it is possible to estimate an available scan gap length by using a structure function at a time period of 10 s. This suggests that it is possible to control scan length and gap length dynamically in order to achieve the best performance of D-VLBI observations.}, domains = {VLBI}, url = {http://www.terrapub.co.jp/journals/EPS/abstract/6102/61030357.html} }

bibtex
T. Hobiger, Y. Koyama, J. Boehm, T. Kondo, and R. Ichikawa, "The effect of neglecting VLBI reference station clock-offsets on UT1 estimates," Advances in Space Research, vol. 43, iss. 4, pp. 910-916, 2009.

@ARTICLE{JASR2009b, author = {Hobiger, Thomas and Koyama, Yasuhiro and Boehm,Johannes and Kondo, Tetsuro and Ichikawa, Ryuichi}, title = {The effect of neglecting VLBI reference station clock-offsets on UT1 estimates}, journal = {Advances in Space Research}, year = {2009}, volume = {43}, pages = {910-916}, number = {4}, abstract = {Very Long Baseline Interferometry (VLBI) allows to monitor universal time (UT1) by conducting regular international experiments. Such dedicated observation networks are equipped with different hardware components, which require different processing strategies when the data are correlated. As the timing units at each stations are usually offset with respect to universal time (UTC) this effect should be considered during correlation processing. Thus, it is investigated how neglecting of these offsets theoretically impacts the estimation of UT1. Three different strategies for the proper handling of the timing offset will be discussed and their advantages/drawbacks will be pointed out. Moreover, it is studied how neglecting of these timing offsets affects UT1 time-series and how such a missing correction can be applied a posteriori. Although the discussed effect is for most of the UT1 experiments smaller than the formal error of the estimates, it is important to consider station clock offsets properly in next-generation VLBI systems, which are expected to improve accuracy of results by about one order of magnitude.}, doi = {doi:10.1016/j.asr.2008.11.005}, domains = {VLBI} }

bibtex
R. Ichikawa, T. Hobiger, Y. Koyama, and T. Kondo, "An Evaluation of the Practicability of Current Mapping Functions Using Ray-traced Delays from JMA Mesoscale Numerical Weather Data," Proc. of the International Symposium on GPS/GNSS 2008 (peer-reviewed), iss. 1, pp. 5-12, 2008.

@ARTICLE{GNSS2008b, author = {Ichikawa, Ryuichi and Hobiger,Thomas and Koyama,Yasuhiro and Kondo, Tetsuro}, title = {An Evaluation of the Practicability of Current Mapping Functions Using Ray-traced Delays from JMA Mesoscale Numerical Weather Data}, journal = {Proc. of the International Symposium on GPS/GNSS 2008 (peer-reviewed)}, year = {2008}, pages = {5-12}, number = {1}, abstract = {We have developed a new tool to obtain atmospheric slant path delays by ray-tracing through the meso-scale analysis data for numerical weather prediction developed by Japan Meteorological Agency (JMA) with 10 km horizontal resolution (hereafter, we call this "JMA 10km MANAL data"). These data is operationally used for the purpose of weather forecast and considered for our study. We have created ray-tracing routines and named the tools "KAshima RAytracing Tools (KARAT)". We evaluated atmospheric parameters (equivalent zenith wet delay and linear horizontal delay gradients) derived from slant path delays using KARAT. We also estimate position changes caused by the horizontal variability of the atmosphere by running simulations using the ray-traced slant delays in order to examine the position error magnitude and its behavior under meso-scale atmospheric disturbances. Finally, we assessed empirical mapping functions, developed for use in space geodesy, by comparison with KARAT slant delays.}, domains = {GPS:troposphere} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Kashima Ray-tracing Service (KARATS) – On-line provision of total troposphere slant delay corrections for East Asian sites," Proc. of the International Symposium on GPS/GNSS 2008 (peer-reviewed), iss. 1, pp. 40-44, 2008.

@ARTICLE{GNSS2008a, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama,Yasuhiro and Kondo, Tetsuro}, title = {Kashima Ray-tracing Service (KARATS) - On-line provision of total troposphere slant delay corrections for East Asian sites}, journal = {Proc. of the International Symposium on GPS/GNSS 2008 (peer-reviewed)}, year = {2008}, pages = {40-44}, number = {1}, abstract = {Numerical weather models have undergone a significant improvement of accuracy and spatial resolution, which makes it feasible to utilize such models for the correction of troposphere excess path delays. In our presentation we will discuss results from our recent studies which confirm the benefit from the appliance of ray-traced data within geodetic analysis. Moreover, we present the Kashima Ray-Tracing Service (KARATS) which will allow the user to reduce atmospheric delays from the observations taken at stations across East Asia. We will discuss all aspects of this service which is expected to be operational at the beginning of November 2008.}, domains = {GPS:troposphere} }

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T. Hobiger, R. Ichikawa, T. Takasu, Y. Koyama, and T. Kondo, "Ray-traced troposphere slant delays for precise point positioning," Earth, Planets and Space, vol. 60, iss. 5, p. e1-e4, 2008.

@ARTICLE{EPSe2008, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Takasu, Tomoji and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Ray-traced troposphere slant delays for precise point positioning}, journal = {Earth, Planets and Space}, year = {2008}, volume = {60}, pages = {e1-e4}, number = {5}, abstract = {Precise satellite orbits and clock information for global navigation satellite systems (GNSS) allow zero-difference position solutions, also known as precise point positioning (PPP) to be calculated. In recent years numerical weather models (NWM) have undergone an improvement of spatial and temporal resolution. This makes them not only useful for the computation of mapping functions but also allows slant troposphere delays from ray-tracing to be obtained. For this study, such ray-traced troposphere corrections have been applied to code and phase observations of 13 sites from the International GNSS Service (IGS) receiver network, which are located inside the boundaries of the Japanese Meteorological Agency (JMA) meso-scale weather model, covering a period of 4 months. The results from this approach are presented together with a comparison to standard PPP processing results. Moreover the advantages and caveats of the introduction of ray-traced slant delays for precise point positioning are discussed.}, domains = {GPS:troposphere}, url = {http://www.terrapub.co.jp/journals/EPS/pdf/2008e/6005e001.pdf} }

bibtex
S. Todorova, T. Hobiger, and H. Schuh, "Using the Global Navigation Satellite System and satellite altimetry for combined Global Ionosphere Maps," Advances in Space Research, vol. 42, pp. 727-736, 2008.

@ARTICLE{JASR2008, author = {Todorova, Sonja and Hobiger, Thomas and Schuh, Harald}, title = {Using the Global Navigation Satellite System and satellite altimetry for combined Global Ionosphere Maps}, journal = {Advances in Space Research}, year = {2008}, volume = {42}, pages = {727-736}, abstract = {For deriving global maps of the Total Electron Content (TEC) from space geodetic techniques usually observations from the Global Navigation Satellite System (GNSS) are taken. However, the GNSS stations are inhomogeneously distributed, with large gaps particularly over the sea surface. Within this study we create Global Ionosphere Maps (GIM) from GNSS data and additionally introduce satellite altimetry observations, which help to compensate the insufficient GNSS coverage of the oceans. The obtained global maps are in 2 h intervals and daily values of Differential Code Biases (DCB) for all the GNSS satellites and receivers are also estimated. The combination of the data from around 160 GNSS stations and two satellite altimetry missions – Jason-1 and TOPEX/Poseidon – is performed on the normal equation level. The comparison between the integrated ionosphere models and the GNSS-only maps shows a higher accuracy of the combined GIM over the seas. The study aims at improved combined global TEC maps, which should make best use of the advantages of each particular type of data and have higher accuracy and reliability than the results derived by the two methods if treated individually.}, doi = {doi:10.1016/j.asr.2007.08.024}, domains = {GPS:ionosphere} }

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T. Hobiger, T. Kondo, and Y. Koyama, "Constrained simultaneous algebraic reconstruction technique (C-SART) – a new and simple algorithm applied to ionospheric tomography," Earth, Planets and Space, vol. 60, iss. 7, pp. 727-735, 2008.

@ARTICLE{EPS2008, author = {Hobiger, Thomas and Kondo, Tetsuro and Koyama, Yasuhiro}, title = {Constrained simultaneous algebraic reconstruction technique (C-SART) - a new and simple algorithm applied to ionospheric tomography}, journal = {Earth, Planets and Space}, year = {2008}, volume = {60}, pages = {727-735}, number = {7}, abstract = {A simple and relatively fast method (C-SART) is presented for tomographic reconstruction of the electron density distribution in the ionosphere using smooth fields. Since it does not use matrix algebra, it can be implemented in a low-level programming language, which speeds up applications significantly. Compared with traditional simultaneous algebraic reconstruction, this method facilitates both estimation of instrumental offsets and consideration of physical principles (expressed in the form of finite differences). Testing using a 2D scenario and an artificial data set showed that C-SART can be used for radio tomographic reconstruction of the electron density distribution in the ionosphere using data collected by global navigation satellite system ground receivers and low Earth orbiting satellites. Its convergence speed is significantly higher than that of classical SART, but it needs to be speeded up by a factor of 100 or more to enable it to be used for (near) real-time 3D tomographic reconstruction of the ionosphere.}, domains = {GPS:ionosphere}, url = {http://www.terrapub.co.jp/journals/EPS/abstract/6007/60070727.html} }

bibtex
T. Hobiger, R. Ichikawa, T. Kondo, and Y. Koyama, "Fast and accurate ray-tracing algorithms for real-time space geodetic applications using numerical weather models," Journal of Geophysical Research, vol. 113, iss. D203027, pp. 1-14, 2008.

@ARTICLE{JGR2008, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Kondo, Tetsuro and Koyama, Yasuhiro}, title = {Fast and accurate ray-tracing algorithms for real-time space geodetic applications using numerical weather models}, journal = {Journal of Geophysical Research}, year = {2008}, volume = {113}, pages = {1-14}, number = {D203027}, abstract = {The atmospheric excess path delay is a major contributor to the error budget of space geodetic positioning applications and should therefore be reduced to the maximum possible extent. Numerical weather models are undergoing improvements with regard to their spatial resolution, which enables the compensation of troposphere propagation errors by applying corrections obtained from ray-tracing through three-dimensional meteorologic fields. Since in the selection of the locations of the grid points priority is given to the requirements of meteorologists rather than the facilitation of efficient ray-tracing algorithms, we propose a method that can resample and refine the large data cubes onto regular grids using a sophisticated and fast method developed at the National Institute of Information and Communications Technology (NICT). Once these data sets are generated, ray-tracing algorithms can be applied in order to compute atmospheric excess path delays in real time for several users using off-the-shelf PCs. We present three different ray-tracing strategies and discuss their advantages and bottlenecks with regard to accuracy and data throughput.}, doi = {doi:10.1029/2008JD010503}, domains = {troposphere:GPS} }

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T. Hobiger, T. Kondo, Y. Koyama, K. Takashima, and H. Schuh, "Using VLBI fringe-phase information from geodetic experiments for short-period ionospheric studies," Journal of Geodesy, vol. 81, iss. 6, pp. 389-401, 2007.

@ARTICLE{JoG07, author = {Hobiger, Thomas and Kondo, Tetsuro and Koyama, Yasuhiro and Takashima, Kazuhiro and Schuh, Harald}, title = {Using VLBI fringe-phase information from geodetic experiments for short-period ionospheric studies}, journal = {Journal of Geodesy}, year = {2007}, volume = {81}, pages = {389--401}, number = {6}, note = {doi:10.1007/s00190-007-0142-4}, abstract = {The usage of Very Long Baseline Interferometry (VLBI) fringe-phase information in geodetic VLBI is a new field of research, which can be used for the detection of short-period (i.e., several minutes) variations (scintillations) of the ionosphere. This paper presents a method for the extraction of such disturbances and discusses how dispersive influences can be separated from intra-scan delay variations. A proper functional and stochastic model for the separation of the different effects is presented and the algorithms are applied to real measurements. In an example, it is shown that a traveling ionospheric disturbance in Antarctica can be detected very precisely. A possible physical origin and the propagation properties of the disturbance are presented and the results are compared with GPS measurements. The benefit of this method for other applications is also discussed.}, domains = {VLBI:ionosphere}, url = {http://www.springerlink.com/content/f42018r3r0rj0751} }

bibtex
T. Hobiger, T. Kondo, Y. Koyama, R. Ichikawa, and R. Weber, "Effect of the Earth’s oblateness on the estimation of global vertical total electron content maps," Geophys. Res. Lett., vol. 34, p. 11113, 2007.

@ARTICLE{GRL07, author = {Hobiger, Thomas and Kondo, Tetsuro and Koyama, Yasuhiro and Ichikawa,Ryuichi and Weber, Robert}, title = {Effect of the Earth's oblateness on the estimation of global vertical total electron content maps}, journal = {Geophys. Res. Lett.}, year = {2007}, volume = {34}, pages = {L11113}, abstract = {Global Navigation Satellite Systems like the Global Positioning System and the Russian counterpart GLONASS permit the estimation of ionosphere parameters in the form of vertical total electron content (vTEC) values. Although the GNSS reference systems are rotation-symmetric ellipsoids, simple approximations of gravitational equipotential surfaces, the modeling of global vTEC maps is carried out in spherical systems, since this simplifies mathematical expressions. Due to the Earth's oblateness this approximation is in slight disagreement to the geometric situation of the observations. Thus it is expected that estimated vTEC values will change when the WGS84 ellipsoid is taken as a reference for all computations. We will discuss both, the direct effect (i.e due to a shift of the ionospheric pierce point) and the indirect effect, caused by a change of the mapping function, on global vTEC values using a single layer model of the ionosphere. We show that the estimated global TEC maps change slightly by up to +/-0.4 TECU when refined mathematical models are considered and we discuss how differential code biases are affected by this change.}, doi = {doi:10.1029/2007GL029792}, domains = {GPS:ionosphere}, owner = {hobiger}, timestamp = {2008.05.06} }

bibtex
T. Hobiger, T. Kondo, and H. Schuh, "Very long baseline interferometry as a tool to probe the ionosphere," Radio Science, vol. 41, iss. 1, p. 1006, 2006.

