Comparative Analysis of The Correction Effect of Different Environmental Loading Products On Global GNSS Coordinate Time Series

The global navigation satellite system (GNSS) coordinate time series is affected by the environmental loading (including atmospheric loading (ATML), hydrological loading (HYDL), non-tidal oceanic loading (NTOL), etc.) and many organizations now provide grid products of these loadings. The temporal and spatial resolutions of these products, the loading models and data sources used are not the same, so the effect of correcting the nonlinear deformation of the GNSS coordinate time series is obviously different. This study mainly selects the three agencies, namely, School and Observatory of Earth Sciences (EOST) in France, German Research Center for Geosciences (GFZ) in Germany, and International Mass Loading Service (IMLS) in the United States, including 6 types of ATML models, 7 types of HYDL models and 5 NTOL models. The classification of these 18 environmental loading models was discussed, and the root mean square (RMS) reduction rate of the GNSS coordinate time series after environmental loading corrections (ELCs) was used to evaluate the performance differences of various models. Our results show that both the different models provided by the same organization and the same model provided by different organizations have different correction effects. Regardless of the models, it has a significant impact on the vertical coordinate time series. In order to correct the nonlinear deformation of the GNSS stations to the greatest extent, based on the above analysis, this study selects the optimal model combination of three environmental loadings as ECMWF_IB+MERRA2+ECCO1, and then explores its influence on the periodic signals in the GNSS coordinate time series. Research suggests that environmental loadings have a significant impact on the amplitude and phase of GNSS time series. Especially in the vertical direction, the largest RMS value can reach 8.42 mm. Before and after ELCs, the maximal difference of the annual amplitude and the half-annual amplitude at global 631 stations can reach 8.96 mm and 1.51 mm, respectively. Among them, 84.60% of the stations were corrected by the optimal environmental loading combination model, thus the nonlinear deformation was weakened.