Electromagnetic Modeling With Wave Tilt And Reflection Coefficient: An Application to Stratified Earth Media Using Radio And Low Frequencies
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Date
2006
Authors
Olowofela, J.A.
Ozebo, V.C.
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Geophysics & Engineering: Institute of Physics (IOP), U.K.
Abstract
Many models using electromagnetic sounding techniques have been formulated for use in
exploration activities. In deriving the governing equations for the models, Maxwell’s
equations are used and the earth is taken as a layered medium. Using these boundary
conditions, the Sommerfeld integrals are obtained for several models. However, the difficulties
and limitations posed by the iterations of the functions, especially the strong oscillations and
slow convergence of the Bessel function, call for a search for new methods. This work aims to
formulate models, with the advantage of bypassing the problems highlighted above, and to
discover new response parameters not considered by the older models due to the limitations of
time. Three measurable field parameters, (1) amplitude of the correction factor to the wave tilt,
(2) phase of the amplitude of the correction factor to the wave tilt and (3) reflection coefficient,
were calculated from this model with various conductivity contrasts over a two-layered earth.
Two cases of a top layer overlying a more conductive basement and a more conductive top
layer overlying a resistive basement were considered with a radio frequency of 125 kHz and a
low frequency of 10 Hz. The model was tested using data from existing models and was then
applied to a homogeneous and a layered earth. Results revealed that the phase of the amplitude
of the correction to the wave tilt was found to be most diagnostic of the changes in layer
parameters. Also, depths of 20 m and 2000 m were achieved with the two respective frequency
values. The reflection coefficient was discovered to be an important parameter for detecting
layered earth structures, in addition to other parameters. Furthermore, an inverse relationship
between the transverse electric and transverse magnetic modes of the reflection coefficient is
established.