@ARTICLE{RadioSci06, author = {Hobiger, Thomas and Kondo, Tetsuro and Schuh, Harald}, title = {Very long baseline interferometry as a tool to probe the ionosphere}, journal = {Radio Science}, year = {2006}, volume = {41}, pages = {RS1006}, number = {1}, note = {doi:10.1029/2005RS003297}, abstract = {In geodetic very long baseline interferometry (VLBI), the observations are performed at two distinct frequencies (2.3 and 8.4 GHz) in order to determine ionospheric delay corrections. This allows information to be obtained from the VLBI observables about the sum of electrons per area unit (total electron content) along the ray path through the ionosphere. Because of the fact that VLBI is a differential technique, the calculated ionospheric corrections depend on the differences of the propagation media over the stations. Additionally, an instrumental delay offset per station causes a bias of the ionospheric measurements. This paper presents a method to estimate ionospheric parameters, that is, values of vertical total electron content from VLBI data, and compares the outcomes to results from other space geodetic techniques. As VLBI observations cover more than two complete solar cycles, the relation to space weather indices on long-term timescales can be shown.}, domains = {VLBI:ionosphere}, url = {http://www.agu.org/pubs/crossref/2006.../2005RS003297.shtml} }

bibtex
P. J. Mendes Cerveira, T. Hobiger, R. Weber, and H. Schuh, "Spatial spectral inversion of SOPAC GPS data," Proceeding of the IAG Scientific Assembly 2005, vol. 130, pp. 194-201, 2006.

@ARTICLE{IAG06, author = {Mendes Cerveira, Paulo Jorge and Hobiger, Thomas and Weber, Robert and Schuh, Harald}, title = {Spatial spectral inversion of SOPAC GPS data}, journal = {Proceeding of the IAG Scientific Assembly 2005}, year = {2006}, volume = {130}, pages = {194 -- 201}, domain = {GPS}, publisher = {Springer} }

bibtex
M. Hawarey, T. Hobiger, and H. Schuh, "Effects of the 2nd order ionospheric terms on VLBI measurements," Geophys. Res. Lett, vol. 32, iss. 11, p. 11304, 2005.

@ARTICLE{GRL05, author = {Hawarey, Mosab and Hobiger, Thomas and Schuh, Harald}, title = {Effects of the 2nd order ionospheric terms on VLBI measurements}, journal = {Geophys. Res. Lett}, year = {2005}, volume = {32}, pages = {L11304}, number = {11}, note = {doi:10.1029/2005GL022729}, abstract = {Current VLBI software packages take into account ionospheric terms of 1st order only. This research investigates the effects of considering additionally the 2nd order terms on geodetic VLBI measurements. The mathematical algorithm follows the framework that has been presented for GPS in the literature. However, the approximation of the Earth's magnetic field and the assumption of a 400-km high ionospheric shell are avoided here by using the IGRF and PIM models to calculate the geomagnetic field vectors and electron densities at 100 representative points along the paths of incoming rays. The 2nd order effects are at the level of 10 pico seconds, which we introduced to the VLBI input files to determine the geodetic impact. Results of the VLBI software OCCAM reveal a maximum difference between baseline lengths with and without 2nd order ionospheric terms equivalent to 0.5 mm. Thus, the effect might become visible in VLBI within a few years.}, domains = {VLBI:ionosphere}, url = {http://www.agu.org/pubs/crossref/2005.../2005GL022729.shtml} }

bibtex
T. Hobiger, J. Boehm, and H. Schuh, "VLBIONOS – Probing the ionosphere by means of very long baseline interferometry," A Window on the Future of Geodesy, Proceedings of the IAG General Assembly, Sapporo, Japan, June 30 – July 11, 2003, vol. 128, pp. 131-136, 2005.

@ARTICLE{IAG05, author = {Hobiger, Thomas and Boehm, Johannes and Schuh, Harald}, title = {VLBIONOS - Probing the ionosphere by means of very long baseline interferometry}, journal = {A Window on the Future of Geodesy, Proceedings of the IAG General Assembly, Sapporo, Japan, June 30 - July 11, 2003}, year = {2005}, volume = {128}, pages = {131 -- 136}, domains = {VLBI:ionosphere}, editor = {F. Sanso}, publisher = {Springer} }

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Books and book chapters papers

M. Alizadeh, D. Wijaya, T. Hobiger, R. Weber, and H. Schuh, "Atmospheric Effects in Space Geodesy," , Boehm, J. and Schuh, H., Eds., Springer Berlin Heidelberg, 2013, pp. 35-71.

@INBOOK{Springer2013, author={Alizadeh, Mahdi and Wijaya, Dudy and Hobiger, Thomas and Weber, Robert and Schuh, Harald}, chapter={Ionospheric Effects on Microwave Signals}, title={Atmospheric Effects in Space Geodesy}, publisher={Springer Berlin Heidelberg}, editor={Boehm, Johannes and Schuh, Harald}, year={2013}, doi={10.1007/978-3-642-36932-2_2}, pages={35-71}, abstract={The ionosphere is a dispersive medium for space geodetic techniques operating in the microwave band. Thus, signals traveling through this medium are—to the first approximation—affected proportionally to the inverse of the square of their frequencies. This effect, on the other hand, can reveal information about the parameters of the ionosphere in terms of Total Electron Content (TEC) of the electron density. This part of the book provides an overview of ionospheric effects on microwave signals. First, the group and phase velocities are defined along with the refractive index in the ionosphere and the ionospheric delay. Then, we focus mainly on the mitigation and elimination of ionospheric delays in the analysis of space geodetic observations, specifically for Global Navigation Satellite Systems (GNSS) and Very Long Baseline Interferometry (VLBI) observations. In particular, we summarize existing models as well as strategies based on observations at two or more frequencies to eliminate first and higher order delays. Finally, we review various space geodetic techniques (including satellite altimetry and radio occultation data) for estimating values and maps of TEC.} }

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Other papers

M. B. Stucke, T. Hobiger, G. Moeller, K. Gutsche, and S. Winkler, "Multi-Receiver Precise Baseline Determination: Coupled Baseline an Attitude Estimation with a Low-Cost Off-The-Shelf GNSS Receiver," in Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023), 2023, pp. 3082-3095.

@INPROCEEDINGS{ION-Stucke23, author = {Stucke, Marvin Bayram and Hobiger, Thomas and Moeller, Gregor and Gutsche, Kevin and Winkler, Stefan}, title = {Multi-Receiver Precise Baseline Determination: Coupled Baseline an Attitude Estimation with a Low-Cost Off-The-Shelf GNSS Receiver}, booktitle = {Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023)}, year = {2023}, volume={}, number={}, pages={3082-3095}, abstract = {Satellite-based formation flying Earth observations are crucial for environmental monitoring and sustainable use of our Earth’s resources. One example is the German mission TanDEM-X, for which the twin satellites TerraSAR-X and TanDEM-X are working in unison to derive highly precise digital elevation models. To interpret the measurement data of such satellites correctly, the post-processing algorithms depend on precise millimeter-level knowledge of their relative position, known as their baseline. One technique for deriving estimates of the required precision is Precise Baseline Determination (PBD) based on measurements from Global Navigation Satellite Systems (GNSS). While the latest advancements in PBD are suitable for meeting the current precision requirements of non-agile missions, future Synthetic Aperture Radar (SAR) projects will require the same precision for agile mission profiles. Additionally, the PBD for agile missions depends on precise knowledge of the satellite’s attitude. Usually, the PBD and the attitude estimation are performed independently from each other. Whereas PBD utilizes GNSS observations with one receiver per spacecraft, the attitude is estimated via star trackers and inertial measurement units. This paper presents a novel approach of simultaneous GNSS-based baseline and attitude estimation, named Multi Receiver Precise Baseline Determination (MR-PBD). Two benefits are expected. Firstly, the achieved precision of the inter-spacecraft baseline estimate will improve, since multiple receivers are used per spacecraft. Secondly, the estimation delivers an additional attitude product, which can be used to improve the existing star-tracker-based attitude estimation. To validate the approach, the observations of a low-cost and low-power GNSS receiver (u-blox ZED-F9P) are utilized and plugged into a Spirent signal generator. By applying MR-PBD a baseline estimate was achieved that is 15% to 40% more precise than the single receiver PBD by utilizing 3 to 12 receivers per spacecraft.}, doi = {10.33012/2023.19469}, url = {https://www.ion.org/publications/abstract.cfm?articleID=19469} }

bibtex
K. Gutsche, T. Hobiger, and S. Winkler, "Addressing Inaccurate Phase Center Offsets in Precise Orbit Determination for Agile Satellite Missions," in Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023), 2023, pp. 3205-3216.

@INPROCEEDINGS{ION-Gutsche23, author = {Gutsche, Kevin and Hobiger, Thomas and Winkler, Stefan}, title = {Addressing Inaccurate Phase Center Offsets in Precise Orbit Determination for Agile Satellite Missions}, booktitle = {Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023)}, year = {2023}, volume={}, number={}, pages={3205-3216}, abstract = {Incorrect offsets between a satellite’s center of mass and the mean phase center of its GNSS antenna pose challenges to the Precise Orbit Determination of many current Earth Observation missions. While extensive efforts have been undertaken to identify and mitigate these errors, they have been based on satellites with slowly varying attitudes. The errors in the offsets, which primarily arise from inaccurate phase center offsets, can usually be derived when highly precise non-gravitational forces are employed. However, with the advent of agile missions, where the satellites perform frequent attitude maneuvers around all three degrees of freedom, inaccurate offsets might affect the POD differently, thereby warranting additional investigation. Based on hardware-in-the-loop simulations, this paper explores the effects of inaccurate offsets on the POD performance of agile satellites. The findings demonstrate that the impact of incorrect offsets is even more critical for these types of missions and the methodologies used for non-agile missions are not as easily applicable. An observability analysis shows that the lever arm, which is typically unobservable in the reduced-dynamic POD of non-agile satellites, becomes directly observable when the satellite performs rapid attitude maneuvers. This property is exploited within the agile POD, where these offsets are additionally estimated. The results demonstrate both a consistent and significant performance improvement in the POD in the presence of biases in the lever arm. These findings further hint at the feasibility of estimating the lever arm for both agile and non-agile satellites in dedicated calibration maneuvers, without the need to rely on highly precise non-gravitational force modeling. }, doi = {10.33012/2023.19258}, url = {https://www.ion.org/publications/abstract.cfm?articleID=19258} }

bibtex
K. Gutsche, T. Hobiger, S. Winkler, and B. Stucke, "PODCAST: Precise Orbit Determination Software for LEO Satellites," in Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), 2022, pp. 3707-3719.

@INPROCEEDINGS{ION-Gutsche22, author = {Gutsche, Kevin and Hobiger, Thomas and Winkler, Stefan and Stucke, Bayram}, title = {PODCAST: Precise Orbit Determination Software for LEO Satellites}, booktitle = {Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022)}, year = {2022}, volume={}, number={}, pages={3707-3719}, abstract = {Precise Orbit Determination (POD) and Precise Baseline Determination (PBD) are indispensable for many of today’s remote sensing satellite missions. With the advent of agile satellite missions, new solutions are needed to cope with frequently occurring maneuvers to fulfill the strict POD requirements imposed by scientific mission goals. The C++ software "Precise Orbit Determination for Complex and Agile Satellite Technology" (PODCAST) aims to create a flexible framework to investigate novel approaches related to POD and PBD of agile and non-agile satellites. PODCAST facilitates this by abiding by a modular concept for all core components needed for POD and thus ensures the complete interchangeability of algorithms and models in the development process. This study gives insights into the modular architecture of PODCAST and the underlying fundamental principles. The capabilities are demonstrated for a GNSS-based POD using simulated observations created for a Sentinel-3A reference trajectory. The obtained results indicate the accomplishable accuracy and precision for given measurement errors using the approaches presented in this work. We further showcase that PODCAST can serve as the foundation for future POD software development and suggest improvements that allow addressing of future mission-critical POD features.}, doi = {10.33012/2022.18485}, url = {https://www.ion.org/publications/abstract.cfm?articleID=18485} }

bibtex
T. Topp and T. Hobiger, "Flow-Based Programming for Real-Time Multi-Sensor Data Fusion," in Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022), 2022, pp. 2492-2502.

