区域与全球高程基准差异的确定

全球高程基准统一是继全球大地测量坐标系及其参考基准统一之后,大地测量学科面临和亟待解决的一个重要问题,也是全球空间信息共享与交换的基础。本文针对区域高程基准与全球高程基准间基准差异确定的理论、方法及实际问题开展研究。利用物理大地测量高程系统的经典理论方法,给出了高程基准差异的定义,并推导了计算基准差异的严密公式,该公式可将高程基准差异确定的现有3种方法统一起来。在此基础上,分析顾及了不同椭球参数对于计算基准差异的影响及量级,同时,高程异常差法还需考虑全球高程基准重力位与模型计算大地水准面位值不一致引起的零阶项改正。利用青岛原点附近152个GPS水准点数据,分别选择GRS80、WGS-84、CGCS2000参考椭球以及EGM2008、EIGEN-6C4、SGG-UGM-1模型,采用位差法和高程异常差法,确定了我国1985高程基准与全球高程基准的差异。其中,EIGEN-6C4模型计算的我国高程基准与WGS-84参考椭球正常重力位U0定义的全球高程基准之间的差异约为-23.1cm。也就是说,我国高程基准低于采用WGS-84参考椭球正常重力位U0定义的全球高程基准,当选取基于平均海面确定的Gauss-Listing大地水准面作为全球高程基准时,我国1985高程基准高于全球基准约21.0cm。从计算结果还可看出,当前重力场模型在青岛周边不同GPS/水准点的精度差别依然较大,这会导致选择不同数据对确定我国85国家高程基准与全球基准之间的差异影响较大,因此,若要实现厘米级精度区域高程基准与全球高程基准的统一,全球重力场模型的精度和可靠性还需要进一步提高。

Determination of Vertical Datum Offset between the Regional and the Global Height Datum

The unification of the global height datum is a key problem to be solved for geodesy after the unification of global geodetic coordination system and three-dimension spatial datum,and the basis of global spatial information sharing and exchange.In this paper,the theoretical and practical problems of vertical datum offset between the regional height datum and the global height datum are studied.Based on the classical theory of the height system in physical geodesy,the definition of the height datum vertical offset is given,and the rigorous formulas for calculating the vertical offset are derived.The formulas can be used to deduce the three methods of the height datum vertical offset determination.On that basis,the influences of different reference system and reference ellipsoid parameters on the calculation of the vertical offset are analyzed.The results show that the reference system and the ellipsoid parameter conversion are very necessary.At the same time,the height anomaly differences method needs to consider the degree zero correction caused by the inconsistency between gravity potential of the global height datum and the one computed by the model.Based on potential difference approach and the height anomaly difference method,the vertical offset between the China 1985 national height datum and the global height datum corresponding to the normal gravity potential U0 of GRS80,WGS-84 and CGCS2000 reference ellipsoidal from the 152 GPS/ leveling points near the origin of Qingdao height origin and the EGM2008,EIGEN-6C4 and SGG-UGM-1 model.The regional datum is 23.1 cm lower than the global datum based on EIGEN-6C4 and WGS-84.When the Gauss-Listing geoid (mean sea surface) is selected as the global height datum,the China 1985 national height datum is 21.0 cm higher than the global height datum.The results also show that there are still large differences among the accuracies of the current gravity field models on these GPS/Levelling points around Qingdao,which will lead to big differences in estimating the vertical datum offset between the China 1985 national height datum and the global height datum with respect to different selected data sets.Therefore,the accuracy and reliability of the current global gravity field models needs to be further improved if they were used for the height datum vertical offset determination.The theoretical and practical results of this paper could be used for the realization of the unification of the regional height datum and the global height datum.