The variety of environmental and engineering applications for helicopter-borne<br>electromagnetic surveys has increased in recent years. Helicopter EM surveys<br>undertaken by Geoterrex-Dighem have been used for:<br>l measuring soil conductivity near oil pipelines to assess corrosion risk,<br>l estimating soil type and depth for pipeline planning,<br>l mapping sand and gravel deposits for aggregate resource exploration,<br>l measuring the extent of salt water invasion into the Florida Everglades,<br>l mapping soil salinity in Australian farmland, assessing groundwater resources,<br>l locating brine leaks from abandoned Texas oil wells,<br>l site characterization and detection of leaks in mine tailings dams,<br>l assessing land slumping hazards in Japan,<br>l measuring ocean bathymetry<br>l locating igneous dikes in coal mines.<br>Magnetic and radiometric data can be collected simultaneously, and have been used to<br>find buried metal structures, and illegally abandoned radioactive sources.<br>The major advantages of helicopter EM over ground EM surveys are the reduced cost for<br>surveys over large areas, the speed of surveying coverage (approx 1000 hectares/hour),<br>and the multiple frequency/multiple depth sample nature of the data, which render a 3-<br>dimensional conductivity image of the ground conditions.


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