The Earth Geopotential Model 2008 (EGM2008) is the latest version of a series of geopotential models developed under the leadership of the National Geospatial-Intelligence Agency (Pavlis et al., 2008). It incorporates harmonic coefficients derived from the GRACE satellite mission, marine gravity anomalies derived from satellite altimetry, and a comprehensive set of terrestrial gravity anomalies. It is likely to become the standard geopotential model used for many applications including orbit modelling and geoid modelling. As such, it is important that it be assessed by means of comparisons with independent or quasi-independent data sets. This paper focusses the assessment on the continent of Africa, probablythe continent for which the details of the Earth's geopotential are least well known. This evaluation has been carried out using three data sets:
• African Geoid Project 2007 geoid model (5' by 5' grid)
• Point gravity anomalies for southern Africa
• GPS/levelling data for 79 points in South Africa
The first two data sets are not truly independent of the EGM2008. Most of the point gravity anomalies in the second data set also formed part of the terrestrial data used in EGM2008. The AGP2007 geoid model (Merry, 2007) usedgravity anomalies which were also used in EGM2008, and it also used harmonic coefficients derived from GRACE tracking data. Nevertheless, there are sufficient differences in the way the data were used for the two data sets to provide a meaningful comparison.