The response of a coincident loop transient electromagnetic system above a uniform earth

Abstract

The response of a coincident horizontal loop transient electromagnetic (TEM) system is expected to decrease as the loop is lifted off the earth. This effect is calculated for a uniformly conducting earth for a range of loop heights, ground conductivities, loop sizes, and delay times. Within the assumptions of the model, the calculations are exact and valid for any height. It is shown that signal attenuation with respect to height does not preclude the use of a helicopter TEM system. It is also shown that for ground TEM surveys where the loop is held off the ground because of brush, the maximum attenuation that could be expected from a uniform half space is less than 20%.