SGU measures and documents variations in the Earth’s magnetic field in time and space and makes forecasts of future changes of the field. Mainly, we measure and document:
the temporal variations of the Earth’s magnetic field at fixed observatory sites, and
- the regional variations within Sweden.
Geomagnetic data are used in research and in various geophysical/geological activities at both national and international level. The demand for geomagnetic information has increased in response to the general development in technology and electronics in the last few decades.
The geomagnetic information is based on continuous measurements at both SGU’s geomagnetic observatories – Fiby, west of Uppsala, and Abisko – as well as on regular measurements at fixed positions in Sweden.
The magnetic maps that are produced by SGU contain information on strength as well as direction of the geomagnetic field vector. The maps are based on measurements at certain points all over Sweden and on the results of a large-scale airborne geomagnetic survey at 3 000 m height done in 1965. This information differs from SGUs ordinary airborne magnetic surveys at low altitude in that it only contains information on the strength of the total magnetic field. A new method where airborne magnetic measurements of the total field are combined with ground based measurements of the magnetic components provides maps of high resolution of the magnetic elements.
The recordings at the observatory sites together with regular recordings at sites of a repeat station network (secular variation network) provide information on the long term changes of the Earth’s magnetic elements in Sweden. This information, e.g. on the changing magnetic declination, is mainly provided for the Swedish Armed Forces, the Swedish Maritime Administration (Sjöfartsverket), the Aviation Agency (LFV) and the National Land Survey (LMV).
SGU can also investigate the magnet field on a smaller, even local scale. We can provide information on magnetic and geographic north (magnetic declination). We can also search for buried magnetic objects, e.g. iron materials or archaeological objects, in the shallow subsurface. Using modern instruments like fluxgate-, proton-, and caesium magnetometer as well as gyrotheodolite, we can provide very dense and precise information on the magnetic field in areas of limited extent.
SGU’s geomagnetic observatories
SGU runs two observatories in Sweden that continuously record variations in the geomagnetic field. They are located in Fiby, 20 km west of Uppsala, and in Abisko. Measurements of the Earth’s magnetic field have been carried out since the 1920s, and SGU has been responsible for these measurements since 1969.
In the spring of 2004 the Fiby observatory (UPS), which came into operation in 1998, replaced the observatory in Lovö, which is closed now. It is one of the twelve observatories in the world whose data are used to produce a three-hourly global index of the geomagnetic field that characterises its activity.
The Abisko observatory (ABK) lies in the northern auroral zone and is therefore one among the observatories whose data are used for characterizing the magnetic variations within this zone.
Data from the two observatories are reported once per hour to the World Data Center C2 in Japan and once per day to the INTERMAGNET Center in Scotland. Geomagnetic data from all the member observatories of the INTERMAGNET program are available on cd-rom.
At both observatories, the three orthogonal components X, Y and Z of the Earth’s magnetic field are observed with fluxgate magnetometers, while the total field F is measured by a proton precession magnetometer. The magnetic data are digitally recorded every second and transferred to SGU’s headquarter in Uppsala via telephone (ISDN) for further processing. Finally, the data are sent by e-mail to different data centres.
Almost all geomagnetic data from the Swedish observatories are available to the public in digital form and may be downloaded from SGU's database.
The UPS geomagnetic observatory is also used for calibrating geomagnetic instruments by utilizing various coil systems. These facilities are still being further improved.
Enquiries and orders:
SGU, Customer Services, Box 670, SE-751 28 Uppsala
Telephone: +46 18-17 90 00
Fax: +46 18-50 10 20