3D Electromagnetic Holographic Imaging in Active Monitoring of Sea-Bottom Geoelectrical Structures
Abstract
During recent years a significant progress has been made in developing new mathematical methods and computer codes for 3D electromagnetic (EM) imaging in active monitoring of sea-bottom geoelectrical structures. In this paper I present an overview of the effective imaging technique based on the principles of electromagnetic holography/migration. The physical principles of EM holography parallel those underlying optical holography and seismic migration. The recorded amplitudes and phases of an EM field scattered by the object form a broadband EM hologram. As in optical and radiowave holography, we can reconstruct the volume image of the object by "illuminating" the broadband EM hologram by the reference signal. While in the optical case this can be performed optically, yielding a visible image, in the case of a broadband EM field the reconstruction is done numerically using computer transformation. In fact EM holography/migration, similar to seismic migration, is based on a special form of downward continuation of the observed field, which can be computed as a solution of the boundary value problem for the adjoint Maxwell's equations. In this paper I consider an application of this approach to the interpretation of a typical Marine Controlled Source EM (MCSEM) survey, which consists of a set of sea-bottom receivers and a moving electrical bipole transmitter. The receivers record the magnitude and the phase of the frequency domain EM field generated by the moving transmitter and scattered back by sea-bottom geoelectrical structures. The combined EM signal in the receivers forms a broadband EM hologram of the sea-bottom geological target. In order to reconstruct the geoelectrical image of the target, we replace a set of receivers with a set of auxiliary transmitters located in the receivers' positions. The strength and the phase of the signal transmitted by these auxiliary transmitters are determined according to the parameters of the observed field in the receivers. These transmitters generate an EM field, which is called a backscattering or migration field. The vector cross-power spectrum of the background field (the field generated by the original transmitter in a medium without a target) and the backscattering field produces a numerical reconstruction of a volume image of conductivity distribution. This imaging method is tested on the typical models of the sea-bottom geoelectrical structures.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMNG42A..05Z
- Keywords:
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- 0540 Image processing;
- 0619 Electromagnetic theory;
- 0629 Inverse scattering;
- 4499 General or miscellaneous