Unconstrained Estimation of VLBI Global Observing System Station Coordinates

Abstract

The International VLBI Service for Geodesy and Astrometry (IVS) is currently setting up a network of smaller and thus faster radio telescopes observing at broader bandwidths for improved determination of geodetic parameters. However, this new VLBI Global Observing System (VGOS) network is not yet strongly linked to the legacy S/X network and the International Terrestrial Reference Frame (ITRF) as only station WESTFORD has ITRF2014 coordinates. In this work, we calculated VGOS station coordinates based on publicly available VGOS sessions until the end of 2019 while defining the geodetic datum by fixing the Earth orientation parameters and the coordinates of the WESTFORD station in an unconstrained adjustment. This set of new coordinates allows the determination of geodetic parameters from the analysis of VGOS sessions, which would otherwise not be possible. As it is the concept of VGOS to use smaller, faster slewing antennas in order to increase the number of observations, shorter estimation intervals for the zenith wet delays and the tropospheric gradients along with different relative constraints were tested and the best performing parametrization, judged by the baseline length repeatability, was used for the estimation of the VGOS station coordinates.