Method and apparatus for positioning a boat by monitoring the magnetic

Abstract

Device for positioning a moving body in a plane indicated by the axes OX and OY by using a magnetic field. A current i, which is the sum of a current i.sub.o at frequency f.sub.o in which f.sub.o .perspectiveto.100 Hz and a current i.sub.1 at frequency f.sub.1 in which f.sub.1 .perspectiveto.10 kHz modulated by bursts of recurring pulses having a period T.sub.o with T.sub.o =1/f.sub.o flows through a conductor. The moving body carries two pairs of magnetometers supplying the components of the magnetic field h.sub.x.sup.o, h.sub.y.sup.o and h.sub.x.sup.1, h.sub.y.sup.1 with respect to axes associated with the moving body about frequencies f.sub.o and f.sub.1. A subassembly, on the basis of the values of h.sub.x.sup.o and h.sub.y.sup.o, supplies a signal U.sub.1 of frequency 2f.sub.o. A subassembly, on the basis of the signal U.sub.1, supplies two signals S.sub.1 and S.sub.2 displaced by T.sub.o /2. Another subassembly supplies signals T on the basis of the values of h.sub.x.sup.1 and h.sub.y.sup.1, which are compared with the signals S.sub.1 and S.sub.2 for supplying a signal S on the basis of signal U.sub.1. Signal S makes it possible to demodulate the components h.sub.x.sup.o and h.sub.y.sup.o, which are thus obtained with their signs, determining without ambiguity the position of the moving body.