Modeling the electromagnetic detection of buried cylindrical conductors

The remote detection of buried structures and tunnels is important to the mining, construction, and defense industries. It is often desirable to identify underground power lines, pipe lines, and utility tunnels which have distinctive electromagnetic cross sections. A computational model for the electromagnetic detection of buried conducting cylinders is described. The source of electromagnetic radiation is either current injection into the soil or a surface based magnetic dipole with possible extensions to airborne platforms. A frequency range of 5-100 kHz is considered. The target conductor is a cylinder buried directly in the soil or placed inside an insulating pipe. The receiver is a magnetic gradiometer held 1 m above the ground, separate from the transmitter. Typically, data are taken in ten point scans above and normal to the buried conductor. Cases where the target conductor is grounded at both ends, one end, or not at all are modeled. The scattered field and field gradient are computed at or above ground level and compared in magnitude and phase with the transmitted signal. Calculated results are compared with experimental tests. Essential factors affecting detection performance are frequency, dynamic range of reception, and proper data processing