FDEM is a low-cost electromagnetic solution for shallow conductor mapping.
- Multiple coil separations and frequencies available.
- Simple operation, allowing survey in any environment (sand, gravel, outcrop, permafrost).
- Inexpensive and straightforward to carry out.
- Simple and accurate quantitative interpretation (location, width, depth, dip and conductance).
- Investigation depth is generally ½ (to ¾) the coil separation in resistive environments.
- Investigation depth is limited by frequency skin depth of conductive surface layer.
- The In-phase component is highly sensitive to coil orientation and spacing.
- Operating survey frequencies and coil separation are optimized to map local geology.
- Readings are normally taken at intervals of ¼ the coil separation.
- Both In-phase and Out-of-phase components of the secondary electromagnetic field are recorded.
- Instruments: MaxMin I (9 frequencies) coupled to a MMC notebook from Apex. Coil separations from xx m to yy m are available.
- In-phase and out-of-phase stacked profile map for each frequency.
HLEM profiles over a weathered kimberlite pipe (loop separation = 75 m, frequency = 888 Hz).
The In-phase anomaly is reversed due to the magnetic nature of the source.
(Geophysics 44, Macnae, 1979)
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