Abstract
Abstract. Absolute magnetic measurements are of great importance in magnetic observatories. They allow not only instrument calibration but also data quality checking. They require the vertical and the geographic or true north as reference directions, usually determined by means of a level and by pointing an azimuth mark, respectively. We present here a novel system able to measure the direction of the magnetic field and of the vertical and true north. A design of a north seeker is proposed taking into account sensor bias as well as misalignment errors. Different methods are derived from this model and measurement results are presented. A measurement test at high latitude is also shown.
Highlights
Measuring the magnetic declination is realized by determining, in a horizontal plane, both magnetic field and geographic or true north direction
When looking to the accuracy of magnetic declination required by international standards like those established by Intermagnet (Intermagnet, 2012), it appears evident that such error must be compensated
A cost-effective fiber-optic gyroscope (FOG) has been used for validating the theory
Summary
Measuring the magnetic declination is realized by determining, in a horizontal plane, both magnetic field and geographic or true north direction (in the rest of this paper, the term true north will be employed). The target azimuth can be established by different methods: by a gyrotheodolite, by pointing at a celestial body such as the Sun in combination with a clock or by using a GNSS system (Newitt et al, 1996). In any case, this target azimuth value is measured prior to the declination measurement and is assumed constant until it is checked again. Today several are operational in different observatories Both GAUSS and AutoDIF use the target pointing principle for the true north measurement. Gonsette et al.: Fog-based automatic true north detection for absolute magnetic declination measurement
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