A Preliminary Geoid Model for Africa

Abstract

Abstract. Precise geoid models are essential for the conversion of GPS-derived heights to heights above sea level. Such a model is under development for the continent of Africa, as part of the African Geoid Project. A uniform 5' grid of gravity anomalies has been derived from terrestrial gravity data and has been combined with a 5' grid for the marine areas derived from satellite altimetry. The combined data set has been used with the EGM96 geopotential model in a remove-restore process to compute the geoid using two-dimensional convolution. The final result is a 5' grid of geoidal heights covering the land mass of Africa. There are significant gaps in the available terrestrial gravity data -these gaps, coupled with the effects of errors in the DEM used for calculating the Gi term and in interpolating gravity anomalies, mean that the accuracy of this geoid model will be variable and generally less than desirable.Nevertheless, comparison with GPS/levelling data covering a small part of South Africa shows an RMS agreement of better than 10cm. Over a larger region (all of Egypt) the agreement is less satisfactory.

A Precise Geoid Model for Africa: AFRgeo2019

“…1, significant data gaps still need to be closed despite great efforts. In fact, since the first basic calculation of an African geoid by Merry (2003) and Merry et al (2005), the point gravity data situation is continuously improving, although the original data of Merry et al (2005) are no longer available. This can be concluded from Table 1.…”

“…As stated earlier, the first attempt to determine a geoid model for Africa "AGP2003" has been carried out by Merry (2003) and Merry et al (2005). Since then, the data base has been further enhanced.…”

“…The first attempt to compute a geoid model for Africa has been made by Merry (2003) and Merry et al (2005). A 5 0 5 0 mean gravity anomaly grid developed at Leeds University was used to compute that geoid model.…”

“…We regret that this data set has never become available since then again. For the geoid computed by Merry et al (2005), the remove-restore method, based on the EGM96 geopotential model (Lemoine et al 1998), was employed. Another geoid model for Africa has been computed by .…”

“…Due to problems with a data set in Morocco, used in the former solution AFRgeo_v1.0 (Abd-Elmotaal et al 2019), the computed geoid has been compared only to the AGP2003 model (Merry et al 2005) in the present paper.…”