Geophysical mapping
Why?
The main purpose of SGU’s geophysical mapping activities is to obtain a picture of bedrock conditions, especially where soil or water covers the bedrock. We therefore carry out measurements of the magnetic field, the gamma radiation, the electromagnetic field and the gravity field. These measurements also provide an opportunity to ‘see’ structures that extend a long way underground (several hundred metres).
Exploration and construction companies, universities and public authorities in various areas use information about geophysical conditions.
For example, variations in the magnetic field and the electromagnetic field provide information about the structures and contents of the bedrock, which are of interest for the purposes of exploration and for mapping weak zones in the bedrock. Measurements of the electromagnetic field, i.e. ground conductivity, are also used to locate groundwater resources.
Data on gamma radiation, i.e. radioactive ionising radiation, is used, inter alia, to discriminate rock types and for the purposes of radon studies and the efforts to achieve a safe radiation environment.
Information about variations in the gravity field is used, among other things, for surveys of the distribution of rocks, to locate groundwater reservoirs and suitable areas for ground heat sources, as well as for navigation and positioning and for calibrating scales and pressure sensors.
Geophysical mapping is important, in particular, for our own surveys of the bedrock, quaternary deposits and sea bottoms. Other geophysical methods, such as georadar and seismics, are among other things used for groundwater mapping.
How?
Measurements of the geomagnetic field, the gamma radiation and the electromagnetic field are carried out from aircraft. The aircraft is equipped with a magnetometer, a gamma spectrometer and low frequency (VLF) receivers. The aircraft flies at an altitude of 60 metres along lines, east to west or north to south, at intervals of 200 metres. The distance between the measured points in the line is about 17 m.
Gravity measurements are carried out mainly along roads by car and, in areas where there are few roads, by snowmobile or helicopter. The distance between measured points is about 1.5 km.
The information is stored in databases and can easily be plotted on maps or imported to various computer programs for further interpretation.
SGU also carries out observations of variations in the earth’s magnetic field over time and space. This information is used, among other things, as a basis for magnetic deviation maps.
More information
Overview of maps and publications