WHU-GRACE-GPD01s: A Series of Constrained Monthly Gravity Field Solutions Derived From GRACE-Based Geopotential Differences

To suppress the correlated noise of Gravity Recovery and Climate Experiment (GRACE) spherical harmonic (SH) solutions, we developed a series of constrained monthly gravity field solutions named WHU-GRACE-GPD01s from August 2002 to July 2016 using GRACE-based geopotential differences. The constrained solutions were estimated using Kaula regularization, and the optimal regularization parameters were adaptively determined from the GRACE data itself through variance component estimation. The performance of the constrained WHU-GRACE-GPD01s solutions was validated against the official SH solutions (GFZ, JPL, and CSR RL06) and mass concentration (mascon) solutions (CSR RL06M) at global and regional scales. The results demonstrate that mass changes derived from the constrained solutions and official SH solutions with DDK4 filtering are in good agreement, but the constrained solutions present weaker longitudinal stripes and have a lower noise level at regional scales (e.g., in the Middle Pacific Ocean and Sahara Desert). Furthermore, regional mass changes (e.g., major river basins, Greenland, and Antarctic ice sheet) inferred from the constrained solutions agree with the ones derived from the official SH solutions with DDK4 filtering. The constrained solutions also have a higher signal intensity and smaller spatial leakages as compared to the CSR RL06 SH solutions with spatial filtering (Gaussian filtering plus de-striping). For the problematic months, the constrained solutions are more reliable than the official SH solutions using spatial filtering or DDK4 filtering, and are closer to CSR RL06M mascon solutions. These validations demonstrate that our constrained solutions are comparable to the official SH solutions and can be used without postprocessing.