Evaluation of the Recent African Gravity Databases V2.x

In the framework of the activities of the IAG Sub-Commission on the gravity and geoid in Africa, a recent set of gravity databases has been established. They are namely: AFRGDB_V2.0 and AFRGDB_V2.2. The AFRGDB_V2.0 has been created using the window remove-restore technique employing EGM2008 as geopotential Earth model complete to degree and order 1800. The AFRGDB_V2.2 has been established using the Residual Terrain Model (RTM) reduction technique employing GOCE DIR_R5 complete to degree and order 280, using the best RTM reference surface. The available gravity data set for Africa, used to establish the above mentioned two independently derived databases, consists of shipborne, altimetry derived gravity anomalies and of land point gravity data. In particular, the data set of point gravity values shows clear deficits with regard to a homogeneous data coverage over the completely African continent. The establishment of the gravity databases has been carried-out using the weighted least-squares prediction technique, in which the point gravity data on land has got the highest precision, while the shipborne and altimetry gravity data got a moderate precision. In this paper a new gravity data set on land and on sea, which became recently available for the IAG Sub-Commission on the gravity and geoid in Africa, located partly in the gap areas of the data set used for generating the gravity databases, has been employed to evaluate the accuracy of the previously created gravity databases. The results show reasonable accuracy of the established gravity databases considering the large data gaps in Africa.