Research On Quasi-geoid Refinement Method And The Application In Irrigation District Of Songyuan

Both the planimetric coordinates of the point and their ellipsoidal heighs which relative to reference ellipsoid can be measured by using GNSS conveniently and accurately currently. However, the height system adopted in China is normal height basing on quasi-geoid. The key issues of the quasi-geoid refinement is how to convert earth height measured by using GNSS to normal height and traditional leveling is be replaced by the formal quasi-geoid refinement because of the former method with intensive labor and heavy workload. The most effective methods that get the same quasi-geoid as the national or local elevation system at present are that the data of Earth gravity field model, ground gravity, DEM and GNSS/level are processed with the method of “remove-recovery”. However, the ground gravity is needed in the “remove-recovery” method. The data of ground gravity is confidential in China, therefore they are difficult to be obtained by the enterprises. In addition, the complicated data are difficult to be processed. It is not easy to apply this Refinement Method in practical engineering projects, especially in those enterprises that have no advanced technology and enough money.The related concepts of quasi-geoid refinement are discussed based on the application in irrigation distract of Songyuan to the research on quasi-geoid refinement method. The factors affecting accuracy of GNSS/level original data acquisition and processing stage analyzed, and the author puts forward some measures related to eliminate or decrease the corresponding error. The author formulates reasonable acquisition and processing program of data. This dissertation will mainly focus on geometric quasi-geoid refinement method with less gravity data basing on some foreign and national literature. The following conclusion are obtained basing on geometric method, EGM2008 and multi-source information fusion.(1) The precision can not meet the requirement of fourth-grade leveling survey using geometric method to refine, on account of vast territory,long water basin and huge height difference;(2)The Maximum between normal high measured by quasi-geoid refinement method basing on EGM2008 and leveling normal high is 49.3 mm. The minimum number between them is 28.7 mm.All check points satisfy with the requirements of fourth-grade leveling precision;(3) The experiment of quasi-geoid refinement method which are based on multi-source information fusion, the inner precision is ±0.101 m and the external precision is ±0.036 m. It can effectively improve the accuracy of quasi-geoid refinement relative to quasi-geoid refinement method based on EGM2008. Meanwhile, it can meet requirements of fourth-grade leveling precision.The above results are gotten by utilizing original data of irrigation district of Songyuan to experience and through accuracy contrastive analysis, this dissertation gets these three conclusions. Overall, it can be concluded that the quasi-geoid refinement method basing on EGM2008 and Quasi-geoid refinement method basing on multi-source information fusion can effectively improve the accuracy of quasi-geoid refinement and meet the requirement of fourth-grade leveling survey through researching on quasi-geoid refinement method and experimental comparison analysis. Moreover, the quasi-geoid refinement method basing on EGM2008 is much faster and less cumbersome,therefore, is more applicable for quasi-geoid refinement in Songyuan irrigation district.