| Precise point positioning(PPP)technology has drawn much attention because its high precision,convenient operation,and being immune to length of the baseline.At present,the PPP technology is able to achieve the centimeter-level positioning accuracy,but it needs a long time to convergence.As the main error source of satellite navigation,tropospheric delay is an important factor that affects the location result of PPP.With the continuous construction and development of reference station network,it has become a hotspot in the field of satellite navigation to use the observation data of regional reference station to provide relevant information for users in the region,and then to improve service efficiency of GNSS system.Based on the above,this paper uses the spherical cap harmonic analysis method to establish regional tropospheric delay model,for the PPP users provide accurate troposphere delay to correct information,so as to avoid estimates the effects of tropospheric delay for positioning algorithm.Compared with the standard PPP method,this method improves the convergence speed of the positioning solution.According to the research objectives of the project,the following research work has been done:(1)This paper introduces the principle and the implementation method of standard PPP technology,analyzes several common function models and mathematical models,and studies the processing methods of various errors involved in PPP and the parameter estimation method of the model implementation.On this basis,the error processing methods and the setting of the filter in GPS PPP with the regional tropospheric delay model correction are studied.(2)The characteristics of atmospheric structure are expounded,and the influence of atmospheric refraction on the positioning of GNSS is analyzed.Several commonly used tropospheric delay processing methods in GNSS navigation and positioning data processing are compared and analyzed.The method of estimating the zenith tropospheric delay(ZTD)in PPP is introduced in detail.Meanwhile,the estimation of tropospheric delay in PPP and its influence on positioning are analyzed experimentally.(3)The spherical cap harmonic analysis method is introduced into the model construction of the regional tropospheric delay,and the solution method and the properties of the spherical cap harmonic function are studied and deduced.ZTD estimated by PPP is used as the observation value,and the regional tropospheric delay model based on spherical coronal harmonic analysis is established.The model can calculate the tropospheric delay information of anywhere in the region without the need of the measured meteorological parameters.In this paper,the accuracy of tropospheric delay calculation results of the model is analyzed.Compared with the IGS delay zenith delay products,the the model's inner concident RMS is 1cm,the external coinciden RMS is 2.6cm.It is shown that more accurate tropospheric delay information can be abtained by using the regional tropospheric delay model based on the spherical cap harmonic analysis method.(5)The regional tropospheric delay model is proposed to provide the enhancement information for PPP users in the region.The PPP method based on regional tropospheric delay model was verified by self-made program,and compared with standard PPP method.The experimental results show that the error amplitude of the PPP method based on the regional troposphere delay model is relatively small in the initial position solution,and after convergence,the positioning accuracy of the two models is comparable.Compared with standard PPP,the convergence rate of PPP method based on regional tropospheric delay model is improved significantly in terms of convergence speed.The convergence speed of zenith direction is increased by 16.7%,and the convergence speed of horizontal direction is increased by 7.1%.The experimental results show that the PPP method based on the regional tropospheric delay model is effective in improving the high precision positioning performance. |
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