Anomalous changes in the ionospheric conditions related to the Wenchuan earthquake of 12 May 2008 are investigated using electron density (Ne) from Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and CHAMP satellites, electric field from DEMETER, and GPS‐total electron content (TEC) maps. The normalized Ne from the DEMETER satellite reveal that the previously reported TEC increments before the earthquake can be considered as fragments of the gradual equatorial ionization anomaly (EIA) enhancements near the epicenter longitude that began approximately 1 month before the earthquake and reached its maximum with an exceptionally large strength index 8 days prior to the main shock. This feature is indirectly confirmed through the CHAMP Ne and GPS TEC data. Following the EIA intensity peak, disturbances in the Ne and O+ density were observed in the nightside. Based on the concurrent electric field and Ne changes, it is suggested that EIA intensification could be triggered by the E field disturbances over the epicenter.
International audienceWe report the processes and results of statistical analysis on the ionospheric electron densitydata measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions(DEMETER) satellite over a period of 6 years (2005–2010), in order to investigate the correlation betweenseismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regionswith frequent earthquakes were selected and then one-dimensional time series analysis between thedaily seismic activity indices and the equatorial ionization anomaly (EIA) intensity indices, which representrelative equatorial electron density increase, were performed for each region. The statistically significantvalues of the lagged cross-correlation function, particularly in the region with minimal effects oflongitudinal asymmetry, indicate that some of the very large earthquakes with M > 5.0 in the low-latituderegion can accompany observable precursory and concurrent EIA enhancements, even though the seismicactivity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanismsof the seismo-ionospheric coupling is consistent with our observation, and the possibility of earthquakeprediction using the EIA intensity variation is discussed
International audienceHere we report multisatellite observations of ionospheric disturbances in relation to theoccurrence of the M8.7 northern Sumatra earthquake of 28 March 2005. The DEMETER (Detection ofElectro-Magnetic Emissions Transmitted from Earthquake Regions) and CHAMP (Challenging MinisatellitePayload) satellite data were investigated to find possible precursory and postevent phenomena. It wasfound that EIA (equatorial ionization anomaly) strength expressed in the apex height, derived from theCHAMP plasma density profile, was intensified along the orbits whose longitudes were close to theepicenter within about a week before and after occurrence of the earthquake. Increases in electron and O+density along the orbits close to the epicenter were also observed in the DEMETER measurements. Thenormalized equatorial plasma density derived from the DEMETER measurements showed intensificationabout a week before and after the earthquake reaching maximum the day after the shock and afterwarddisappearing. In addition, similar behavior of the EIA enhancements related to the M8.0 Pisco earthquake of15 August 2007 was observed. Surveys of space weather and geomagnetic activities excluded thepossibility that these fluctuations were caused by changes in space weather or by a geomagnetic storm.Statistical analyses of the longitudinal variation revealed that the EIA was enhanced in the west of theepicenter and reduced in the east of the epicenter, and this fits the “increased conductivity” model. Basedon these observations, we proposed a revised view of seismo-ionospheric coupling in the region of thegeomagnetic equator, to explain the EIA features observed in this study
This paper proposes a modified stripmap synthetic aperture radar (SAR) signal processing algorithm with an X-band SAR system, using the practical measurement results of automobile-based SAR (Auto-SAR). The quality of the image is degraded due to an unexpected direction change or anisotropy of the target position in radar image measurement. To solve the quality problem, signal processing is required for the vector velocity of each range in the azimuth direction. An X-band chirp pulse system was implemented and optimized by a signal processing algorithm suitable for high resolution. The stripmap SAR images are produced in five places. The validity of the proposed algorithm is verified by comparing impulse response function analysis and experimental images.
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