Theory 
EM surveys induces an electromagnetic current into the ground and measures the resulting field. There are two types of electromagnetic survey:

1- based on frequency domain, it measures the amplitude and phase of an EM induced field (FDEM), 2- based on the time domain, it measures the decay time of an electromagnetic pulse induced by a transmitter (TDEM). The EM system consists of a transmitter and receiver coil which is suspended above the ground. A primary electromagnetic field is output by the transmission coil which induces a secondary field in the ground. The magnitude of the secondary field is proportional to the conductivity of the material (rock type, potential mineralization, groundwater, ground contamination and buried metal man-made objects).

Applications