Frequency Domain Electromagnetics (FDEM) is applicable on soil, rock, and paved surfaces. It is used to map lateral variations in moisture related to seepage through dams, levees, pipelines, or containment walls. It can also be used to delineate the edges of landfills or to detect buried metal objects such as utilities and underground storage tanks.
How does Frequency Domain Electromagnetic (FDEM) Induction work?
The prospecting equipment consists of a current transmitter with its power supply, a transmitting coil, the receiver of the induced fields and a digital recorder (data logger) of the obtained data, which allows its later study and analysis.
With Frequency Domain Electromagnetics (FDEM), electrical currents are induced into subsurface conductors by an operator-held transmitter loop that radiates an electromagnetic field (EM). As the EM energy encounters different subsurface materials, eddy currents are induced creating secondary electromagnetic fields. This secondary field is recorded at the surface by a receiver loop.
A data logger measures the components of the secondary field that are in-phase with the transmitted EM energy, and that portion which is 90-degrees out of phase (the quadrature component). Under normal subsurface conditions, the in-phase component is strongly affected by the presence of buried metallic objects, while the quadrature component is directly related to terrain conductivity.
Deliverables
Typical deliverables include plan maps of project location and interfering cultural structures, colour-contour maps of metal and earth conductivity responses, and interpretation maps with the cultural responses and subsurface responses clearly separated.
