Improved Resolution of a GRACE Gravity Field Model by Regional Refinements

The available gravity field models derived from data of the GRACE mission (tapley and Reigber (2001)) have provided us with an unprecedented accuracy in gravity field determination. Nevertheless the projected GRACE baseline accuracy has not been achieved yet. One reason out of many could be the insufficient modelling of the satellite data by a global representation by means of spherical harmonics. To extract the signal information present in the satellite and sensor data to full content, it seems reasonable to improve global solutions by regional recovery strategies. Especially in the higher frequency part of the spectrum the gravity field features differ in different geographical areas. Therefore the recovery procedure should be adapted according to the characteristics in the respective area. In the approach presented here in a first step a global gravity field represented by a spherical harmonic expansion up to a moderate degree has to be derived. It is then refined by regionally adapted high resolution refinements being parameterized by splines as space localizing base functions. In this context a special attention is paid to the signal to noise ratio in different geographical areas. The approach is demonstrated by examples based on the analysis of the original GRACE Level 1B data.