Improvement of Sudan Gravity Field Using Geopotential and Altimetry Data

The gravity measurements in Sudan are sparse and few compared to the country area. The currently available measurements were conducted for the sake of mining and oil exploration between the 1970s and mid of 1980s. However, in precise geodetic works such as geoid determination, the gravity data must be dense and have good quality to obtain reliable solutions. This study uses global geopotential models (GGMs) and altimetry to fill gaps in gravity measurements over land and the Red Sea, respectively. We validate the GGM-based free-air gravity anomalies (FAA) with the terrestrial ones to select the best-fit model for inland filling. We use three GGMs (EGM2008, XGM2019e, and EIGEN6C4) truncated at 760 degrees/order in the validation to select the best-fit model. The selection of the best-fit model is based on the consistency between GGM and terrestrial anomalies and the minimization of their standard error (SE). In addition, the topographic effect has been considered; therefore, the topographic effect (TE) is calculated and applied. The altimetry data were employed in filling the Red Sea marine area adjacent to Sudan. To reduce the error propagation, the validated points were refined by setting the differences between the terrestrial, GGM data, and TC to a certain range according to the quality of the validation data. The final combination of the terrestrial, GGM, and altimetry data is introduced as a newly improved gravity grid of Sudan; statistical and numerical results are also presented.