Enhancing GRACE-FO Gravity Field Solutions: A Comparative Assessment and Novel Combination of ACT Products

The performance degradation of one onboard accelerometer of the GRACE-FO mission presents a significant challenge to the scientific community. This issue has been largely mitigated by transplanting data from the other fully functional accelerometer. Various accelerometer data transplant (ACT) products have been developed using distinct methodologies, each showing different performances in gravity field recovery. In this study, we conduct a systematic evaluation of three available ACT products—JPL-ACT and JPL-ACH from NASA's Jet Propulsion Laboratory, and TUG-ACT from Graz University of Technology—utilizing a uniform Level-1B data processing approach. Our analysis reveals that these ACT products exhibit inconsistent quality across different time periods. Consequently, we introduce a novel approach combining these ACT products at the normal equation level to enhance gravity field solution accuracy. Compared to solutions using the JPL-ACT, the combined solution gives a notable noise reduction of 5% to 12% depending on the choice of post-processing filters and the replacement of C₂₀/C₃₀ coefficients, which doubles the noise reduction achieved by the next best individual ACT product, JPL-ACH. Furthermore, the C₂₀ coefficient derived from the combined solution agrees better with the Satellite Laser Ranging (SLR) benchmark, compared to those derived from individual ACT products. This advancement largely reduces the spurious 161-day signal observed in polar regions. Regarding the C₃₀ coefficient, while JPL-ACT solutions exhibit suboptimal estimates, the JPL-ACH, TUG-ACT, and combined solutions all contribute to substantial improvements.