Establishment of the Gravity Database AFRGDB_V1.0 for the African Geoid

Abstract

In the framework of the IAG African Geoid Project it is needed to have a uniform gridded gravity data set to compute the geoid using Stokes’ integral in the frequency domain by 1-D FFT technique. The available gravity data set consists of land point gravity data as well as shipborne and altimetry derived gravity anomaly data. The available gravity data set has a lot of significant gaps allover the continent. The establishment of the gravity database AFRGDB_V1.0 for the African geoid has been carried out using an iterative process employing a tailored reference model and weighted least-squares prediction technique. The point gravity data on land has got the highest precision, while the shipborne and altimetry gravity data got a moderate precision. In each iteration step, the data gaps are filled with the tailored reference model computed at the previous iteration step, getting the lowest precision within the prediction technique. The weighted least-squares prediction technique is thus carried out to estimate gridded gravity anomalies, which are used to estimate a new tailored reference model employing two harmonic analysis techniques. The gravity database on a uniform grid size of 5^′× 5^′ has been established by the developed process. It has been validated with real data. A standard deviation of the residuals is about 9 mgal. 68% of the data points have residuals less than 4 mgals.