Study On The Methods Of Refining The Regional Quasi-geoid On The Basis Of CQG2000

Precise determination of local geoid is an important part in fields such as geodesy and geophysical as well as an important basic survey project.Regional geoid determination with centimeter-level precision is the hotspot research of modern geodesy.It has important scientific significance to establish a regional quasi-geoid with high-precision,high-resolution by GPS,leveling measurement,modern theories and methods the of determining the Earth's gravitational field.In this paper,the relations between elevation system and datum plane are introduced systematically.Also,various methods that are used to refine geoid are included in this paper. The author mainly studied the standard model of the Earth's gravity field and topographic correction model with GPS data.The theory and implementation steps of refining the geoid are presented with removal - fitting - the restoration.Through specific examples,the accuracy and practicability are compared,thus obtaining some significant conclusions.Second,as there exists many deficiency in traditional GPS-leveling data,the author applies the most practical machine learning algorithms - Support Vector Machine SVM to the establishment of geoid.And the selection of SVM's parameters and kernel function parameters are also analyzed and studied in this paper.The author finally verifies the effectiveness of this algorithm through practical instances.Third,though the accuracy is low,CQG2000 has a high-resolution and reflects the physical nature of China's quasi-geoid variation trend.In light of this,by the principles of removal-to-restoration,the author puts forward eliminating trend surface by CQG2000 before modeling the unconformity values by SVM algorithm which has a high-precision of fitting. Combined with practical project of Harbin quasi-geoid,the reliability and practicability of this method is verified.Finally,in the long span project,as there exists many shortcomings such as the author large accumulative errors,low economic efficiency in traditional transmitting methods,an idea-establishing a regional strip quasi-geoid by removal-to-restoration based on CQG2000-is put forward to achieve transformation from geodetic elevation to leveling elevation with a high-precision quickly,solving the problems in the long span project such as commendably the transmission of leveling elevation and unification of altitude datum and having high practical values and economic benefits.