Electromagnetic interferometry in wavenumber and space domains in a layered earth

With interferometry applied to controlled-source electromagnetic data, the direct field and the airwave and all other effects related to the air-water interface can be suppressed in a data-driven way. Interferometry allows for retreival of the scattered field Green’s function of the subsurface or, in other words, the subsurface reflection response. This reflection response can then be further used to invert for the subsurface conductivity distribution. To perform interferometry in 3D, measurements on an areal grid are necessary. We discuss 3D interferometry by multidimensional deconvolution in the frequency-wavenumber and in the frequency-space domains and provide examples for a layered earth model. We use the synthetic aperture source concept to damp the signal at high wavenumbers to allow large receiver sampling distances. Interferometry indeed increases the detectability of a subsurface reservoir. Finally, we discuss the dependency of the accuracy of the retrieved reflection response on the two crucial parameters: the conductivity of the seabed at the receiver location and the stabilization parameter of the least-squares inversion.

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Robust Synthetic Aperture Imaging of Marine Controlled-Source Electromagnetic Data

IEEE Transactions on Geoscience and Remote Sensing ◽

10.1109/tgrs.2020.2966727 ◽

2020 ◽

Vol 58 (8) ◽

pp. 5527-5539

Author(s):

Xiaolei Tu ◽

Michael S. Zhdanov

Keyword(s):

Synthetic Aperture ◽

Synthetic Aperture Imaging ◽

Controlled Source ◽

Electromagnetic Data

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Inversion of frequency-domain marine-controlled-source electromagnetic data using genetic algorithm

10.1190/segam2017-17783322.1 ◽

2017 ◽

Author(s):

Mohit Ayani ◽

Subhashis Mallick ◽

Jürg Hunziker ◽

Lucy MacGregor

Keyword(s):

Genetic Algorithm ◽

Frequency Domain ◽

Controlled Source ◽

Electromagnetic Data

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Inversion of helicopter electromagnetic data to a magnetic conductive layered earth

Geophysics ◽

10.1190/1.1598113 ◽

2003 ◽

Vol 68 (4) ◽

pp. 1211-1223 ◽

Cited By ~ 50

Author(s):

Haoping Huang ◽

Douglas C. Fraser

Keyword(s):

Magnetic Permeability ◽

Field Data ◽

Model Parameters ◽

Relative Importance ◽

Magnetic Polarization ◽

Inversion Algorithm ◽

Layered Earth ◽

Electromagnetic Data ◽

Airborne Electromagnetic ◽

True Values

Inversion of airborne electromagnetic (EM) data for a layered earth has been commonly performed under the assumption that the magnetic permeability of the layers is the same as that of free space. The resistivity inverted from helicopter EM data in this way is not reliable in highly magnetic areas because magnetic polarization currents occur in addition to conduction currents, causing the inverted resistivity to be erroneously high. A new algorithm for inverting for the resistivity, magnetic permeability, and thickness of a layered model has been developed for a magnetic conductive layered earth. It is based on traditional inversion methodologies for solving nonlinear inverse problems and minimizes an objective function subject to fitting the data in a least‐squares sense. Studies using synthetic helicopter EM data indicate that the inversion technique is reasonably dependable and provides fast convergence. When six synthetic in‐phase and quadrature data from three frequencies are used, the model parameters for two‐ and three‐layer models are estimated to within a few percent of their true values after several iterations. The analysis of partial derivatives with respect to the model parameters contributes to a better understanding of the relative importance of the model parameters and the reliability of their determination. The inversion algorithm is tested on field data obtained with a Dighem helicopter EM system at Mt. Milligan, British Columbia, Canada. The output magnetic susceptibility‐depth section compares favorably with that of Zhang and Oldenburg who inverted for the susceptibility on the assumption that the resistivity distribution was known.

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