Improved determination of elevations from the global positioning system (GPS)

The wide spread use of the GPS for precise height determination has established geoid computation as a practically relevant product of physical geodesy. The geoid is the equipotential surface of the Earth's gravity field, which corresponds most closely wi th mean sea level, and is commonly used as the vertical datum for topographic elevations. A gravimetric geoid of Scandinavia (NKG96) is to be used by Norwegian surveyor to transform GPS heights to Norwegian Height Datum (NHD). However, NKG96 does not exactly coincide with NHD. This is due to a combination of the approximations required in gravimetric geoid computation, systematic errors in height and gravity data, and the exact definition of the height system. The departure of the height datum from the equipotential geoid is a few decimeters in Scandinavia. Moreover, long wavelength (>500 km) discrepancies of approximately 1 m exist in NKG96 when compared with the GPS and NHD data. GPS and levelling data are widely used to empirically verify gravimetric geoid solutions. Instead, this project will use these c ontrol data as an additional source of geoid information specially to improve the determination of heights from GPS.