Research And Application Of Local Quasi-Geoid Based On GNSS Leveling

In recent years,GNSS technology has developed rapidly,and it is an irreversible trend to replace traditional leveling measurement with high-precision,all-weather,high-efficiency and high-economic.The results of GNSS positioning is the ellipsoidal height,while the actual engineering application in China is the normal height of the quasi-geoid as the datum.The conversion of ellipsoidal height into normal height has become a research hotspot and difficulty in the field of geodetic survey.The normal height of measuring points can be obtained directly through GNSS measurement to provide services for surveying and mapping production.There are many elevation conversion methods.It is a reliable and feasible method to obtain the normal height of measure points through the interpolation of the quasi-geoid.This article has done the main work as follows:1.The polynomial model,least square configuration model,semi-parametric model,moving surface model and polyhedral function model are specifically analyzed.This paper gives the detailed fitting process and selection method of the five models and model parameters are given.2.In order to reduce the loss of fitting accuracy,this paper adopts three methods and measures to ensure the reliability of data sources.The methods include repeated measurement(small area),data centralization,programmed automatic point selection and programmed coarse error detection.It obtains relatively ideal results through examples.3.In order to further improve the fitting accuracy of the models,this paper adopts the"remove-restoration" method.The method based on the interpolated EGM2008 global gravity model to improve the constructed local quasi-geoid.4 In this paper,in terms of the accuracy evaluation of fitting results,in addition to the coincidence accuracy of internal and external as the main evaluation index,residual distribution,minimum and maximum residuals and the rate of change of elevation anomaly are also adopted as supplementary reference items for the evaluation of regional range.5.For GNSS leveling data of two instance areas of large and small size,the six-parameter polynomial model,the least square configuration model,the semi-parameter model and the moving surface model and the polyhedral function model that are suitable for the smaller area are reasonably selected to fit the two instance areas according to the technical scheme designed in this paper.The applicability of EGM2008 model was analyzed through the analysis of fitting results and residual comparison.Finally,the quasi-geoid models of two example regions are determined and the corresponding parameters are given.