@INPROCEEDINGS{ION-Topp22, author = {Topp, Thomas and Hobiger, Thomas}, title = {Flow-Based Programming for Real-Time Multi-Sensor Data Fusion}, booktitle = {Proceedings of the 35th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2022)}, year = {2022}, volume={}, number={}, pages={2492-2502}, abstract = {Flow-based programming (FBP) splits software functionality into modules which are triggered by data elements flowing from one module to the next. Thus, modules, which are not directly dependent on data from each other, can run independently and applications can be parallelized on a basic level what is a major improvement for the performance of multi-sensor data fusion algorithms. This paper discusses the flow-based software INSTINCT, which is a solid framework for implementing PNT algorithms and helps to reduce development times by making algorithms reusable. It provides an intuitive graphical user interface (GUI) that makes it usable in research and teaching. Inside the software, a variety of file formats and sensors for IMU und GNSS data processing are implemented. The realization of an INS/GNSS loosely-coupled Kalman filter flow is discussed and the results are compared to a flow representing a single point positioning (SPP) solution. Finally, a performance study of the algorithm on a 4th generation Intel CPU is presented, demonstrating that real-time capabilities can be ensured even on older systems.}, doi = {10.33012/2022.18429}, url = {https://www.ion.org/publications/abstract.cfm?articleID=18429} }

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T. Hadas, M. Bender, G. Marut, and T. Hobiger, "Real-Time GNSS Meteorology in Europe – Hurricane Lorenzo Case Study," in 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS, 2021, pp. 8321-8323.

@INPROCEEDINGS{IEEE-Hadas21, author = {Hadas, Tomasz and Bender, Michael and Marut, Grzegorz and Hobiger, Thomas}, title = {Real-Time GNSS Meteorology in Europe - Hurricane Lorenzo Case Study}, booktitle = {2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS}, year = {2021}, volume={}, number={}, pages={8321-8323}, abstract = {Near real-time estimation of zenith total delays (ZTD) of Global Navigation Satellite Systems (GNSS) signals is operationally performed in Europe. We demonstrate that high accuracy ZTD can be provided even in real-time. Using a state-of-the-art processing strategy we estimate ZTD and horizontal gradients for 162 permanent stations in Europe over 100 days in 2019, covering the event of hurricane Lorenzo. The accuracy of real-time ZTD with respect to the final ZTD product varies from 3.3 to 10.4 mm. The accuracy of real-time ZTD with respect to the ICON numerical weather prediction model varies from 4 mm to 18 mm and we notice station-specific biases, reaching up to ±10 mm. We demonstrate that horizontal gradients show signatures under the severe weather during hurricane Lorenzo in 2019.}, doi = {10.1109/IGARSS47720.2021.9554690}, url = {https://ieeexplore.ieee.org/abstract/document/9554690} }

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T. Lambertus and T. Hobiger, "Single point positioning by means of particle filtering on the GPU," in 2019 European Navigation Conference (ENC), 2019, pp. 1-9.

@INPROCEEDINGS{IEEE-Lambertus19, author = {Lambertus,Tomke and Hobiger,Thomas}, title = {Single point positioning by means of particle filtering on the GPU}, booktitle = {2019 European Navigation Conference (ENC)}, year = {2019}, volume={}, number={}, pages={1-9}, abstract = {High demands on accuracy and reliability of real-time navigation and positioning applications require the exploitation of multiple sensors. However, in many cases, the relations between the state vector and the observation space are of non-linear mathematical nature or observations have stochastic properties which deviate from those of Gaussian normal distributions. Thus, the extended Kalman filter and its variants are not always the most suitable choice. For such problems a particle filter, or more generally, sequential Monte Carlo methods, can increase the reliability of the estimates. Since particle filters are well-suited for parallel data processing, it will be shown how single point positioning GNSS solutions can be obtained when using a graphics processing unit (GPU) as a massive parallel computing device. The implementation of this approach and evaluation of its performance concerning real-time capability will be discussed as well as its precision and accuracy compared to a standard Kalman filter solution.}, doi = {10.1109/EURONAV.2019.8714148}, url = {https://ieeexplore.ieee.org/abstract/document/8714148} }

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T. Hobiger and T. Otsubo, "Combination of space geodetic techniques on the observation level with c5++," in NICT IVS Technical Development Center News, 2013, pp. 29-32.

@INPROCEEDINGS{TDC13c, author = {Hobiger,Thomas and Otsubo,Toshimichi}, title = {Combination of space geodetic techniques on the observation level with c5++}, booktitle = {NICT IVS Technical Development Center News}, year = {2013}, number = {33}, pages = {29-32}, abstract = {Multi-technique space geodetic analysis software has been developed which allows to combine data on the observation level. This novel concept is being tested with SLR, GPS and VLBI data. Results show that the combination of space geodetic data on the observation level leads to a consistent improvement of station position repeatability, Earth orientation parameters, etc. Furthermore, estimation of common parameters (troposphere or clocks) at co-located sites helps to improve the solution further and derive an utmost physically consistent model of the concerned parameters.}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_33.pdf} }

bibtex
K. Takefuji, M. Sekido, H. Ujihara, M. Tsutsumi, S. Hasegawa, Y. Miyauchi, R. Ichikawa, Y. Koyama, and T. Kondo, "Toward a Precise Frequency Comparison with VLBI Technique," in NICT IVS Technical Development Center News, 2013, pp. 25-28.

@INPROCEEDINGS{TDC13b, author = {Takefuji,Kazuhiro and Sekido,Mamoru and Ujihara,Hideki and Tsutsumi,Masanori and Hasegawa,Shingo and Miyauchi,Yuka and Ichikawa,Ryuichi and Koyama,Yasuhiro and Kondo,Tetsuro}, title = {Toward a Precise Frequency Comparison with VLBI Technique}, booktitle = {NICT IVS Technical Development Center News}, year = {2013}, number = {33}, pages = {25-28}, abstract = {We have been studying a frequency comparison technique using VLBI between distant stations. There are three important issues in our precise frequency comparison project with VLBI, one is the use of a efficient antenna and broad band receiver to obtain a good signal to noise ratio (SNR), second is a highly stable and reliable signal transfer, third is solving time delay caused by the ionosphere and the atmosphere. These three issues should be solved for precise frequency comparison by using a VLBI technique. This report describes some experiments to tackle to these issues}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_33.pdf} }

bibtex
M. Sekido, K. Takefuji, H. Ujihara, T. Hobiger, M. Tsutsumi, S. Hasegawa, Y. Miyauchi, R. Ichikawa, Y. Koyama, and T. Kondo, "Development of Wide-band VLBI system (Gala-V)," in NICT IVS Technical Development Center News, 2013, pp. 11-14.

@INPROCEEDINGS{TDC13a, author = {Sekido, Mamoru and Takefuji,Kazuhiro and Ujihara,Hideki and Hobiger,Thomas and Tsutsumi,Masanori and Hasegawa,Shingo and Miyauchi,Yuka and Ichikawa,Ryuichi and Koyama,Yasuhiro and Kondo,Tetsuro}, title = {Development of Wide-band VLBI system (Gala-V)}, booktitle = {NICT IVS Technical Development Center News}, year = {2013}, number = {33}, pages = {11-14}, abstract = {The project mission of our group is realization of compact VLBI system for precise frequency comparison between distant atomic frequency standards. For this mission, development of a new wide-band VLBI observation system named Gala-V is in progress.}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_33.pdf} }

bibtex
T. Hobiger, M. Sekido, and R. Ichikawa, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2012 Annual Report, 2013, pp. 287-290.

@INPROCEEDINGS{IVSAR12, author = {Hobiger,Thomas and Sekido,Mamoru and Ichikawa,Ryuichi}, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2012 Annual Report}, year = {2013}, number = {NASA/TP-2013-217511}, pages = {287-290}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2012.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2012/pdf/acnict.pdf} }

bibtex
M. Nakamura, Y. Takahashi, J. Amagai, T. Gotoh, M. Fujieda, R. Tabuchi, T. Hobiger, S. Hama, Y. Yahagi, T. Takahashi, and S. Horiuchi, "Results of the Time Comparison Experiments Between the QZS-1 and Ground Time Management Station," in Proceedings of the 2012 International Technical Meeting of The Institute of Navigation, 2012, pp. 513-520.

@INPROCEEDINGS{nakamura2012, author = {Nakamura, M. and Takahashi, Y. and Amagai, J. and Gotoh, T. and Fujieda, M. and Tabuchi, R. and Hobiger, T. and Hama, S. and Yahagi, Y. and Takahashi, T. and Horiuchi, S.}, title = {Results of the Time Comparison Experiments Between the QZS-1 and Ground Time Management Station}, booktitle = {Proceedings of the 2012 International Technical Meeting of The Institute of Navigation}, year = {2012}, number = {}, pages = {513 - 520}, abstract = {}, url={http://www.ion.org/publications/abstract.cfm?articleID=9986} }

bibtex
R. Ichikawa, T. Hobiger, Y. Koyama, and T. Kondo, "Impact of Atmospheric Delay Reduction Using KARAT on GPS/PPP Analysis," in Geodesy for Planet Earth, 2012, pp. 781-787.

@INPROCEEDINGS{ichikawa2012, author={Ichikawa, Ryuichi and Hobiger, Thomas and Koyama, Yasuhiro and Kondo, Tetsuro}, title={Impact of Atmospheric Delay Reduction Using KARAT on GPS/PPP Analysis}, booktitle={Geodesy for Planet Earth}, year = {2012}, number = {136}, pages = {781-787}, abstract = {}, doi={10.1007/978-3-642-20338-1_98}, }

bibtex
T. Hobiger, R. Ichikawa, M. Sekido, Y. Koyama, and T. Kondo, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2011 Annual Report, 2012, pp. 238-241.

@INPROCEEDINGS{IVSAR11, author = {Hobiger,Thomas and Ichikawa,Ryuichi and Sekido,Mamoru and Koyama, Yasuhiro and Kondo,Tetsuro }, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2011 Annual Report}, year = {2012}, number = {NASA/TP-2012-217505}, pages = {238-241}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2011.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2011/pdf/acnict.pdf} }

bibtex
H. Takiguchi, M. Kimura, T. Kondo, T. Hobiger, A. Ishii, R. Ichikawa, Y. Koyama, Y. Takahashi, F. Nakagawa, M. Nakamura, R. Tabuchi, S. Tsutshiya, S. Hama, T. Gotoh, M. Fujieda, A. Masanori, T. Li, and J. Amagai, "Inter-comparison Study of Time and Frequency Transfer between VLBI and Other Techniques," in NICT IVS Technical Development Center News, 2011, pp. 32-37.

@INPROCEEDINGS{TDC11c, author = {Takiguchi,Hiroshi and Kimura, Moritaka and Kondo, Tetsuro and Hobiger,Thomas and Ishii, Atsutoshi and Ichikawa, Ryuichi and Koyama,Yasuhiro and Takahashi,Yasuhiro and Nakagawa,Fumimaru and Nakamura,Maho and Tabuchi,Ryo and Tsutshiya,Shigeru and Hama,Shinichi and Gotoh,Tadahiro and Fujieda,Miho and Aida Masanori and Li,Tingyu and Amagai,Jun}, title = {Inter-comparison Study of Time and Frequency Transfer between VLBI and Other Techniques}, booktitle = {NICT IVS Technical Development Center News}, year = {2011}, number = {32}, pages = {32-37}, abstract = {We carried out the intercomparison experiments between VLBI and other techniques to show the capability of VLBI time and frequency transfer by using the current geodetic VLBI technique and facilities as the summary of the experiments that we carried out since 2007. The results from the two different types of experiments show that the VLBI is more stable than GPS but is slightly noisier than two new two-way techniques (TW(DPN), ETS8(TCE)), and VLBI can measure the correct time difference as same as ETS8(TCE)}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_32.pdf} }

bibtex
T. Hobiger, J. Amagai, M. Aida, and T. Gotoh, "A GNSS-R system based on software-defined-radio," in NICT IVS Technical Development Center News, 2011, pp. 7-10.

@INPROCEEDINGS{TDC11b, author = {Hobiger, Thomas and Amagai, Jun and Aida, Masanori and Gotoh, Tadahiro}, title = {A GNSS-R system based on software-defined-radio}, booktitle = {NICT IVS Technical Development Center News}, year = {2011}, number = {32}, pages = {7-10}, abstract = {Multipath signals (e.g. ground reflections) for GNSS are phenomena which need to be avoided by all means to maintain a high positioning accuracy. On the other side, the remote sensing community has an increasing interest in analyzing such reflections as they provide valuable information about the physical characteristics of the reflection area. This technology is called GNSS-Reflectometry (GNSS-R) and operates, similar to a passive radar, with two antennas in order to monitor direct and reflected signals (see e.g. Gleason et al.(2005)). No commercial GNSS-R are available and most of the existing solution focus on hardware processors with a post-processing chain realized in software. This paper presents the GNSS-R system developed by NICT which utilized software defined radio methods to deal with most of the processing stages in software rather than utilizing ASIC or FPGA based hardware solutions}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_32.pdf} }

bibtex
T. Otsubo, T. Hobiger, T. Gotoh, T. Kubooka, M. Sekido, H. Takiguchi, and H. Takeuchi, "Software ”c5++” for Combined Space-Geodetic Analysis," in NICT IVS Technical Development Center News, 2011, pp. 5-6.

@INPROCEEDINGS{TDC11a, author = {Otsubo, Toshimichi and Hobiger, Thomas and Gotoh, Tadahiro and Kubooka, Toshihiro and Sekido, Mamoru and Takiguchi, Hiroshi and Takeuchi, Hiroshi}, title = {Software ”c5++” for Combined Space-Geodetic Analysis}, booktitle = {NICT IVS Technical Development Center News}, year = {2011}, number = {32}, pages = {5-6}, abstract = {}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_32.pdf} }

bibtex
T. Hobiger, H. Takiguchi, R. Ichikawa, M. Sekido, Y. Koyama, and T. Kondo, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2010 Annual Report, 2011, pp. 229-232.

