Research On Ocean Tide Loading And Ocean Tide Loading Displacement Model Estimated By GPS

The effect of Ocean Tide Loading(OTL) has been one of the important and indispensable factors for the high accuracy navigation positioning, especially for the coastal region. Now the research is mainly at using global ocean tide models to correct the effect of OTL, but the accuracy of the existing global ocean models is high in deep sea and poorer in the coastal region, thus affecting the overall precision of the global ocean models. Therefore, in order to improve the positioning accuracy, high precision of ocean tide models are needed urgently.OTL displacement inversion based on Global Navigation Satellite System(GNSS), has a unique advantage given the rapid development of GPS(Global Positioning System) technology. It is global coverage, all-weather, low cost in comparison to gravity and very long baseline interferometry measurement on OTL.In this research, OTL and OTL displacement model estimated by GPS are studied. The basic theory of ocean tide and OTL are systematic researched. In order to improve the overall accuracy of global ocean tide model, the local tide models are used to refine the global ocean tide model in coastal region. OTL displacement model are inversed based on GPS Precise Point Positioning(PPP), and many new algorithms of estimating OTL displacement are proposed. The main work and contributions of this thesis are as follows:(1) Based on the effect of OTL on the high accuracy GPS precise positioning in coastal area, the correction models of ocean tide are applied to Hong Kong. The effect of solid tide, ocean tide and pole tide on GPS precise positioning are analyzed and compared, the results show that greatest effect is solid tide, followed by ocean tide, the minimal effect is pole tide, and the magnitudes of the three effects are centimeters, centimeters and millimeters; The effect of tide loading on GPS static positioning is smaller than that on dynamic positioning. The research result also shows long-term continuous observation cannot completely eliminate the influence of the tides which have periodic change.(2) The problem of the ocean tide effect on satellite gravity is discussed. The FES2004 and GOT00 global ocean tide models are used to estimate the loading effect up to harmonic degree 60, and the difference of the two ocean tide models is considered as the error estimation. The comparison between the numerical results and the standard deviation of gravity recovered with GRACE shows that the effect of ocean tide on satellite gravity is more serious than the error of the GRACE below degree 35 and the global ocean tide model error on GRACE is equal to the local tide effect.(3) The distribution of global ocean tide model accuracy is researched based on local tide models with high precision, the result shows that the accuracy of global ocean tide models is poorer in coastal area. A method which uses local tide model to refine global ocean tide model are put forward, and the results before and after refinement are compared and analyzed. The results in the paper have revealed that using local tide model to refine global ocean tide models could effectively improve the overall accuracy of global ocean tide models.(4) For lack of tide stations in Hong Kong to build high-precision local tide model, this paper has studied and proposed the GPS dynamic PPP algorithm with the overlapping period of three hours to obtain coordinate time series of GPS stations in Hong Kong, and used harmonic analysis method combined with the least squares fitting to effectively build the high-precision regional OTL displacement model of Hong Kong.(5) This study proposes a method to estimate ocean tide loading displacement parameters precisely, in which the effects of three-dimensional ocean tide loading displacements are estimated as unknown parameters at each epoch by precision point positioning; then, the amplitudes and phase lags of eight principal constituents are extracted from the time series of the ocean tide loading displacement using the harmonic analysis method. Comparing with conventional method,this method could effectively avoid the low computing efficiency and the rank-defect caused by excessive unknown parameters.(6) Because the residual errors of GPS could lead to solving the ocean tidal constituent parameters with long convergence time to get the stable value and the solar-related constituent have poor precision in GPS positioning model, the paper firstly carried out the research on establishing ocean tidal models with high precision by combining the global ocean tidal models and GPS PPP, and put forward an new algorithm which uses the global ocean tidal model as a priori information in PPP to solve the ocean tidal loading displacements. Comparing with conventional PPP, the results in the paper have revealed that the new algorithm can obviously accelerate the convergence speed of each tidal constituent and effectively improve the precision of tidal constituents, and the model based on this method have comparative precision with the global ocean tidal model obtained from the refinement of local tide model.