Regional Ionospheric TEC Modeling And Spatio-temporal Variation Characteristics Analysis

Improving the accuracy of satellite navigation and positioning has always been a hot topic tracked and researched in the field of navigation,but there are many factors that affect the positioning accuracy,such as system hardware delay,tropospheric delay,multipath effect,ionospheric delay,clock difference,et al.Since the US abolished the SA policy,ionospheric delay is the most important source of error affecting GPS satellite positioning accuracy.At present,the ionospheric empirical model and GIM have limited correction effects on ionospheric delay,especially in China,where IGS stations are sparse,resulting in that the GIM has a large deviation in China.Therefore,the establishment of regional ionospheric model has important value for improving the accuracy of satellite positioning technology in this region.With the gradual completion of the regional CORS,data security is provided for the establishment of the regional ionospheric model.Therefore,based on the theory that the signals of different frequency have different delay in the ionosphere,the regional ionospheric model is established by using the dual-frequency GPS signal of CORS.The regional ionosphere model is studied and the regularity of the ionospheric temporal and spatial changes are analyzed.This paper mainly does the following research work:(1)The basic conditions of the ionosphere are introduced and the theoretical basis for the ionospheric delay of the signal are derived.The various influencing factors affecting the ionosphere are analyzed,including the height of the single layer ionosphere,the activity intensity and the period of the sun.The various ionospheric models are compared and the advantages and disadvantages of various ionospheric models are summarized.In this paper,the polynomial ionospheric model is selected to establish the regional ionospheric model based on CORS data.(2)The different methods of cycle slip detection and repair are studied.Combining the advantages and disadvantages of different methods,the combination of ionospheric residual method and Melbourne-Wübbena method has good effect on the detection and repair of double-frequency observations.The influence of hardware delay on the calculation of the total electronic content of the ionosphere is analyzed.The hardware delay of the GPS system is calculated,and the hardware delay of the satellite and the hardware delay of the receiver are separated.The verification shows that the required accuracy is met.Introduce several frequently-used satellite coordinate interpolation methods.By comparing the accuracy of the interpolation results obtained by satellite interpolation in these interpolation methods,the sliding Lagrange interpolation method is used to calculate the precise ephemeris interpolation.the satellite elevation angle,azimuth and ionospheric puncture point position are calculated.According to the method of carrier phase smoothing pseudorange,it is concluded that the smoothing coefficient interval with good smoothing effect is 15~20.(3)According to the continuity of the ionosphere,the regional polynomial model and the hardware delay characteristics of the GPS system,the solution method of the polynomial ionosphere model with constraints is proposed.The regional ionospheric model of Gansu Province is established by using GSCORS data.The GMT is used to make the ionospheric map of Gansu Province,and the internal and external conformity accuracy is evaluated.The results show that the polynomial ionospheric model with constraints of 1 by 2 order can completely describe the ionospheric variation in Gansu Province;The IONEX standard ionospheric product IONEX,which is officially released for use by users,can improve the correction of ionospheric delay errors in the region.(4)The time and spatial variation laws of the ionosphere are studied according to the single station ionosphere model and the regional ionosphere model.The results show that the ionosphere has obvious temporal and spatial variation laws,for example,the ionosphere is calm at night,and the ionosphere TEC gradually increases with the rising of the sun during the day.The maximum value can be reached between UT04:00 and UT06:00;the ionospheric TEC is generally higher in the spring and autumn,The peak will appear between May and October,The ionospheric TEC is generally calm in the summer and winter seasons;The ionosphere TEC in the year with frequent solar activity is higher than the year in which the solar activity is relatively calm,with obvious periodicity of solar activity.The ionosphere changes with latitude has the law that the TEC value decreases with increasing latitude.The spatial-temporal variation of the ionosphere provides a reference for further improving the accuracy of ionospheric modeling.