## Grids of gravity gradients at satellite altitude (SPW)

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Model Characteristics
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Gravity gradient grids at satellite altitude from the space-wise approach (SPW), with
error estimates.
Gravity gradients are computed from GOCE data only. Time span is indicated in the product
name. Data are provided on a 0.2 degree grid.
Input
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Externally calibrated GOCE GG (EGG_NOM_2_); GRF to IRF attitude quaternions (EGG_IAQ_1b);
Precise Science Orbit (SST_PSO_2), also including the EFRF to IRF quaternions.
A state-of-the-art a priori global gravity field model is used for covariance modelling.
Ancillary data: tide model, ephemeris, Earth rotation parameters.
Algorithm
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An SST model is derived by first estimating the along track gravitational potential by
applying the energy conservation approach to kinematic orbits. Then a spherical grid of
potential values is computed at mean satellite altitude by local collocation and the
spherical harmonic coefficients are derived by numerical integration from the grid values.
SGG data are reduced by the SST model and processed by applying a time-wise filter to
reduce the strongly time correlated noise of the gradiometer and a space-wise local
collocation to estimate spherical grids of gravity gradients at mean satellite altitude.
The whole procedure is iterated by using the spherical harmonic coefficients derived from
the estimated grids in order to recover the signal frequencies cancelled out by the
time-wise filter and to improve the rotation from gradiometer to local orbital reference
frames. Error estimates are based on Monte Carlo simulations.
Additional information can be found at
GRD updated model information