Low-Degree Spherical Harmonic Coefficients for GRACE/GRACE-FO Gravity Field Models From the Fingerprint Approach

Abstract

Low-degree coefficients of time-variable gravity field models from Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) capture large-scale mass changes within the Earth system. However, some of these coefficients are either missing (e.g., degree-1 coefficients) or poorly determined (e.g., $C_{20}$). Such a situation is exacerbated particularly over the GRACE-FO period when one of the accelerometers carries elevated noise. In this study, we present a framework for estimating low-degree coefficients using the fingerprint approach. Our results demonstrate that this method can reliably estimate multiple coefficients simultaneously, producing degree-1, $C_{20}$, and $C_{30}$ estimates that are comparable to the currently recommended solutions, both in direct comparisons and in the context of estimating mass changes over the Antarctic Ice Sheet. This framework not only provides an alternative approach for determining low-degree coefficients currently identified as problematic in GRACE/GRACE-FO gravity field models, but also shows potential for addressing other degraded low-degree coefficients that may emerge during future GRACE-FO operations.