A Multi‐Source GRACE Fusion Solution via Uncertainty Quantification of GRACE‐Derived Terrestrial Water Storage (TWS) Change

Abstract In analyzing terrestrial water storage (TWS) data observed by Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On satellites, quantifying uncertainties proves challenging due to the scarcity of sufficient independent observations of mass changes at scales commensurate with these missions. Moreover, owing to the diverse geophysical background models and processing techniques utilized by data processing centers, reaching consistent mass change estimations within specific regions of published solutions often proves arduous. We, therefore, quantified the uncertainty of the GRACE‐derived TWS changes by using the generalized three‐cornered hat method without relying on any prior knowledge and fused it to generate a higher‐quality solution. The findings reveal that of the six solutions, the Center for Space Research spherical harmonics (SH) solution exhibits the lowest uncertainty and highest signal‐to‐noise ratio (SNR) at both global and basin scales, and the Goddard Space Flight Center Mascon solution outperforms other Mascon counterparts. The fusion solution has an average 36.56% reduction in uncertainty and a 1.92‐fold improvement in SNR at the basin scale, and the improvement in SNR is particularly significant in regions with drastic mass changes. The global distribution patterns of the uncertainties associated with Mascon and SH solutions exhibit distinct differences. Mascon solutions result in significant signal leakage around regions characterized by the most substantial global mass variability. Additionally, transient mass changes triggered by super earthquake events in the ocean also produce similar “scars” in the global spatial distribution of uncertainties. The analysis of 142 basins worldwide shows that basins with more significant TWS annual oscillations have larger uncertainties but also better SNR.