@INPROCEEDINGS{IVSAR10, author = {Hobiger,Thomas and Takiguchi,Hiroshi and Ichikawa,Ryuichi and Sekido,Mamoru and Koyama, Yasuhiro and Kondo,Tetsuro }, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2010 Annual Report}, year = {2011}, number = {NASA/TP-2011-215880}, pages = {229-232}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2010.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2010/pdf/acnict.pdf} }

bibtex
T. Hobiger, H. Takiguchi, R. Ichikawa, M. Sekido, Y. Koyama, and T. Kondo, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2009 Annual Report, 2010, pp. 261-264.

@INPROCEEDINGS{IVSAR09, author = {Hobiger,Thomas and Takiguchi,Hiroshi and Ichikawa,Ryuichi and Sekido,Mamoru and Koyama, Yasuhiro and Kondo,Tetsuro }, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2009 Annual Report}, year = {2010}, number = {NASA/TP-2010-215860}, pages = {261-264}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2009.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2009/pdf/acnict.pdf} }

bibtex
T. Hobiger, T. Gotoh, J. Amagai, T. Kondo, and Y. Koyama, "GPU based GNSS software receivers – status quo and plans," in NICT IVS Technical Development Center News, 2010, pp. 10-13.

@INPROCEEDINGS{TDC10a, author = {Hobiger, Thomas and Gotoh, Tadahiro and Amagai,Jun and Kondo,Tetsuro and Koyama, Yasuhiro}, title = {GPU based GNSS software receivers - status quo and plans}, booktitle = {NICT IVS Technical Development Center News}, year = {2010}, number = {31}, pages = {10-13}, abstract = {Software receivers for GNSS are a flexible and cheap alternative to hardware solutions, and the usage of graphics processing units (GPUs) allows to operate the receiver even in real-time (Ho- biger et al., 2010). Recent developments with this receicer technology are summarized and plansfor new applications are stated in this report}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_31.pdf} }

bibtex
T. Hobiger, T. Gotoh, T. Otsubo, T. Kubooka, M. Sekido, H. Takiguchi, and H. Takeuchi, "Automated processing of VLBI experiments with c5++," in NICT IVS Technical Development Center News, 2010, pp. 14-16.

@INPROCEEDINGS{TDC10b, author = {Hobiger, Thomas and Gotoh,Tadahiro and Otsubo,Toshimichi and Kubooka,Toshihiro and Sekido, Mamoru and Takiguchi, Hiroshi and Takeuchi, Hiroshi}, title = {Automated processing of VLBI experiments with c5++}, booktitle = {NICT IVS Technical Development Center News}, year = {2010}, number = {31}, pages = {14-16}, abstract = {Processing of space geodetic techniques should be carried out with consistent and utmost up-to-date physical models. Therefore, c5++ is being developed, which will act as a framework under which dedicated space geodetic applications can be created. Due to its nature, combination of different techniques as well as automated processing of VLBI experiments will become possible with c5++}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_31.pdf} }

bibtex
H. Takiguchi, Y. Koyama, R. Ichikawa, T. Gotoh, A. Ishii, T. Hobiger, and M. Hosokawa, "VLBI Measurements for Frequency Transfer," in NICT IVS Technical Development Center News, 2010, pp. 21-24.

@INPROCEEDINGS{TDC10c, author = {Takiguchi, Hiroshi and Koyama, Yasuhiro and Ichikawa, Ryuichi and Gotoh, Tadahiro and Ishii, Atsutoshi and Hobiger, Thomas and Hosokawa, Mizuhiko}, title = {VLBI Measurements for Frequency Transfer}, booktitle = {NICT IVS Technical Development Center News}, year = {2010}, number = {31}, pages = {21-24}, abstract = {We carried out the intercomparison experiment between VLBI and GPS to show that VLBI can measure the correct time difference. We produced an artificial delay change by stretching the Coaxial Phase Shifter which was inserted in the path of the reference signal from Hydrogen maser to the Kashima 11m antenna. Concerning the artificial changes, VLBI and the nominal value of Coaxial Phase Shifter show good agreement, i.e. less than 10ps. Thus it is concluded that the geodetic VLBI technique can measure the time differences correctly.}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_31.pdf} }

bibtex
R. Ichikawa, T. Hobiger, S. Hasegawa, M. Tsutsumi, Y. Koyama, and T. Kondo, "Kashima RAy-Tracing Service:KARATS," in NICT IVS Technical Development Center News, 2010, pp. 25-28.

@INPROCEEDINGS{TDC10d, author = {Ichikawa,Ryuichi and Hobiger,Thomas and Hasegawa,Shingo and Tsutsumi,Masanori and Koyama,Yasuhiro and Kondo,Tetsuro}, title = {Kashima RAy-Tracing Service:KARATS}, booktitle = {NICT IVS Technical Development Center News}, year = {2010}, number = {31}, pages = {25-28}, abstract = {The ray tracing tools, which we have named ’KAshima RAytracing Tools (KARAT)’, are capable of calculating total slant delays and ray-bending angles considering real atmospheric phenomena. We compared PPP solutions using KARAT with that using the Global Mapping Function (GMF) and Vienna Mapping Function 1 (VMF1) for GPS sites of the GEONET (GPS Earth Observation Network System) operated by Geographical Survey Institute (GSI). Our comparisons show the KARAT solutions are almost identical or slightly better than the solutions using VMF1 and GMF with linear gradient model for horizontal and height positions. In addition we have started the web-base service “KARATS” for reducing atmospheric delay error from the RINEX file.}, url = {http://www2.nict.go.jp/aeri/sts/stmg/ivstdc/news_31/pdf/tdcnews_31.pdf} }

bibtex
T. Hobiger, M. Kimura, H. Takefuji, T. Oyama, Y. Koyama, T. Kondo, T. Gotoh, and J. Amagai, "GPU Based Software Correlators – Perspectives for VLBI2010," in IVS 2010 General Meeting Proceedings – ”VLBI2010: From Vision to Reality”, 2010, pp. 40-44.

@INPROCEEDINGS{IVSGM09_01, author = {Hobiger,Thomas and Kimura, Moritaka and Takefuji, Hiroshi and Oyama, Tomoaki and Koyama, Yasuhiro and Kondo, Tetsuro and Gotoh, Tadahiro and Amagai, Jun}, title = {GPU Based Software Correlators – Perspectives for VLBI2010}, booktitle = {IVS 2010 General Meeting Proceedings - ''VLBI2010: From Vision to Reality''}, year = {2010}, number = {NASA/CP-2010-215864}, pages = {40-44}, abstract = {Caused by historical separation and driven by the requirements of the PC gaming industry, Graphics Processing Units (GPUs) have evolved to massive parallel processing systems which entered the area of non-graphic related applications. Although a single processing core on the GPU is much slower and provides less functionality than its counterpart on the CPU, the huge number of these small processing entities outperforms the classical processors when the application can be parallelized. Thus, in recent years various radio astronomical projects have started to make use of this technology either to realize the correlator on this platform or to establish the post-processing pipeline with GPUs. Therefore, the feasibility of GPUs as a choice for a VLBI correlator is being investigated, including pros and cons of this technology. Additionally, a GPU based software correlator will be reviewed with respect to energy consumption/GFlop/sec and cost/GFlop/sec.}, domains = {VLBI}, url = {http://ivscc.gsfc.nasa.gov/publications/gm2010/hobiger1.pdf} }

bibtex
T. Hobiger, T. Gotoh, T. Otsubo, T. Kubooka, M. Sekido, H. Takiguchi, and H. Takeuchi, "C5++ – Multi-technique Analysis Software for Next Generation Geodetic Instruments," in IVS 2010 General Meeting Proceedings – ”VLBI2010: From Vision to Reality”, 2010, pp. 212-216.

@INPROCEEDINGS{IVSGM09_02, author = {Hobiger, Thomas and Gotoh, Tadahiro and Otsubo, Toshimichi and Kubooka, Toshihiro and Sekido, Mamoru and Takiguchi, Hiroshi and Takeuchi, Hiroshi}, title = {c5++ - Multi-technique Analysis Software for Next Generation Geodetic Instruments}, booktitle = {IVS 2010 General Meeting Proceedings - ''VLBI2010: From Vision to Reality''}, year = {2010}, number = {NASA/CP-2010-215864}, pages = {212-216}, abstract = {Processing of space geodetic techniques should be carried out with consistent and utmost up-to-date physical models. Therefore, c5++ is being developed, which will act as a framework under which dedicated space geodetic applications can be created. Due to its nature, combination of different techniques as well as automated processing of VLBI experiments will become possible with c5++.}, domains = {VLBI}, url = {http://ivscc.gsfc.nasa.gov/publications/gm2010/hobiger2.pdf} }

bibtex
B. Petrachenko, A. Niell, D. Behrend, B. Corey, J. Boehm, P. Charlot, A. Collioud, J. Gipson, R. Haas, T. Hobiger, Y. Koyama, D. MacMillan, Z. Malkin, T. Nilsson, A. Pany, G. Tuccari, A. Whitney, and J. Wresnik, "Design Aspects of the VLBI2010 System," in Progress Report of the VLBI2010 Committee, 2009, p. 56.

@INPROCEEDINGS{VLBI2010R, author = {Petrachenko, Bill and Niell, Arthur and Behrend, Dirk and Corey, Brian and Boehm, Johannes and Charlot, Patrick and Collioud, Arnoud and Gipson, John and Haas, R{\"u}diger and Hobiger, Thomas and Koyama, Yasuhiro and MacMillan, Dan and Malkin, Zinovy and Nilsson, Tobias and Pany, Andrea and Tuccari, Gino and Whitney, Allan and Wresnik, Joerg}, title = {Design Aspects of the VLBI2010 System}, booktitle = {Progress Report of the VLBI2010 Committee}, year = {2009}, pages = {pp 56}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/misc/V2C/PR-V2C_090417.pdf} }

bibtex
H. Takiguchi, Y. Koyama, R. Ichikawa, T. Gotoh, A. Ishii, and T. Hobiger, "A Comparison Study of VLBI and GPS Carrier Phase Frequency Transfer – Part II -," in NICT IVS Technical Development Center News, 2009, pp. 26-29.

@INPROCEEDINGS{TDC09c, author = {Takiguchi, Hiroshi and Koyama, Yasuhiro and Ichikawa, Ryuichi and Gotoh, Tadahiro and Ishii, Atsutoshi and Hobiger, Thomas}, title = {A Comparison Study of VLBI and GPS Carrier Phase Frequency Transfer - Part II - }, booktitle = {NICT IVS Technical Development Center News}, year = {2009}, number = {30}, pages = {26-29}, abstract = {To show the frequency stability of local baseline, we carried out long term VLBI experiment together with GPS and DMTD measurement. And, we compared the results provided from these three techniques. The results are strongly correlated at long term period. The frequency stability of VLBI is surpassing the stability of atomic fountain at 105 seconds or longer.}, domains = {GPS, GPU, Troposphere}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_30/pdf/tdcnews_30.pdf} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Accelerating the computation of ray-traced troposphere delays by GPUs," in NICT IVS Technical Development Center News, 2009, pp. 6-8.

@INPROCEEDINGS{TDC09b, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Accelerating the computation of ray-traced troposphere delays by GPUs}, booktitle = {NICT IVS Technical Development Center News}, year = {2009}, number = {30}, pages = {6-8}, abstract = {The computation of ray-traced slant delays from numerical weather models is a demanding task, if a large number of rays have to be processed or if real-time operation is anticipated. Thus, propagation solvers have been ported to graphics processing unit (GPU), which provides huge parallel processing performance at low cost. A comparison with results obtained on the CPU verify that modern graphic cards can provide identical results, but significantly accelerate the computation by nearly a factor of 20.}, domains = {GPS, GPU, Troposphere}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_30/pdf/tdcnews_30.pdf} }

bibtex
T. Gotoh, T. Hobiger, J. Amagai, Y. Koyama, and T. Kondo, "Development of a GPS software receiver based on K5/VSSP and a GPU," in NICT IVS Technical Development Center News, 2009, pp. 3-5.

@INPROCEEDINGS{TDC09a, author = {Gotoh, Tadahiro and Hobiger, Thomas and Amagai, Jun and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Development of a GPS software receiver based on K5/VSSP and a GPU}, booktitle = {NICT IVS Technical Development Center News}, year = {2009}, number = {30}, pages = {3-5}, abstract = {Graphics processing units provide low-cost massive parallel computing performance, which can be utilized for the implementation of a GPS software receiver. In order to realize a real-time capable system the crucial stages of the receiver should be optimized to suit the requirements of a parallel processor. First results from such a receiver development are presented together with a short overview of the hard- and software systems.}, domains = {GPS, GPU}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_30/pdf/tdcnews_30.pdf} }

bibtex
J. Boehm, H. Spicakova, L. Plank, K. Teke, A. Pany, J. Wresnik, S. Englich, T. Nilsson, H. Schuh, T. Hobiger, R. Ichikawa, Y. Koyama, T. Gotoh, T. Kubooka, and T. Otsubo, "Plans for the Vienna VLBI Software VieVS," in Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009, 2009, pp. 161-164.

@INPROCEEDINGS{EVGA09a, author = {Boehm, Johannes and Spicakova, Hana and Plank, Lucia and Teke, Kamil and Pany, Andrea and Wresnik, Joerg and Englich, Sigrid and Nilsson, Tobias and Schuh, Harald and Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Gotoh, Tadahiro and Kubooka, Toshihiro and Otsubo, Toshimichi}, title = {Plans for the Vienna VLBI Software VieVS}, booktitle = {Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009}, year = {2009}, number = {-}, pages = {161-164}, domains = {VLBI} }

bibtex
A. Pany, J. Boehm, H. Schuh, T. Hobiger, and R. Ichikawa, "Modeling azimuthal asymmetries of the troposphere delay during a 14-days typhoon period in Tsukuba," in Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009, 2009, pp. 44-48.

