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Kamil Teke
Type of contribution: oral

GNSS zenith delays and gradients in the analysis of VLBI Intensive sessions

Kamil Teke, Hacettepe University Johannes B"{o}hm, Vienna University of Technology Matthias Madzak, Vienna University of Technology Younghee Kwak, Vienna University of Technology Peter Steigenberger, Deutsches Zentrum f"{u}r Luft- und Raumfahr

Very Long Baseline Interferometry (VLBI) is the only space geodetic technique which is sensitive to Universal Time (UT1). VLBI Intensive sessions of the International VLBI Service for Geodesy and Astrometry (IVS) are observed for the rapid production of UT1. However, the accuracy achieved with those sessions is still below what could be expected from formal uncertainties of the estimates and one of the reasons is the inappropriate modelling of azimuthal asymmetries of the troposphere delays, because usually no gradients are modelled or estimated. To overcome that deficiency, we introduced troposphere zenith delays and horizontal total gradients estimated from the observations of Global Navigation Satellite Systems (GNSS) i.e. the solutions of the Center for Orbit Determination in Europe (CODE) and the International GNSS Service (IGS) in the analysis of VLBI Intensive sessions carried out in 2013. We compared our results with the length of day (LOD) estimates of a CODE solution of GNSS observations. We get the best agreement of LOD in standard deviation of differences between the solution with zenith wet delays and gradients from CODE and LOD from CODE for XK Intensive sessions. The improvement of agreement compared to the standard IVS solution is largest for XK sessions with gradients from IGS and CODE and for XU sessions with gradients from IGS. The improvement is as large as 6 microseconds. We do not see any additional significant improvement of LOD agreement when external zenith wet delays are introduced.