GEOPHYSICAL EXPLORATION METHOD AND APPARATUS USING THE VERTICAL ELECTRIC COMPONENT OF A VLF FIELD AS A REFERENCE

• US 3,594,633 A
• Filed: 03/06/1969
• Issued: 07/20/1971
• Est. Priority Date: 03/09/1968
• Status: Expired due to Term

• Current Assignee: Barringer Anthony Rene
• Original Assignee: Barringer Anthony Rene
• Inventors: BARRINGER ANTHONY RENE
• Application Number:
  US04/804,780
• Time in Patent Office: 866 Days
• US Class Current: 324/76.11
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: G01V 3/17 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

A geophysical exploration method and apparatus utilizing VLF fields produced by distant transmitters as a source of primary field. The vertical electric alternating field component of the primary field is used as a stable reference against which variations in magnetic alternating field components caused by inhomogeneities in earth conductivity can be measured.

Claims

1. Apparatus for sensing distortions in an electromagnetic field which penetrates the earth, said electromagnetic field being radiated by a source of electromagnetic energy, said electromagnetic field comprising a generally horizontal alternating magnetic field which is distorted when it intersects inhomogeneities in earth conductivity, and a substantially vertical alternating electric field component, said apparatus comprising:

electric field sensing means for receiving a signal having a fixed phase relationship to said vertical electric field component including means for amplifying said signal, first magnetic field sensing means for receiving a signal responsive to the amplitude of a first directional component of said magnetic field including means for amplifying said signal, said first magnetic field sensing means being substantially unresponsive to electric fields, first phase detector means connected to said first magnetic field sensing means and referenced by a signal derived from said electric field sensing means for producing a first voltage proportional in amplitude to the amplitude of a portion of the first magnetic field component having a predetermined phase relationship to the phase of said vertical electric field component, and means connected to said first phase detector means for measuring the said first voltage.

2. Apparatus as claimed in claim 1 wherein said signal derived from said electric field sensing means is in phase with said vertical electric field component.

3. Apparatus as claimed in claim 1 wherein said signal derived from said electric field sensing means is in phase quadrature with said vertical electric field component.

4. Apparatus as claimed in claim 3 wherein said first magnetic field component is horizontal.

5. Apparatus as claimed in claim 1 wherein a second magnetic field sensing means is provided for receiving a signal responsive to the amplitude of a second directional component of said magnetic field including means for amplifying said signal, said second magnetic field sensing means being substantially unresponsive to electric fields, wherein second phase detector means is connected to said second magnetic field sensing means and is referenced by a signal derived from said electric field sensing means for producing a second voltage proportional in amplitude to the amplitude of a portion of said second magnetic field component having a predetermined phase relationship to the phase of said vertical electric field component, and wherein means connected to the second phase detector means is provided for measuring the said second voltage.

6. Apparatus as claimed in claim 1 wHerein the frequency of said electromagnetic field is between about 14-30 kHz. and said apparatus is positioned at least about 5 wavelengths away from said source.

7. Apparatus for sensing distortions in an electromagnetic field which penetrates the earth, said electromagnetic field being radiated by a source of electromagnetic energy, said electromagnetic field comprising a generally horizontal alternating magnetic field which is distorted when it intersects inhomogeneities in earth conductivity, and a substantially vertical alternating electric field component, said apparatus comprising:

electric field sensing means for receiving a signal having a fixed phase relationship to said vertical electric field component including means for amplifying said signal, first magnetic field sensing means for receiving a signal responsive to the amplitude of a first directional component of said magnetic field including means for amplifying said signal, said first magnetic field sensing means being substantially unresponsive to electric fields, first phase detector means connected to said first magnetic field sensing means and referenced by a signal derived from said electric field sensing means and in phase with said vertical electric field component, said first phase detector means producing a first voltage, and means connected to said first phase detector means for measuring the said first voltage.

8. Apparatus as claimed in claim 7 wherein there is second phase detector means connected to said first magnetic field sensing means and referenced by a signal derived from said electric field sensing means and in phase quadrature with said vertical electric field component, said second phase detector producing a second voltage, and wherein means is provided for measuring said second voltage.

9. An airborne method of measuring the conductivity of the earth comprising determining the tilt angle of an alternating electric field component of an electromagnetic wave radiated by a distant source of electromagnetic energy, said tilt angle being determined by the following steps:

a. traversing a predetermined region of the earth to be explored, b. receiving, at known positions in said region, a first signal proportional in amplitude to the amplitude of the vertical portion of said alternating electric field at known positions in said region, c. contemporaneously receiving a second signal proportional in amplitude to the amplitude of a horizontal component of said alternating electric field and separating from said second signal a component that is in phase quadrature with said first signal, said horizontal component having a predetermined direction, and d. comparing variations in said quadrature component with reference to said first signal.

10. Apparatus for measuring the conductivity of the earth in a given region by determining the relative amplitudes of vertical and horizontal components of an alternating electric field of an electromagnetic wave radiated by a distant source of electromagnetic energy, comprising:

a. first electric field sensing means for receiving a signal having a fixed phase relationship to said vertical electric field component including means for amplifying said signal, b. second electric field sensing means for receiving a signal having a fixed phase relationship to a horizontal electric field component including means for amplifying said signal, said horizontal electric field component having a predetermined direction, c. a 90* phase shifter connected to said first electric field sensing means, d. first phase detector means connected to said second electric field sensing means and referenced by said phase shifter for producing a first voltage proportional in amplitude to the amplitude of a portion of the said horizontal electric field component that is in-phase quadrature with the phase of said vertical electric field component, and e. means connected to said first phase deTector means for measuring the said second voltage.