Mission simulation and semi-analytical gravity field analysis for GOCE SGG and SST

Abstract

GOCE will be the first satellite mission equipped with a gravity gradiometer. In order to achieve maximum precision and spatial resolution, the instrument is guided around the Earth in an extremely low orbit, employing active along track drag-free control and angular control by magnetic torquers. Furthermore, the orbit trajectory is determined very accurately by continuous and three-dimensional GPS satellite-to-satellite tracking. These mission characteristics are modelled by a system of two sequential simulators. The sensor system simulator computes the interaction of the complete sensor system and provides time series or power spectral densities of the gradiometer components. The mission simulator derives the geoid and gravity model performance. It takes as input mission and orbit parameters, expected GPS performance as well as the gradiometer error spectral densities derived from the sensor system simulator. The computational effort of the actual data analysis can only be managed by powerful computer systems, in principle, due to the large number of observations and unknown gravity field parameters. In this article a Semi-Analytical Approach is presented; it is a simple and fast alternative to a direct solution. It is based on simplifying assumptions, which allow to use FFT-techniques. It can be divided in two approaches: the 1D-FFT approach, and the 2D-FFT approach or torus-approach. In several case studies, the basic properties of the two approaches are shown and a comparison to the direct solution is carried out. The Semi-Analytical Approach will be used as Quick-Look Tool in the official ESA GOCE gravity field processing. © 2006 Springer-Verlag Berlin Heidelberg.