Some Key Issues Relating To High Precision GPS Positioning And Crustal Deformation Analysis

The main issues relating to high precision GPS positioning and crustal deformation analysis with GPS are: One is how to obtain high precision positioning GPS results; the other is how to extract correct deformation information through reasonable analysis approaches. In this paper, GPS phase observation equation, various error corrections, the datum of differential GPS, ambiguity resolution, data processing schemes, reference frame and deformation analysis methods are systematically studied. The main research works and results are following:1 Zero difference phase observation model and error models are analyzedZero difference phase observation equation is derived in detail based on radio propagation principle. A few of basic issues about absolute and relative GPS positioning are expatiated. The calculation of theoretical station-satellite distance is discussed in detail. The error models including antennas phase offsets, troposphere delay errors, Earth rotation, and tidal loadings are numerically analyzed.2 The orbit improvement model for high precision positioning is presentedThe essential of GPS orbit determination is determining the orbital initial conditions (orbital elements) and perturbation parameters (usually are radiation model parameters). The implementation of orbit improving for high precision positioning is actually the procedure of precise orbit determination; the dynamic model of GPS satellite motion is studied. The partial derivatives of the measurements with respect to orbital parameters are given through numerical integration with the variation equations.3 Proposed the concept that parameter constraint adjustment unifies free network adjustmentsClassical free network adjustment, enclosed network adjustment, general rank-deficient free network adjustment, and weighted rank-deficient free network adjustment can all be expressed by indirect adjustment with conditions. The direct resolution formula of unknown parameters under common situation is given. All kinds of solutions including precision estimations can be transformed each other by means of the normal equations and the datum conditions. We define the adjustment problem with priori accuracy information of unknown parameters as "parameter constraint adjustment". As long as we define proper constraints (weights) to these parameters, the adjustment method almost represents all kinds of adjustments numerically. As defining tight constraints to part of parameters, it is equivalent to classical free network adjustment or enclosed network adjustment; as defining same loose constraints to all parameters, it is equivalent to classical rank-deficient free network adjustment; as defining sameloose constraints to part of parameters while looser to other parameters, it is equivalent to quasi-stability free network adjustment.Presented two schemes to solve datum issues of GPS surveying using parameter constraint adjustment: One scheme is using tight constraints to the stations standing for datum at baseline processing step; the alternative is realized by following two steps: First, to obtain the results of free network adjustment using loose constraints to all stations, then transform the solutions into the results under datum condition through coordinate similarity transformation.4 Proposed a new method for single epoch GPS positioning--damped LAMBDA algorithmBased on the concept of parameter constraint adjustment, through adding a damped factor (matrix) into the normal equation of single epoch GPS positioning to solve rank-deficient problem, the ill-condition of ambiguity covariance matrix is ameliorated. Combining with LAMBDA method, we put forward anew method for single epoch GPS positioning--damped LAMBDA algorithm. This method onlyuses one epoch observation data, no need considering cycle-slip problem. The accuracy requirement of the approximate coordinates can be relaxed, and ambiguity search time is saved. This method can be used in many cases. With help of filtering or smoothing, damped LAMBDA algorithm can reach l-2mm level pr...