Filling GRACE Gaps Using GRACE-Derived Time Varying Model

Using time-variable gravity field models has recently become essential for studying the hydrology change, ice melting, Earth’s crust deformation, etc. One of the most successful missions for establishing the time-variable gravity field model is the Gravity Recovery and Climate Experiment (GRACE) mission and its successor GRACE-Follow On (GARCE-FO) mission. However, the eleven-month gap between the end of GRACE's life span and the start of GRACE-FO observations hinders the study continuation. This investigation is devoted to model the GRACE data using time-variable gravity field model employing a smart least-squares regression technique. The GRACE-derived time-variable gravity field model is validated first using available GRACE data used in the modeling technique (to measure the internal precision of the model) as well as using available GRACE data which have not been used in the modeling technique (to measure the external accuracy of the model). The assessment of the derived model has been carried out at two different levels in the frequency domain (through the harmonic coefficients and the degree variances) and in the space domains (through the total water storage change in Africa). The GRACE-derived time-variable gravity field model has then been used to fill in the GRACE/GRACE-FO gap. A comparison among the existing techniques of filling-in the GRACE gaps versus the derived technique within the current investigation is given and widely discussed. This study is supported by the National Natural Science Foundations of China (NSFC) under Grants 41874023, 41721003, 41631072.

Keywords: GRACE, GRACE-FO, Gravity, GRACE gap, TWS, Least square adjustment.