A New Belgian Geoid Determination: BG96

Abstract

Using new available data sets, a new geoid determination, named BG96, has been carried out in Belgium. Firstly, a gravimetric quasi-geoid was calculated with the Stokes and the least squares collocation methods. Then the gravimetrically determined quasi-geoid was transformed to geoid undulations and the latter was adjusted to the 35 BEREF points (Belgian Reference-GPS levelling points).

Two new techniques have been applied in this computation: a) Fast integration to evaluate the Stokes, the terrain correction and the potential integrals. Comparisons of the fast integration and the straightforward summation have been made in terms of time consumption and accuracy. It turns out that compared with the straightforward evaluation, the new technique consumes only 5 % of CPU time without losing accuracy; b) A combined adjustment has been used to optimally adjust the gravimetric geoid undulations to the GPS levelling points. This allows for elimination of the long wavelength errors due to the geopotential model used and the local deformations due to the DTM and gravity information in the gravimetric solution.

The final result, BG96, has an absolute accuracy of about 3 ~ 4 centimetres and a relative accuracy of about 1 ~ 2 ppm for short distances from 25 to 50 km and 0.3 ~ 0.5 ppm for mean distances from 200 to 300 km.