Study On The Algorithm And Effects Of GNSS High Order Ionospheric Delay Correction

The ionospheric delay correction is one of the key problems to be solved in GNSS navigation and positioning technology.Under the collective effects of various physical and geophysical mechanisms,the ionospheric structure and physicochemical changes are very complex.The influence of ionosphere on the propagation of radio waves is highly nonlinear and heterogeneous.Therefore,it is necessary to carry out in-depth study to eliminate or reduce the impact of ionospheric errors on GNSS navigation and positioning.Based on the data from International GNSS Service analysis center and the Continuous Operational Reference Stations,for the problem of high-order ionospheric delay correction,the following research work is mainly carried out:(1)The cause of the system Difference Code Bias(DCB)of the GNSS is analyzed,and the general method of separating the satellite DCB and the receiver DCB is provided.Then,using the actual measured data of IGS stations at different latitudes,the DCBs of satellites and receivers with 60-day time span are separated and the stability is evaluated respectively.The results show that the DCB values of satellites and receivers are unstable,and the change of DCB in medium and high latitudes is relatively stable,however,in the low latitude area,the DCB is greatly affected by the geomagnetic and solar activities,the stability is obviously worse.The daily variation of DCBs' time delay for satellites and receivers can reach 2.021TECU and3.085TECU.(2)The influence of solar activity and magnetic storm on the numerical value of high-order ionospheric effect is analyzed.Then,considering the high-order ionospheric delay,Precision single point positioning(PPP)experiments are performed to quantitatively analyze the correction values of the high-order ionospheric delay to the PPP solution coordinates.The experimental results show that the correction values of the high-order ionospheric delay in the X,Y and Z directions are 1.89mm,3.90mm,8.45mm in the WGS84 coordinate system,respectively,in the active period of the sun and geomagnetic field,and 1.2 mm,2.40 mm,3.91 mm,respectively,in the stationary period,which shows that the influence of the high order term of the ionospheric delay on the PPP positioning with the mm scale is significant both in the active and the stationary phases of the sun and geomagnetic field.(3)An improved polynomial model named POLY-SIN is proposed based on the advantages of the Polynomial model and the Trigonometric Series Function model.Combining with the CORS data of Jiangsu Province,the modeling accuracy of POLY-SIN model and the completely 2-Dimentional Polynomial Model(9-DPM)is compared The results show that the error of the POLY-SIN model and 9-DPM are 1.181TECU,1.291TECU,and the relative error are 8.29%and 9.39%,respectively,which shows that the accuracy of the POLY-SIN model is 8.5%higher than that of the 9-DPM model.(4)In order to further improve the modeling accuracy of regional ionospheric delay correction,a fusion model named BP + POLY-SIN model is constructed by using H-BP algorithm to compensate the error of POLY-SIN model.In the same actual data and sample selection,the error of BP + POLY-SIN model is 1.106TECU and the relative error is 7.76%.Compared with 9-DPM model and POLY-SIN model,BP + POLY-SIN model has the highest accuracy,which is 14.3%higher than that of 9-DPM model.