VERY LOW FREQUENCY METHOD
Introduction:-
VLF measures perturbations in the magnetic field of radio waves. The perturbations are cause by geologic subsurface features. Thus by examining the nature of the magnetic field's perturbations we can identify anomalous areas in the subsurface.
 VLF is used in several applications. Aquifers and groundwater and can be located. Leachate can be identified for environmental investigations. Geotechnical applications include fault and overburden mapping. Also, likely mineral deposits can be discovered for mining surveys.
 VLF techniques utilizes a plane-wave radio signal (15-30 kHz) emanating from one of several worldwide radio transmitters used for submarine communications. Military transmitters provide radio signal coverage for all of North America. The magnetic field of the military's radio signal (primary field) causes electric currents to be induced in conductive geologic units or structures
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