GRACE Follow-On Accelerometer Data Recovery

In Gravity Recovery and Climate Experiment (GRACE) Follow-on (GRACE-FO) mission, similar to its predecessor GRACE, the twin satellites are equipped with three-axis accelerometers, measuring the non-gravitational forces. After 1 month in orbit, during the in-orbit-checkout phase, the noise on GRACE-D accelerometer measurements elevated and resulted in systematical degradation of the data. For this reason, the GRACE-D data need to be replaced by synthetic data, the so-called transplant data, officially generated by the GRACE-FO Science Data System (SDS). The SDS transplant data are derived from the GRACE-C accelerometer measurements, by applying time and attitude corrections. Furthermore, model-based residual accelerations due to thruster firings on GRACE-D were added, proven to improve the data quality in gravity field recovery. However, preliminary studies of GRACE-FO data during the single accelerometer months show that the low degree zonal harmonics, in particular C20 and C30, are sensitive to the current transplant approach. In this work, we present a novel approach to recover the GRACE-D ACT1B data by incorporating non-gravitational force models and analyze its impact on monthly gravity field solutions. The results show the improved ACT1B data not only contributed to a noise reduction but also improved the estimates of the C20 and C30 coefficients. The application of this new approach demonstrates that the offset between Satellite Laser Ranging (SLR) and GRACE-FO derived C30 time series can be reduced by the use of the alternative accelerometer product.