Global gravity field solutions based on a simulation scenario of GRACE SST data and regional refinements by GOCE SGG observations

GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) has the potential of deriving the global gravity field with unprecedented accuracy in the high resolution spectral part. The usual way is to model the gravity field by spherical harmonics up to a degree limited by the numerical stability of the recovery procedure. A disadvantage of this kind of gravity field representation is the lack of flexibility in modeling the inhomogeneous gravity field of regions with variable rough gravity field features. An alternative approach is to determine a global gravity field solution with high long and medium wavelength accuracy, e.g. based on GRACE SST observations up to a moderate degree, and improve this global solution in regions with characteristic gravity field features by an adapted regional recovery procedure. The individual gravity field features in these regions can be modeled by space localizing base functions like spherical spline functions. The advantage of this method is the possibility of adjusting the spline representation and the recovery procedure according to the regional gravity field structures and the specific data distribution. As a first indicator of a rough gravity field the structure of the topography or geophysical a-priori information can be used as a criterium. The resolution of the regional gravity field can be further improved by a subsequent iteration step. If neccessary, several regional solutions with global coverage can be merged by means of quadrature methods to obtain a global solution. Simulation results are presented to demonstrate this approach. Due to the regionally adapted recovery strategies this method provides better results than calculating a spherical harmonics solution by recovering the potential coefficients directly.