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Passive geophysical prospection system based upon the detection of the vertical electric field component of telluric currents and method therefor

  • US 4,686,475 A
  • Filed: 07/12/1984
  • Issued: 08/11/1987
  • Est. Priority Date: 07/12/1984
  • Status: Expired due to Term
First Claim
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1. A passive geophysical prospection system for determining the identity and depth of strata under the earth'"'"'s surface by detection of the time-varying vertical electric field component of telluric currents from said strata, said strata having overburdens and inhomogeneities contained therein, said time-varying electric field component of said telluric currents having an audio bandwidth in a low frequency window from zero frequency to a high cutoff frequency and wherein said high cutoff frequency is related to the depth of said strata, said system being capable of outputting information to an operator corresponding to the prospection depth of said system and the identity of strata found at said prospection depth including the identity of said overburdens and inhomogeneities, said system comprising:

  • means responsive to said time-varying vertical electric field component of said telluric currents for producing an output signal,means connected to said producing means for adjusting the impedance of said producing means to maximize said output signal, when said output signal is maximized said impedance of said producing means substantially matches the impedance of said earth'"'"'s surface and said output signal varies in time with said time-varying vertical electric field component,means connected to said adjusting means and receptive of said maximized output signal from said adjusting means for tuning said maximized output signal in said audio bandwidth by decreasing the high cutoff frequency end of said audio bandwidth, the value of said high frequency cutoff end of said audio bandwidth being indicative of said prospection depth in said strata, said tuning means being capable of extending all frequencies of said maximized output signal through said audio bandwidth as a tuned signal, said tuning means having soft roll-off characteristics of minus 3 dB to minus 6 dB per octave, andmeans connected to said tuning means and receptive of said tuned signal from said tuning means for generating an output containing said information corresponding to said identity of said strata including said identity of said overburdens and inhomogeneities at said prospection depth.

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