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Description:
The AFRgeo2019 gravimetric geoid model was computed in the framework of the IAG African Geoid Project. The available gravity information comprises land and sea data, the latter consisting of shipborne point data and altimetry-derived gravity anomalies along tracks. This dataset suffers from significantly large data gaps, that were filled by using the EIGEN-6C4 model on a 15' x 15' grid prior to the gravity reduction scheme. The window remove-restore technique was used to generate reduced anomalies having a minimum variance to minimize the interpolation errors, especially at the large data gaps. The EIGEN-6C4 global model, complete to degree and order 2190, has served as the reference model. The AFH16S30 30'' X 30'' and the AFH16M03 3' X 3' models have been used to represent the fine and coarse digital terrain models, respectively. The reduced anomalies were gridded on a 5' X 5' grid employing an un-equal weight least-squares prediction technique. The geoid undulations from the reduced gravity anomalies were computed by employing Stokes' integral with Meissl modified kernel. Finally, the restore step within the window remove-restore technique took place generating the full gravimetric geoid. In the last step, the computed geoid was scaled to the DIR_R5 GOCE satellite-only model by applying an offset and two tilt parameters. The DIR_R5 model was used because it turned out that it represents the best available global geopotential model approximating the African gravity field. A direct comparison between AFRgeo2019 and the former geoid model AGP2003 clearly shows the achieved improvement.
References:
H. Abd-Elmotaal, N. Kühtreiber (1999). Improving the geoid accuracy by adapting the reference field. Physics and Chemistry of the Earth, Part A, 24(1), pp. 53-59. DOI: 10.1016/S1464-1895(98)00010-6
H. Abd-Elmotaal, N. Kühtreiber (2003). Geoid determination using adapted reference field, seismic Moho depths and variable density contrast. Journal of Geodesy, 77(1 - 2), pp. 77-85. DOI: doi.org/10.1007/s00190-002-0300-7
H. Abd-Elmotaal, N. Kühtreiber, K. Seitz, B. Heck (2020). A Precise Geoid Model for Africa: AFRgeo2019. International Association of Geodesy Symposia. DOI: doi.org/10.1007/1345_2020_122
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