Research And Application Of Regional Quasi-geoid Refinement Method

The geoid is the gravity equipotential surface that is combined with the average sea surface and extends inside the continent.its shape can reflect information such as changes in material structure and density within the Earth's interior.The determination of high-precision and high-resolution geoid can provide important guarantees for geoscience-related disciplines,national defense construction and national economic development.This paper studies and analyzes some problems in the process of refinement of the geoid.The main work of the thesis is summarized as follows:1.Aiming at the long-wave errors of the ultra-high-order gravity field models EGM2008,GECO and EIGEN-6C4,the internal coincidence accuracy of the internationally published Super-high-order gravity field models such as EGM2008,GECO and EIGEN-6C4 and the low-order gravity field models such as GOCO03 S,GO_CONS_GCF_2DIR_R5 and GO_CONS_GCF_2TIM_R5 are analyzed.The external coincidence accuracy of each model is checked by the measured GNSS/leveling data.The accuracy of the six models in different order combinations is analyzed,and the reliable truncation order is selected to determine the combined gravity field model.The calculation results show that the combined gravity field model can improve the accuracy of the gravity field model elevation anomaly,and its accuracy is optimized by 23%.2.In order to solve the problem of elevation information in the process of spherical harmonic synthesis on the earth surface,in the process of spherical harmonic synthesis,the gradient field method is used to expand the gravity field functional in the process of spherical harmonic synthesis,and the gradient method is improved by the comprehensive coefficient method.The computational efficiency and the applicability of the gradient method in the spherical harmonic synthesis process.The calculation results show that based on the terrain model data and the ultra-high-order gravity field model,the gradient method can be used to reduce the approximation error caused by the elevation information by using the gradient method to extend the gravity field functional such as elevation anomaly and gravity disturbance to a certain order.The extent to which the actual application is irrelevant.3.The residual terrain model?RTM?technique is used to compensate the truncation error of the GECO of the ultra-high-order gravity field model.The calculation results show that when the terrain fluctuation changes greatly,the calculated standard deviation of residual elevation anomalies reaches cm level,and the standard deviation of residual elevation anomalies calculated when the terrain is relatively flat is mm level.That is to say,the larger the terrain fluctuation,the gravity field model The effect of the truncation error on the elevation anomaly is more obvious.4.Taking full account of the influence of terrain on gravity and geoid,the influence of terrain on gravity and geoid is studied based on plane approximation and spherical approximation.The calculation results show that the influence of spherical approximate terrain on gravity is about twice the influence of plane approximation on gravity;when the terrain is relatively flat,the influence of terrain on gravity and geoid can be neglected,and when the terrain fluctuation is large,it must be considered.5.The gradient method,combined gravity field model,RTM technology and topographic correction are used to calculate the gravity geoid in a region along the Yangtze River and parts of Tibet and Xinjiang,and good results are obtained.