Investigation Of Co-seismic Ionospheric Disturbance Based On GPS TEC

The short-term prediction of earthquakes is mainly based on the observation of precursory phenomena,but not every earthquake can show us omens.Because of complicate causes of earthquakes,limited and difficult detection technology,medium and short term forecast as well as imminent earthquake prediction still need to be devoloped continuously.The secondary pressure waves generated by earthquakes and tsunamis will be coupled with the atmosphere to affect plasma in the ionosphere and to change density of total electron content.Therefore we need to take advantage of global position system to obtain co-seismic ionospheric TEC and analyze its disturbance qualitatively and quantitatively.It's a developing seismic research method in recent years.This thesis contains detailed exploration and analysis of GPS measurement of total electron content and a set of methods of co-seismic ionospheric disturbance research.Then we use constant GPS dual frequency observation data of Nepal Mw7.8 earthquake in 2015 as an example to calculate and to analyze co-seismic ionospheric disturbance.All of content is based on these following sections:(1)Discripution of basic definitions and characteristics of ionosphere and introduction of layer structure of the upper atmosphere and vertical structure of ionosphere.Periodic and aperiodic changes of ionosphere and their influence factors,and several traditional or new detection techniques.Besides,we also collect the research background and theories at present in the field of GPS ionosphere and the disturbance analysis of total electron content in order to foreshadowing subsequent sections.(2)Introduction of earth observation of global position system,particular description of the reason why electromagnetic signals carry ionospheric delay,principle of GPS dual frequency measurements.This paper also introduces the principle and meaning of smoothing carrier phase measurements with pseudo-range measurement method,the thin shell model of ionosphere,and principles and method of calculating total electron content with GPS data.(3)Summarizing on several methods and analyses of co-seismic ionospheric disturbance research.It consists of total electron content disturbance data statistics both in time domain and frequency domain,noise suppression and image analysis.We also systematically explain how to research propagation characristics of co-seismic ionospheric,that is how to calculate horizontal propagation rates of disturbance,how to obtain propagation directions,and how to distinguish types of the waves related to earthquake(acoustic wave,Rayleigh wave,and gravity wave).(4)Taking the Nepal Mw7.8 earthquake in 2015 as an example,we calculate exact numerical values of total electron content on this day based on GPS observation data then conduct statistical analysis and spectrum analysis to research comprehensively the spatiotemporal characteristics of disturbance propagation.Rely on data and image results,we obtain when the co-seismic disturbance appears obvious abnormal phenomena,how long it lasts,and what is the trend of its variation.So that we can obtain directions from epicenter to surrounding seismic area,values and ranges of horizontal propagation rates and center frequencies from frequency spectrums,and then we analyze the respective types of waves related to this earthquake.