The gravimetric geoid of Sudan

Abstract

The gravimetric geoid for the Sudanese subcontinent was computed on a grid defined by the geographical coordinates 4°N–22°N, 22°E–36°E. This geoid was referred to the geodetic reference system 1980 (GRS80) and transformed to the local datum in the Sudan (Adindan datum). The precise transformation parameters between GRS80 and Adindan datum were determined from the comparison of the gravimetric geoid and its corresponding astrogeodetic geoid. The free-air co-geoid was computed from the combination of surface gravity data using a modified Stokes's kernel and the recently published GODDARD EARTH MODEL (GEM-T1) potential coefficient set. The surface gravity data consist of 1° × 1°, 10′ × 10′ and point anomaly data. Corresponding GEM-T1 anomalies were subtracted from the gravity anomalies. The atmospheric and topographic attraction effect on the gravity anomalies as well as their by-product indirect effect on the computed co-geoid is critically examined. Also the effect of neglecting the ellipticity of the reference ellipsoid on the computed geoid is outlined.