Metal Detection

Introduction

Although EM-31 and Magnetics are often used to map subsurface metal, it lack spatial resolution and accuracy to map individual buried metal objects such as drums. Geonics offers an instrument, the EM-61, which has considerable improved lateral resolution and accuracy over EM-31 and Magnetics. The manufacturers claim that the EM-61 can detect a single 55 gallon drum at depths of 3 metres. EM-61 can best be described as a high sensitivity, high resolution, time-domain (EM) metal detector than can detect both ferrous and non-ferrous metals. It can also be operated in trailer or backpack mode, depending on site and application. Also note that an off-the-shelf metal detector typically used to find shallow coins does not have the penetration capability needed for engineering and environmental site investigations.

Limitations

• The EM-61 does not have the penetration of EM-31 and Magnetics.

• EM-31 records both quadrature (conductivity) and in-phase (subsurface metal) components. The EM-61 cannot measure the quadrature component which is often valuable in locating buried pipes.

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