Estimating $$C_{30}$$ coefficients for GRACE/GRACE-FO time-variable gravity field models using the GRACE-OBP approach: Fid-Bau Portal

Estimating $$C_{30}$$ coefficients for GRACE/GRACE-FO time-variable gravity field models using the GRACE-OBP approach

Sun, Yu / Li, Yang / Guo, Xiang / Guo, Jinyun

Abstract Recently, $$C_{30}$$ coefficients of time-variable gravity field models from GRACE and GRACE-Follow On (GRACE/GRACE-FO) are reported to contain larger uncertainties when only one of the two onboard accelerometers is fully functional, which mainly concerns the GRACE-FO period and the final stage of the GRACE period. Using these problematic coefficients leads to incorrect mass change (rate) estimates, especially over Antarctic Ice-Sheet (AIS), and a replacement with those from satellite laser ranging (SLR) is currently recommended. In this study, we aim to discuss the possibility of improving the $$C_{30}$$ coefficients by extending the GRACE-OBP approach that has previously been applied to the estimation of geocenter motion and variations in the Earth’s dynamic oblateness. Such an approach mainly relies on GRACE/GRACE-FO level 2 products and an ocean bottom pressure model, and it produces compatible coefficients with the GRACE/GRACE-FO product labeled as GSM. With a numerical experiment, we demonstrate the effectiveness of the proposed approach and identify the optimal implementation parameter setup. The resulting $$C_{30}$$ coefficient time series is generally consistent with those based on SLR and the original solutions from the GRACE dual-accelerometer period, but with differences in the annual amplitude estimates. Then, we obtain $$C_{30}$$ coefficients based on real data and check the AIS mass change time series with and without replacing the original ones with our solution. Our $$C_{30}$$ solution ensures consistent linear trend estimates for the dual- and single-accelerometer periods.