Short Note: The Location of TEM Transmitter Loops Underground and in Rugged Terrain

The size, shape and location of transmitter loops is of fundamental importance in the design of both surface and drillhole TEM surveys. The shape and location of the loop, with respect to a target conductor, strongly affects the level of electro-magnetic coupling between the loop and the conductor. The effect of sloping terrain on the coupling field of a surface loop is shown for several terrains. In the case of transmitter loops located underground, both maximum and minimum coupling can be obtained at several positions and attitudes of conductors located around the loop. Transmitter loops located on sloping terrain or in inclined mine workings can often provide greater control over the level of energisation of the target conductor than loops located on a flat terrain. In these circumstances it is possible to determine conductor location and attitude with greater accuracy. Computing the electro-magnetic coupling fields of transmitter loops, for various attitudes of the target conductor, is mandatory when designing TEM surveys and interpreting survey data.