Geodetic Analysis of Orthometric Height Variations in Mainland China Using GRACE, Hydrological Models, and GPS Data

Temporal variations of hydrological mass cause changes in geoid height and surface deformation, resulting in time variation of orthometric height. The daily gravity recovery and climate experiment (GRACE) gravity field model and global hydrological models consistent with the temporal resolution of daily global positioning system (GPS) data were employed in this study to estimate the orthometric height variations in mainland China. Based on the spherical harmonic function (SHF) and Green’s function, the orthometric height variations of ten major river basins in mainland China showed obvious submonthly and annual fluctuations. The annual amplitude of orthometric height variations was distributed according to latitude and decreased gradually with an increase in latitude. Among the 249 selected GPS stations, >96.8% positively correlated with both daily GRACE and hydrological models derived orthometric height variations, with the GPS stations in the Southwest River Basin having the best correlation. To compare with the daily GPS vertical displacement, it is necessary to consider the surface loading derived from satellite gravity data or hydrological models in relation to their temporal resolution. By removing the surface loading effect from the GPS height, it was observed that the hydrological load was best corrected using the hydrological model instead of GRACE solutions. Finally, we analyzed the vertical tectonic motion of the main tectonic blocks in mainland China by removing the loading derived from the hydrological model and discussed the main influencing factors of tectonic motion.