The Research Of Regional Quasi-geoid Refinement Based On GPS/Leveling Data

In recent years, with more and more countries continue to invest and research on satellite technology, satellite positioning technology has been greatly developed, for its 3D location and velocity measurement, accurate timing, real-time throughout the day, free resources and other prominent advantages, so global positioning system(GPS) in the field of Surveying and mapping has been widely used. In order to obtain high-precision point flat position, while also obtaining high-precision elevation, determined centimeter quasi geoid is necessary. Quasi geoid with high resolution and high accuracy can guarantee the use of GPS direct determination of orthometric height or normal high, Give full play to its advantages in the field of Surveying and mapping, Improve work efficiency, bring direct economic benefits. The research of high precision quasi geoid has strong practical value. It has also become a hot issue for Surveying and mapping scholars and committed to study it.In this paper, we firstly introduce the research background and the domestic and foreign like the development condition of the geoid, Then introduced the system of regional quasi geoid refinement principle and related methods, emphatically introduced the commonly used method of GPS/ level geometry in engineering, including function model fitting method, statistical model fitting method and synthetic model fitting method. And analyzed the error sources of the quasi geoid. On this bases, remove-restore technique which based on the EGM2008 model is detailed introduced.This paper takes two different types of survey area as examples, and use the methods of plane fitting, the curve fitting, the two curve fitting, the weighted average fitting, the three spline fitting to fitting Quasi-geoid. According to the condition of the measurement area, several schemes are designed. The advantages and disadvantages of each fitting method is analyzed by the means of accuracy and the difference of fitting error value. Then take the remove-restore technique which based on the EGM2008 gravity field model, The refined calculation test area for quasi geoid, and refinement the quasi geoid in survey area.The experiment of two engineering survey areas shows that:Based on the GPS/ leveling data, the accuracy of the Quasi-geoid can reach centimeter level and can meet the demand of four grade levelling measurement. When the design is reasonable, the partial fitting method can achieve three grade levelling measurement. The fitting method combined with the remove-restore technique can improve the fitting precision.