Gravity Field Model In The Application Of Engineering Control Network

In current days, GPS technology has been widely used in geodesy, engineering surveying, photogrammetry and remote sensing, crustal movement monitoring, deformation monitoring, geodynamics, and other research areas, it can simultaneous determine precise three-dimensional geodetic coordinate. Once the local geoid is determined, the ellipsoidal height of GPS point can be easily transformed to quasi-geoid height through precise quasi-geoid to replace the geometric leveling. The Earth gravity model and the determination of geoid is the main research area of gravity satellite, and the achievement of the gravity satellite research is another revolutionary breakthrough after GPS technology, which not only led to change in modern geodesy but also promote the development of other related disciplines. In precise engineering surveying, by combining high resolution gravity model with high precise GPS surveying, it is possible to improve the accuracy of GPS height transformation.The key problem of transferring GPS leveling is to get an optimal combination of different gravity models and a reasonable selection of different fitting methods. Along with the successful launching of GOCE gravity satellite which takes gravity gradient as main observations and its related production of gravity model which greatly improves the accuracy and resolution of the Earth gravity model, and it is necessary to apply it to GPS leveling transformation. It is common to use both of GPS and total station in current precise engineering survey, which leads to the transformation problem between normal and vertical system. Because of the low precision of gravity model in the past, the effect of the problem is ignored. But now, with the latest available gravity field model, it is possible to calculate the vertical deflection and apply it to precise engineering survey.Considering the problems mentioned above, the thesis proposes the method of using the latest higher precise EGM2008 and SGG gravity model to replace the gravity model in the past and analyzes the precision of height anomaly calculated respectively by two models. The thesis also applies the two models to the method of recovery - fitting- restore of GPS leveling transformation which can effectively remove the system error caused by height anomaly. Based on this the thesis analyzes the fitting accuracy of plane method. quadratic surface method, two-surface method, inverted double surface method and spline function method that is used to height anomaly fitting and validates the precision respectively by actual data of a actual tunnel project. According to the characteristic of precise engineering survey, the thesis proposes the precise GPS and total station data processing method taking the vertical deflection into account. The method first transform the total station observation data from normal to vertical system and then process data together with GPS data. According the actual tunnel project example, the result shows that the effect of the earth gravity model on plane control network can not be ignored.