Feasibility of gravity field recovery from GRACE line-of-sight (LOS) gradiometry observations using the torus approach

The dedicated satellite gravity field mission \textsc{Grace} employs the concept of satellite-to-satellite tracking in low-low mode (\textsc{sst}-ll). The ratio between the precise inter-satellite K-band range and the range acceleration (ρ/\ddot{ρ}) can be treated approximately as a line-of-sight (\textsc{los}) gradiometry observable. Theoretically, this observable has a similar pattern as the gravity gradient tensor along-track component Vxx. The \textsc{Grace} \textsc{los} gradiometry data from both real and simulated range and range acceleration observations are processed by the torus-based semi-analytical approach to recover the gravity field. The torus-based approach shows its efficiency in gravity field determination in terms of the time and storage requirements and its flexibility of dealing with any geopotential functional. Our preliminary results show that the estimated spherical harmonic coefficients are not accurate enough compared to a reference model. The major reason would be that the ≈ 220 km baseline of \textsc{Grace} does not fulfill the \textsc{los} gradiometry assumption of a sufficiently small baseline. Another possible reason is the additional error from interpolation, which can be improved by iteration.