Study On Ionospheric STEC Extraction Based On GPS Observation Data

Ionospheric delay errors have severely affected the GNSS positioning mode and service range.Accurate and reliable ionospheric error correction is the key to ensuring the positioning accuracy of a large number of single-frequency users in the GNSS market and reducing the convergence time of precision single-point positioning users It is of great significance to study the extraction of the ionosphere,accurately model the ionosphere,and improve the accuracy of satellite navigation positioning,speed measurement,and timing.In this paper,the algorithms of the more commonly used methods for extracting the ionosphere include carrier phase Smooth pseudorange,based on GIM interpolation methods,and the non-differential and non-combined precision point positioning method proposed in recent years are implemented.And the GPS observation data of two sets of zero/short baseline stations of IGS from December 1,2018 to December 30,2018(DOY335 to DOY364)are used to analyze the feasibility of three methods from the two aspects of the accuracy of STEC extraction and the stability of the determined station receiver DCB.Using the GPS observation data of 7 sets of zero/short baseline stations at different altitudes in the northern hemisphere,the advantages,disadvantages and the applicability of the above three different methods are studied from the two aspects of the accuracy of the extracted STEC and the stability of the determined station receiver DCB.Finally,the influence of the ionospheric anomaly induced by the extraordinarily large magnetic storm event on September 8,2017(DOY 251)was analyzed and discussed.The research content of this article includes the following conclusions1.For zero/short baseline stations,whether it is the carrier phase smoothing pseudo-range method,the non-differential non-combined PPP method,or the GIM interpolation-based method,the extracted STEC can mostly reflect the change trend ofthe ionosphere.The determined DCB information of the station receiver can also meet the accuracy requirements of positioning and navigation.Therefore,all three STEC extraction methods can be used to extract ionospheric information above the station along the line of sight2.The method of non-combined PPP extraction of STEC can be applied to extraction of STEC in all latitudes,especially above 40 0 N.The method of carrier phase smoothing pseudorange is applicable to STEC in areas between 30°N and 40°N Extraction,and the GIM-based interpolation method is more suitable for the extraction of STEC from the equator to 30°N.The average monthly deviation between the DCB information of the station receivers separated by different methods and the DCB information of the station receivers released by IGS is within Ins,which can meet the accuracy of positioning and navigation3.During the active period of geomagnetic activity,the non-differential and non-combined PPP method has sufficient accuracy guarantee whether it is the extraction accuracy of STEC or the determined DCB information of the station receiver.Therefore,before and after the active period of geomagnetic activity,it is recommended to use non-differential non-combined PPP method to extract STEC.