Quasi-geoid BG03 computation in Belgium

The estimate of a high precision quasi-geoid is nowadays a relevant goal in Geodesy, since from this surface can be derived the geoid. As it is well known, the geoid, i.e. the equipotential surface of the Earth gravity field which is close to the mean ocean surface, can be used in combination with GPS observations to estimate orthometric heights. This is of particular relevance, since this can be done in a faster and cheaper way than using spirit leveling, although with lower precision (which is however sufficient in many practical applications). In 1996, the last estimate of the Belgium quasi-geoid BG96 was computed with the Stokes and the least square collocation methods (Pâquet et al 1997). This quasi-geoid has a precision of 3 to 4 cm in the area well covered by gravity data , which was assessed through comparison with GPS/leveling derived undulations with 36 BEREF points. Since now the gravity coverage of Belgium is completed a higher precision for the geoid could be reached for the south-eastern part and in the northern part of the country. In this paper, a new estimate of the Belgium quasi-geoid (BG03) is presented. The main improvements with respect to the previous computation are related to gravity data coverage, DTM refinements and new global geopotential models. So, this estimate can be considered a significant step forward in quasi-geoid computation for this area and a basis for a future estimate which will be obtained by merging gravity and GPS/leveling data.