Abstract: The invention concerns processes for immunizing nautical vessels against the disturbances that they cause to the magnetic field of the earth, consisting in supplying immunization loops of such a vessel with a set of alternating currents producing inside the volume of the vessel a homogeneous and alternating inductor field, isolating the alternating signal issuing from the alternating field at the measuring base and calculating the induced magnetization, wherein it allows to separate the induced magnetization from the permanent magnetization in the magnetic signature of a vessel while reducing the duration of measuring time required.

Abstract: A device for measuring the gradient of a magnetic field comprises on the same support two magnetooptical layers separated by a half-wave plate. A linearly polarized light beam successively passes through these three optical components and its polarization plane rotates by a value proportional to the gradient of the field in its propagation direction.