A portable single axis magnetic gradiometer

The single axis magnetic gradiometer based on two compact detector compensa tion (CDC) fluxgate ringcore sensors separated 20 cm is described. Despite its high stability and precision better than 1 nT, the calibration procedur es are not straightforward. Firstly, the mono-axial measurement does not pr ovide vector information about the magnetic field. Secondly, one of the sen sors measures the ambient magnetic field and is used to compensate for the main field at both sensors. Several methods have been developed for charact erization of the 2 gradiometer, and the calibration of the gradient measure ments is achieved by using a magnetic dipole of strength 2 mAm(2). In a coi l facility, the gradient can be determined with an accuracy of 0.3 nT/m(RMS ). (C) 2001 Elsevier Science B.V. All rights reserved.