Merging Terrestrial and Satellite Gravity Data for Africa: A Possibility to Fill-in the Data Gaps

The major challenge that the IAG Sub-Commission on gravity and geoid in Africa faces is the significantly large gravity data gaps. It is essential to properly tackle this issue for all geodetic applications in Africa due to the large interpolation errors occur at these large gaps. Simple interpolation (using any type of interpolation technique) of the gravity data does not add new information at the large data gaps, and the solution is free there. Global Earth gravity models offer themselves as a possible way to fill-in such large data gaps, provided that they approximate the African gravity field to an acceptable extent. In this paper, all recently available Earth's geopotential models have been examined compared to the available terrestrial gravity data of Africa. This includes both satellite-only models and combined models. The comparison has been made at different levels: descriptive statistics, histograms, standard deviations and visual maps. The results prove that generally the combined models give better approximation to the Earth's gravity field in Africa. Both combined models SGG-UGM-2 and EIGEN-6C4 give comparable good fit to the African gravity field (standard deviation of the residuals of 10.36 and 10.42 mGal, respectively). The satellite-only models may be used to detrend the African geoid, especially as we miss GNSS stations with known orthometric height all-over the continent. The best satellite-only models that fit the African gravity field are Tongji-GMMG2021S and GO_CONS_GCF_2_DIR_R6 (standard deviation of the residuals of 24.76 and 24.83 mGal, respectively).