Geophysical aerial measurements, apparent resistivity (display service)
Description
The display service shows the apparent resistivity in a simplified break with 200 times 200 meters resolution. The underlying information can be ordered in the data set Geophysical flight measurements, electromagnetic fields, VLF (detailed), then with a higher resolution.
The apparent resistivity does not represent absolute values of soil resistivity but shows only relative changes from a presumed normal value. The default value is set to 5000 Ωm.
The map of apparent resistivity reflects the composition of both bedrock and soil layers. Deep sensing is dependent on the ground's conductivity. In rocky areas and areas with thin soil cover, the map mainly shows the resistivity of the bedrock. In areas with high clay strength, depth sensing is limited due to the low resistivity, and the map therefore shows mainly the resistivity of the soil layers.
The map is produced from data collected with aerial measurements where the so-called VLF method (Very Low Frequency) has been used. SGU's VLF measurement system records both the amplitude and phase of the magnetic field in three orthogonal directions. By registering signals from two different transmitters simultaneously, the apparent electrical resistivity of the ground can be calculated using a method developed by Becken and Pedersen (2003).
Resources
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https://resource.sgu.se/service/wms/130/flyggeofysik-skenbar-resistivitet |