Research On High-Precision Tropospheric Delay Modeling And Application

Tropospheric delay error is an important factor affecting the accuracy of GNSS data calculation and PPP positioning effect.Among them,the longer convergence time of PPP is the key factor restricting its application.Practice has proven that high-precision tropospheric delay correction can effectively shorten the convergence time of PPP.Therefore,it is of great significance to study and correct the tropospheric delay to improve the effect of GNSS navigation and positioning.Based on the study of GNSS tropospheric delay correction methods,the types of modified model and modeling principles,we developed the high-precision global and regional tropospheric delay empirical models.In addition,the accuracy and applicability of different global tropospheric empirical models are analyzed,and the new models are applied to PPP for verification and analysis.The specific research contents and results of this thesis are as follows:1.We analyzed the temporal-spatial variation characteristics of the tropospheric zenith delay in the Australian mainland,and established a tropospheric delay correction model A_ZTD based on polyhedral functions and trigonometric functions.Compared with the GZTD,UNB3,UNB3m,and UNB4 models,the accuracy of the A_ZTD model in the Australian region(Bias:-0.15cm,RMSE:5.24cm)is significantly improved,which is more suitable for fine correction of troposphere delay in Australia.2.Since the GZTD model sets the elevation correction coefficient as a constant,the model has certain limitations in some regions.In this study,a global tropospheric delay model R_GZTD that takes the spatiotemporal variation of the zenith delay with the altitude change coefficient into account is established.In view of the problem that the commonly used troposphere(function)model has overfitting and loses the details of the tropospheric delay,this study established a model named GTDM that can effectively avoid the problem.3.For comparison,this paper adds multiple global experience models(GPT2w,GZTD,UNB3,UNB3m,UNB4)to analyze the accuracy of new models(R_GZTD,GTDM)from various data sources and perspectives.Results show that the accuracy(R_GZTD,Bias:0.48cm,RMSE:3.79cm;GTDM,Bias:0.60cm,RMSE:3.83cm)and stability of the new model are better than other models.The R_GZTD model significantly improves the accuracy of the zenith delay at high altitudes,while the GTDM model retains the details of the tropospheric delay to a greater extent.In addition,the accuracy of each model on seven continents is analyzed,and the results show that the R_GZTD model has strong applicability in the region,which can greatly improve the correction effect of regional tropospheric delay.4.The PPP positioning performance of different tropospheric correction strategies is discussed.Results show that the PPP positioning accuracy based on the new model R_GZTD is better than the correction of the Saastamoinen model.The convergence time is about 33.8%shorter than the parameter estimation method,and about 79.4%shorter than the correction of the Saastamoinen model.Additionally,the higher resolution precision and time resolution of the tropospheric delay correction model,the stronger positioning performance that can be achieved.