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Correcting surface loading at the observation level: impact on global GNSS and VLBI station networks

Männel, Benjamin; Dobslaw, Henryk; Dill, Robert; Glaser, Susanne; Balidakis, Kyriakos; Thomas, Maik; Schuh, Harald

FG Satellitengeodäsie

Time-dependent mass variations of the near-surface geophysical fluids in atmosphere, oceans and the continental hydrosphere lead to systematic and significant load-induced deformations of the Earth’s crust. The Earth System Modeling group of Deutsches GeoForschungsZentrum (ESMGFZ) provides vertical and horizontal surface deformations based on numerical models of the global geophysical fluids in atmosphere, oceans and the continental hydrosphere with a spatial resolution of 0.5∘ and a temporal sampling of down to 3 h (Dill and Dobslaw in J Geophys Res 118(9):5008–5017, 2013. https://doi.org/10.1002/jgrb.50353). The assessment of conventionally—i.e. without consideration of non-tidal loading models—processed global GNSS datasets reveals that large parts of the residual station coordinates are indeed related to surface loading effects. Residuals explained by the models often have a pronounced annual component, but variability at other periodicities also contributes to generally high correlations for 7-day averages. More than 10 years of observations from about 400 GNSS and 33 VLBI stations were specifically reprocessed for this study to incorporate non-tidal loading correction models at the observation level. Comparisons with the corresponding conventional processing schemes indicate that the coordinate repeatabilities and residual annual amplitudes decrease by up to 13 mm and 7 mm, respectively, when ESMGFZ’s loading models are applied. In addition, the standard deviation of the daily estimated vertical coordinate is reduced by up to 6.8 mm. The network solutions also allow for an assessment of surface loading effects on GNSS satellite orbits, resulting in radial translations of up to 4 mm and Earth orientation parameters (EOP). In particular, the VLBI-based EOP estimates are critically susceptible to surface loading effects, with root-mean-squared differences reaching of up to 0.2 mas for polar motion, and 10 µs for UT1-UTC.