Remote sensing seismology

Seismic waves

Seismic waves produced by earthquakes travel through the atmosphere and are amplified in the F layer of the ionosphere at 350 km altitude. Rayleigh waves propagating at the ground surface can also be followed in the ionosphere as illustrated in the figure below.

Wave propagation in the atmosphere
[Artru et al., 2001]

The SPECTRE products can be used to observe the ionosphere disturbance due to the seismic activity. The following figure shows the evolution of the TEC over Japan after the Tokachi-Oki earthquake of September 2003. One can see ionospheric waves propagating from the epicentre. The nearest waves are induced by the atmospheric pulse genrated over epicentral area. These ionospheric waves propagate more slowly than those induced at farther distances by the Rayleigh waves propagating at 3.5 km/s from the epicentre. These results have been provided by the SPECTRE algorithm using the GPS measurements of the satellite PRN13 over the receivers of the Japanese GPS network. The map in the top-left corner of the figure present positions of the IPP by red dots.

Wave propagation in the atmosphere
[Crespon, 2007]

The SPECTRE products could also be compared to the DEMETER measurements in order to study the correlations between seismic events and ionosphere disturbance.

Tsunami detection

Tsunamis can also be detected by the ionospheric disturbance they induce. The movie below (214 kB) shows the TEC variations over Japan resulting from the propagation of a tsunami created by the Peru earthquake of June 23rd 2001 (the tsunami reached the Japanese coasts 24 hours after the earthquake.) One can see on the movie the TEC estimations at the IPPs (i.e. intersections between the GPS rays and the ionosphere), the tsunami being detected by the fast variations of the TEC (blue and red fringes).

Tsunami detection near Japan coast
[Ducic, 2003]

Land deformation monitoring

Land deformations can be easily observed by SAR interferometry by combination of two images taken at two different moments. Unfortunately variations of the TEC alter the radar path delay of each measurement and thus deteriorate the quality of the interferometry image. Therefore, the SPECTRE products could be used to correct interferometry images since variations of the path delays are related to the ionospheric TEC. The figures below are an example of such a processing. The TEC has been estimated over Lebanon at the instants of two SAR images. After processing of the TEC maps, it is possible to provide an image showing the corrections to apply to the interferometry image.

Correction for SAR interferometry images
[Ducic, 2003]

Over-horizon radar monitoring

The range of over-horizon radars depends on the ionospheric state since the electromagnetic waves reflect on the ionosphere. Therefore, knowledge of the TEC can be helpful to get precise radar imaging or to set up the over-horizon radar parameters to observe a given area.

Principle of over-horizon radars
© ONERA

Precise point positioning with mono-frequency receivers

Mono-frequency receivers are not robust to variations of the ionosphere TEC since the path delay of the GPS rays depends on the TEC. Therefore, knowledge of the ionosphere TEC is a solution to correct data provided by mono-frequency receivers and to perform precise point positioning.

Telecommunication disruption

Organisations or laboratories performing spaceweather studies or checking/using the impact of the ionosphere on telecommunications can also be interested in using the SPECTRE products. The figure below present HF radio blackout induced by solar flare and monitored by the Culgoora observatory of IPS.

Disturbances of HF radio communication
© IPS

References

Artru, J., P. Lognonne and E. Blanc (2001), Normal modes modelling of post-seismic ionospheric oscillations, Geophysical Research Letters 28, 697-700.
Crespon F. (2007), Tomographie 2D et 3D de l'ionosphere par GPS: applications aux aleas geophysiques, PhD., Institut de Physique du Globe de Paris.
Ducic V. (2003), Tomographie de l'ionosphere et de la troposphere par GPS. Applications aux risques naturels et amelioration de l'interferometrie SAR, PhD., Institut de Physique du Globe de Paris.


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