**Interpreting the GOCE Gravitational Gradients over the Congo Basin**
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Martinec, Zdenek ^{1}; Vermeersen, Bert^{2}; van der Wal, Wouter^{2}; Novak, Pavel^{3}; Sebera, Josef^{3}; Baur, Oliver^{4}; Tsoulis, Dimitrios^{5}; Sneeuw, Nico^{6}; Haagmans, Roger^{7}
^{1}Dublin Institute for Advanced Studies, IRELAND; ^{2}echnical University Delft, Astrodynamics and Space Missions, NETHERLANDS; ^{3}New Technologies for Information Society, Faculty of Applied Sciences, University of West Bohemia, CZECH REPUBLIC; ^{4}Austrian Academy of Sciences, Space Research Institute, AUSTRIA; ^{5}Aristotle University of Thessaloniki, Department of Geodesy and Surveying, GREECE; ^{6}University of Stuttgart, Institute of Geodesy, GERMANY; ^{7}European Space Agency, NETHERLANDS
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Within the GOCE+ Theme 2 project GOCE-GDC funded by ESA spatial grids of gravitational gradients at satellite altitude and grids of gravitational gradients downward continued to several reference surfaces closer to ground have been applied for structural studies over two geographic regions. In Africa, one of the study areas of the project, the main aim is focused on the refinement of the model of sedimentary rocks over the Condo basin such that satellite gravity and gradiometry data are optimally adjusted. First, the 5-parameter Helmert's transformation is applied to transform the original Kadima et al. (2011) sedimentary model to a spatial position that resembles the gravity data over the basin. The transformation is defined by 2 translation, 1 rotation and 2 scale parameters that are searched by the method of steepest descent. The same procedure is applied to the Laske and Masters (1997) 1x1 degree sedimentary model for CONGO basin. The resulting transformed sedimentary models are only slightly changed with respect to the originals but they largely improve the fit of the gravity data over the Congo sedimentary basin. However, there are still a few features of free-air gravity anomaly remaining unfitted by the sedimentary models. Secondly, the transformed sedimentary models are used to find the vertical density distribution of sedimentary rocks. The free-air gravity anomaly can be optimally interpreted by a constant sedimentary density. Such a model does not, however, fit well the vertical gradient of gravity. Therefore, a density model is extended by including a linear increase in sedimentary density. The least-squares procedure is applied to find the parameters of density model by adjusting both gravity and vertical gradient of gravity.