Refining Of Quasi-geoid Based On The Relative Height Anomaly Difference Adjustment

Aiming at the requirements of engineering applications of cm-level quasi-geoid, the dissertation proposed a method for obtaining local cm-level quasi-geoid from known gravity anomalies and other data. Through making full use of the high-frequency information within gravity observations, firstly the relative difference of height anomaly was obtained with high accuracy, and then by making a strict controlled adjustment on GPS/leveling points, the gravimetrical quasi-geoid was mandatorily constrained to the GPS quasi-geoid, and finally the numerical grid model of cm-level local quasi-geoid was established. In the dissertation the following work has been completed.1. The conventional theories and methods for the determination of geoid and/or quasi-geoid were discussed. Then taking the establishment of CGGM2000, the remove-and-restore technique for refining the quasi-geoid and the theory of GPS/leveling fitting were also researched.2. The sensitivity of vertical deflections and height anomaly difference obtained using the former to the high frequency terrain information was studied. The formula of the gravity anomaly correction term for height anomaly was derived and analyzed quantitatively. The defects of the GPS/leveling fitting method were also analyzed.3. A method was proposed for the refining of the local quasi-geoid using vertical deflections, gravity anomalies, GPS/leveling comprehensively, which was called relative height anomaly difference adjustment.4. The adjustment method that deals with grid height anomaly difference was studied. The problems were analyzed in the application of the parametric adjustment in which weights are determined in terms of distances in strongly constrained adjustment of large grid where there exist systematic errors. Two parametric adjustment methods that apply to grid data were proposed. One is the grid adjustment method in which weights were determined in terms of the distance from the observed point to the control point; and the other is the step-wise adjustment method that relies on route.5. The relative accuracy and absolute accuracy in the refining of quasi-geoid using the height anomaly difference adjustment were calculated and discussed for plains and mountainous areas respectively.