GPS-TEC Derivation And Study On Ionospheric Changes In Guilin Region

Global satellite navigation and positioning system(Global Navigation Satellite System,GNSS)positioning accuracy has been a hot topic in the field of navigation,in which ionospheric delay error is the most important error source for satellite positioning accuracy.Ionospheric delay can cause GPS to produce deviations of several meters or even hundreds of meters during positioning.Therefore,it is very important to monitor the variation and distribution of ionosphere.Monitoring the variation patterns of ionospheric VTEC(VTEC)is of great importance for improving satellite positioning accuracy,preventing natural disasters and studying ionospheric physics in depth.At present,empirical models are commonly used internationally to estimate global ionospheric VTEC.However,a large number of studies have confirmed that there is a large difference between the estimated value of the empirical model for the VTEC of the ionization layer in the low latitude region and the measured VTEC value of the ionization layer.Guilin is located in an abnormal ionospheric region at low latitudes,so the variation characteristics VTEC ionosphere in this area are complicated.Therefore,using the GPS dual-frequency observation data over Guilin to study the variation characteristics of ionospheric VTEC in Guilin area is of great significance for the establishment of ionospheric model suitable for low latitude areas in China.The main research work in this paper is as follows:(1)The ionospheric monolayer model is introduced,and the formulas for calculating the elevation angle,azimuth angle and puncture point of the GPS satellite model are derived in detail.Deficiencies in calculating ionization layer VTEC by pseudo-range method and carrier phase method are analyzed.A method for calculating VTEC using smoothing filtering algorithm is proposed.The algorithm is based on the VTEC calculated by the carrier phase method,and the weighted average of the difference between the VTEC obtained by the pseudo-range method and the VTEC obtained by the carrier phase method is used as the correction factor to obtain the final ionization layer VTEC.(2)The effects of hardware delays in GPS satellites and receivers on the solution VTEC the ionosphere were studied.Advantages and disadvantages of various GPS system hardware delay inversion algorithms are analyzed.It includes spherical harmonic function model method,generalized trigonometric series model method,grid method,polynomial model method and so on.(3)Combined with polynomial model,an algorithm of 2 times 2 order polynomial function model combined with smooth filtering is proposed to solve the VTEC of ionization laye.At the same time,this algorithm,pseudo-range method and carrier phase method are used to simultaneously process the GPS dual-frequency observation data of Guilin Observatory of the National Observatory.The residual graph of the three algorithms is compared and analyzed.(4)The double-frequency observation data of Guilin Observatory in 2017～2019 are retrieved by using GPS algorithm of 2 times 2 order polynomial function model combined with smooth filter.A map of the VTEC intensity of the ionosphere in Guilin for three years was obtained.The daily,seasonal,annual and spatial variations of the ionosphere in Guilin region were analyzed and summarized.