Analysis Of The Impacts Of Severe Geomagnetic Storms On Global GNSS Observation Signals And Positioning Accuracy

Geomagnetic storm is a global space disturbance event caused by the impact of high-speed plasma clouds striking the earth.When a severe magnetic storm occurs,the magnetic field in the earth space fluctuates violently,which makes the space weather environment change significantly and causes the ionospheric electron density abnormal disturbance.When the Lband signals emitted by the GNSS satellite pass through the ionosphere,it will be affected by the abnormal ionospheric electron density disturbance,which makes the ionospheric delay error increase sharply,the signals are frequently lost,or even unable to work,seriously affecting accuracy and reliability of GNSS navigation,positioning and timing.Therefore,the paper used globally distributed GNSS observation data and TEC data from the MADRIGAL database to conduct research on 12 severe magnetic storms that have occurred since 2000.Firstly,by defining two indices of the number of loss of lock(LoL)on GNSS observation satellites at a single site(SLGS)and the global average rate of loss of lock on GNSS observation signals(GLGS),the influence of severe magnetic storm on GNSS observation signals was evaluated,and the relationship model between evaluation indices and geomagnetic index was established.Then the relationship between signal LoL and ionospheric anomaly was studied.Finally,the positioning accuracy of GNSS sites during magnetic storm was evaluated.The research results are of great significance for evaluating and guaranteeing the functions of navigation,positioning,timing,communication and other functions of GNSS during the severe magnetic storm.The main research contents include:(1)The two evaluation indices of SLGS and GLGS are proposed.Based on the preprocessing of the original data,the method of eliminating noise sites is introduced,and the definition of SLGS and GLGS were described in detail.In order to eliminate the influence of the satellite elevation angle on the research results,the optimal satellite elevation angle threshold is determined to be 10°;(2)The spatio-temporal evolution characteristics of GNSS observation signals LoL during 12 severe magnetic storms are analyzed.The results show that the time-varying sequences of SLGS and GLGS have high correlation with the geomagnetic index Dst.Through statistical analysis of 12 research cases,it is found that the maximum value of GLGS and the intensity of geomagnetic storm show an exponential correlation,and then establish a relationship model between the maximum value of GLGS and the strength of geomagnetic index Dst;(3)Based on the total electron content(TEC)data provided by Madrigal database,the correlation between differential TEC,relative differential TEC and SLGS spatial distribution is analyzed.The results show that there is a large positive phase storm and negative phase storm abnormal disturbance in the main phase and the early of recovery phase on severe geomagnetic storms.The spatial distribution has a good correspondence with the global distribution of SLGS;(4)Based on the above research,the influence of the severe magnetic storm on the positioning accuracy of GNSS is analyzed.The results show that during the main phase and the early of recovery of the severe magnetic storm,GNSS positioning is significantly affected,the accuracy is significantly reduced,and even the positioning is interrupted,which seriously affects the GNSS positioning function.Due to the magnetic storm,the geometric dilution of precision(GDOP)increases significantly,and the maximum value reaches 15,higher than the normal value(2-3);The latitude,longitude and elevation errors are also significantly higher than the calm level,with maximum values of 8.95 m,5.19 m and 15.42 m,respectively.