Evaluation of VGOS and legacy S/X VLBI observations with non-tidal loading corrections

Abstract

Non-tidal surface loading (NTSL) is not traditionally corrected in geodetic measurements due to its relatively low modelling accuracy; however, it can displace geodetic sites by up to several centimeters, significantly affecting the precision of geodetic parameters of interest. This study assesses the impact of NTSL corrections within Very Long Baseline Interferometry analysis by integrating NTSL data from the International Mass Loading Service and analyzing it using the Vienna VLBI and Satellite Software (VieVS). Specifically, we analyze 141 VLBI Global Observing System (VGOS) sessions and 755 legacy S/X sessions from 2019 to 2023. Our findings reveal that incorporating NTSL corrections results in improvements in BLR for approx. 79 % of the VGOS and 68 % of the S/X baselines. Similarly, the analysis of SHR reveals improvements in all VGOS stations and in approx. 74 % of S/X stations after NTSL corrections. A detailed analysis of the improvement in BLR of individual baselines following NTSL corrections shows that on average, the improvement in individual baselines in VGOS sessions is approx. 7 %, compared to only 2.7 % in S/X sessions. VGOS baselines consistently exhibit lower baseline noise variance than S/X baselines, with the latter being approx. six times higher on average, suggesting better overall performance and higher precision in measurements of VGOS technology. The variance reduction coefficient (R) further demonstrates that, a greater proportion of VGOS baselines (46 %) provides the expected reduction in variance (0.5 ≤ R ≤ 1) compared to S/X baselines (26 %). Within this expected range of improvement, VGOS baselines showed an average improvement of 6.3 %, compared to 1.3 % for S/X baselines confirming that baselines in VGOS sessions benefit more from NTSL correction than those in S/X sessions.