@INPROCEEDINGS{EVGA09b, author = {Pany, Andrea and Boehm, Johannes and Schuh, Harald and Hobiger, Thomas and Ichikawa, Ryuichi}, title = {Modeling azimuthal asymmetries of the troposphere delay during a 14-days typhoon period in Tsukuba}, booktitle = {Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009}, year = {2009}, number = {-}, pages = {44-48}, domains = {VLBI, Troposphere} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Provision of real-time troposphere delay corrections by utliziation of general purpose graphics processing units," in Proceedings of the IEEE International Geoscience and Remote Sensing Symposium, 2009.

@INPROCEEDINGS{IGARSS09a, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Provision of real-time troposphere delay corrections by utliziation of general purpose graphics processing units}, booktitle = {Proceedings of the IEEE International Geoscience and Remote Sensing Symposium}, year = {2009}, number = {--}, pages = {n.a.}, domains = {GPS, troposphere, InSAR} }

bibtex
T. Hobiger, H. Takiguchi, R. Ichikawa, M. Sekido, Y. Koyama, and T. Kondo, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2008 Annual Report, 2009, pp. 287-290.

@INPROCEEDINGS{IVSAR08, author = {Hobiger,Thomas and Takiguchi,Hiroshi and Ichikawa,Ryuichi and Sekido,Mamoru and Koyama, Yasuhiro and Kondo,Tetsuro }, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2008 Annual Report}, year = {2009}, number = {NASA/TP-2009-214183}, pages = {287-290}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2008.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2008/pdf/acnict.pdf} }

bibtex
T. Hobiger, M. Furuya, Y. Kinoshita, R. Ichikawa, and Y. Koyama, "Ray-traced troposphere slant delays from numerical weather models as corrections for InSAR," in Proceedings of the IEEE International Geoscience and Remote Sensing Symposium, 2009.

@INPROCEEDINGS{IGARSS09b, author = {Hobiger, Thomas and Furuya, Masato and Kinoshita, Youhei and Ichikawa, Ryuichi and Koyama, Yasuhiro}, title = {Ray-traced troposphere slant delays from numerical weather models as corrections for InSAR}, booktitle = {Proceedings of the IEEE International Geoscience and Remote Sensing Symposium}, year = {2009}, number = {--}, pages = {n.a.}, domains = {GPS, troposphere, InSAR} }

bibtex
Y. Koyama, M. Sekido, T. Hobiger, H. Takiguchi, and K. Tetsuro, "Developments of Automated Data Processing System for Ultra Rapid dUT1 e-VLBI Sessions," in Measuring the future, Proceedings of the Fifth IVS General Meeting, Andrey Finkelstein and Dirk Behrend(Editors, 2008, pp. 405-409.

@INPROCEEDINGS{IVSGM08c, author = {Koyama, Yasuhiro and Sekido, Mamoru and Hobiger,Thomas and Takiguchi, Hiroshi and Tetsuro, Kondo}, title = {Developments of Automated Data Processing System for Ultra Rapid dUT1 e-VLBI Sessions}, booktitle = {Measuring the future, Proceedings of the Fifth IVS General Meeting, Andrey Finkelstein and Dirk Behrend(Editors}, year = {2008}, number = {ISBN 978-5-02-025332-2}, pages = {405-409}, domains = {VLBI} }

bibtex
H. Takiguchi, Y. Koyama, R. Ichikawa, T. Gotoh, A. Ishii, T. Hobiger, and M. Hosokawa, "VLBI measurements for time and frequency transfer," in Proc. of the European Frequency and Time Forum 2008, 2008.

@INPROCEEDINGS{EFTF08, author = {Takiguchi, Hiroshi and Koyama, Yasuhiro and Ichikawa, Ryuichi and Gotoh,Tadahiro and Ishii,Atsutoshi and Hobiger,Thomas and Hosokawa,Mizuhiko}, title = {VLBI measurements for time and frequency transfer}, booktitle = {Proc. of the European Frequency and Time Forum 2008}, year = {2008}, number = {1}, domains = {VLBI:GPS} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Real-time ray-tracing through numerical weather models for space geodesy," in NICT IVS Technical Development Center News, 2008, pp. 31-33.

@INPROCEEDINGS{TDC08e, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Real-time ray-tracing through numerical weather models for space geodesy}, booktitle = {NICT IVS Technical Development Center News}, year = {2008}, number = {29}, pages = {31-33}, abstract = {Numerical weather models have undergone an improvement of spatial and temporal resolution in the recent years, which made their use for space geodetic applications feasible. Ray-tracing through such models permits the computation of total troposphere delays and ray-bending angles. At the National Institute of Information and Communications Technology (NICT) the so-called KAshima RAy-tracing Tools (KARAT) have been developed which allow to obtain troposphere delay corrections in real-time. Together with fine-mesh weather models from the Japanese Meteorological Agency (JMA) huge parts of the East Asian region, including Japan, Korea, Taiwan and East China, can be covered. Thus a short overview about the capabilities and functions of KARAT will be given and computation performance issues will be discussed. The ray-traced total troposphere slant delays can be used as a correction of space geodetic data on the observation level. Additionally, an overview will be given about the upcoming on-line service, which permits the reduction of troposphere delays from user-submitted data.}, domains = {VLBI:troposphere}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_29/pdf/tdcnews_29.pdf} }

bibtex
M. Sekido, T. Kondo, J. Wagner, T. Hobiger, K. Kokado, H. Takiguchi, Y. Koyama, R. Haas, J. Ritakari, and S. Kurihara, "Development of e-VLBI Technologies for Ultra-rapid UT1 Measurement," in NICT IVS Technical Development Center News, 2008, pp. 28-30.

@INPROCEEDINGS{TDC08d, author = {Sekido, Mamoru and Kondo, Tetsuro and Wagner, Jan and Hobiger, Thomas and Kokado, Kensuke and Takiguchi, Hiroshi and Koyama, Yasuhiro and Haas, R{\"u}diger and Ritakari, Jouko and Kurihara, Shinobu}, title = {Development of e-VLBI Technologies for Ultra-rapid UT1 Measurement}, booktitle = {NICT IVS Technical Development Center News}, year = {2008}, number = {29}, pages = {28-30}, abstract = {Ultra-rapid UT1 measurements have been realized under the collaboration between NICT, GSI(Japan), Onsala Observatory(Sweden),and Metsaehovi Radio Observatory(Finland). This achievement was made by a combination of software and hardware technologies with components of so called e-VLBI. This paper describes the components, which contributed the Ultra-rapid UT1 measurements.}, domains = {VLBI}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_29/pdf/tdcnews_29.pdf} }

bibtex
H. Takiguchi, Y. Koyama, R. Ichikawa, T. Gotoh, A. Ishii, T. Hobiger, and M. Hosokawa, "Comparison Study of VLBI and GPS Carrier Phase Frequency Transfer using IVS and IGS data," in NICT IVS Technical Development Center News, 2008, pp. 23-27.

@INPROCEEDINGS{TDC08c, author = {Takiguchi, Hiroshi and Koyama, Yasuhiro and Ichikawa, Ryuichi and Gotoh, Tadahiro and Ishii,Atsutoshi and Hobiger, Thomas and Hosokawa, Mizuhiko}, title = {Comparison Study of VLBI and GPS Carrier Phase Frequency Transfer using IVS and IGS data}, booktitle = {NICT IVS Technical Development Center News}, year = {2008}, number = {29}, pages = {23-27}, abstract = {We compare the frequency transfer precision between VLBI and GPS carrier phase using IVS and IGS observation data in order to confirm the potential of VLBI time and frequency transfer. The results show that VLBI time transfer is more stable than GPS time transfer on the same baseline and same period.}, domains = {VLBI}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_29/pdf/tdcnews_29.pdf} }

bibtex
T. Hobiger, M. Sekido, Y. Koyama, and T. Kondo, "Integer least squares adjustment for VLBI," in NICT IVS Technical Development Center News, 2008, pp. 8-11.

@INPROCEEDINGS{TDC08b, author = {Hobiger, Thomas and Sekido, Mamoru and Koyama, Yasuhiro and Kondo,Tetsuro}, title = {Integer least squares adjustment for VLBI}, booktitle = {NICT IVS Technical Development Center News}, year = {2008}, number = {29}, pages = {8-11}, abstract = {Teunissen (1996) presented an algorithm which considers the integer nature of unknown parameters within least-squares adjustment. This method has been successfully applied within GNSS analysis where it helps to solve phase ambiguities. For this study the algorithm has been adopted to the needs of VLBI data processing and applied to simulated and real VLBI data. In particular, it is shown how this algorithm improves the estimation of ambiguities for next-generation VLBI (VLBI2010) and it is discussed how it can be used for the automated phase delay connection of fringe phase data.}, domains = {VLBI}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_29/pdf/tdcnews_29.pdf} }

bibtex
R. Ichikawa, T. Hobiger, Y. Koyama, and T. Kondo, "A Comparison between Current Mapping Functions and Ray-traced Slant Delays from JMA Mesoscale Numerical Weather Data," in NICT IVS Technical Development Center News, 2008, pp. 3-7.

@INPROCEEDINGS{TDC08a, author = {Ichikawa, Ryuichi and Hobiger, Thomas and Koyama, Yasuhiro and Kondo,Tetsuro}, title = {A Comparison between Current Mapping Functions and Ray-traced Slant Delays from JMA Mesoscale Numerical Weather Data}, booktitle = {NICT IVS Technical Development Center News}, year = {2008}, number = {29}, pages = {3-7}, abstract = {We have estimated atmospheric slant delays using the KAshima RAytracing Tools (KARAT) through the JMA 10 km MANAL data.The comparisons between KARAT-based slant delays and empirical mapping functions indicate large biases ranging between 18 and 90 mm for summer season, which are considered to be caused by a significant variability of water vapor. We also compared PPP processed position solution using KARAT with that using the latest mapping function for the two week GEONET data sets. The KARAT solution were almost identical to the solution using GMF with linear gradient model, but some cases were slightly worse under the extreme atmospheric condition. Though we need further investigations to evaluate the capability of KARAT to reduce atmospheric path delays under the various topographic and meteorological regimes, the KARAT will be the powerful tool to reduce atmospheric path delay with the numerical weather model improvement.}, domains = {VLBI:GPS:troposphere}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_29/pdf/tdcnews_29.pdf} }

bibtex
H. Takiguchi, Y. Koyama, R. Ichikawa, T. Gotoh, A. Ishii, T. Hobiger, and M. Hosokawa, "VLBI measurements for time and frequency transfer," in Proc. of the 24th Asia-Pacific Workshop on Time and Frequency 2008, 2008.

@INPROCEEDINGS{ATF08, author = {Takiguchi, Hiroshi and Koyama, Yasuhiro and Ichikawa, Ryuichi and Gotoh,Tadahiro and Ishii,Atsutoshi and Hobiger,Thomas and Hosokawa,Mizuhiko}, title = {VLBI measurements for time and frequency transfer}, booktitle = {Proc. of the 24th Asia-Pacific Workshop on Time and Frequency 2008}, year = {2008}, number = {1}, domains = {VLBI:GPS} }

bibtex
R. Ichikawa, T. Hobiger, Y. Koyama, and T. Kondo, "Real-Time Ray-Tracing through Numerical Weather Models for Space Geodesy," in Measuring the future, Proceedings of the Fifth IVS General Meeting, Andrey Finkelstein and Dirk Behrend(Editors, 2008, pp. 168-172.

@INPROCEEDINGS{IVSGM08b, author = {Ichikawa,Ryuichi and Hobiger,Thomas and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Real-Time Ray-Tracing through Numerical Weather Models for Space Geodesy}, booktitle = {Measuring the future, Proceedings of the Fifth IVS General Meeting, Andrey Finkelstein and Dirk Behrend(Editors}, year = {2008}, number = {ISBN 978-5-02-025332-2}, pages = {168-172}, domains = {troposphere} }

bibtex
T. Hobiger, R. Ichikawa, M. Sekido, H. Takiguchi, T. Kondo, and Y. Koyama, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2007 Annual Report, 2008, pp. 220-223.

@INPROCEEDINGS{IVSAR07, author = {Hobiger,Thomas and Ichikawa,Ryuichi and Sekido,Mamoru and Takiguchi,Hiroshi and Kondo,Tetsuro and Koyama, Yasuhiro}, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2007 Annual Report}, year = {2008}, number = {NASA/TP-2008-214162}, pages = {220-223}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2007.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2007/pdf/acnict.pdf} }

bibtex
T. Gotoh, T. Hobiger, R. Ichikawa, T. Feldmann, and D. Piester, "Application of ray-traced troposphere delays to GPS time transfer," in Proc. 52nd Meeting of the Japan Society for Aeronautical and Space Sciences, 5-7 Nov 2008, Awaji Yumebutai International Conference Center, Hyogo, Japan, 2008, pp. 1322-1326.

@INPROCEEDINGS{JSASS08, author = {Gotoh, Tadahiro and Hobiger,Thomas and Ichikawa,Ryuichi and Feldmann,Thorsten and Piester,Dirk}, title = {Application of ray-traced troposphere delays to GPS time transfer}, booktitle = {Proc. 52nd Meeting of the Japan Society for Aeronautical and Space Sciences, 5-7 Nov 2008, Awaji Yumebutai International Conference Center, Hyogo, Japan}, year = {2008}, editor = {D. Behrend and K. Baver}, pages = {1322-1326}, domains = {GPS:troposphere} }

bibtex
T. Hobiger, R. Ichikawa, and Y. Koyama, "MK3TOOLS – Seamless Interfaces for the Creation of VLBI Databases from Post-Correlation Output," in Measuring the future, Proceedings of the Fifth IVS General Meeting, Andrey Finkelstein and Dirk Behrend(Editors, 2008, pp. 153-156.

