Method for Determining Changes in Earth Resistivity by Measuring Phase Difference Between Magnetic Field Components.
DEPARTMENT OF THE NAVY WASHINGTON D C
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Method and apparatus for detecting tunnels beneath an area of the earths surface wherein an oscillator couples a current into a linear conductor at the earths surface to generate a magnetic field in the earth beneath the area. Phase angle measuring means measures phase difference between the vertical and horizontal components of the magnetic field at selected points along a line parallel to the linear conductor to detect abrupt changes in earth resistivity, changes in resistivity indicating the presence and horizontal position of a tunnel. Author
- Magnetic and Electric Field Detection and Detectors