Comparison of common VLBI and GNSS estimates in CONT17 campaign

CONT17 is an observation campaign of continuous Very Long Baseline Interferometry (VLBI) sessions for a period of 15 days, carried out by the International VLBI Service for Geodesy and Astrometry (IVS). This campaign represents an interesting opportunity for the inter-comparison of space geodetic techniques given that they share the same observability conditions in co-located sites. In this work, VLBI estimates of Earth orientation parameters (EOP), station coordinates and troposphere—zenith total delays (ZTD) and gradients—are compared to those estimated by means of Global Navigation Satellite Systems (GNSS) observations. We considered solutions from different software packages and processing techniques for this analysis, including all the available IVS and IGS (International GNSS Service) solutions and two VLBI series obtained by the authors. This extensive analysis provides a representative view of the inter-technique differences under the same observation conditions. We considered in the analysis the two VLBI legacy S/X networks that took part in the CONT17 campaign. We found that the EOP WRMS with respect to IGS final products is similar to previous CONT campaigns, even using global VLBI solutions that assimilate the data from both CONT17 legacy-1 and legacy-2 networks. Repeatabilities of estimated VLBI antenna coordinates of the legacy-1 network have a similar behaviour than GNSS-based repeatabilities in east and north components and slightly worse in up component whereas the repeatabilities of the legacy-2 network are smaller than legacy-1 network and similar to the IGS combined solution. Finally, troposphere inter-technique differences in terms of ZTD and gradients also show a similar agreement to different sources of GNSS-based troposphere estimates.