Electromagnetic induction (EMI), also referred to as low frequency electromagnetics (LFEM), is frequently used for geophysical survey on archaeological sites where soil environs may prove problematic to magnetic methods of prospection, and when the potential for buried structures, such as cairns or building foundations, may warrant combination of two or more geophysical techniques.

TARGET uses EMI to measure both apparent resistivity (quadrature) and apparent magnetic susceptibility (in-phase), employing a frequency domain electromagnetic (FDEM) sensor containing 1 transmitting coil and 4 receiving coils. The sensor transmitting coil generates a time varying primary magnetic field, which propagates above and below ground generating alternating currents (eddy currents) within the soil and the objects it contains, thereby creating a secondary magnetic field proportional to the rate of change of the primary magnetic field. Measurements are recorded by the receiving coils mounted within the sensor probe at set distances from the transmitting coil, with a total 8 individual data sets acquired simultaneously.

TARGET uses EMI as an accompaniment to magnetometry, with successful mapping of buried remains including

Castle foundations
Moated sites
Prehistoric enclosures & tumuli
Deserted medieval settlements
Ammunition dumps

See TARGET’s ‘Example Data’ page for images of archaeological remains successfully identified using EMI/LFEM.