Underground structure detection by surface magnetic gradient measurements

This problem involves magnetic induction methods to locate and determine the depth of a subsurface line source of magnetic field. The origin of the field may be self-generated or induced by a surface transmitter. The experimental method requires measuring the horizontal gradient of either the vertical or horizontal component of the field rather than the field itself so as to increase signal to noise ratio. A mathematical outline is presented and experimental results are discussed. Keywords: underground detection, electromagnetic theory, magnetic induction, tunnels, underground structures, imagin