Satellite Orbit Determination And Atmospheric Error Modeling Based Wide-area BDS Reference Stations

The emergence of global navigation satellite system(GNSS)and satellite navigation technology has greatly influenced the mode of production in various industries and the way of life of the public.In recent years,with the rapid development of economy and the rise of new technologies such as artificial intelligence,cloud computing and automatic driving,users have put forward higher requirements for GNSS technology,hoping to obtain real-time precise positioning services with high accuracy,high timeliness,unity and high concurrency.When users carry out real-time precise positioning,they generally need the infrastructure,software algorithm and realtime correction data products provided by the GNSS continuously operating reference stations(CORS),such as precise satellite orbit,satellite clock offset,atmospheric delay correction,etc.,so it has great research significance and practical value to study the key technologies and theoretical methods related to real-time precise positioning data processing and service system.Aiming at several key technologies of data processing and service of real-time precise positioning correction,this paper focuses on the improvement of precision orbit determination accuracy of Beidou satellite,optimization and prediction of ionospheric error empirical model and real-time modeling,modeling of tropospheric delay fusion for multi-source data.This paper optimizes and improves the relevant theories and algorithms,and constructs a set of real-time precise positioning service system to provide various types of real-time precise positioning service products,so as to promote the application and promotion of BDS high-precision positioning.The specific research work and contribution of this dissertation are as follows:1)Analyzed the development trend of high-precision satellite navigation and positioning technology,discussed the progress of precise point positioning(PPP)technology,and systematically analyzed the correction information of satellite orbit,ionospheric delay and tropospheric delay that PPP technology relies on,as well as the research and development status of GNSS real-time precise service system.2)Systematically analyzed the error sources,influence magnitude and commonly used error processing strategies in GNSS real-time precise positioning,introduced the observation equation of GNSS precise positioning,and discussed the commonly used parameter estimation methods such as least square,Kalman filter and square root information filter.3)Studied the theory of precise orbit determination observation equation,dynamic model,parameter estimation method and perturbation model.Proposed a method of orbit dilution of precision(ODOP)to quantitatively analyze the influence of the distribution of ground reference stations on the precision orbit determination precision.Based on the data of China's national reference stations and MGEX reference stations,the high-precision orbit of Beidou satellites was estimated.The accuracy of single Beidou and joint orbit determination methods are compared and analyzed.Analyzed the contribution of reference stations in China region to the precise orbit determination of Beidou satellites,and analyzed the rationality of the number of stations in China region in the Beidou satellites precise orbit determination.4)Studied the correction methods of ionospheric delay empirical model and fitting model,and proposed a method of IRI-2016 model optimizing using Beidou GEO-TEC,Calculated and generated IG index per hour in China using the characteristic of Beidou GEO-TEC not affected by the temporal and spatial gradient pollution of ionosphere.The obtained IG index was regarded as an effective driving force for the IRI-2016 model to generate short-term ionospheric parameters,and effectively improved the effect of IRI-2016 model in China.Taking IRI-2016 model as the background,integrated GNSS Tec data in China,the IG12 numerical distribution map in China was calculated.The spherical cap harmonic function was used to fit the relationship between IG12 and geographic longitude and latitude,and the time-domain prediction was carried out.The short-term and high-precision prediction of ionospheric state was realized;Based on the national CORS,calculated the real-time ionospheric delay grid fitting model products,and evaluated the accuracy of the products.5)Studeid the tropospheric correction model based on real-time GNSS observation data,and estimated the tropospheric delay of reference stations by real-time multi system PPP method.Based on the meteorological data model,GPT2 w model and GNSS-PPP model,proposed and established a kind of tropospheric fusion model suitable for China,and the accuracy of the model was tested by selecting stations all over the country.In this paper,the fusion model was compared with meteorological model,GPT2 w empirical model and GNSS-PPP inversion tropospheric model,and analyzed systematically by season,longitude and latitude,elevation and special geographical environment.6)Designed and developed a set of service system including data management,real-time product computing,real-time product broadcasting and terminal real-time positioning based on the key technologies proposed in each chapter of this paper.Tested the accuracy of terminal positioning Jiangsu and Beijing.Proposed a security protection method of real-time precise positioning service system that meets the relevant national security requirements,and studied the method of system security protection strategy,information audit and information dissemination.Based on the products of precise satellite orbit and clock difference,PPP accuracy test of terminal positioning was carried out.The real-time tropospheric delay correction model can significantly improve the positioning performance of the elevation direction,and the addition of ionosphere and tropospheric product constraints can significantly improve the convergence rate of PPP and the positioning accuracy of the overall test period.