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Abstract
Since its introduction in the early 1980¡¯s, the Global Positioning System (GPS) has become an important tool for high-precision surveying and geodetic applications. Carrier phase measurements are the key to achieving high accuracy positioning results. This research addresses one of the most challenging aspects in the GPS data processing algorithm, especially for precise GPS static positioning, namely the definition of a realistic stochastic model. Major contributions of this research are:
(a) A comparison of the two data quality indicators, which are widely used to assist in the definition of the stochastic model for GPS observations, has been carried out. Based on the results obtained from a series of tests, both the satellite elevation angle and the signal-to-noise ratio information do not always reflect the reality.
(b) A simplified MINQUE procedure for the estimation of the variance-covariance components of GPS observations has been proposed. The proposed procedure has been shown to produce similar results to those from the standard MINQUE procedure. However, the computational load and time are significantly reduced, and in addition the effect of a changing number of satellites on the computations is effectively dealt with.
(c) An iterative stochastic modelling procedure has been developed in which all error features in the GPS observations are taken into account. Experimental results show that by applying the proposed procedure, both the certainty and the accuracy of the positioning results are improved. In addition, the quality of ambiguity resolution can be more realistically evaluated.
(d) A segmented stochastic modelling procedure has been developed to effectively deal with long observation period data sets, and to reduce the computational load. This procedure will also take into account the temporal correlations in the GPS measurements. Test results obtained from both simulated and real data sets indicate that the proposed procedure can improve the accuracy of the positioning results to the millimetre level.
(e) A novel approach to GPS analysis based on a combination of the wavelet decomposition technique and the simplified MINQUE procedure has been proposed. With this new approach, the certainty of ambiguity resolution and the accuracy of the positioning results are improved.