@INPROCEEDINGS{IVSGM08a, author = {Hobiger,Thomas and Ichikawa,Ryuichi and Koyama, Yasuhiro}, title = {MK3TOOLS - Seamless Interfaces for the Creation of VLBI Databases from Post-Correlation Output}, booktitle = {Measuring the future, Proceedings of the Fifth IVS General Meeting, Andrey Finkelstein and Dirk Behrend(Editors}, year = {2008}, number = {ISBN 978-5-02-025332-2}, pages = {153-156}, domains = {VLBI} }

bibtex
R. Ichikawa, M. Sekido, T. Hobiger, T. Kondo, and Y. Koyama, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2006 Annual Report, 2007, pp. 216-219.

@INPROCEEDINGS{IVSAR06b, author = {Ichikawa,Ryuichi and Sekido,Mamoru and Hobiger,Thomas and Kondo,Tetsuro and Koyama, Yasuhiro}, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2006 Annual Report}, year = {2007}, editor = {D. Behrend and K. Baver}, number = {NASA/TP-2007-214151}, pages = {216--219}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT) for the year 2006.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2006/pdf/acnict.pdf} }

bibtex
S. Todorova, H. Schuh, T. Hobiger, and M. Hernandez-Pajares, "Global models of the ionosphere obtained by integration of GNSS and satellite altimetry data," in Vermessung und Geoinformation (VGI), 2007, pp. 80-89.

@INPROCEEDINGS{VGI07, author = {Todorova, Sonya and Schuh, Harald and Hobiger, Thomas and Hernandez-Pajares, Manuel}, title = {Global models of the ionosphere obtained by integration of GNSS and satellite altimetry data}, booktitle = {Vermessung und Geoinformation (VGI)}, year = {2007}, volume = {92}, number = {2}, pages = {80--89}, abstract = {The high free-electron and ion density in the ionosphere disturbs both the group and phase velocity of the signals of all space geodetic techniques, operating in the microwave band. In first approximation this delay is proportional to the so-called Slant Total Electron Content (STEC) along the ray path and can be corrected only if the measurements are carried out at two distinct frequencies. On the other hand, this effect allows information to be gained about the parameters of the ionosphere in terms of Total Electron Content (TEC) values. The classical input data for the development of Global Ionosphere Maps (GIM) of the total electron content is obtained from dual-frequency Global Navigation Satellite System (GNSS) observations. However, the GNSS stations are inhomogeneously distributed, with large gaps particularly over the sea surface, which lowers the precision of the GIM over these areas. On their part, dual-frequency satellite altimetry missions such as Jason-1 provide information about the ionosphere precisely above the sea surface. Due to the limited spread of the measurements and some open questions related to their systematic errors, the ionospheric data from satellite altimetry is used only for cross-validation of the GNSS GIM so far. It can be anticipated however, that some specifics of the ionosphere parameters derived by satellite altimetry will partly balance the inhomogeneity of the GNSS data. In this study we create two-hourly GIM from GNSS data and additionally introduce satellite altimetry observations, which help to compensate the insufficient GNSS coverage of the oceans. Furthermore, this method allows the independent estimation of systematic instrumental errors, affecting the two types of measurements. Thus, besides the daily values of the Differential Code Biases (DCB) for all GNSS satellites and receivers, also a constant daily bias for the Jason-1 satellite is estimated and investigated.}, domains = {GPS:ionosphere}, url = {http://www.ovg.at/uploads/media/VGI_2007-2_05_Todorova_Hobiger_Schuh_Hernandez-Pajares.pdf} }

bibtex
H. Takiguchi, T. Hobiger, A. Ishii, R. Ichikawa, and Y. Koyama, "Comparison with GPS time transfer and VLBI time transfer," in NICT IVS Technical Development Center News, 2007, pp. 20-21.

@INPROCEEDINGS{TDCnews07c, author = {Takiguchi, Hiroshi and Hobiger, Thomas and Ishii, Atsutoshi and Ichikawa, Ryuichi and Koyama, Yasuhiro}, title = {Comparison with GPS time transfer and VLBI time transfer}, booktitle = {NICT IVS Technical Development Center News}, year = {2007}, number = {28}, pages = {20--21}, abstract = {To compare the results with Global Positioning System (GPS) Time Transfer and Very Long Baseline Interferometry (VLBI) Time Transfer, we carried out the geodetic VLBI experiments for four times. The averaged formal error (1 sigma) of the clock offsets that were estimated every one hour in the geodetic VLBI analysis procedure (CALC/SOLVE), was 33 picoseconds. Especially,in the case of using K5/VSSP32 system, the averaged formal error was 29 picoseconds. The results of the VLBI time transfer were very consistent with the results of the GPS time transfer. The difference of both results was about +/-500 picoseconds. In term of frequency stability, the Allan deviation showed that VLBI time transfer is more stable than GPS time transfer between 2000 seconds to 60000 seconds (uncertainty of under 3x10-14 ).}, domains = {VLBI:GPS}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_28/pdf/tdcnews_28.pdf} }

bibtex
H. Schuh, B. Johannes, R. Heinkelmann, T. Hobiger, P. J. Mendes Cerveira, A. Pany, E. Tanir, K. Teke, S. Todorova, and J. Wresnik, "Vienna IGG Special Analysis Center Annual Report 2006," in International VLBI Service for Geodesy and Astrometry 2006 Annual Report, 2007, pp. 208-211.

@INPROCEEDINGS{IVSAR06a, author = {Schuh, Harald and Boehm Johannes and Heinkelmann, Robert and Hobiger, Thomas and Mendes Cerveira, Paulo Jorge and Pany, Andrea and Tanir,Emine and Teke, Kamil and Todorova, Sonja and Wresnik, Joerg}, title = {Vienna IGG Special Analysis Center Annual Report 2006}, booktitle = {International VLBI Service for Geodesy and Astrometry 2006 Annual Report}, year = {2007}, editor = {D. Behrend and K. Baver}, number = {NASA/TP-2007-214151}, pages = {208--211}, abstract = {Among other studies in 2006, the Institute of Geodesy and Geophysics (IGG) at the Vienna University of Technology has carried out Monte-Carlo simulations to assist the development of a new geodetic VLBI system (VLBI2010). These investigations are critical for the definition of the observing strategy and network configuration, and it has been shown that the troposphere is the limiting factor for the precision and accuracy of the new system.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2006/pdf/acigg.pdf} }

bibtex
R. Ichikawa, T. Hobiger, Y. Koyama, and T. Kondo, "An Evaluation of Geodetic Position Error Simulated using the Fast Ray Tracing Algorithms through the JMA Mesoscale Numerical Weather Data," in NICT IVS Technical Development Center News, 2007, pp. 20-21.

@INPROCEEDINGS{TDCnews07b, author = {Ichikawa, Ryuichi and Hobiger, Thomas and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {An Evaluation of Geodetic Position Error Simulated using the Fast Ray Tracing Algorithms through the JMA Mesoscale Numerical Weather Data}, booktitle = {NICT IVS Technical Development Center News}, year = {2007}, number = {28}, pages = {20--21}, abstract = {We simultaneously calculate atmospheric parameters (zenith total delay and a gradient vector) and position errors estimated from atmospheric slant path delays obtained by new ray tracing technique [Hobiger et al., 2007] through the meso-scale numerical weather data with 10 km horizontal resolution. In this numerical calculation we find that the large horizontal position errors up to 40 mm associated with severe rain fall event.}, domains = {VLBI:GPS:troposphere}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_28/pdf/tdcnews_28.pdf} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Kashima Ray-Tracing Service (KARATS) – Fast ray-tracing through numerical weather models for real-time positioning applications," in NICT IVS Technical Development Center News, 2007, pp. 16-19.

@INPROCEEDINGS{TDCnews07a, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Kashima Ray-Tracing Service (KARATS) - Fast ray-tracing through numerical weather models for real-time positioning applications}, booktitle = {NICT IVS Technical Development Center News}, year = {2007}, number = {28}, pages = {16--19}, abstract = {Numerical weather models (NWMs) have undergone a significant improvement of accuracy and spatial resolution. Therefore such models can be used to correct for the excess delay which is caused when signals are propagation through the troposphere. The Kashima Ray-Tracing Service (KARATS) is capable of reading, re-griding and ray-tracing NWMs which cover East Asia countries including Japan, Korea, Taiwan and parts of China and Russia. Optimized algorithms and the upcoming multi-core technology permit real-time computation of troposphere corrections. First tests have shown that KARATS is capable to remove nearly all of the tropospheric delay and that precision and accuracy of estimated station coordinates are improved significantly.}, domains = {VLBI:GPS:troposphere}, url = {http://www2.nict.go.jp/w/w114/stsi/ivstdc/news_28/pdf/tdcnews_28.pdf} }

bibtex
T. Hobiger, R. Ichikawa, Y. Koyama, and T. Kondo, "Kashima Ray-Tracing Service (KARATS) -Fast ray-tracing through numerical weather models for real-time positioning applications in East Asia," in Proceedings of the 18th European VLBI for Geodesy and Astrometry Working Meeting, Geowissenschaftliche Mittteilungen, 2007, pp. 181-185.

@INPROCEEDINGS{EVGA07a, author = {Hobiger, Thomas and Ichikawa, Ryuichi and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {Kashima Ray-Tracing Service (KARATS) -Fast ray-tracing through numerical weather models for real-time positioning applications in East Asia}, booktitle = {Proceedings of the 18th European VLBI for Geodesy and Astrometry Working Meeting, Geowissenschaftliche Mittteilungen}, year = {2007}, number = {79}, pages = {181--185}, abstract = {Numerical weather models (NWMs) have undergone a significant improvement of accuracy and spatial resolution. Therefore such models can be used to correct for the excess delay which is caused when signals are propagation through the troposphere. The Kashima Ray-Tracing Service (KARATS) is capable of reading, re-griding and ray-tracing NWMs which cover East Asia countries including Japan, Korea, Taiwan and parts of China and Russia. Optimized algorithms and the upcoming multi-core technology permit real-time computation of troposphere corrections. First tests have shown that KARATS is capable to remove nearly all of the tropospheric delay and that precision and accuracy of estimated station coordinates are improved significantly.}, domains = {VLBI:GPS:troposphere}, url = {http://mars.hg.tuwien.ac.at/~evga/proceedings/All_papers.pdf} }

bibtex
T. Hobiger, Y. Koyama, and T. Kondo, "MK3TOOLS \& NetCDF – storing VLBI data in a machine independent array oriented dataformat," in Proceedings of the 18th European VLBI for Geodesy and Astrometry Working Meeting, Geowissenschaftliche Mittteilungen, 2007, pp. 194-195.

@INPROCEEDINGS{EVGA07b, author = {Hobiger, Thomas and Koyama, Yasuhiro and Kondo, Tetsuro}, title = {MK3TOOLS \& NetCDF - storing VLBI data in a machine independent array oriented dataformat}, booktitle = {Proceedings of the 18th European VLBI for Geodesy and Astrometry Working Meeting, Geowissenschaftliche Mittteilungen}, year = {2007}, number = {79}, pages = {194--195}, abstract = {In the beginning of 2002 the International VLBI Service (IVS) has agreed to introduce a Platform-independent VLBI exchange format (PIVEX) which permits the exchange of observational data and stimulates the researchacross different analysis groups. Unfortunately PIVEX has never been implemented and many analysis software packages are still depending on prior processing (e.g. ambiguity resolution and computation of ionosphere corrections) done by CALC/SOLVE. Thus MK3TOOLS which handles MK3 databases without CALC/SOLVE being installed has been developed. It uses the NetCDF format to store the data and since interfaces exist for a variety of programming languages (FORTRAN, C/C++, JAVA, Perl,Python) it can be easily incorporated in existing and upcoming analysis software packages.}, domains = {VLBI}, url = {http://mars.hg.tuwien.ac.at/~evga/proceedings/All_papers.pdf} }

bibtex
T. Hobiger, T. Kondo, and H. Schuh, "VLBI as a Tool to Probe the Ionosphere," in International VLBI Service for Geodesy and Astrometry 2006 General Meeting Proceedings, 2006, pp. 344-348.

@INPROCEEDINGS{IVSmeet06a, author = {Hobiger, Thomas and Kondo, Tetsuro and Schuh, Harald}, title = {VLBI as a Tool to Probe the Ionosphere}, booktitle = {International VLBI Service for Geodesy and Astrometry 2006 General Meeting Proceedings}, year = {2006}, editor = {Dirk Behrend and Karen Baver}, number = {NASA/CP-2006-214140}, pages = {344--348}, abstract = {By a method, developed within project VLBIonos at the IGG, Vienna it is possible to estimate ionospheric parameters in terms of vertical total electron content from VLBI data without any external information (Hobiger et al., 2006). This paper deals with the results from this approach and cross-validates them against GPS, satellite altimetry data and measurements of solar flux. As geodetic VLBI observations cover more than two complete solar cycles, longer than all other space geodetic techniques using radio signals, the relation to space weather indices on long time-scales can be shown. It can be stated that the overall agreement between VLBI and GPS is within the formal error of each technique and that both systems detect the same periods of ionospheric variations.}, domains = {VLBI:ionosphere}, url = {ftp://ivscc.gsfc.nasa.gov/pub/general-meeting/2006/pdf/hobiger1.pdf} }

bibtex
T. Hobiger, T. Kondo, K. Takashima, and H. Schuh, "Detection of Short Period Ionosphere Variations from VLBI Fringe Phases," in International VLBI Service for Geodesy and Astrometry 2006 General Meeting Proceedings, 2006, pp. 348-350.

