Combined Gravity Solution from SLR and GRACE/GRACE-FO

Abstract The recovery of Earth’s time variable gravity field from satellite data relied heavily on Satellite Laser Ranging (SLR) before the recent GRACE and GRACE Follow-On satellite gravity missions. Currently, the monthly gravity solutions from GRACE/GRACE-FO provide important global information about the temporal variations of gravity field. However, there are a few low-degree coefficients derived from GRACE/GRACE-FO that are not well determined, because of the satellite gravity mission configuration and issues with the accelerometer data. These low-degree coefficients can be determined reasonably well using SLR data from the dedicated SLR satellite configuration and can be used to replace the less well-determined values from GRACE/GRACE-FO. A more rigorous and consistent approach is to directly combine SLR and GRACE/GRACE-FO gravity solutions in a simultaneous solution. This paper presents a combination strategy for gravity field recovery from combined SLR and GRACE/GRACE-FO mission data. To correctly account for all correlations, the combination is performed at the information (normal) equation level. The coefficients C20 and C30 are determined mainly from SLR by renaming C20 and C30 parameters in GRACE/GRACE-FO information equations. The results show that the combined products are improved in comparison with the nominal GRACE/GRACE-FO gravity solutions. The gravity field products are evaluated by comparing different gravity solutions through coefficient-wise comparison, equivalent water height variations and mass changes over selected areas.