How we implement electromagnetic surveying into our bespoke solutions packages

In electromagnetic (EM) surveying, the electrical conductivity of the ground is measured as a function of depth and/or horizontal distance. Different rocks, buried structures and objects exhibit different values of electrical conductivity. Mapping variations in electrical conductivity can identify anomalous areas worthy of further geophysical or intrusive investigation.

Owing to the rapid data collection methodologies utilising GPS positioning systems, the EM mapping method is often used as a reconnaissance-style survey to rapidly characterise sites for environmental, geotechnical or hydrogeological purposes prior to intrusive investigations to assist with the optimised targeting of intrusive investigation strategies.

EM methods

EM techniques can be broadly divided into two types. The first one, based on frequency domain, measures the amplitude and phase of an EM-induced field (FDEM). The second one, based on the time domain, measures the decay time of an EM pulse induced by a transmitter (TDEM). In FDEM mapping, the electrical conductivity of the ground is measured as a function of depth and/or horizontal distance. Mapping variations in conductivity can indicate anomalous areas worthy of further geophysical or intrusive investigation. The typical set-up for the resistivity survey consists of a transmitter coil with one or more receiver coils. The size of the coil is proportional to the depth of investigation (the greater the area of the coil, the greater the depth of investigation).

The RSK Geophysics team deploys a variety of EM instruments, from which the best is selected for finding the target objects.

Method/instrument Typical depth of penetration (bgl) Common applications
Shallow FDEM (i.e., EM31 or CMD Explorer) Down to 6 m To detect or map geological variations, groundwater contaminants, any subsurface feature associated with changes in the ground conductivity, buried metalwork and ore bodies.
Deep FDEM (i.e., EM34 or WalkTEM) Down to 60 m To detect or map contaminant plumes and to undertake groundwater or geological exploration.
Shallow TDEM (i.e., EM61) Down to 3–4 m Advanced metal detector, to detect ferrous and non-ferrous metals, buried structures, underground storage tanks and unexploded ordnance.
Deep TEM (i.e., G-TEM) Down to 100m Deep geology, hydrogeology and mineral exploration.

Advantages of EM

  • Versatile: detection of small changes in conductivity can be used to identify features in the ground, including detection of buried metallic objects and waste material
  • Cost effective: single operator, making surveys fast and reducing field and project time
  • Speed: high-speed continuous coverage of large areas using accurate GPS for positioning

Other geophysical surveys techniques

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RSK Geosciences is part of the RSK group of companies

The RSK group is a leading integrated environmental, engineering and technical services business offering bespoke end-to-end solutions to a variety of sectors. Headquartered in the UK but with an established presence throughout Europe, Africa, the Middle East, Asia and Australia, RSK helps organisations around the world achieve their business aspirations in a sustainable and efficient manner.