Mapping the near-surface electrical conductivity with DEMETER satellite VLF data
Abstract
Electromagnetic methods in geophysics are useful tools in hydrology and environmental studies. They provide maps of the near-surface electrical conductivity with depth. The well known Very Low Frequency (VLF) sounding technique is revisited in this study with the emphasis on applications using the anthropogenic VLF wave recorded by satellites. The source is the electromagnetic (EM) signal transmitted in the 15 - 20 kHz frequency band by several VLF station located on the Earth surface. The micro-satellite DEMETER (CNES - France) measured the electric and magnetic fields in this frequency range at 700 km altitude. The ICE \citep{Berthelier2006456} and IMSC \citep{Parrot2006441} sensors on-board the aircraft measured respectively and simultaneously the electric (E) and magnetic (B) component of the EM field. Theoretical calculations \citep{Wait2} have shown how this field depended on near-surface properties for earth surface and aircraft measurements. Here we investigate for the first time the modeling of these VLF waves measured at satellite altitudes taking into account the effect of the ionosphere. We show that the theoretical EM field is consistent with the measurements by the satellite. The results suggest that the DEMETER data may be used to study the Earth near-surface properties. We study the relationship between the EM impedance (the ratio between the tangential component E and B EM field) and the Earth conductivity. The ratio has the advantage of being independent on the antenna's current moment. We compare theoretical and observed impedances as a function of the Earth conductivity.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMNS41B1683L
- Keywords:
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- 0500 COMPUTATIONAL GEOPHYSICS;
- 0689 ELECTROMAGNETICS / Wave propagation;
- 0900 EXPLORATION GEOPHYSICS;
- 2487 IONOSPHERE / Wave propagation