Electromagnetic (EM) methods include some of the most employed geophysical techniques used for environmental and geotechnical studies. EM methods employ active sensing technology in which a generated EM field is used to induce secondary EM response in the mediums being investigated. EM sensors can be divided into two categories, frequency domain and time domain. Frequency domain instruments measure the amplitude and phase of the induced electromagnetic field while time domain instruments measure the decay time of the induced field.
All EM surveys provide measurements of variability in subsurface conductivity, which can be naturally occurring (differing lithologic materials), or man-made (soil/groundwater contaminants or buried metal). As compared to magnetometer-based investigations, EM instruments have the added capability of detecting non-ferrous as well as ferrous metallic objects.
Some applications of EM methods include: