GOCE Gravity Gradients: Combination with GRACE and Satellite Altimetry

Abstract

GOCE gravity gradients are a new satellite observable, which are given in the instrument frame that is only indirectly connected to the Earth. A rotation to other frames requires to take the different accuracies of the gradients into account. We show that replacing the less accurate gradients with model information allows to rotate the tensor, but for the diagonal gradients $V_{XX}$ and $V_{YY}$ the model information can reach up to 50 % in the Local-North Oriented Frame, whereas it is only a few percent for $V_{ZZ}$. We also show that in the direct comparison of GOCE gravity gradients and satellite altimetry derived gradients one has to account for the difference between the along-track altimeter derivatives and the GOCE gradients in a Cartesian frame, as well as the dynamic ocean topography signal. A validation of GOCE using ERS-1 data shows that both data sets are consistent at levels where GOCE is sensitive. For high spatial resolutions below 40 km wavelength GOCE does not contribute, as expected.