Study of the TEC data obtained from the DORIS stations in relation to seismic activity

Ionospheric data obtained from the DORIS system are used in this paper. The DORIS system is composed of
several ground-based beacons which emit at two frequencies (400 MHz and 2 GHz) and of receivers on board
several satellites (currently SPOT2, SPOT4, SPOT5, Topex-Poseidon, Jason1 and Envisat). Thanks to the density
of its network coverage (∼50 stations), DORIS provides information on the ionosphere. The TEC (Total Electron
Content) parameter which is the electron density integrated over the vertical could be obtained from DORIS
measurements. In a first step, the paper describes the way to obtain the TEC data from the DORIS ionospheric
measurements, and comparisons of the results are done with the IRI2001 model. In a second step, TEC values
are used to search for correlation between ionospheric perturbations and seismic activity. Earthquakes of magnitude
larger than 5 are chosen close to the ground-based DORIS stations. Among other results, the statistics
show that, during the night time and at geomagnetic latitude close to the equator (<10°), TEC amplitude fluctuates
at the time of the earthquakes as it is expected, but also 2 days and 5 days before.

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