Establish Vertical Datum Theories And Methods Of Research

A unified height datum is needed for the constructions of national economy and defence as well as engineering applications. Due to the development of GPS, which is representative of spatial geodetic measure technology, and the satellite altimeter technology, it is possible to unify the local height datums in different countries (or regions) to the World Height Datum (WHD). And the unification of height datums has been made in some countries. Therefore, merging the 1985 Chinese National Height Datum (CNHD85) into a unified international one is of scientific and practical importance.This dissertation presents the theory and method on the establishment of height datums. And some problems on the geocenter motion are also studied. First, the defmation and status of height datums is introduced and some problems on the local height datums established by the mean sea level, which is defined by the tide gauge data, are discussed. Then the research progresses in recent years are analysed. At last, the necessity of the modernization of CNHD85 is presented to us.Before the transformation and unification of height datums is made, it is necessary that different surfaces used for the definations of height datums should be introduced, and their relationships are also needed studying. Then the origin vertical shift of CNHD85 with respect to WHD is calculated from geopotentials. And the systematic difference and its distribution of CNHD85 is analyzed from the difference of height anomalies. At last, the systematic difference of the mean sea level at Qingdao tide gauge is further testified from the sea surface topography model.As for the transformation between the local height datums, three methods are summarized, which are the direct method, the indirect method and the coordinate transformation method. Their respective application fields are also analysed.In fact, the transformation and unification of the local height datums have relations to the mean sea level variation at the shore where the tide gauges are located. The theory and method on the determination of the sea level relative variation by tide gauge data is introduced in the dissertation. Considering the effect of the crustal vertical motion, the absolute variation cannot be drawn only using the tide gauge data. Therefore, another method is proposed, which is to survey at the tide gauge by GPS firstly, then to combine the coordinates of the tide gauge with ITRF. So a stable and unified reference surface is provided to seperate the crustal vertical motion and the sea level absolute variation.Finally, the rule of geocenter motion is studied. And its effects on the height datum are also discussed in the dissertation. A robust spectral analysis method is put forward, which is a combination of robust estimation and spectral analysis. The tune series of geocenter motion is computed and analyzed based on the method. Then the periodic properties of geocenter motion in the X, Y, Z components are summarized. Considering the statistical precision of the GPS observations, the geometrical distribution of GPS stations and their physical stablility, a new method to determine the parameters of geocenter motion is studied and analyzed. In order tohave a better understanding of its effect on the height datum origin, the rule of geocenter motion in the horizontal and vertical components are also analyzed and some useful conclusions are drawn.