12. Incorporating Topographic-Isostatic Information into GOCE Gravity Gradient Processing

Global high-resolution digital terrain models provide precise information on the Earth’s topography, which can be used to determine the high- and mid-frequency constituents of the gravity field (topographic-isostatic signals). By using a Remove-Compute-Restore concept these signals can be incorporated into many methods of gravity field modelling. Due to the smoothing of observation signals such a procedure benefits from an improved numerical stability in the calculation process. In this paper the Rock-Water-Ice topographic-isostatic gravity field model is presented that we developed in order to generate topographic-isostatic signals which are suitable to smooth gravity gradients observed by the satellite mission GOCE. In contrast to previous approaches, this model is more sophisticated due to a three-layer decomposition of the topography and a modified Airy-Heiskanen isostatic concept. By using measured GOCE gravity gradients, the degree of smoothing is analyzed, showing a significant reduction of the standard deviation (about 30 %) and the range (about 20–40 %). Furthermore, we validate the performance of the generated topographic-isostatic signals by means of a wavelet analysis.