Study On Seismo-ionospheric Phenomena Based On Electric Density Data Record By SWARM And DEMETER Satellite

Seismo-ionospheric phenomenon is the response of complex physical or chemical processes occurring in the ionosphere during earthquake preparation.This phenomenon has been continuously reported and attracts more and more attention.It has been regarded as one of the more promising and effective means for monitoring seismic activity.With the development of space exploration technology in recent years,many countries have launched satellites for earthquake monitoring,obtained a large number of observation data,and carried out a lot of research work on seismoionospheric phenomena.But due to the complex features of earthquake,the high dynamic characteristic of the ionosphere,the multiple source of the observation data and the difference of the analysis methods,up to now,the coupling mechanism of the seismo-ionospheric phenomanon has not been unified understanding.It is still difficult to be applied to earthquake prediction.Therefore,it is necessary to find out its obvious short-imminent feature and explore the internal law of seismic activity and ionospheric change.The DEMETER is the first satellite dedicated to earthquake and volcano monitoring.It has acquired a large number of observations and cteated a new era in seismo-ionospheric phenomena research.The SWARM constellation,composed of three satellites and launched by European space agency in 2013,is successful to carry out three-dimensional synchronous observation.That greatly improved the observation efficiency and spatial resolution comparing to a single satellite,and provided a new way for seismo-ionospheric phenomena research.Based on the observation data of Demeter satellite and SWARM constellation,the seismo-ionospheric phenomenon has been studied by two different methods in this paper.The ionosphere background information and the abnormality extraction methods for satellite observation data have been explored.The case studies and the statistic analysis have been carried out base on different parameters.The main content and conclusions are as follows:(1)A systematical analysis has been conducted base on the previous research results of the seismo-ionospheric phenomenon.Then the relationship between the magnitudes and the appearing days before the earthquakes has been found.The spatial distribution characteristic of the ionospheric anomaly has been summarized.The relationship between magnitudes and the distances to epicenter has been explored.The main response characteristics of ionosphere to seismic activity have been conclued,for example,the space scale,the sensitivity,the diversity,the instantaneity and so on.(2)Based on the observation data of DEMETER satellite and SWARM constellation,the background analysis of the observed data was carried out from the two aspects of spatial distribution and time series.The spatial distribution of the observed data changes with months,seasons and years.The time series of the observed data had a variety of periodic components,and the dominant periodic components were different with the change of latitude.The phenomenon as 'annual anomaly','semiannual anomaly' and 'equinoctial asymmetry anomaly' existing in the low ionosphere are also found in the ionosphere at the satellite height in middle and low latitude.The time series curves of the research areas with same latitude and different longitude have better correlation,especially at night.The spatial distribution characteristics of two sets of satellites observation data at different orbital altitudes are basically the same,but the values of these data are quite different.The spatial distribution characteristics of two sets of satellites observation data in adjacent orbits are basically consistent,but there are significant differences on both sides of the magnetic equator at noon.(3)Based on the observation data of DEMETER satellite,the global magnitude M>7 and continental magnitude M>6 earthquakes during its operation are analyzed.It was found that more than 70% of the earthquakes could observe abnormal changes before the earthquake,with enhanced anomalies or weakened anomalies,and mainly ones are enhanced anomalies.The analysis results of multiple seismic events show that there are enhanced anomalies near the epicenter,and they mainly occur in 0 to 15 days before the earthquake.The intensity of anomaly increases with the increase of earthquake magnitude and decreases with the increase of earthquake depth.The anomaly positions of the northern and southern hemispheres are different.The statistical analysis is used for the quantitative assessment of anomalies.The statiscical results show that the anomaly has a significant characteristic greater than 3?.The analysis results of random events by same analytical method prove that the anomalies are correlated with seismic events.(4)Based on the observation data of SWARM constellation,the rapid disturbance changes in orbit observation were extracted,and the typical earthquake cases were analyzed,and the correlation between the type of disturbance and earthquake was explored.The differences of orbits of three satellites are used to analyze the space range of the disturbance,and to calculate and its possible space propagation characteristics.It can be applied to identify whether the ionospheric disturbance is related to earthquake or not.To further confirm the correlation between the disturbance and the earthquake,the disturbances in seismic and non-seismic areas,as well as the disturbances before and after earthquake are compared.The results show that the disturbances have no significant difference between seismic and non-seismic areas,but the pre-earthquake disturbances have an advantage in quantity compared with that in post-earthquake.In addition,the results of the random events didn't show the same feture as the seismic events.This means that the disturbance before the earthquake has a certain correlation with earthquake preparation.(5)By comparing the analysis results of single satellite and satellite constellation,the future seismic ionospheric phenomena based on satellite observation are prospected,and the orbital design reference scheme is proposed for the future satellite constellation observation.This will help to better understand the characteristics of ionospheric background changes,understand the seismic ionospheric phenomenon and its coupling process,and provide reference for the research on the seismic ionospheric phenomenon based on satellite constellation design and the development of earthquake prevention and disaster reduction in China.