CROSS-BOREHOLE ELECTROMAGNETIC PROBING TO LOCATE HIGH-CONTRAST ANOMALIES

Electromagnetic (EM) probing between boreholes is useful for locating high-contrast geophysical anomalies such as a tunnel. Theoretical and experimental studies of EM field interaction with a tunnel show that minima in the received signal can be used for locating the tunnel. The theoretical studies show that as a transmitter and receiver are lower in separate boreholes, the ominia can be interpreted easily to yield both the lateral and vertical positions of the tunnel. The main mechanism of EM field interaction with the tunnel appears to be diffraction, and the spatial variation of the fifeld strength is affected by the tunnel shape.-Authors