Electromagnetic Methods
Electromagnetics uses inductive techniques to measure conductivity of the subsurface without the need of electrodes or ground contact. The methods include frequency domain electromagnetics (Geonics EM-31, EM-34, EM-38 and GSSI Profiler), time domain electromagnetics (Geonics EM-61, Geonics PROTEM systems and White handheld systems), and VLF systems. Depending on the target, the depth of investigation can range from a few meters to several hundred meters.
Frequency Domain systems measure the magnitude and phase of an induced current. The readings can be integrated with a sub-meter GPS system to facilitate quick and accurate data collection. GeoView uses frequency domain electromagnetics to map:
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Metallic buried debris
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Conductive (ionic) ground water contamination
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Archaeological artifacts
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Mine spoils
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Variable geological conditions
Time domain systems generate a pulsed current into the ground and measure the decay rate of a secondary magnetic field to determine the bulk conductivity of the subsurface. GeoView uses time domain systems to:
- Locate unexploded ordinance
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Locate buried ferrous and non-ferrous metal for environmental and archaeological studies
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Map saltwater plumes
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Determine thickness of contaminate plumes
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Map thickness of geologic strata
- Locate underground storage tanks
VLF systems measure the local tilt and ellipticity of very low frequency broadcasts. VLF data is used to:
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Map water bearing fractures
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Locate ore bodies
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Locate faults
