Electromagnetic methods fall in two categories: frequency domain and time domain.
In the frequency domain method, the transmitter emits a sinusoidal varying current at a specific frequency. Because the mutual inductance between the transmitter and conductor is a complex quantity, the electromagnetic force induced in the conductor will be shifted in phase with respect to the primary field. At the receiver, the secondary field generated by the currents in the conductor will also be shifted in phase by the same amount. Frequency domain measures the amplitude and phase of an induced electromagnetic field.
Time domain measures the decay time of an electromagnetic pulse induced by a transmitter. EM surveys will measure variability in subsurface conductivity, which can be naturally occurring (differing lithologic materials), or man-made (soil/groundwater contaminants or buried metal).
Applications of time domain and frequency domain:
- Aquifer description
- Identification of fractures and fissures
- Mapping spots brine
- Groundwater Contamination
- Leak Detection inorganic pollutants
- Leaking landfill
- Maps of saline soils
- Intrusion of salt water
- Detection of septic systems
- Detection of buried tanks
- Characterization of buried waste
- Delimitation disposition pits / trenches
- Buried fuel tanks
- The size and limits of buried deposits
- Determination of the sliding plane
- Maps of groundwater contamination
- Unexploded bombs (UXO)
- Historical complex
- Observation posts