The Study Of Seismic Ionospheric Anomalies Based On GNSS

Seismic ionospheric anomalies are hot issues in the study of ionospheric physics and seismic physics.The occurrence of pre-earthquake anomalies and coseismic anomalies embodies the coupling between the Earth's lithosphere,the neutral atmosphere and the ionosphere.The high frequency and continuous GNSS observation method provides a good technical basis for the study of seismic ionospheric anomalies.Anomalous analysis of ionospheric TEC data based on GNSS data has yielded many research results.Time series and other analysis methods are mostly based on the local TEC time series of abnormal changes,not in the analysis process to eliminate ionospheric six months,27 days,13.5 days and other factors such as cyclical changes in the results of abnormal analysis.Based on the assumption of the ionospheric thin layer,the two-dimensional modeling of the ionosphere is used to compress the total electron content on the GNSS ray path to the puncture point.In the case of not fitting modeling STEC abnormal data directly projected to the puncture point,can show the high precision two-dimensional spatial distribution and propagation of ionospheric anomalies,avoid the accuracy of error analysis in the process of fitting.Three dimensional tomography of the ionosphere is an analytical technique which can be used to show the physical properties of the ionosphere in three or four dimensional space in recent years.It can be used to monitor the vertical electron motion in geomagnetic storms,ionospheric disturbances and ionospheric anomalies.But because of the traditional chromatographic methods are mainly based on the international reference ionosphere model(IRI)as background,iterative method is heavily dependent on the initial value of the accuracy in the iterative process,the ionospheric anomalies due to small magnitude,easy to be submerged iterative error analysis results is not ideal.In addition,due to the lack of observation data,such as the problem,the traditional ionospheric tomography time is 1-2 hours,while the ionospheric anomaly changes rapidly,a few minutes will be a huge change in space form.Therefore,high temporal resolution tomography algorithms have yet to be realized.The main objective of this paper is to systematically analyze the problems of ionospheric anomaly detection algorithm,and propose an anomaly detection methodwhich can eliminate the ionospheric long period variation.Analysis of abnormal seismic ionospheric and GNSS observation data based on the existing high precision,high time resolution,accurate extraction of seismic ionospheric anomalies in time and space distribution and dissemination process,to obtain meaningful research results.The research work of this paper is mainly focused on the following aspects:1.The physical characteristics of the ionosphere,the existing ionospheric sounding technique and the ionospheric empirical model are systematically introduced.At the same time,the method of obtaining ionospheric TEC by GNSS technology is described in detail,and the calculation method of 2D and 3D modeling is also presented.Three dimensional ionospheric tomography is a typical inverse problem.In this paper,the iterative and non iterative reconstruction algorithms are analyzed.However,due to the inhomogeneity of the GNSS ray distribution,the iterative method can be used to solve the ill posed problem.2.The ionospheric anomaly detection method is systematically analyzed,and propose a method based on singular spectrum analysis method,can change for a long period of time from the ionospheric seismo ionospheric anomaly detection factors,and the ionosphere in Nepal earthquake precursory anomaly analysis has verified the validity and accuracy of the method.3.Based on the moving average trend analysis,two-dimensional dSTEC analysis,and the method of 3D tomography without initial value,the ionospheric anomaly of Tohoku earthquake in Japan was extracted and analyzed.It is found that the ionospheric disturbance occurs at UTC 6:00 after the earthquake.Two dimensional dSTEC analysis results show that over the epicenter area appeared negative ionospheric abnormal distribution of massive north-south symmetry,then the annular corrugated to spread around,which is annular corrugated alternate form,that caused by the earthquake related activities of the acoustic gravity wave,Rayleigh wave caused the ionospheric free electron in the region around the sports cause to reduce the peak after the electronic content,forming negative anomalies.The subsequent wave crest also brings a large number of free electrons to form a new positive anomaly.Japan GEONET observation network data with high density,high time resolution of a 3D tomography epoch.The results show that the same horizontal distribution can be detected,and the propagation of the electrons from the bottom to the top of the region is detected,and the diffusion of the electrons to the 200-500km is detected.4.By using the singular spectrum analysis method for anomaly detection of Nepal earthquake ionospheric anomaly detection based on the abnormal time is third days before the earthquake,and to determine the range of regional anomalies.At the same time,based on the GIM data,the results are very consistent with the singular spectrum analysis.In order to further analyze the abnormal fine spatial form and propagation mechanism,using ionospheric tomography,from March 26th to April 9th the results as background field for anomaly detection on April 23rd results,the detection results and the above singular spectrum analysis and satellite trajectory puncture point STEC method results.Three dimensional tomographic results to further reflect the changes with the height of the ionospheric anomalies:Ionospheric anomalies occurred in April 23rd 9:00?15:00UT,the peak position is about 30?N,105?E,200?400km mainly distributed in the height range of 100-300km;with the increase of height,the abnormal peak gradually increased,to expand the scope of the abnormal;300?500km,with the increase of height,abnormal peak decreased,abnormal narrowing with height variation regularity and abnormal vertical distribution of ionospheric electron density consistent.