Improved GNSS Gravity Potential Leveling Method

The emergence of GNSS has brought revolutionary progress to the spatial positioning technology,and its excellent positioning performance has created accurate spatial geodetic coordinates for people.With the development and improvement of GNSS technology,the requirement of positioning accuracy is getting higher and higher,and the plane accuracy has reached the millimeter level,but there are still some problems that need to be improved in elevation.The GNSS height measured by GNSS positioning technology is based on the geodetic height of the WGS-84 reference ellipsoid,while the elevation used in the project is based on the normal height of the quasi-geoid.Because the datum of the two are inconsistent,the GNSS geodetic height can not be directly applied to practice.How to convert the geodetic height obtained by GNSS survey into the normal height that can be used in engineering is a work of practical significance and has a very broad application prospect.Based on this,this paper studies the above problems,the main research work and the final results are as follows:(1)based on the difference GNSS technique and GPS gravity potential leveling theory,this paper presents a method to calculate the normal height difference between two points,that is,the improved GNSS gravity potential leveling method.This method can provide highprecision geodetic height difference between two points in space thr-ough differential GNSS technology,and does not need to consider the gravity potential of the leveling surface of the national elevation starting point.it is a fast method to obtain the normal height between the two points.In this paper,starting from the normal height defined by Molodensky,according to the elevation anomaly data of several known points,the gravity field models such as EGM96,EGM2008 and EIGEN-6C4 are tested respectively.It is found that the EIGEN-6C4 model is the optimal model and used as the gravity field model selected in this experiment In the Lishan campus survey area of Xi’an University of Science and Technology,we calculate the height differences between different points based on GPS height fitting method,GPS gravity potential leveling method,single point GNSS gravity leveling method and improved GNSS gravity potential leveling method,and the median errors are ±0.0371m,±0.0434m,±0.1641m and±0.0368m,respectively.The accuracy of improved GNSS gravity potential leveling is much higher than that of other methods,and the accuracy of single point GNSS gravity leveling method is the lowest,while the accuracy of GPS height fitting method and GPS gravity potential leveling method is between the former two.The accuracy of the improved GNSS gravity potential leveling is ±0.007m higher than that of the GPS gravity potential leveling.In Taibai Mountain survey area,we calculate the height differences between different points based on GPS gravity potential leveling method and improved GNSS gravity potential water method,and the median errors are ±0.049m and ±0.039m,respectively.The accuracy of the improved GNSS gravity potential leveling is ±0.010m higher than that of the GPS gravity potential leveling.Whether in the plain area or in the mountain area,the improved GNSS gravity potential leveling is an effective and rapid method to determine the normal height difference.(2)when using the GPS gravity level method to calculate the normal height difference,it is necessary to consider the gravity potential of the national height starting point,and its error will further affect the height difference.The height difference calculation of the improved GNSS gravity potential leveling method has nothing to do with the selection of elevation datum.In addition,the factors that affect the accuracy of the improved GNSS gravity leveling are geodetic height difference,gravity field model,average normal gravity and so on,in which the geodetic height difference is the biggest,the average normal gravity is the second,and the gravity field model is the smallest.(3)although the accuracy of geodetic height difference can reach millimeter level by using the method of precision point positioning,it takes a long time.After experimental verification,it is found that the accuracy of geodetic height difference is ±0.031m after 2 hours.With the increase of observation time,the accuracy of geodetic height difference becomes higher and higher,and the accuracy of geodetic height difference after 24 hours is ±0.006m.Using differential GNSS to observe for 2 hours,the accuracy of geodetic height difference is ±0.005m.Therefore,in order to obtain high-precision geodetic height difference in a short time,differential GNSS observation method is preferred.