Ionospheric TEC Anomaly Detection And Analysis During Earthquake

The research on ionospheric anomalies originated from the 9.2 magnitude earthquake that occurred in Alaska in the 1960s.In recent decades,many scholars have conducted relevant research and made certain achievements.With the rapid development of GPS technology since the 21st century,more and more attention has been paid to using GPS to study ionospheric anomalies during earthquakes.Compared with traditional ionospheric altimeter,GPS monitoring is more accurate in terms of monitoring height,time resolution and spatial resolution,so it is introduced into the study of seismic ionospheric anomalies.At present,the research mainly focuses on the analysis and discussion of a single earthquake case,and few statistical analysis of multiple earthquake cases.Based on this,this paper uses GPS data to calculate ionospheric TEC and detect the ionospheric TEC anomalies during the two strong earthquakes in Japan,and makes a comprehensive analysis from the time scale and space scale.Finally,it makes a statistical analysis of the earthquake cases in the recent 18 years in Japan.Some characteristics of ionospheric TEC anomalies during earthquakes are found.Mainly completed the following work:(1)The influence of space environment(geomagnetic activity and solar activity)on the ionosphere is expounded by understanding the cause of earthquake formation,the formation of ionosphere,the stratified structure of ionosphere,the total electron content(TEC)and the change characteristics of the ionosphere,and the two explanations of the seismic-ionosphere coupling principle in the academic circle.(2)To solve ionospheric TEC based on GPS data,firstly,the GPS observation data should be preprocessed;secondly,the STEC on the oblique path of signal propagation should be solved through carrier phase smoothing pseudo-distance;finally,the MF projection function is converted to the VTEC in the zenith direction over the station.The data of the ionospheric TEC in spring,summer,autumn and winter in high and low solar activity years were analyzed through the data of the CODE analysis Center GIM ionospheric grid in one day.(3)The accuracy of four commonly used ionospheric TEC anomaly detection methods was compared.Ionospheric TEC was selected as the background value during the quiet time of the space environment in one month,and the TEC value of the first 22 days was selected to predict the TEC value of the last eight days.The residual error,relative accuracy and root mean square error of sliding time window method,sliding quartile distance method,time series method and Kalman filter method are compared and analyzed respectively.The experiment shows that the sliding time window method has the lowest prediction accuracy,while Kalman filter method has the highest accuracy.The advantages and disadvantages of the four methods and their applicable scope are summarized.In the comprehensive analysis,Kalman filter is used to detect ionospheric TEC anomalies during earthquakes.(4)Ionospheric VTEC calculated based on GPS data was used to analyze the earthquake cases of Fukushima 9.0 earthquake in 2011 and Kumamoto 7.3 earthquake in 2016.Abnormal information of ionospheric TEC was detected by Kalman filtering method.Under the exclusion of the influence of solar and geomagnetic activities,The time series of ionospheric TEC for 20 days during the two earthquakes(15days before and 5 days after the earthquake)were comprehensively analyzed from the perspective of time and the global ionospheric anomalies(space),and the anomalies and the causes of the anomalies during the two earthquakes were summarized and discussed.(5)The cases of earthquakes with Mw6.5 magnitude or above in Japan during the 18 years from 2005 to 2023 were analyzed statistically,and the occurrence times and distribution of ionospheric TEC anomalies during the earthquakes(pre-earthquake and post-earthquake)were calculated.In addition,the number of ionospheric TEC anomalies,distribution of positive and negative anomalies,abnormal regions and maximum locations of anomalies of Mw6.5-7.0 and above Mw7.0 earthquakes were counted respectively,and the characteristics of ionospheric TEC anomalies during earthquakes were summarized.