In this paper, the spectral methods based on the input output system theory (IOST) were used to compute quantities related to the gravity field. These method are almost equivalent to least squares collocation (LSC) method in the accuracies of results, but they can use both isotropic and non-isotropic power spectral density functions (PSDs
) easily. The recovery of the gravity field is made by combining salellite altimeter data and sea gravity data. The results show that higher prediction accuracies are always obtained when using non-isotropic information instead of the isotropic one.