Research On Application In Co-seismic Ionospheric Disturbances Monitoring Using GNSS

Many solid earth events can induce detectable disturbances in the ionosphere,such as earthquake,tsunami and volcano explosion.In the recent years,GNSS has been wildly used in geoscience fields.Therefore,detecting co-seismic Ionospheric disturbances(CIDs)by GNSS has become the hot issue.This thesis aimed at studying on the technologies and methods of detecting the CIDs triggered by earthquake and tsunami by ground-based GNSS systematically so as to providing technical support for future earthquake and tsunami warning.In the thesis,we focus on several primary aspects,including the TIDs series extraction and its propagation characteristics analyzing methods,CIDs recognition,as well as the effect factors,such as earthquake types and satellite geometric conditions.Main work and contributions are listed as follow:(1)According to the coupling theory of the atmosphere,we've analyzed the propagation characters to support the ionospheric disturbances detection in theory.The surface rupture and the propagation of Rayleigh wave can produce up-propagated acoustic gravity waves(AGWs),reaching ionosphere after 8-10min,and they propagate at each velocity horizontally in the ionosphere.Tsunami waves can press the atmosphere and produce gravity waves(GWs),and velocity of the induced disturbances is similar to tsunami.GWs appends about 60min to get to the ionosphere,and the disturbances always arrived with 10min horizontal delay.(2)Elaborated the method of extracting ionospheric TEC from GNSS observation data.We adopted Slogan-Golay filter to process data,which can be regarded as a kind of multi-poly fit.We also introduced several method of analyzing the propagation characters of the ionospheric disturbances,namely,geometric analytic method,2-dimension disturbance graph,time-distance graph and frequency-spectrum graph,and they have their own merit and demerit,so we comprehensively applied all the methods in analysis.(3)Aimed at the different station distribution,we analyzed four worldwide earthquake examples.We genergally analyzed the propagation characters of the co-seismic ionospheric disturbances(CIDs),such as their waveforms,arrival times,directions,velocities and frequencies,verifying there are various types of disturbances with different propagation characters.(4)Focusing on the earthquake types(inverse-slip,strike-slip or mix type),both inverse and mix earthquakes(with vertical displacements)can trigger detectable CIDs,but strike-slip earthquakes(without vertical displacements)cannot trigger CIDs,further verifying CIDs are induced by vertical displacements.And we also discussed the influence of satellites' ray paths on detecting CIDs.The sightlines sometimes only go through the positive(negative)energy part,or go through both the positive and negative part equally,which may influence the amplitudes of disturbances,affecting signal recognition.