The impact of estimating common tropospheric parameters for co-located VLBI radio telescopes on geodetic parameters during CONT17. Issue 9 (1st May 2022) - Kitpracha, Chaiyaporn
Abstract: The Continuous Very Long Baseline Interferometry (VLBI) campaign 2017 (CONT17) differs from previous CONT campaigns as there are three independent networks observing in parallel; two legacy VLBI networks observing in S/X band (Legacy-1 and Legacy-2) and one VGOS (the next generation VLBI system: VLBI2010) network observing in broadbrand. Co-located VLBI radio telescopes across the networks could be combined to strengthen the geodetic solutions from CONT17 by using local ties. Moreover, it is widely known that the co-located VLBI radio telescopes observe common effects such as the tropospheric delays in a similar way. Therefore, we can not only combine the station coordinates, but we can also combine the tropospheric parameters. In this work, we focused on the impact of combining the tropospheric parameters obtained at co-located VLBI telescopes on the estimated geodetic parameters during CONT17. We considered three case studies where we combined: (i) the Legacy-1 and the Legacy-2 networks, (ii) the Legacy-1 and the VGOS networks, and (iii) the Legacy-1, the Legacy-2, and the VGOS networks. The results show an improvement in station position repeatability when combining the tropospheric parameters w.r.t. applying only local ties by 28 %, 15 %, and 26 % respectively. Station coordinates at the VLBI radio telescopes of the Legacy-1 network were not affected by this approach as they were used for the datum definition. In addition, the baseline length repeatabilities show no improvement when combining the tropospheric parameters. Moreover, the agreement between the tropospheric parameters from VLBI and tropospheric parameters from independent GNSS data analysis and ray-tracing through ERA5 improves due to the network combination.