The magnetic calibration and test laboratory of the Nurmijärvi Geophysical Observatory services aviation and space industry as well as manufacturers and users of ground based magnetic instruments.
The calibration of a sight compass is performed in the absolute house of the observatory on the same pillar where also the absolute values of the magnetic field (e.g. declination) are measured. A non-magnetic Askania circle base is used to rotate the compass and to read the rotation angles. A fluxgate magnetometer in the variation house records the variation of the declination during the compass calibration.
Airplanes need to check their magnetic direction sensing elements: a flux valve or a magnetic compass. Compass swing bases at airfields serve for this task. The compass swing base need to be magnetically sufficiently clean and the direction of the magnetic field at the base need to be known.
The Nurmijärvi magnetic calibration and test laboratory has equipment and knowledge to make these measurements at airfields. A usual procedure is to start the research with a regular grid of total field measurements with a proton magnetometer. The geographic azimuth is measured with two GPS satellite receivers and the magnetic declination with two DI-theodolites.
In the magnetic calibration and test laboratory several parameters of a magnetometer can be measured: