Spectral analysis of the horizontal loop electromagnetic profiling data over a conductive half-plane
Abstract
Most interpretive methods in geophysical prospecting involve
the analysis of a single signal which may be a spatial or time
domain record of a given deterministic geophysical variable
representing the anomaly of interest. In the present
development, the electromagnetic (EM) response resulting from
the interaction of the fields due to a thin plate-like conductor
and the horizontal loop EM prospecting (HLEM) system is the
pertinent geophysical variable.
The interpretation of ground EM response due to a conductive
thin plate is carried out through Fourier analysis. The
introductory EM response 1S based on the rudimentary model 1n
which a thin conductive plate is simulated by a single
current filament which lies at or near the top edge of the
plate. The am~litude spectrum 1S derived from analytical
expressions of the response of the above model through
Fourier transformation. In the transform domain, highly
simplified expressions result from which the depth and the quality
of the conductive target can be estimated. In fact, depth can
be determined directly from the slope of the amplitude spectrum
which constitutes the first method of depth estimation herein
described.
A second method for estimating depth using harmonic.;..> analysis is
described . This method is based on the value of the wave number at
which the real component of the Fourier transform drops off to
zero. It is demonstrated that this value depends on the depth of
the wire model if the coil separation 1S kept constant. Spectral
information on depth is available at zero or higher harmonics.
This method yields two depths (making it hard to choose the
correct one) and may be effectively use 1n areas where depth of
occurrence of the orebody is roughly known. The use of the slope
method to get a rough estimate of depth and the final
determination thereof using the harmonic method are described.
Citation
M.Sc. ThesisSponsorhip
University of NairobiPublisher
Faculty of Science, University of Nairobi
Description
Master of Science Thesis