The Study Of Height Datum Unification Based On The Earth’s Gravity Field Models

Currently, the height datum unification has a great significance application for the defense industry, the national economic construction and the large construction projects. With the fast development of the space geodetic techniques like the Global Navigation Satellite System and the satellite altimetry, unifying the local height datum of the country or region to the global height datum has become possible, and it is gradually implemented in the regions of Europe and North America. Therefore, unifying the national vertical datum 1985 to the global height datum has a great theoretical and practical significance.The first task of the paper was to analyze the current situation of the height datum unification in domestic and overseas, and explain the necessity of the height datum modernization. Then the basic concepts of the height datum were briefly introduced, and the problem of establishing height datum on the mean sea level from the long-term observation of tide stations was discussed. Besides, some Earth’s Gravity Field Models and its main characteristics, the methods of the height datum unification based on the gravity field models and the factors that may affect the unification were introduced. Finally, the GNSS/leveling data was used to calculate the vertical deviations of local height datums and the global geoid in regions North America and Europe, the mean sea surface model was used to calculate the vertical deviations of local height datums and the global geoid at tidal stations in Asia-Pacific region. The task of the paper was to study the feasibility of the height datum unification methods based on the Earth’s Gravity Field Models. The main work is as follows:(1) The height datum related concepts was introduced, including the concepts of orthometric height, normal height and geodetic height, the definition of geoid, quasi-geoid and their determination methods. Then we discussed the problems about obtaining the mean sea level by the long-term tide gauges observation in the establishment of a height datum.(2) The main Earth’s Gravity Field Models and its characteristics were introduced. The height datum unified methods based on the gravity field models, and the factors that may affect the height datum unification, such as the mean sea level, tides, land vertical movements along the coast. The problems of data processing in the height datum unification were studied, including the difference of geoid calculated by different gravity field models and the truncation errors effection to the models accuracy, the reference systems consistency of the GNSS/leveling data.(3) North American Vertical Datum NAVD88, Canada Vertical Datum CGVD2013 and Europe Height Datum UELN-95/98 were briefly introduced, then GNSS/leveling data was used to calculate the vertical deviation between the local height datums and the global geoid in, and the mean sea surface model was used to calculate the vertical deviation of the local height datums and the global geoid at tidal stations in Asia-Pacific region. Finally, the feasibility of the height datum unification methods based on the Earth’s Gravity Field Models was studied.