Determination of the Quasi-Geoid of Xinjiang and Tibet Areas and the Normal Height of Mt. Everest Based on EGM2008

Abstract

The normal height H* is the height above the quasi-geoid, which coincides with the geoid in the ocean but slightly deviates from the geoid in terrestrial areas. In Mainland China, the height datum system is based on the quasi-geoid. The GPS technique provides the geodetic coordinates of an arbitrary point P on the ground with an accuracy of better than 1 cm. Hence, if the quasi-geoid is given, the normal height can subsequently be determined. In this study, we focus on the determination of the quasi-geoid of the Xinjiang and Tibet areas with a spatial resolution of 5' × 5' as well as the normal height of Mt. Everest based on a newly released gravity field model EGM2008, which is complete to a degree and order of 2159. We determine the quasi-geoid of Xinjiang and Tibet areas using the digital elevation model of the Shuttle Radar Topography Mission (SRTM), and determine the normal height of Mt. Everest using its geodetic coordinates provided by the Chinese State Bureau of Surveying and Mapping. Based upon the framework of Molodensky theory and EGM2008, we determined the 5' × 5' quasi-geoid of the Xinjiang and Tibet areas and the normal height of Mt. Everest. Our results show that: (1) the accuracy of the determined 5' × 5' quasi-geoid of Xinjiang and Tibet areas is around 0.2 m compared with 21 GPS leveling points distributed quite separately in the Xinjiang area (in the Tibet area the GPS/leveling data are not available except for the point at Mt. Everest); (2) the normal height of Mt. Everest is 8847.20 m, which is very close to the value provided by the fourth geodetic surveying campaign on Mt. Everest by the Chinese State Bureau of Surveying and Mapping (the difference is 0.1 m).