Comparison of GNSS residuals displacementswith environmental loading models

All geodetic technique observations (DORIS, GNSS, SLR and VLBI) have been processed up to the end of 2024 in order to compute the  second update of the International Terrestrial Reference Frame 2020, namely ITRF2020-u2024 (https://itrf.ign.fr/en/solutions/ITRF2020-u2024). Following the IERS conventions, no environmental loading corrections have been applied besides ocean tides.

We also compute daily GNSS solution using the GINS software in iPPP (precise point positioning with integer ambiguity resolution) for the 2000-2025 period, and orbit/clock products from the CNES/CLS analysis center.

In parallel, the IERS Global Geophysical Fluid Center has provided atmospheric, induced oceanic and hydrological loading estimates for all permanent stations based on the latest ECWMF reanalysis (ERA5) and the barotropic ocean model TUGO-m (http://loading.u-strasbg.fr/ITRF2020/).

In this paper, we present a comparison of both the combined ITRF2020-u2024 and our daily GNSS residual displacements to environmental (atmosphere, ocean and continental hydrology) loading estimates. In more details, we show that the ERA5-based reanalyzes are in better agreement with the geodetic observations than the MERRA2 (Modern-Era Retrospective Analysis for Research and Applications, Version 2) reanalysis. We also show the improvement of the ERA5-land, a re-run of the land component of the ECMWF ERA5 climate reanalysis, versus the original ERA5 hydrological component.

Finally, we also show that a dynamic ocean response to pressure and wind is more suitable to model high frequency ocean non-tidal loading effects than the classical inverted barometer (IB) approximation.