Evaluation of the Electromagnetic Gradiometer Concept for Detection of Underground Structures—Theory and Application

An improved capability for subsurface structure detection is needed to support military and non‐proliferation requirements for inspection and for surveillance of activities of threatening nations. As part of the U.S. Department of Energy program to apply geophysical methods to detect and characterize underground facilities, Sandia National Laboratories (SNL) initiated an electromagnetic induction (EMI) project to evaluate low frequency electromagnetic (EM) techniques for subsurface structure detection. Low frequency, in this case, extends from kilohertz to hundreds of kilohertz. An EM gradiometer survey procedure had already been utilized for borehole imaging of coal seams and had successfully been applied in a surface mode to detect a drug smuggling tunnel. The SNL project has focused on building upon the success of that procedure and applying it to surface and low altitude airborne platforms. Part of SNL's work with Raton Technology Research has focused on improving that technology through improved hard...