GPS拟合高程代替五等水准测量精度分析与探讨
Analysis and discussion of GPS elevation replacing the five grade leveling
XIE Xiangcheng，FENG Guangyin，YANG Jun
（Jingjiang Survey Bureau of Hydrology and Water Resources, The Hydrological Bureau of Changjiang Water Resources Commission,Jingzhou,Hubei,434000,China）
Abstract： In recent years，the Global Positioning System is widely applied in the fields of Surveys． The horizontal precision in GPS surveying has been high，which can satisfy the demand of precision in some horizontal control network．But the precision of height in GPS surveying needs a further improve .so the study of GPS height transform system has important meanings for the application of GPS .This arises by the disagreement between GPS height system and level height system ,so the results of GPS surveying must process the transform of height system，which Can satisfy the need of engineering．The paper mostly studies height transform and particularly discusses mathematic fitting model， At last in this paper, fitting of a regional GPS elevation and comparative analysis of the accuracy of the standard height is proposed the use of GPS observations plus a known elevation point of seeking to be determined point of elevation fitting way to describe grade GPS network geometry fitting height can reach the standard of ordinary measurement accuracy.
Keywords：GPS height；height anomaly；height transform；elevation fitting；precision analysis
为了满足工程建设和地形测量的需要，测区都要进行平面和高程控制测量。近几年以来，GPS卫星定位技术已在许多领域得到了广泛的应用，目前使用GPS进行测量，能容易得到WGS-84系统下的三维坐标，将观测数据通过处理可以很容易得到观测点的国家或地方三维坐标，平面精度一般都能达到精度要求，但是得到的高程成果不一定满足工程建设要求，特别在山区误差更大。GPS得到的是大地高程（椭球高），实际应用中所采用的高程为海拔高程(正常高)，两者之间存在高程异常值的差异，本文结合工作实际，从高程异常拟合函数、转换常数解算及实践应用等几个方面，来论述GPS测量中的拟合高程值代替等外水准的可行性以及应用。
1 GPS拟合高程的方法及精度
GPS测量得到的大地高程H与实际应用中所采用的海拔高程h之间存在高程异常值的差异，即h = H - ξ，ξ为该点的高程异常值(又称大地水准面差距)，如图1.1所示。高程异常随地形变化和地区地层的密度等有很大关系，要想获得精确的正常高就要获取准确的高程异常值。目前，高程异常值的获取方法大致有以下几种：
①、从国家高程异常值图上查取或者从全球高程异常模型中得到，如国际上广泛采用的
OSU
图1.1.大地高与正常高
Fig 1.1. Geodetic height and normal height
②、从局部地区的精化大地水准面模型中得到；这种方法精度较高，在几个厘米至十几个厘米
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