Morphological Characteristics Of Ionospheric Disturbance Caused By Typhoon Based On Ground And Occultation GPS

The ionosphere is the main source of positioning errors for Global Navigation Satellite System(GNSS).When the ionosphere is in a calm state,the use of differential techniques or GNSS multi-frequency technology will effectively reduce the impact of ionospheric errors.Typhoon can cause small and medium-scale ionospheric disturbances,which poses a serious threat to the safe operation of GNSS.However,the regularity and coupling mechanism of typhoon-induced ionospheric disturbances are still unclear,and there is a lack of systematic and complete research.In this paper,the regularity and coupling mechanism of ionospheric disturbance caused by typhoon are studied in the following aspects.1)The basic principle,main algorithm and general flow of extracting ionospheric TEC from dual-frequency GPS are introduced.Based on this method,the ionospheric TEC value from Beijing Fangshan GPS station(BJFS)in 2018 is extracted.Compared with the GIM products provided by IGS,the ionospheric TEC value extracted in this paper is highly accurate,and its root mean square is 2.78 TECU.The accuracy is related to the season and local time.The accuracy of TEC in autumn and winter is higher than that in spring and summer,and in night is higher than that in daytime.2)Three ionospheric TEC anomaly detection methods are introduced:sliding interquartile range method,Kalman filter and the correlation coefficient method used in this paper.Using the above method to detect the anomaly of the ionospheric TEC during the 8.1 magnitude earthquake in Nepal in 2015,the results show that all three methods can effectively detect the ionospheric TEC anomalies before and after the earthquake,and the TEC anomalies detected by the correlation coefficient method is more consistent with the number and time of earthquake occurrence.3)Correlation analysis of ionospheric scintillation index S4,??and rate of TEC index(ROTI)based on the annual observation data of Shenzhen ionospheric scintillation monitoring receiver.The results show that there is a strong correlation between S4,??and ROTI on the date of frequent occurrent of ionospheric scintillation.For example,the correlation coefficient of S4,acp and ROTI are 0.73 and 0.62 in 2015 045.The feasibility of using ROTI to represent ionospheric scintillation is verified based on Hong Kong CORS data.4)Three typhoons that made landfall on China in 2016 are selected as typical cases.The morphological characteristics of ionospheric disturbances affected by typhoons are comprehensively analyzed using ionospheric TEC extracted from ground-based GPS,ionospheric scintillation data,digital altimeter and COSMIC/FY-3C occultation data.The results show that the ionospheric TEC shows positive anomalies and the ionospheric scintillation intensity increases before typhoon's landfall.On the vertical scale,anomalies have occurred in E,F1 and F2 layers of the ionosphere too.Based on this,it is analyzed that the uplift of the turbulent layer may be the cause of the ionospheric disturbance before and after typhoon's landfall.Figure 34 table 2 reference 79.