Combined modeling of the Earth's gravity field from GRACE and GOCE satellite observations: a numerical study

A numerical study has been conducted in order to estimate how a gravity field model obtained from GOCE data can be improved in the range of low degrees by addition of GRACE data. The GRACE data are simulated as inter-satellite accelerations. Different types of noise in the inter-satellite accelerations are considered, including white noise. The gravity field model is represented as a series of spherical harmonics; the Stokes coefficients are computed by a least-squares adjustment. It is shown that the incorporation of GRACE data may improve a GOCE-based gravity field model up to degree 120 or even higher depending on the type of noise in the inter-satellite accelerations. Moreover, the joint model at lower degrees may show a significantly higher quality that either a stand-alone GOCE-based or a stand-alone GRACE-based model. It is important, however, that proper covariance matrices of the involved data sets are used in the joint data processing.