Research On Wide-Area Real-Time GNSS Three-Dimension Ionospheric Tomography

The ionosphere is an important part of the upper atmosphere,which not only protects the earth from the direct effects of solar ultraviolet radiation and high-energy particles of the universe,but also affects the propagation of radio waves,which is closely related to human production and life.At the same time,the ionosphere is also an important research topic in space and atmospheric science.Monitoring and studying the ionosphere can improve human understanding of the formation mechanism of the ionosphere and master the temporal and spatial changes of the ionosphere.Traditional atmospheric detection methods,such as radiosondes and meteorological satellites,are difficult to achieve large-scale,continuous observation due to high observation costs.In recent years,with the continuous construction and improvement of the Global Navigation Satellite System(GNSS)based on Beidou,GPS,GLONASS,and Galileo systems,and the extensive deployment of terrestrial GNSS tracking station networks,ionospheric tomography based on multiple GNSS will bringing unprecedented opportunities for monitoring and research of the ionosphere.Combining GNSS observation of National BDS Augmentation Service System and Crustal Movement Observation Network of China,it is of great significance to establish a wide-area three-dimensional ionospheric model covering China’s scope for ionospheric monitoring and research in China.Based on wide-area real-time GNSS three-dimensional ionospheric tomography,this paper systematically studies multiGNSS ionospheric delay extraction,ionospheric tomography model and ionospheric reconstruction algorithm,and then establishes a real-time ionospheric threedimensional tomographic model covering the Chinese region.The application verification of ionospheric tomography model in GNSS single-frequency pseudorange positioning and ionospheric disturbance during magnetic storm is preliminarily realized.The main work and conclusions of this paper are as follows:(1)In the wide-area three-dimensional ionospheric tomography of GPS,the widearea three-dimensional ionospheric tomography based on multi-GNSS is further studied.The influence of ionospheric delay extraction accuracy on tomography modeling of different navigation systems is analyzed.A multi-system ionospheric tomography algorithm refined by stochastic models.The measured data shows that compared with the single GPS observation data,the multi-GNSS observation data can effectively improve the effective grid correction rate of the ionosphere region to be inverted and the number of observation rays in the grid.The regional improvement rate in China is 6%and 100%respectively,the problem of insufficient observation data in ionospheric tomography has been improved.The average error of the multi-GNSS ionospheric tomography inversion results compared with the peak density of the ionospheric F2 layer measured by the Ionosonde is 0.96×105el·cm-3.Compared with electron density measured by the SWARM satellite over the peak height of the F2 layer,the average error is 1.0×105el·cm-3.At the same time,the accuracy of the inversion results is significantly improved by the multi-system ionospheric delay weighting strategy,and the convergence accuracy can reach 1.6TECU on average.(2)Combined with the traditional MART algorithm,an adaptive AMART algorithm and a filter-based FMART algorithm are proposed.The AMART algorithm uses electron density information to assign weights to individual grids during ionospheric tomography and adaptively adjusts the relaxation factor.The experimental results show that the AMART algorithm can effectively speed up the convergence compared with the MART algorithm.The average number of iterations of MART and AMRT is 12 and 9 times respectively.In the MART algorithm,the empirical model such as IRI is generally used as the initial background field.For the limitations of the empirical model,the accuracy is often limited.In this paper,the filtering and MART algorithm are combined,and the inversion result of the previous epoch is used as the initial background field to improve the accuracy of initial background,and thus improve the accuracy of the inversion results,the average error of the ionospheric F2 layer peak density of inversion results compared with Ionosonde is 0.12×105el·cm-3.(3)Due to the limited viewing angle of the ground-based GNSS,the horizontal observation ray is less,resulting in lower vertical resolution of the inversion results of ionospheric tomography.In this paper,three-dimensional ionospheric tomography is performed by combining ground-based/occultation observation data,which combines the advantages of ground-based GNSS in time resolution and occultation observation data in vertical resolution.Comparing with the radio occultation inversion results and the Ionosonde,the results show that the peak density accuracy of the ionospheric F2 layer inversion by the ground/occultation joint method can reach 0.82×105el·cm-3 and 0.12×105el·cm-3 respectively.(4)Based on the above model and algorithm research,this paper implements the wide-area real-time ionospheric tomography software module based on GNSS distributed high-precision data processing platform FUSING,and applies it to the ionospheric delay enhancement service in wide-area precision positioning and monitoring of ionospheric disturbances during magnetic storms.Based on the GNSS distributed high-precision data processing system,real-time access to the widearea/global GNSS tracking station data stream,real-time extraction of ionospheric delay,and wide-area ionospheric tomography,realizing wide-area enhanced services and realtime monitoring of the ionosphere.In the GNSS positioning,the three-dimensional ionospheric model is applied to the single-frequency SPP ionospheric delay correction.The measured results show that the correction effect is better than the CODE GIM model.In the study of ionospheric disturbance,this paper analyzes the ionospheric anomalies during magnetic storms by using magnetic storms in late March 2015 as an example.Combined with GIM and three-dimensional ionospheric tomography,the results show that the obvious ionosphere anomaly occurred in both 2D and 3D space during the magnetic storm,which verifies the influence of magnetic storm on ionospheric disturbance.