The metal objects are either at shallow depth or are larger targets.Ĭompared to the surface resistivity method, the electromagnetic conductivity method can be performed more rapidly, small changes in conductivity can be For locating metal objects, the signal response is stronger when The EM31-DL instrument has an optimum depth range of about 15 to 20 feet (6 meters). The EM31Ĭonductivity readings increase in relative proportion to the increase in pH of the soils and groundwater in the area of the high conductivity feature The EM31 curve shown below is a typical EM31 response to a high conductivity feature, such as a brine pit, that does not contain metal. Maps when surveying an area for underground metal utilities, buried electric cables, and landfills that contain buried metal. This inverse of EM readings over buried metal for the EM31 can be seen in EM31 color contour As the EM31 instrument crosses the midpoint and retreats from the buried metal object, the electromagneticĬonductivity response generally mirrors the advancing EM response. When advancing toward a buried metal object, the EM31 conductivity readings increase slightly at first and then rapidly decrease, sometimes below the backgroundĮlectromagnetic conductivity of the subsurface soils. The electromagnetic conductivity curve shown above is a typical EM31 response to buried metal when transversing perpendicular to the object's orientation. Out over any surface conditions, and under most geologic conditions including those of high surface resistivity such as sand, gravel, asphalt, permafrost,Ībove is a photo of the truck-mounted 18-foot (6-meter) deep EM conductivity meter and also a representation of the EM response to a buried metal Unlike the resistivity method, EM31 meter measurements can be made without electrodes or ground contact (non-destructive). Of the subsurface soil, rock, and groundwater (quadrature phase (quad-phase) component) and the magnetic susceptibility responses to any buried ferrousĪnd non-ferrous metal (in-phase component), using a patented electromagnetic inductive technique. The EM31-DL is a frequency-domain instrument that can simultaneously measure the electromagnetic conductivity (terrain or ground conductivity) What is the EM31 Electromagnetic Conductivity (EM) Terrain Conductivity Meter The EM instruments above are excelent for locating buried trenches, burial pits, landfills, and brine pits, and also the extentĪnd depth of inorganic and salt plumes emanating from landfills, industrial ponds, and brine pits. uses the new EM61-MK2 which is twice as accurateĪbove are the shallow (0' to 20') EM conductivity meter (white pole), the deeper (up to 100') EM conductivity meter (hoops), and the EM metal detector owns and uses for conducting anĮlectromagnetic conductivity survey are the Geonics EM31-DL and the Geonics EM61-MK2. There are severalĬompanies that manufacture electromagnetic conductivity instruments worldwide. Generally, an electromagnetic conductivity (EM) instrument consists of a frequency-domain or time-domain conductivity meter. Low pH groundwater, and salty or briny groundwater, all have a relatively high conductivity. Sand, granite, dry subsurface soils, and neutral pH groundwater all have a relatively low conductivity. Geologic variations, groundwater contaminants, or any subsurface feature associated with changes in groundĬonductivity can be investigated using electromagnetic conductivity.Ĭonductivity is the inverse of resistivity therefore, a low conductivity reading would be somewhat analagous to a high resistivity value. What is Electromagnetic Conductivity (EM) Terrain ConductivityĮlectromagnetic conductivity (also known as terrain conductivity) measures the conductivity of the subsurface which includes soil, groundwater, What is Electromagnetic Conductivity (Terrain Conductivity)
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