Ellipsoidal Equal-Area Panel Mascons from GRACE Intersatellite Geopotential Differences: A Preliminary Assessment over China

Abstract

We present a mascon-type solution that partitions the Earth's surface into contiguous, gap-free, equal-area panels defined directly on the reference ellipsoid via an authalic-latitude mapping, eliminating the need for a constant-radius approximation or subsequent rescaling. Each panel is treated as a locally curved point mass, yielding a closed-form kernel for the GRACE intersatellite geopotential differences (GPD), which serve as observations. Panel masses are estimated in a Bayesian (maximum a posteriori) framework using a diagonal prior covariance informed by the temporal variability of an independent hydrological field. The regularized normal equations are solved by preconditioned conjugate-gradient least squares (CGLS) with L-curve stopping, avoiding the assembly or factorization of any large matrix and enabling the full monthly inversion to run on standard workstation hardware. Based on this framework, a preliminary global inversion was performed for 4,704 ellipsoidal panels for each of 155 monthly WHU/SGG GPD datasets spanning April 2002 to July 2016. For a preliminary assessment, the results were clipped to China and evaluated against the official JPL, CSR, and GSFC mascon solutions. Overall, the solution reproduces the dominant spatial patterns, seasonal amplitude, and secular trends of the reference products, with spatial correlations ranging from 0.73 to 0.82 for annual amplitude and 0.67 to 0.74 for trend, and a spatial correlation of 0.80 with JPL-M for a single-month (September 2005) verification. Basin-averaged time series for China's nine major river basins reproduce reported drought events, with discrepancies against the reference mascons confined mainly to an arid basin. These results demonstrate that the proposed ellipsoidal-panel parametrization offers an efficient, transparent, and reproducible alternative for regional mass inversion.