Regional Ionospheric Modeling Based On Tha Data Of Ground-based Multi-GNSS And Validation

The TEC(Total Electron Content)is extracted by multi-GNSS no-difference combined and GF(Geometry-Free)observations in this paper.The regional ionospheric model of Europe,China and Hebei province are established with low-order harmonic function model,slant ionospheric model based on single satellite and polynomial ionospheric model based on single satellite.The inverse computation of rove-sites' STEC(Slant Total Electron Content)treated as the referential value is compared with the model to get the model residual in different areas.The GIM(Grid Ionospheric Model)offered by CODE(Centre of Orbit Determination in Europe)and dual-layer ionospheric model offered by UPC(Technical University of Catalonia)are regarded as referential model to calculated the fitting accuracy of other regional model,and applying these models in single-system and double-system single-frequency pseudo-range point positioning assessment.The advantage of slant ionospheric model based on single satellite and polynomial ionospheric model based on single satellite are prominent in the comprehensive comparison of these regional ionospheric models.The main contents of this paper are as follows:1)The steps of extracting ionospheric TEC with no-difference no-combined and GF observations are elaborated comprehensively.The types,character and evaluating method of DCB(Differential Code Bias)are introduced.2)The common ionospheric delay correction models are concluded comprehensively.One class of models are global ionospheric models,which could divided into empirical models and function grid models;another class of models are regional ionospheric models,which contain low-order harmonic function model,slant ionospheric model based on single satellite and polynomial ionospheric model based on single satellite.3)Each regional ionospheric model fitting accuracy reflected by inverse computation model residual shows the result that:? the accuracy of regional ionospheric models based on no-difference combined observation are higher than GF observation;? the accuracy of SIM is the highest in the seven regional models,which could even 80%better than referential models;? dual-layer models accuracy is higher than single-layer models,which can reach 10%in Europe;? SIM can apply to the area well,in which ionosphere is abnormal and have strenuous activity;? polynomial ionospheric model based on single satellite is better than other models in Hebei province which is close to SIM;? the fitting accuracy of dual-layer model GAGE(Research group of Astronomy and GEomatics)is the best one in grid models.4)The single-system and double-system single-frequency pseudo-range point positioning assessment shows that:? compared with single-system,the precision of double-system point positioning is better,which is 50%higher than single BDS and 10%higher than single GPS;? the positioning precision of SIM is 50%,35%higher than referential models and 20%higher than low-order harmonic function grid model;?the positioning precision of models based on no-difference combined observation is 20%higher than that based on GF observation;? the positioning precision of POLY(POLYnomial Ionospheric Model)is close to SIM;? in referential models,the positioning precision of dual-layer model is 25%higher than single-layer model of CODE;? the positioning precision of dual-layer model GAGE is close to SIM in Europe,and the advantage of both need to be research deeply;? the positioning precision of each model is the same with the model residual fitting precision.