Electromagnetic Techniques
Very Low Frequency (VLF) Surveys
Outline
Very-Low-Frequency (VLF) surveying is a continuous-wave (frequency domain) electromagnetic technique that uses low-frequency radio transmissions as the source. When these intersect a buried conductor they induce eddy currents that generate a secondary magnetic field concentric around the source of the currents. VLF surveys involve measuring the orientation of this field. As the instrument passes perpendicularly over a vertical target the vector orientation changes from a maximum on one side to a minimum on the other side. The method is primarily used in mineral exploration work but has also been successfully applied in engineering and groundwater surveys to detect conductive fault zones and other sub-vertical conductors.
