Regional Static Gravity Field Modeling Using the GRACE-FO LRI Observations

Abstract

Global static gravity models produced as spherical harmonic (SH) coefficients have a wide range of applications in geodesy, geophysics, oceanography, and satellite dynamics. It has been established that more information can be extracted from the observations using regional modeling compared to global spherical harmonic analysis. The GRACE Follow-On (GRACE-FO) mission carries a technology demonstrator Laser Ranging Interferometer (LRI) in addition to the K-band ranging (KBR) system. KBR is capable of recovering gravity signals up to ~60 CPR (~350 km half-wavelength spatial scale), whereas LRI recovers up to ~200 CPR (~105 km half-wavelength spatial scale), beyond which the sensor noise dominates the signal. Static gravity model GGM05C revealed localized deficiencies in recovering gravitational signals especially over Africa, South America, and the Himalayas within the 10-36 mHz (~55-200 CPR) frequency band. Our analysis aims to demonstrate that regional gravity field modeling can recover these high frequency signal content which may be suppressed by global gravity field modeling. We use the Line-of-sight Gravity Difference (LGD) observations derived from 4 years of GRACE-FO LRI measurements and recover the regional gravity field solutions up to degree 180 (~117 km half-wavelength spatial scale). This is done by using the spherical radial basis functions (SRBF), which allows us to adapt the model resolution and regularization to be carried out based on the signal characteristics and the data coverage of each study area. We use the Tikhonov regularization approach to stabilize ill-conditionedness during the inverse problem. The resulting recovered regional solutions show smoother signals over oceans and simultaneously recover the additional high-frequency gravity signals over Africa, South America and the Himalayas. Since the regions selected for gravity field recovery have limited terrestrial data coverage, we compared our results with the global static gravity field model GOCO2025s. This model incorporates GRACE-FO LRI observations in its gravity field estimation. Therefore, although GOCO2025s is a global model, it provides a useful reference for assessing the signal recovery of our regional solutions in terms of gravity functionals such as gravity disturbance and geoid height.