-
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. }
}
-
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 }
}
-
T. Hobiger, D. Piester, and P. Baron, "A correction model of dispersive troposphere delays for the ACES microwave link," Radio Science, vol. 48, pp. 1-12, 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},
pages={1-12},
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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/}
}
-
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, Ruediger 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}
}
-
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}
}
-
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}
}
-
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}
}
-
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, Ruediger 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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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, Ruediger 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}
}
-
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}
}
-
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.
-
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.
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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, Ruediger 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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
-
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}
}
[...] I had some time and I did some update on my scientific publications and I also generated this histogram showing the peer-reviewed papers of the last years. 2008 has [...]