@INPROCEEDINGS{IVSmeet06b, author = {Hobiger, Thomas and Kondo, Tetsuro and Takashima, Kazuhiro and Schuh, Harald}, title = {Detection of Short Period Ionosphere Variations from VLBI Fringe Phases}, booktitle = {International VLBI Service for Geodesy and Astrometry 2006 General Meeting Proceedings}, year = {2006}, editor = {Dirk Behrend and Karen Baver}, number = {NASA/CP-2006-214140}, pages = {348--350}, abstract = {The usage of fringe phase information from VLBI measurements is a new and challenging field of research, which can be utilized for the detection of short period variations (scintillations) of the ionosphere. A method for the extraction of such disturbances has been developed and it is discussed how dispersive influences can be separated from intra-scan delay variations. It is shown that a short period variation can be detected very precisely, if the SNR is high enough. Physical origins of such disturbances are discussed and fields of application will be mentioned. This paper is an extended abstract of the paper Hobiger et al. (2006)}, domains = {VLBI:ionosphere}, url = {ftp://ivscc.gsfc.nasa.gov/pub/general-meeting/2006/pdf/hobiger2.pdf} }

bibtex
A. Krankowski, T. Hobiger, H. Schuh, W. Kosek, and W. Popinski, "Wavelet Analysis of TEC Measurements Obtained Using Dual Frequency Space and Satellite Techniques," in Proc. of the Journees 2005, 2006, pp. 290-293.

@INPROCEEDINGS{Jour06, author = {Krankowski, Andrzej and Hobiger, Thomas and Schuh, Harald and Kosek, W. and Popinski, W.}, title = {Wavelet Analysis of TEC Measurements Obtained Using Dual Frequency Space and Satellite Techniques}, booktitle = {Proc. of the Journees 2005}, year = {2006}, pages = {290--293}, abstract = {An extensive database of Total Electron Content (TEC) measurements has become available from both ground- and space-based observations. Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) observations collected at the IGS (International GNSS Service) and the IVS (International VLBI Service for Geodesy and Astrometry) stations over Europe were used to obtain TEC data during the time interval 1995 till 2003. In this paper, the wavelet analysis is used to determine the wavelet time-frequency spectra of TEC data above one European collocation station - Wettzell. The GPS and VLBI TEC time series of quiet and disturbed ionospheric conditions, utilized in this study, cover one solar cycle. A very good agreement between semidiurnal, diurnal, semiannual, and annual oscillations of TEC estimated using GPS and VLBI observations was obtained. The diurnal and annual oscillations are the most energetic and clearly visible ones especially during increasing and maximum solar activity.}, domains = {VLBI:GPS:ionosphere}, url = {http://syrte.obspm.fr/journees2005/s5_04_Krankowski.pdf} }

bibtex
H. Schuh, B. Johannes, R. Heinkelmann, T. Hobiger, S. Todorova, and J. Wresnik, "Vienna IGG Special Analysis Center Annual Report 2005," in International VLBI Service for Geodesy and Astrometry 2005 Annual Report, 2006, pp. 245-248.

@INPROCEEDINGS{IVSAR05, author = {Schuh, Harald and Boehm Johannes and Heinkelmann, Robert and Hobiger, Thomas and Todorova, Sonja and Wresnik, Joerg}, title = {Vienna IGG Special Analysis Center Annual Report 2005}, booktitle = {International VLBI Service for Geodesy and Astrometry 2005 Annual Report}, year = {2006}, editor = {D. Behrend and K. Baver}, number = {NASA/TP-2006-214136}, pages = {245--248}, abstract = {In 2005 the Institute of Geodesy and Geophysics (IGG) at the Vienna University of Technology continued its investigations in atmospheric research for geodetic VLBI: Among other topics, it was dealing with the neutral atmosphere in terms of long time series of tropospheric parameters and with the ionosphere in particular by determining ionospheric parameters from VLBI observations. Furthermore, it started simulation studies which are dedicated to the new VLBI2010 observing system.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2005/pdf/acigg.pdf} }

bibtex
S. Todorova, T. Hobiger, and H. Schuh, "Combination of GPS and satellite altimetry data for global ionosphere maps," in Proceedings of the International Scientific Conference SGEM 2006, June 12-16, 2006, Albena, Bulgaria, 2006, pp. 265-277.

@INPROCEEDINGS{SGEM06, author = {Todorova, Sonja and Hobiger, Thomas and Schuh, Harald}, title = {Combination of GPS and satellite altimetry data for global ionosphere maps}, booktitle = {Proceedings of the International Scientific Conference SGEM 2006, June 12-16, 2006, Albena, Bulgaria}, year = {2006}, volume = {2}, pages = {265--277}, domains = {GPS:ionosphere:satellite altimetry} }

bibtex
S. Todorova, T. Hobiger, R. Weber, and H. Schuh, "Using GPS for determination of the ionosphere," in Proceedings of the International Scientific Conference SGEM 2005, June 13-17, 2005, Albena, Bulgaria, 2005, pp. 605-613.

@INPROCEEDINGS{SGEM05, author = {Todorova, Sonja and Hobiger, Thomas and Weber,Robert and Schuh, Harald}, title = {Using GPS for determination of the ionosphere}, booktitle = {Proceedings of the International Scientific Conference SGEM 2005, June 13-17, 2005, Albena, Bulgaria}, year = {2005}, pages = {605--613}, domains = {GPS:ionosphere} }

bibtex
H. Schuh, B. Johannes, R. Heinkelmann, T. Hobiger, and S. Todorova, "Vienna IGG Special Analysis Center Annual Report 2004," in International VLBI Service for Geodesy and Astrometry 2004 Annual Report, 2005, pp. 221-224.

@INPROCEEDINGS{IVSAR04a, author = {Schuh, Harald and Boehm Johannes and Heinkelmann, Robert and Hobiger, Thomas and Todorova, Sonja}, title = {Vienna IGG Special Analysis Center Annual Report 2004}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 Annual Report}, year = {2005}, editor = {D. Behrend and K. Baver}, number = {NASA/TP-2005-212772}, pages = {221--224}, abstract = {In 2004 the Institute of Geodesy and Geophysics (IGG) at the Vienna University of Technology has continued its investigations in atmospheric research for geodetic VLBI. Among other items, it started the comparison and combination of long time series of tropospheric parameters within the IVS (``VLBI for climate studies''). So far, six analysis centers (ACs) have agreed to take part (four ACs already submitted). This will allow a robust combination of the tropospheric parameters and a reliable determination of trends and seasonal signals in the time series.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2004/pdf/acigg.pdf} }

bibtex
R. Ichikawa, M. Sekido, H. Takeuchi, Y. Koyama, T. Hobiger, and T. Kondo, "Analysis Center at National Institute of Information and Communications Technology," in International VLBI Service for Geodesy and Astrometry 2004 Annual Report, 2005, pp. 231-234.

@INPROCEEDINGS{IVSAR04b, author = {Ichikawa, Ryuichi and Sekido, Mamuro and Takeuchi, Hiroshi and Koyama, Yasuhiro and Hobiger, Thomas and Kondo, Tetsuro}, title = {Analysis Center at National Institute of Information and Communications Technology}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 Annual Report}, year = {2005}, editor = {D. Behrend and K. Baver}, number = {NASA/TP-2005-212772}, pages = {231--234}, abstract = {This report summarizes the activities of the Analysis Center at National Institute of Information and Communications Technology (NICT, former CRL) for the year 2004. By using the state-of-art e-VLBI systems, we performed the international EOP session between Westford and Kashima, differential VLBI measurements for the precise tracking the spacecraft HAYABUSA and geodetic experiments. In particular, we achieved the most rapid estimation of UT1-UTC with a latency of four and half hours. In addition, we performed ionospheric studies, the development of automatic GPS data processing system, and satellite communication experiments.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2004/pdf/acnict.pdf} }

bibtex
T. Hobiger, T. Kondo, and H. Schuh, "Estimation of absolute TEC values by VLBI," in Proceedings of the 17th Working Meeting on European VLBI for Geodesy and Astrometry, 2005, pp. 102-106.

@INPROCEEDINGS{EURVLBI05a, author = {Hobiger, Thomas and Kondo, Tetsuro and Schuh, Harald}, title = {Estimation of absolute TEC values by VLBI}, booktitle = {Proceedings of the 17th Working Meeting on European VLBI for Geodesy and Astrometry}, year = {2005}, editor = {M. Vennebusch and A. Nothnagel}, pages = {102--106}, abstract = {Geodetic VLBI observations are carried out at two distinct frequencies in order to determine ionospheric delay corrections. Each ionospheric delay corresponds to the total electron content (TEC) along the ray path through the ionosphere. Because VLBI is a differential technique the observed ionospheric delays represent the differences of the behavior of the propagation media above each two stations. Additionally, there is a constant instrumental delay offset per baseline that contributes to the observed ionospheric delay. This instrumental offset is independent of azimuth and elevation in which the antennas point what allows to separate it from the variable ionospheric parameters for each station which can be represented by different functional approaches. Instrumental offsets can be separated from the ionospheric parameters by a least-squares fit. Additional parameters of a model, which relates TEC values measured at the intersection point of the ray path with the infinitely thin ionospheric layer to vertical TEC values above the station, are estimated. The results agree well with other techniques like GPS, what will be shown, too.}, domains = {VLBI:ionosphere}, url = {http://www.evga.org/Documents/proceedings17wm.pdf} }

bibtex
T. Hobiger and T. Kondo, "An FX software correlator based on Matlab," in Proceedings of the 17th Working Meeting on European VLBI for Geodesy and Astrometry, 2005, pp. 34-38.

@INPROCEEDINGS{EURVLBI05b, author = {Hobiger, Thomas and Kondo, Tetsuro}, title = {An FX software correlator based on Matlab}, booktitle = {Proceedings of the 17th Working Meeting on European VLBI for Geodesy and Astrometry}, year = {2005}, editor = {M. Vennebusch and A. Nothnagel}, pages = {34--38}, abstract = {Normally data obtained by very long baseline interferometry (VLBI) are correlated by designated processors containing wired logic components. Additionally, several software correlators, which are able to do the same tasks, were designed in the last years. These software systems are more flexible and can be adopted easier for special tasks than hard-wired correlators. Usually such systems are coded in Assembler, Fortran or C/C++ in order to gain maximum speed. We have chosen Matlab 6.5, a commercial mathematical software package, to implement an FX correlator including single band delay search. Functionality is similar to IP-VLBI(K5/VSSP) software correlator, developed at Kashima Space Research Center, NICT, and other data formats (Mark5) can be analyzed using conversion tools. The software correlator presented here is not able to provide high data throughput but development and debugging times were much less than with other programming languages.}, domains = {VLBI}, url = {http://www.evga.org/Documents/proceedings17wm.pdf} }

bibtex
T. Hobiger, "VLBI as a tool to probe the ionosphere," PhD Thesis , 2005.

@PHDTHESIS{phd05, author = {Hobiger, Thomas}, title = {VLBI as a tool to probe the ionosphere}, school = {Inst. of Geodesy and Geophysics, Vienna Univ. of Technology}, year = {2005}, abstract = {Precise measurements with dual frequency instruments have a long tradition in geodesy. Among several techniques Very Long Baseline Interferometry (VLBI) started its routine observations already in the late 80ies and has carried them out until today. The dual frequency receiving systems, operating at X- and S-band, were designed to correct ionospheric time delays within geodetic analysis. The potential for ionospheric research of this correction was disregarded until the community around the Global Position System (GPS) showed that parameters of the ionosphere can be deduced from dual frequency satellite measurements. With this thesis a method has been developed, which enables estimation of similar parameters from dual frequency VLBI measurements without any external information. Due to the fact that VLBI is a differential technique, the calculated ionospheric corrections depend on the differences of the propagation media over the stations. Additionally, an instrumental delay offset per station causes a bias of the ionospheric measurements. Within this thesis a method is presented, which is capable of estimating ionospheric parameters, i.e. values of vertical total electron content, from VLBI data. The obtained results are cross-validated against GPS, satellite altimetry data and theoretical models of the ionosphere. As VLBI observations cover more than two complete solar cycles, longer than all other space geodetic techniques using radio signals, the relation to space weather indices on long time-scales can be shown. Generally it can be stated that the overall agreement between VLBI and GPS is within the formal error of each technique and that both systems detect the same periods of ionospheric variations. But only VLBI is able to reveal long period signals like the solar cycle, since it covers a sufficiently long time-span. Apart from explanations for small biases among the techniques also deficiencies of theoretical models are discussed. Instrumental biases, a by-product of ionospheric parameter estimation, demonstrate how receiving systems evolved with the time, as instrumental changes are absorbed in this parameter. The usage of (fringe) phase information from VLBI measurements is a new and challenging field of research, which can be utilized for the detection of short period variations (scintillations). A method for the extraction of such disturbances is discussed and by an example it is shown that such a short period variation can be detected very precisely. Therefore VLBI can be used to detect both, long-term trends and short period variations of the ionosphere and thus it can contribute to ionospheric research as a new independent technique.}, domains = {VLBI:ionosphere}, issn = {1811-8380}, publisher = {Veroeffentlichung des Instituts fuer Geodaesie und Geophysik}, series = {Geowissenschaftliche Mitteilungen}, url = {http://aleph.ub.tuwien.ac.at/F/CBMVL7ADL37B93U3KFBFLTPN34UGNESM8AKK4CJLPXY45FLE63-00313?func=full-set-set&set_number=023237&set_entry=000008&format=999}, volume = {75} }

bibtex
T. Hobiger and H. Schuh, "Modelling Vertical Total Electron Content from VLBI Observations," in International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings, 2004, pp. 306-310.

