Analysis of Non-Tidal Loading Deformation at VLBI Sites

Abstract

Very Long Baseline Interferometry (VLBI) is one of the geodetic techniques used to establish the International Terrestrial Reference Frame (ITRF). It relies on data collected from multiple antennas situ- ated at various locations across the Earth’s surface. However, the accuracy of VLBI measurements can be compromised by Earth’s crust deformation caused by a range of geophysical factors, including plate tectonics, solid Earth tide-induced loading, atmospheric pres- sure variations, and redistribution of water masses, both over land and in the oceans. Among these factors, non-tidal loading (NTL) deformations can also lead to positional shifts in VLBI sites, thus affecting measurement accuracy. To address these NTL effects in VLBI analysis, geophysical models are employed to correct the displacement of VLBI stations. The objective of this study is to compare the NTL products obtained from different loading services, such as the VieAPL, ESMGFZ, IMLS, and EOST. The evaluation of how these NTL products impact VLBI analysis is carried out using the VieVS software. This assessment entails the computation of baseline length repeatability and station height standard deviation, both before and after applying the loading corrections.