Deriving long-term geocenter motion estimates for geophysical applications

The geocenter motion describes the relative motion between the Earth’s center-of-mass and center-of-figure, representing one of the largest-scale mass redistributions in the Earth system. Accurate determination of geocenter motion is essential for the realization of the terrestrial reference frames (TRF) and for the full-spectrum monitoring of global mass variations. Traditionally, geocenter motion can be estimated directly from Satellite Laser Ranging (SLR) by tracking orbital motion with ground stations since the 1990s or indirectly from gravity fields provided by the Gravity Recovery and Climate Experiment (GRACE) since 2002. However, SLR-derived geocenter motion estimates are generally unsuitable for studying long-term mass changes because the secular trend is absorbed by the linear definition of the TRF. Additionally, only low-degree gravity fields were available before GRACE (e.g., from SLR), resulting in significant signal leakage errors in geocenter estimates. In this study, we derive the geocenter motion from low-degree gravity fields (up to degree and order 5) after properly addressing signal leakage effect. By combining the leakage-corrected land mass patterns with self-consistent ocean mass fingerprints, we generate geocenter motion estimates and compare them with those derived from GRACE, geophysical models, and the SLR direct tracking method. The trends in our estimates are consistent with GRACE and models, while the SLR direct estimates yield opposite trends, leading to significantly underestimated global ocean mass change rates. Our study provides promising results for deriving long-term estimates of geocenter motion, enabling the study of mass changes in the global oceans and polar ice sheets back to the 1990s.