Preliminary geoid over Zambia

In the determination of the preliminary geoid over Zambia, we compare three methods of the modified Stokes formula: that of Vincent and Marsh, a modified Wong and Gore method, and a modified spectral weighting method, with the final solution being estimated by the modified Wong and Gore procedure. The geoid over Zambia (based on GRS80) is rising from north-east to south-west. It coincides with the reference ellipsoid in the north-western and southern regions of Zambia. The preliminary estimate indicates maximum and minimum values of about 13.7 and −16.8m, respectively. The mean geoid over the area is −2.8m. Formal analysis of global root mean square errors for the three models leads us to conclude that for an integration cap radius of about 3 or less, the modified formula using optimal spectral weighting is superior to the Vincent and Marsh method, and to the modified and unmodified Wong and Gore.