A Study On Simulated Geoid In China And Its Adjacent Regions

In this thesis, the short waves of the geoid are calculated by observed geophysical data, and the middle- and long-waves of geoid are calculated by low orders of the earth gravity model (such as EGM96), then their superposition is the simulated geoid obtained. The effects on the determination of geoid of individual geophysical data are discussed and the reasonable integration ranges are proposed. The GPS-levelling is used to add constraints on the simulated geoid, and the "remove-restore" method and the multi-quadric function method are used to interpolation, so as to obtain the refined geoid.The geoid undulations are the direct reflection of the earth internal density distributions. The long-wave parts are prominent in frequency domain of the geoid undulations. They reflect the abnormal density distribution in the deep earth or the mantle. The short waves of the geoid are strong related with the lithosphere loading and ground topography. So if we know the earth internal structures and its geodynamic processes, we can determine a unique geoid. Theoretically, in the simulation of the geoid, not only the effects of topography and the density distribution in the crust, but also the effects of the mantle abnormal density should be taken into consideration. The density of the mantle can be calculated by the velocities of seismic waves, and then their effects on the geoid can be calculated by internal loading theory. But the viscosity structures of the mantle bring a large uncertainty of the geoid, in addition, the dynamical effects of the mantle convection are also need to be considered. However, the relevant theoretical problems are complex and the computation loading is very heavy. By using the middle- and long-wave parts of the recent earth gravity model (such as EGM96), the effects of the mantle are calculated. And the topographical data, the interface undulation data, and the lateral heterogeneous density distribution data, are then used to simulate the short-wave parts of the earth gravity model. The superposition of the two parts gives the theoretical simulated geoid.As the interface in the earth located in different depth, so when their effects on the geoid are calculated, different integration range should be used. However, as we use potential functions directly in our study, the convergent speed of the calculation is very slow, the global integration must be taken. So we need consider the effects of the earth curvature. In global integration, the requirement of the data coverage and the computation are comparative high. In this thesis, a moving coordinate system is used to overcome the effects of the earth curvature. And a differential calculation concept is proposed that assumes the difference of geoid calculated between the central point and its marginal point is constant when the integration area is far away from the central point. An experimental method is developed to statistic the efficientintegration range for geoid calculation.Because the simulated geoid only reflects the differences of the real geoid, their values may have a systematic error, so GPS-levelling data are used to constrain the geoid interpolations. For improving the accuracy of the geoid conversion, the "remove-restore" method and the multi-quadric function method are used to geoid interpolation. Through comparing with the geoid values of known points, our method has some significant improvements on the geoid determination method used before.