Sensing of gradient electromagnetic fields from subsurface conducting targets

Electromagnetic techniques are presented for the problem of remotely locating buried conductors at depths on the order of 10 meters or more. The frequency ranges used vary from 5 kHz to 100 kHz. The subsurface is excited by bistatic or near-monostatic geometries. The sources for excitation include horizontal magnetic dipole (HMD), vertical magnetic dipole (VMD), and horizontal electric dipole (HED). Results emphasize the gradient receiver response of the field induced by the presence of the subsurface conductors. The gradient response is defined here to be the response of two opposing polarity (subtracting) magnetic dipole antennas displaced on the order of 5 meters from one another. Results are presented for a wire 10 meters beneath the surface