Daily Regional Gravity Field Estimation Using GRACE Follow‐On Line‐of‐Sight Gravity Differences

Abstract As a complement to the conventional monthly global solutions by Gravity Recovery and Climate Experiment series of gravimetric satellites, this study proposes an alternative method for estimating daily regional gravity field by utilizing the orbital Line‐of‐Sight Gravity Difference. The method is based on Slepian and B‐spline basis functions for spatial and temporal parameterizations, respectively. Such parameterization of regional gravity field can be used to estimate total water storage change in a way compatible with surface mass estimation previously designed in the framework of global gravity field determination. The formal uncertainty of daily mass changes recovery is ∼5 Gt, equivalent to ∼3 cm of equivalent water height over 400 2 km 2 . In the evaluation part, the method is applied to the 2020 Bangladesh flood and the 2021 Australian flood. Our approach demonstrates strong agreement with the previous mascon‐based studies, yielding Nash‐Sutcliffe Efficiency values exceeding 0.81, and capturing the onset and recession of the flooding events. Additionally, we investigate the impact of data gaps, occasionally occur in the space‐borne missions employing intersatellite laser ranging system. Our findings indicate that the B‐spline parameterization effectively determines surface mass changes even with missing data rates up to 20% or with gap lengths no longer than 2 days, highlighting its reliability for continuous monitoring in challenging observational scenarios. By providing a new methodological framework for daily‐scale monitoring from satellite gravimetry, this work advances our understanding of the rapid evolution of climate extremes, which will ultimately facilitate future disaster monitoring and adaption efforts.