Electromagnetic measurement of coal roof-beam thickness

In underground coal mines where coal is left in the roof or floor after mining, it is often necessary to measure the<br>thickness of the remaining coal. Radar and radar-like techniques have been attempted in the past but have met with<br>limited success. By taking advantage of the resistive contrast between the coal and the surrounding rock<br>electromagnetic sounding (EM) has been proposed as a feasible technique to achieve non-intrusive coal thickness<br>measurements.