The 1999 GFZ pre-CHAMP high resolution gravity model

In preparation of the CHAMP gravity and magnetic field satellite mission, a completely new satellite-only gravity field solution named GRIM5 is currently under development by GFZ Potsdam and GRGS in Toulouse. Based on the full variance-covariance matrix of this solution and terrestrial and altimetry derived surface gravity data, a new high resolution global gravity field model up to degree and order 359 will be computed. The solution will be calculated by a rigorous combination of full variance-covariance matrices from the satellite-only model and the land and ocean surface gravity data, with block-diagonal structured variance-covariance matrices from the high resolution terrestrial and altimeric gravity information provided by the U.S. National Imagery and Mapping Agency (NIMA) and, in case of altimetry derived information, by GFZ Potsdam and CLS in Toulouse. For this new solution the spherical harmonic degree and order for the full variance-covariance matrix will be extended to 140, compared to degree 100 for previous GFZ solutions and degree 70 for the EGM96 model. It can be shown by preliminary investigations, based on former satellite solutions, that, due to the extension of the full normal equation system, the quality of the final model will be increased significantly for this frequency range. Quality parameters for such investigations are derived from the internal error parameters from the least squares approach and from comparisons with external independent gravity and geoid information. The new high resolution combination model will represent a major improvement towards a series of new gravity field models with unprecedented accuracy and resolution from the CHAMP, GRACE and GOCE gravity field missions. With these missions long, medium and even parts of the short wavelengths will be dominated by satellite data, while the rest of the spectrum will be determined solely from surface data. Therefore the presented combination technique can be extended also to the computation of high resolution CHAMP, GRACE and GOCE based gravity field models.