Troposphere gradients from the ECMWF in VLBI analysis |
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Authors: | Johannes Boehm Harald Schuh |
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Institution: | 1. Institute of Geodesy and Geophysics, Vienna University of Technology, Gu?hausstra?e 27-29, 1040, Vienna, Austria
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Abstract: | Modeling path delays in the neutral atmosphere for the analysis of Very Long Baseline Interferometry (VLBI) observations has
been improved significantly in recent years by the use of elevation-dependent mapping functions based on data from numerical
weather models. In this paper, we present a fast way of extracting both, hydrostatic and wet, linear horizontal gradients
for the troposphere from data of the European Centre for Medium-range Weather Forecasts (ECMWF) model, as it is realized at
the Vienna University of Technology on a routine basis for all stations of the International GNSS (Global Navigation Satellite
Systems) Service (IGS) and International VLBI Service for Geodesy and Astrometry (IVS) stations. This approach only uses information
about the refractivity gradients at the site vertical, but no information from the line-of-sight. VLBI analysis of the CONT02
and CONT05 campaigns, as well as all IVS-R1 and IVS-R4 sessions in the first half of 2006, shows that fixing these a priori
gradients improves the repeatability for 74% (40 out of 54) of the VLBI baseline lengths compared to fixing zero or constant
a priori gradients, and improves the repeatability for the majority of baselines compared to estimating 24-h offsets for the
gradients. Only if 6-h offsets are estimated, the baseline length repeatabilities significantly improve, no matter which a
priori gradients are used. |
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Keywords: | Troposphere modeling Troposphere gradients VLBI ECMWF |
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