Recovery of the Earth's Gravity Field from GOCE Satellite Gravity

We have investigated the technique for a direct computation of observation equations from GOCE SGG data in the gradiometer reference frame. Based on SGG simulated data along a 28-day perturbed orbit, we have estimated numerically the effects of various (static and time-varying) gravitational geopotential constituents on the components of the gravity gradient tensor. We have seen that within the measurement bandwidth the recovery of harmonic coefficients is not deteriorated by the considered temporal variations of the gravity field. In order to de-correlate the gravity gradients affected by colored noise, we have proposed a simple non-recursive filter technique, which incorporates SGG observations within a floating time interval of a length comparable to the GOCE measurement bandwidth. We have examined this technique for two different noise schemes: (1) the a-priori given PSD of noise and (2) a PSD of noise estimated from the misfit of the sum of measured diagonal components of the gradient tensor. We have applied the proposed filter in a least- squares estimation of spherical harmonic coefficients of the Earth's gravitational potential from 28-day simulated SGG data contaminated by colored noise. The solution for coefficients up to degree 180 has been obtained without additional stabilization. The solution provides for coefficients of degrees higher than 34 the mission's baseline geoid accuracy.