High-Resolution GRACE Monthly Spherical Harmonic Solutions

Mass transport estimates based on filtered Gravity Recovery and Climate Experiment (GRACE) monthly spherical harmonic gravity field solutions generally suffer from resolution loss and signal attenuation. To develop high-resolution solutions from GRACE Level-1B data, this study proposes a new regularization method. Transforming spatial constraints from GRACE-based filtered mass changes into the spectral domain and imposing them on spherical harmonics, we resolve high-resolution gravity field solutions expressed as spherical harmonics instead of mascons. The proposed method greatly enhances the spatial resolution and signal strength of spherical harmonic solutions. Using the presented method, we have produced a time series of high-resolution (degree 180) spherical harmonic solutions named Tongji-RegGrace2019, which can be directly used without further smoothing. To evaluate Tongji-RegGrace2019, we conduct the global (trend and annual amplitude) and regional comparisons (groundwater loss signals over India, hydrology signals over river basins, and ice melting signals over Greenland, Antarctica Peninsula and Patagonia) among various GRACE solutions. Our analyses show that Tongji-RegGrace2019 agrees well with Center for Space Research and Jet Propulsion Laboratory mascon solutions in terms of signal power and spatial resolution. Over the selected areas, the correlation coefficients of mass changes between Tongji-RegGrace2019 and mascon solutions are at least 82%. Compared to the filtered solution, higher spatial resolution and stronger signal power are achieved by Tongji-RegGrace2019 and mascon solutions, which have the potential to retrieve signals at a smaller spatial scale. Over Patagonia Icefield, the improvement of trend estimates by Tongji-RegGrace2019 with respect to the filtered solution is about 150%.