Abstract
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 one month in orbit, during the in-orbit-checkout phase,
the noise on GRACE-D accelerometer measurements elevated and results in
systematical degradation of the data. For this reason, the GRACE-D data
needs 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 is 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 improve 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.