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Armin Hofmeister
Type of contribution: oral

Influence of the horizontal resolution of numerical weather models on ray-traced delays for VLBI analysis

Armin Hofmeister, Technische Universit"at Wien Daniel Landskron, Technische Universit"at Wien Johannes B"ohm, Technische Universit"at Wien

Ray-traced delays offer the opportunity of an alternative way to correct the influences of the troposphere on observations of space geodetic applications such as Very Long Baseline Interferometry (VLBI). Compared to the standard approach, where the slant delays for the tropospheric correction are determined via estimated zenith delays and the application of mapping functions, the ray-tracing approach estimates the slant delays directly for the actual ray paths of the observations. In order to determine the actual ray paths and the slant delays of the observations, the ray-tracing method requires information about the troposphere in terms of refractivity values. These can be derived from meteorological data provided by a numerical weather model (NWM). Because the NWM builds the data base for ray-tracing, the selection of an appropriate NWM is of major concern. In this respect also the chosen horizontal resolution of the NWM may have significant impact on the resulting ray-traced slant delays. This aspect shall be investigated. In order to assess the effect of the horizontal resolution of the NWM on the ray-traced delays, we use our new ray-tracing program RADIATE to determine the delays. As meteorological data input we utilize a NWM from the European Centre for Medium-Range Weather Forecasts (ECMWF) with different horizontal resolutions, e.g. 0.125 deg x 0.125 deg and 1 deg x 1 deg. As observational data input we use the CONT11 campaign of the International VLBI Service for Geodesy and Astrometry (IVS) covering 15 days of continuous VLBI observations. In the first step we compare the estimated ray-traced delays derived from the same NWM with different horizontal resolutions in order to see the direct effect on them. In the next step we investigate the impact of the different horizontal resolutions of the NWM on the VLBI analysis. Therefore we apply the ray-traced slant delays in VLBI analysis to assess the effect in terms of baseline length repeatability.