Contribution to solving the orientation problem for an automatic magnetic observatory
- 1International Institute of Earthquake Prediction Theory and Mathematical Geophysics 79, b2, Warshavskoe shosse, 113556 Moscow, Russia
- 2Geophysical Center of RAS, 3 Molodezhnaya St., 119296 Moscow, Russia
- 3Institut de Physique du Globe de Paris, UMR7154, CNRS – 1 Rue Jussieu, 75005 Paris, France
- 4Centre National d'Etudes Spatiales, 2, Place Maurice Quentin, 75001 Paris, France
Abstract. The problem of the absolute calibration of a vectorial (tri-axial) magnetometer is addressed with the objective that the apparatus, once calibrated, gives afterwards, for a few years, the absolute values of the three components of the geomagnetic field (say the Northern geographical component, Eastern component and vertical component) with an accuracy on the order of 1 nT. The calibration procedure comes down to measure the orientation in space of the three physical axes of the sensor or, in other words, the entries of the transfer matrix from the local geographical axes to these physical axes. Absolute calibration follows indeed an internal calibration which provides accurate values of the three scale factors corresponding to the three axes – and in addition their relative angles. The absolute calibration can be achieved through classical absolute measurements made with an independent equipment. It is shown – after an error analysis which is not trivial – that, while it is not possible to get the axes absolute orientations with a high accuracy, the assigned objective (absolute values of the Northern geographical component, Eastern component and vertical component, with an accuracy of the order of 1 nT) is nevertheless reachable; this is because in the time interval of interest the field to measure is not far from the field prevailing during the calibration process.