The impact of estimating common tropospheric parameters for co-located VLBI radio telescopes on geodetic parameters during CONT17

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 S/X band (Legacy-1 and Legacy-2) one VGOS (the next generation system: VLBI2010) network broadbrand. Co-located radio telescopes across the could be combined to strengthen geodetic solutions CONT17 by using local ties. Moreover, it is widely known that co-located observe common effects such tropospheric delays a similar way. Therefore, we can not only combine station coordinates, but also parameters. In this work, focused on impact of combining parameters obtained at estimated during CONT17. We considered case studies where combined: (i) Legacy-1 Legacy-2 networks, (ii) (iii) Legacy-1, Legacy-2, networks. results show an improvement position repeatability when w.r.t. applying ties 28%,15%, 26% respectively. Station coordinates were affected approach they used for datum definition. addition, baseline length repeatabilities no agreement between GNSS data analysis ray-tracing through ERA5 improves due combination.