How does station position modelling affect the VLBI scale in ITRF2020?

Paper i proceeding, 2024

In the most recent realization of the International Terrestrial Reference System, the ITRF2020, it was found that the VLBI scale parameter has a positive drift after 2013.75.
While several possible reasons for this apparent VLBI scale drift are being discussed in the IVS community, a clear explanation for the issue has not been identified yet.
In this study, we investigate reasons for the apparent VLBI scale drift in the ITRF2020 using the CATREF software, applying the same approach as used for the ITRF2020 production.
We compare the models of discontinuities and post-seismic deformation used for VLBI station positions and velocities with those for co-located GNSS stations, and estimate the impact of these model differences on the VLBI scale drift.
The analysis reveals that one of the main factors causing the scale drift can be non-linear behavior of the Ny-Ålesund station and Wettzell station.