Development of a Geoid Model by Geometric Method

Abstract

Engineering projects require orthometric heights of points where as Global Navigation Satellite System (GNSS) provide height above ellipsoid. Thus, to make use of GNSS in engineering surveying, the relationship between ellipsoidal height and orthometric height as a function of position needs to be established through geoid modeling. In this study, an attempt has been made to develop a geoid model using the geometric method. Observations were taken in a network of sixteen stations spread over 600 km2 around Dehra Dun, India. GPS observations were taken using dual frequency geodetic GPS receivers and leveling done using digital levels with 0.1 mm accuracy. Orthometric height of stations from developed model have been found to be near to those from field levelling which is considered most accurate. Further, the values have been compared with those obtained from the recent GOCE–GRACE–LAGEOS geoid model EIGEN6C3stat. It has been found that the geometric model provides far better accuracy than that obtained from the global geoid model. Therefore, it can be concluded that the geometric method of geoid modeling can better be used for reduction of GPS observed ellipsoidal height to orthometric height in a local area. This model may gainfully be employed in a project area as a substitute for densification of leveling lines, thereby reducing the project cost substantially.