@INPROCEEDINGS{IVSmeet04a, author = {Hobiger, Thomas and Schuh, Harald}, title = {Modelling Vertical Total Electron Content from VLBI Observations}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings}, year = {2004}, editor = {Nancy R. Vandenberg and Karen D. Baver}, number = {NASA/CP-2004-212255}, pages = {306--310}, abstract = {The vertical total electron content (VTEC) can be understood as the sum of electrons in a column ranging in zenith direction from the ground through the ionosphere with a footprint size of one square meter. Although VLBI is a differential technique it is possible to derive absolute TEC values for each station from VLBI observations as shown in prior papers and presentations. At the Institute of Geodesy and Geophysics, Vienna, investigations of the functional and stochastical model have been made. An approach dealing with trigonometric functions that allows direct conclusions on amplitudes and phases of the sub-daily periods is presented. Other strategies using piece-wise linear functions and an extended piece-wise linear approach with adaptive interval widths are shown, too. The usage of kernel functions, in this case of Gaussian type, as a very general approach for modelling the ionosphere, is illustrated. The weights of a delay observable used for the stochastical model should also consider the zenith distance on each station and a corresponding weighting function is applied.}, domains = {VLBI:ionosphere}, url = {ftp://ivscc.gsfc.nasa.gov/pub/general-meeting/2004/pdf/hobiger2.pdf} }

bibtex
T. Hobiger and H. Schuh, "How VLBI Contributes to Ionospheric Research," in International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings, 2004, pp. 437-441.

@INPROCEEDINGS{IVSmeet04b, author = {Hobiger, Thomas and Schuh, Harald}, title = {How VLBI Contributes to Ionospheric Research}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings}, year = {2004}, editor = {Nancy R. Vandenberg and Karen D. Baver}, number = {NASA/CP-2004-212255}, pages = {437--441}, abstract = {Geodetic VLBI observations are carried out at two distinct frequencies in order to determine ionospheric delay corrections. Each ionospheric delay corresponds to the total electron content (TEC) along the ray path through the ionosphere. Because VLBI is a differential technique the observed ionospheric delays represent the differences of the behaviour of the propagation media above each two stations. Additionally, there is a constant instrumental delay offset per baseline that contributes to the observed ionospheric delay. This instrumental offset is independent of azimuth and elevation in which the antennas point which allows us to separate it from the variable ionospheric parameters for each station which can be represented by different functional approaches. If horizontal gradients in the ionosphere above the stations are neglected we are able to separate the instrumental offsets from the ionospheric parameters by a least-squares fit. A weakness of this approach is the assumption that the TEC values are assigned to the station coordinates but not to the geographical coordinates of the intersection point of the ray path and the infinitely thin ionospheric layer. Nevertheless, the results agree well with results of other techniques like GPS on short and long time scales.}, domains = {VLBI:ionosphere}, url = {ftp://ivscc.gsfc.nasa.gov/pub/general-meeting/2004/pdf/hobiger3.pdf} }

bibtex
T. Hobiger, S. Todorova, and H. Schuh, "Ionospheric Parameters Obtained by Different Space Geodetic Techniques during CONT02," in International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings, 2004, pp. 442-446.

@INPROCEEDINGS{IVSmeet04c, author = {Hobiger, Thomas and Todorova,Sonya and Schuh, Harald}, title = {Ionospheric Parameters Obtained by Different Space Geodetic Techniques during CONT02}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings}, year = {2004}, editor = {Nancy R. Vandenberg and Karen D. Baver}, number = {NASA/CP-2004-212255}, pages = {442--446}, abstract = {The goal of the CONT02 campaign in October 2002 was the acquisition of the best possible VLBI data to demonstrate the high accuracy of which VLBI is capable. The campaign provides the chance to study the ionosphere continously over a period of more than two weeks by means of VLBI. Vertical total electron content (VTEC) values above the contributing stations were determined. By comparison with results from other techniques, like GPS or satellite altimetry, systematic differences could be detected of which the reasons are still unclear. Anyway, the histograms of the differences show that generally the agreement is very good between the parameters derived by VLBI and the results from other space geodetic techniques. This is also confirmed by Fourier and wavelet analyses which reveal variations with the same periods (diurnal, semi-diurnal and quarter-diurnal) in GPS and VLBI time series.}, domains = {VLBI:ionosphere}, url = {ftp://ivscc.gsfc.nasa.gov/pub/general-meeting/2004/pdf/hobiger1.pdf} }

bibtex
H. Schuh, B. Johannes, and T. Hobiger, "Vienna IGG Special Analysis Center Annual Report 2003," in International VLBI Service for Geodesy and Astrometry 2004 Annual Report, 2004, pp. 197-200.

@INPROCEEDINGS{IVSAR03, author = {Schuh, Harald and Boehm Johannes and Hobiger, Thomas}, title = {Vienna IGG Special Analysis Center Annual Report 2003}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 Annual Report}, year = {2004}, editor = {N. R. Vandenberg and K. D. Baver}, number = {NASA/TP-2004-212254}, pages = {197--200}, abstract = {Since July 2003 the combined tropospheric parameters determined at IGG (Schuh and Boehm, 2003) are regular IVS products provided by the IVS Data Centers one month after the availability of each new session database. Additionally, a forthcoming project within IVS-TROP has been initialized that is dealing with the combination of long time series of tropospheric parameters derived from VLBI for climate studies. The IGG has continued its research on the determination of ionospheric parameters from VLBI data.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2003/pdf/acigg.pdf} }

bibtex
W. Winkler, B. Bogensberger, W. Karel, M. Kistenich, G. Pacher, A. Pany, A. Roncat, G. Summer, J. Boehm, T. Hobiger, R. Weber, and H. Schuh, "VIEPROJ1 – A Students’ VLBI Project," in International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings, 2004, pp. 105-108.

@INPROCEEDINGS{IVSmeet04d, author = {Winkler,Wolfgang and Bogensberger, Boris and Karel,Wilfried and Kistenich,Michael and Pacher,Gerold and Pany,Andrea and Roncat, Andreas and Summer, Gerhard and Boehm, Johannes and Hobiger, Thomas and Weber, Robert and Schuh, Harald}, title = {VIEPROJ1 - A Students' VLBI Project}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 General Meeting Proceedings}, year = {2004}, editor = {Nancy R. Vandenberg and Karen D. Baver}, number = {NASA/CP-2004-212255}, pages = {105--108}, abstract = {The VLBI project VIEPROJ1 was planned and executed involving university students doing the main work in every step. It was part of the lecture (diploma course) ``Auswertung geodaetischer Weltraumverfahren'' (space geodetic techniques), within the curriculum of Vermessung und Geoinformation (geodesy and geoinformation) at the Vienna University of Technology. The lecture was held by Prof. Harald Schuh and Prof. Robert Weber.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/general-meeting/2004/pdf/winkler1.pdf} }

bibtex
T. Hobiger, J. Boehm, and H. Schuh, "VLBIONOS – Probing the ionosphere by means of very long baseline interferometry," in Oesterreichische Zeitschrift fuer Vermessung \& Geoinformation (VGI), 2003.

@INPROCEEDINGS{VGI03, author = {Hobiger, Thomas and Boehm, Johannes and Schuh, Harald }, title = {VLBIONOS - Probing the ionosphere by means of very long baseline interferometry}, booktitle = {Oesterreichische Zeitschrift fuer Vermessung \& Geoinformation (VGI)}, year = {2003}, number = {1/2003}, abstract = {In geodetic VLBI the observations are performed at two distinct frequencies (2.3 and 8.4 GHz) in order to determine ionospheric delay corrections. This allows to gain information from VLBI observables about the sum of electrons (total electron content - TEC) along the ray path through the ionosphere. Due to the fact that VLBI is a differential technique only the differences in the behavior of the propagation media over the stations determine the leading signs and the absolute values of the observed ionospheric delays. However, there is an instrumental delay offset per baseline that shifts the measurements by a constant value. This offset is thought to be independent of the azimuth and elevation in which the antennas point what allows to separate the ionospheric parameters for each station from the ionospheric offsets per baseline in a least-squares adjustment process. In first tests of this method Fourier coefficients up to 4th order plus a constant value and a linear trend representing the vertical TEC (VTEC) were estimated. Slant TEC (STEC) values are converted into VTEC values by a mapping function. The disadvantage of this approach is the assumption that these values are assigned to the station coordinates coordinates but not to the geographical coordinates of the intersection point of the ray path and the infinite thin ionospheric layer. The precision of the estimated values is about 2-3 TEC units (TECU). These results agree within 5-15 TECU with other techniques like GPS which. A second approach, developed at the TU-Vienna, using piece-wise linear functions provides better results.}, domains = {VLBI:ionosphere} }

bibtex
T. Hobiger, J. Boehm, S. Todorova, and H. Schuh, "The project "VLBIonos" – how VLBI contributes to ionospheric research," in Proceedings of the 16th Working Meeting on European VLBI for Geodesy and Astrometry, 2003, pp. 291-298.

@INPROCEEDINGS{EVLBI03, author = {Hobiger, Thomas and Boehm, Johannes and Todorova, Sonya and Schuh, Harald}, title = {The project "VLBIonos" - how VLBI contributes to ionospheric research}, booktitle = {Proceedings of the 16th Working Meeting on European VLBI for Geodesy and Astrometry}, year = {2003}, editor = {W. Schwegmann and V. Thorandt}, pages = {291--298}, abstract = {In geodetic Very Long Baseline Interferometry (VLBI) the observations are performed at two distinct frequencies (2.3 and 8.4 GHz) in order to determine ionospheric delay corrections. This allows information to be obtained from the VLBI observables about the sum of electrons (total electron content - TEC) along the ray path through the ionosphere. Due to the fact that VLBI is a differential technique, only the differences in the behavior of the propagation media over the stations determine the values of the observed ionospheric delays. However, in a first simple approach, an instrumental delay offset per baseline shifts the TEC measurements by a constant value. This offset is independent of the azimuth and elevation of the observed radio source and allows separation of the ionospheric parameters for each station from the instrumental delay offsets per baseline in a least-squares adjustment. In first tests of this method Fourier coefficients up to the 4th order plus a constant value and a linear trend were estimated to represent the vertical TEC (VTEC). Slant TEC (STEC) values are converted into VTEC values by a mapping function. A disadvantage of this approach is the assumption that these values are assigned to the station coordinates but not to the geographical coordinates of the intersection point of the ray path and the infinitely thin ionospheric layer. The precision of the estimated values is about +/- 5 to +/- 7 TEC units (TECU). The results obtained from VLBI agree with a standard deviation of +/- 10 TECU with other techniques like GPS, and rarely exceed 20 TECU. A second approach, developed at the TU Vienna, using piece-wise linear functions (VTM – Vienna TEC model) was also tested.}, domains = {VLBI:ionosphere}, url = {ftp://ftp.leipzig.ifag.de/pub/analysis/papers/291-Hobiger.pdf} }

bibtex
H. Schuh, J. Boehm, and T. Hobiger, "Vienna IGG Special Analysis Center Annual Report 2002," in International VLBI Service for Geodesy and Astrometry 2004 Annual Report, 2003, pp. 261-264.

@INPROCEEDINGS{IVSAR02, author = {Schuh, Harald and Boehm, Johannes and Hobiger, Thomas}, title = {Vienna IGG Special Analysis Center Annual Report 2002}, booktitle = {International VLBI Service for Geodesy and Astrometry 2004 Annual Report}, year = {2003}, editor = {N. R. Vandenberg and K. D. Baver}, number = {NASA/TP-2003-211619}, pages = {261--264}, abstract = {In April 2002, the Institute of Geodesy and Geophysics (IGG), Vienna, was asked by the IVS Directing Board to coordinate the IVS Pilot Project - Tropospheric Parameters. This project aims at providing tropospheric parameters (total and wet zenith delays) on a regular basis as IVS products. As of January 2003, seven IVS Analysis Centers have joined the project and the combined time series determined so far are of high quality (Schuh et al., 2003). The IGG also continued its research on the determination of ionospheric parameters using VLBI data.}, domains = {VLBI}, url = {ftp://ivscc.gsfc.nasa.gov/pub/annual-report/2002/pdf/acigg.pdf} }

bibtex
S. Todorova, T. Hobiger, R. Weber, and H. Schuh, "Regional ionosphere modelling with GPS and comparison with other techniques," in Proceedings of the Symposium "Modern Technologies, Education and Professional Practice in the Globalizing World", November 06-07, Sofia, 2003, 2003.

@INPROCEEDINGS{SGEM03, author = {Todorova, Sonja and Hobiger, Thomas and Weber,Robert and Schuh, Harald}, title = {Regional ionosphere modelling with GPS and comparison with other techniques}, booktitle = {Proceedings of the Symposium "Modern Technologies, Education and Professional Practice in the Globalizing World", November 06-07, Sofia, 2003}, year = {2003}, domains = {GPS:ionosphere} }

bibtex