GOCE - Low Orbit Mission Phase Data Analysis
Stummer, Claudia; Schack, Peter; Pail, Roland; Gruber, Thomas

Since March 2009 GOCE has been orbiting the Earth and made it possible to map the Earth’s gravity with unprecedented accuracy. To reach this goal GOCE has been flying in a very low altitude of about 255 km. In the first two years of the mission the fuel consumption was much lower than expected. Hence, it was possible to extend the mission lifetime, and to lower the orbit altitude by about 20 km in the final phase of the mission. The goal of these measures is to improve the accuracy and spatial resolution of the resulting Earth’s gravity field model. While the extension of the mission phase results in an increased redundancy of the observations, several simulation studies have revealed that the accuracy of the higher degrees of the spherical harmonic spectrum can be increased significantly by the orbit lowering, resulting in parallel also in an increase of spatial resolution.
The purpose of this contribution is to analyse the new GOCE gradiometer data, which are now measured in an even rougher environment due to the increase of the drag force acting on the satellite. Data of the three phases of orbit lowering are compared against each other, and with the data acquired before the orbit lowering. The data quality will be investigated in spectral domain in terms of power spectral densities of residuals, computed as differences between the actual observations and reference gradients computed from the 4th release of GOCE time-wise gravity field model, but also in space domain in order to investigate potential degradation in near polar-areas related to the coupling with common mode signals. Finally, the impact of the increased signal content (due to the orbit lowering) and the data quality in the final phase on the gravity field solution shall be evaluated.