Geophysical flight measurements, electromagnetic fields, VLF (detailed)
Description
In its flight measurements, SGU uses the so-called VLF method (Very Low Frequency), which is a conceptually simple but effective method for obtaining information on how well the ground conducts current. The method is to measure the magnetic fields induced by currents in the ground, which in turn arise due to interaction with radio waves from transmitters in the VLF band.
Geophysical flight measurements, electromagnetic fields, VLF (detailed) contain information on the magnetic component (H) of the electromagnetic field in the VLF band (frequency band 15-30 kHz), which varies according to the electrical conductivity of the ground. This is calculated for coordinate points, from measurements taken from aircraft at low altitude.
All measurements have been made with a 3-axis antenna that measures the amplitude and phase of the magnetic vector components.
The method's depth perception varies with how well the ground conducts electric current, from a few hundred meters in crystalline bedrock to a few tens of meters in conductive thick clay layers.
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