Process for determining the position of a moving object using magnetic gradientmetric measurements

DETAILED DESCRIPTION OF AN EMBODIMENT Consider a point in the plane defined by the trajectory of the source and by the observation site.
Alternately, the plane of movement of the source known with respect to the observation site could be used.
In general, the observation site may itself be moving with an arbitrary but known movement.
The invention uses the quasi-static contribution of the electromagnetic signature of the source.
This type of signature may be due to the presence of ferromagnetic elements in construction materials of the mobile and then corresponds to a magnetostatic contribution.
In the case of submarine sources, it may also be the quasi-static envelope of the very low frequency electromagnetic signature, as it was demonstrated in document reference [10].
In the invention, the electromagnetic measurements are output from scalar magnetometers used in a gradientmeter, the positions of which are known at each instant.
These sensors provide access to the modulus of the useful magnetic signal, unlike vector, magnetic or electrical sensors that measure one or several components of the electromagnetic signal.
The invention provides access to the azimuth of the source, the direction and the sign of its speed vector, and to the r/V parameter where r is the distance from the source to the sensor and V is the modulus of the speed, from a single observation site and for a reference instant.
The r/V parameter emphasizes the distance ambiguity related to this type of measurement.
When one of the components of the speed vector or its modulus or a source-sensor distance at one or more reference instants can be known in advance or can be estimated by means of a complementary technique (acoustic Doppler, radar, laser distance meter, etc.
), the tracking problem in the plane then becomes observable, except for a single phantom solution.
The invention contains details of a solution based on use of the Doppler phenomenon for narrow band acoustic sources and an industrial application using a priori information, but other possibly active solutions are perfectly possible as a function of the application domain and indiscretions emitted by the source