Combined IVS Contribution to the ITRF2020

AbstractThe ITRF2020 is the upcoming official solution of the International Terrestrial Reference Frame and is the successor to the currently used ITRF2014. The global ITRF2020 solution is based on an inter-technique combination of the four space-geodetic techniques VLBI, GNSS, SLR, and DORIS. In this context, the Combination Centre of the IVS (International VLBI Service for Geodesy and Astrometry) operated by the Federal Agency for Cartography and Geodesy (BKG, Germany) in close cooperation with the Deutsches Geodätisches Forschungsinstitut at TUM (DGFI-TUM, Germany) generates the final VLBI contribution of the IVS. This is achieved by an intra-technique combination utilizing the individual contributions of multiple IVS Analysis Centres (ACs). For the IVS contribution to the ITRF2020, sessions containing 24 h VLBI observations from 1979 until the end of 2020 were re-processed by 11 different ACs and submitted to the IVS Combination Centre. As a result, datum-free normal equations containing station coordinates and source positions as well as full sets of Earth Orientation Parameters (EOP) are delivered. In order to ensure consistency of the combined solution, time series of EOP and station coordinates were generated and further investigated for validation. Finally, the IVS contribution to the ITRF2020 comprises session-wise normal equations including EOP and station coordinates provided in SINEX format. In order to assess the quality of the contributions by the individual IVS ACs, internal as well as external comparisons of the estimated EOP are carried out, with the combined solution as well as external time series (e.g., IERS Bulletin A) serving as a reference. Additionally, the scale of the IVS contribution is investigated as VLBI is one of the space geodetic techniques realizing the scale of the ITRF. The evaluation of the contributions by the ACs, the combination procedure, and the results of the combined solution for station coordinates and EOP will be presented.