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Abstract:
In the framework of gravity field modelling from satellite mission data, the PoliMi group had designed and developed a space-wise approach based on multi-step collocation, which has been applied to process gradiometric data, like those observed by GOCE. Briefly, this space-wise approach consists of an along-orbit filtering to reduce noise variance and correlation, a local gridding over data patches, and a spherical harmonic analysis by numerical integration; the scheme is iterated till convergence. While the gradiometric observation is directly a functional of the gravity field, with satellite-to-satellite tracking (SST) missions, like GRACE or NGGM/Magic, the main observable becomes a geometric quantity, namely the range or range-rate between pairs of satellites.To properly process this kind of observables by the space-wise approach, a conversion from the geometric quantity to an along-orbit gravity functional is required. For example, potential can be retrieved by energy balance approach, first derivatives by Hill’s equations, second derivatives by exploiting accelerometers on board the satellites as a gradiometer. The space-wise approach has been properly adapted to take one of this functional as input. The main modification is at the gridding level, where suitable covariance modelling is required, also considering the time-variable gravity signal.The proposed algorithms are applied to different simulated scenarios, assessing the accuracy of the solution by Monte Carlo sampling. In these simulations the payload is considered to be quantum instrumentation, and the performances of the space-wise approach in retrieving both static and time-variable gravity field with gradiometric and SST mission profiles were analysed.
