Research On Modeling Of Regional Ionosphere Based On GNSS And Application In PPP

The ionosphere is an important component of the earth's atmosphere.The delay error of the radio signal passing through the ionosphere is one of the important error in GNSS navigation and positioning.High-precision ionospheric delay products are of great significance to improve the positioning accuracy and convergence speed of GNSS precise point positioning.In this paper,we focus on the application of Un-combined precise point positioning to extract the ionospheric delay for inversing the regional ionospheric model and study the application of ionospheric delay information in precise point positioning.The main contents and conclusions of this paper are as follows:(1)Using the data of MGEX observation network,it extracts ionospheric delay observation with UC-PPP algorithm and dual-frequency carrier phase smoothing pseudo-range algorithm and separates the GPS/BDS DCB through the spherical harmonic model.By comparison,the accuracy of the GPS/BDS DCB separated by the ionospheric delay observation using the UC-PPP algorithm is about 0.2 ns higher than the DCB accuracy of the ionospheric delay observed by the double-frequency carrier phase smoothing pseudo-range extraction.(2)The stability of GPS / BDS DCB in one month was analyzed by using MGEX DCB product for one year,and the influence of DCB correction on single frequency PPP positioning is analyzed.The experimental results show that the monthly stability index of GPS satellite DCB is below 0.1ns,the stability of BDS satellite DCB is less than 0.4ns,and GPS DCB is more stable than BDS DCB.Furthermore,within a short time frame,the GNSS original observations without DCB correction will affect the positioning accuracy of single frequency PPP.(3)By means of the UC-PPP algorithm,which is constrained by the ionosphere,the ionospheric observations without DCB are separated and then use the improved spherical harmonic model to invert the ionospheric information in China.Compared with the GIM grid,the model is consistent with the regional ionospheric activity in China,and the maximum deviation is not more than 5tecu,and the difference is the lowest in the high latitude region.(4)It analyzes the difference between the conventional LC-PPP model and UC-PPP model,and the GIM model and the regional ionospheric model in China are used as the prior information to constrain the UC-PPP model.The experiment is carried out with GPS/BDS observation data.The results show that the convergence speed and short time positioning accuracy of the UC-PPP model with additional ionospheric constraints are better than those of the LC-PPP model,and the long-term localization results of the two models are consistent.At the same time,the convergence speed of UC-PPP using the regional ionospheric model as a priori information is faster than that of UC-PPP using GIM grid model as a priori information.In addition,the convergence speed and positioning accuracy of GPS PPP are higher than BDS PPP.(5)We study the ionospheric delay interpolation model SIM of regional station and compare the accuracy of SIM model,GIM grid model,and Chinese regional ionospheric model.The effects of three kinds of ionospheric delay correction schemes on the single frequency PPP positioning results are analyzed from the aspects of convergence time and positioning accuracy.Meanwhile,the influence of the baseline length on the accuracy of ionospheric delay interpolation is also studied.The results show that,within the short observation time,interpolation region ionosphere station location with the highest accuracy correction,followed by the regional ionospheric model,while the positioning accuracy of the GIM grid model is the lowest.However,under the condition of long time observation,the final results of three kinds of ionospheric delay correction schemes are similar.In the region,the baseline length has some influence on the interpolation accuracy of SIM,but it has little effect on the final positioning result.