Comparison of GRACE Follow-On Level-2 data from RL06 and RL06.1: Assessing the impact of the new accelerometer transplant data

The GRACE-D accelerometer data shows large bias jumps starting from 21 June 2018. The GRACE Follow-On (GRACE-FO) Science Data System (SDS) centers (CSR, JPL and GFZ) use a transplant technique applying GRACE-C accelerometer data to replace that of GRACE-D. To improve the accuracy of non-gravitational measurements acting on the satellites, the GRACE-FO SDS centers recently released an updated hybrid-transplant accelerometer data for GRACE-D, which uses measurements from both satellites. Accordingly, updated (RL06.1) Level-2 (L2) monthly gravity solutions using the new accelerometer data are being released. In this work, we will present our results on quantification of the changes/improvements in the RL06.1 L2 solutions from all three SDS centers relative to RL06. We also explore the possibility of validating the changes using independent datasets. We first compare the low-degree harmonic coefficients C_{20} and C_{30} with those from SLR (TN-14) and examine their agreement at seasonal and interannual timescales. Using various spectral-domain analysis tools, we detect the spectral bands of spherical harmonic degrees and orders where the major changes in RL06.1 are observed. We then quantify the impact of such spherical harmonic coefficients on surface mass change estimates over the GRACE-FO period. Moreover, we quantify the noise reduction in monthly mass change solutions from RL06.1 (relative to RL06) over open oceans. For the latter analysis, we also detect the spatial regions as well as months which show the largest noise reduction and discuss the possible causes behind that. Our work is aimed at helping the GRACE-FO SDS to evaluate the improvement by new accelerometer transplant data.