The accuracy of the Global Positioning System (GPS) as an instrument for measuring the integrated water vapor content of the atmosphere has been evaluated by comparison with concurrent observations made over a 14-day period by radiosonde, microwave water vapor radiometer (WVR), and Very Long Baseline Interferometry (VLBI). those derived from Global Positioning System observations. The improvement is shown in terms of reduction of rms of length-of-day estimates w.r.t. We find an improvement when (1) using ray-traced delays from a numerical weather model, and (2) when estimating tropospheric gradients within the analysis of Intensive sessions. We identify the asymmetry of the tropospheric delays as the major error source, and we provide two strategies to improve the results, in particular of those Intensives which include the station Tsukuba in Japan with its large tropospheric variation. Due to the importance of UT1 estimates for the prediction of Earth orientation parameters, as well as any kind of navigation on Earth or in space, there is not only the need to improve the timeliness of the results but also their accuracy. Very Long Baseline Interferometry (VLBI) Intensives are one-hour single baseline sessions to provide Universal Time (UT1) in near real-time up to a delay of three days if a site is not e-transferring the observational data. capabilities for Kalman filtering, phase delay solutions, and spacecraft tracking. First comparisons with other VLBI software packages show a very good agreement, and there are plans to add further features to VieVS, e.g. ![]() The parameterization with piece-wise linear offsets at integer hours in the least-squares adjustment provides flexibility for the combination with other space geodetic techniques. VieVS is equipped with the most recent models recommended by the IERS Conventions. MATLAB is the high-end programming language of the students at the Vienna University of Technology and at many other institutes worldwide. ![]() The programming language MATLAB is used, which considerably eases the programming efforts because of many built-in functions and tools. New VLBI (Very Long Baseline Interferometry) data analysis software (called Vienna VLBI Software, VieVS) is being developed at the Institute of Geodesy and Geophysics in Vienna taking into consideration all present and future VLBI2010 requirements.
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