Improved modelling for future VLBI contributions to ITRF

Paper in proceeding, 2023

In the latest realization of the International Terrestrial Reference System, ITRF2020, the VLBI scale seems to have a drift after 2013.75. The reason for this is not yet understood. In this work we investigate if it could be caused by one of the models used in the VLBI data analysis. To begin with, we show that the drift is reduced by 40 % if two additional breaks are added to the Ny-Ålesund station. Furthermore, we investigate the impact of the models for gravitational deformation, thermal deformation, pole tide, geophysical loading, celestial reference frame, and post seismic deformations. Our results show that none of the models could explain of the scale drift completely, although by changing models for geophysical loading and post seismic displacement, the drift could be reduced by 20 %. The results also showthat some models – like those for thermal deformation, pole tide, and geophysical loading– could introduce seasonal signals in the estimated scale if not applied in the VLBI analysis.