Imaging Underground Structures Using Broadband Electromagnetic Induction

Abstract

Broadband electromagnetic induction is a promising technique for the detection and location of underground structures. Along with being simple to use and allowing rapid data acquisition, underground structures can be detected by this method either because the large volume of air necessary for human occupancy will be manifested as an electrical conductivity low relative to the host formation or because there could exist a large metallic mass associated with either structural support or the mission of the facility that would constitute a relative conductivity high. The use of broadband information literally offers an additional dimension, that being depth, to the level of information that can be gleaned from acquired data since, by varying the operating frequency, the probing depth changes. A three‐dimensional tomographic imaging algorithm is applied to broadband data acquired at two underground structure sites to reconstruct the relative spatial variations in electrical conductivity. A pair of parallel sub...