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Synergy of the GOCE and GRACE satellite missions

Pavel Ditmar(1), Xianglin Liu(1) and Roland Klees(1)

(1) Delft University of Technology, Kluyverweg 1, 2629 HS Delft, Netherlands

Abstract

GRACE and GOCE missions exploit different measurement concepts to map the Earth's gravity field. The GRACE k-band data are not sensitive to the cross-track gravity field component, and, therefore, result in a very anisotropic error behavior. On the other hand, the GOCE gravity gradiometer will measure all the diagonal components of the gravity gradient tensor, so that the error behavior will be much more isotropic. Finally, for both satellite missions accurate GPS tracking data are available, which can be used to compute precise kinematic satellite orbits and, ultimately, the Earth's gravity field. A viable research question, therefore, is how these two satellite missions may complement each other and how the result of a joint data processing would differ from those obtained from the two missions separately. To answer this question, a numerical study has been performed. The following data sets have been generated: (i) a set of GOCE accelerations that can be derived from a satellite orbit by a three-point numerical differentiation; (ii) similar sets of accelerations for both GRACE satellites; (iii) a set of GOCE gravity gradiometer data; and (iv) a set of range-rate linear combinations that can be derived from GRACE range-rate data. Importantly, all the considered data types can be directly related to parameters of the Earth's gravity field. Each of the data sets is contaminated by a realistic frequency-dependent noise. Furthermore, noise in GRACE data is scaled in such a way that the accuracy of the gravity field model derived from it is close to the accuracy of state-of-the-art GRACE models. The simulation shows that the mean gravity field model obtained by a joint processing of GOCE and GRACE data is much more accurate in a wide range of spherical harmonic degrees than models obtained on the basis of data from only one satellite. We explain this by the fact that errors in each stand-alone solution are unevenly distributed over the orders. Due to the anisotropic error pattern in GRACE data, the least accurately determined harmonics in the corresponding models are the nearly-sectorial ones. On the other hand, the most inaccurate harmonics in GOCE-based solutions are the nearly-zonal ones, which can be attributed to the extended polar gap in GOCE data. Thus, GOCE and GRACE data contain complementary information. To fully exploit this complementarity, we recommend to process GRACE and GOCE data jointly whenever possible.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry