The electromagnetic (EM) method uses induction to measure the electrical conductivity of the sub-surface. A primary alternating electric current of known frequency and magnitude is passed through a coil creating a primary magnetic field in the space surrounding the coil. The eddy currents generated in the ground induce a secondary current in underground conductors which results in an alternating secondary magnetic field, which is sensed by the receiving coil. The secondary field is distinguished from the primary field by a phase lag. The ratio of the magnitudes of the primary and secondary currents is proportional to the terrain conductivity. The depth of penetration is influenced by the coil separation and orientation.
No ground contact is required in electromagnetic (EM) surveys. This eliminates direct electrical coupling problems and allows much more rapid data acquisition. This application can give way to extremely sensitive and accurate data acquisition, capable of detecting variations in conductivity of as little as 3%.
No ground contact is required in electromagnetic (EM) surveys. This eliminates direct electrical coupling problems and allows much more rapid data acquisition. This application can give way to extremely sensitive and accurate data acquisition, capable of detecting variations in conductivity of as little as 3%.
Applications for Electromagnetic (EM) Surveys
- Regional geologic studies
- Engineering site investigations
- Hydrogeological investigations
- Detection of sub-surface cavities
- Mapping of Leachate and contaminant plumes
- Location and orientation of buried metallic objects
- Archeological investigations