Research On Urban Quasi-geoid Refinement Based On High Precision GNSS/Leveling Data

For a city or region,the use of quasi-geoid can make the survey fast and efficient,promote the development and construction of cities and regions,and has important social benefits and scientific research significance.A quasi-geoid model?hereinafter referred to as the"present model"?was built in 2001 in a city.With the rapid development of China,the area of urban built-up areas has been expanding.In addition,the model was established earlier,which makes the effective coverage of the present model insufficient to meet the needs of urban construction and development in some areas,especially in the periphery,edge and mountainous areas.Therefore,in view of the unbalanced coverage of the city's existing model,this paper refines the model based on the current model,so that it can provide more effective services for the urban area after optimization.The main contents of this paper are as follows:?1?Using GAMIT/GLOBK and precision leveling data processing software,GNSS observation data and leveling data are processed respectively.The results show that the baseline NRMS values are all less than 0.3,the corrections are basically within?±2 cm?,the average relative accuracy of the network is 1.98×10^-8,the total median error of the leveling is?±0.51 mm?per kilometer and the accidental median error is?±0.36 mm?per kilometer.The data obtained above are pretreated.?2?The best fitting model and the best selection of fitting points.Using polynomial and polyhedral function fitting models,by changing the parameters of the model and analyzing based on different point selection methods,the experiment shows that the polyhedral function fitting effect is the best,and the number of points selected by synthesis method is the best.In order to further improve the fitting effect,the EGM2008 model combined with the"removal-recovery"method is used.The results show that the method achieves better accuracy than the direct method.?3?The regional analysis based on the existing model shows that the distribution of elevation anomaly difference has a certain spatial relationship,and then three schemes are adopted to optimize the model.The results show that the optimization effect is enhanced in turn,among which the optimization scheme based on the existing model has the best accuracy.Finally,based on this scheme,the optimal refinement model is determined by selecting the optimal number of points.The model has a high accuracy of±0.08cm in the interior and±0.38cm in the exterior,and can satisfy the relevant surveying and mapping tasks which are lower than this accuracy requirement.Moreover,through the difference analysis,it is concluded that the new model has no regional distribution characteristics,that is to say,the optimal model can adapt to all regions of the city,so as to better serve urban construction.