GB2469432A

GB2469432A - Submarine magnetic detection buoys

Info

Publication number: GB2469432A
Application number: GB8828107A
Authority: GB
Inventors: Jean-Louis Lescourret
Original assignee: Crouzet SA
Current assignee: Thales Avionics SAS
Priority date: 1987-12-23
Filing date: 1988-12-01
Publication date: 2010-10-20
Anticipated expiration: 2008-12-01
Also published as: FR2775083B1; IT8848628A0; DE3842296A1; GB8828107D0; FR2775083A1; GB2469432B

Abstract

A submarine detection buoy comprises a float 1 supporting an antenna 2 connected to emission and supply means 3, which are connected by way of an assembly 5 for mechanical stabilisation relative to the water and current supply to a non-magnetic case 11 containing means for processing, multiplexing data to the emission means and measuring orientation of the case in the water. The case is connected to a detector unit 10 which is in turn connected mechanically to a ballast means 9. The detector unit comprises an omnidirectional magnetic resonance probe, the means for measuring the orientation of the case comprising means for measuring the three components of the terrestrial magnetic field with respect to the case, and rigid connecting means being provided between the case and the detector unit.

Description

DESCRI PT ION

SUBMARINE MAGNETIC DETECTION BUOYS

The present invention relates to the field of

passive submarine detection. Up until now passive submarine detection systems have essentially comprised hydrophones. Effectively, it is considered that the sensitivity of magnetic detection systems, including more sophisticated systems such as nuclear or electronic omnidirectional niagnetic.-resonance magnetic detectors, are not adequate for providing satisfactory results when immersed.

One object of the present invention is to provide a submarine detection buoy connected to a magnetic field detector of the magnetic resonance type and to an electronic system which allows the detector to be used in highly sensitive detection ranges.

Another object of the present invention is to provide such a magnetic detector buoy which is compatible with existing transmission and dropping systems for hydrophone buoys.

In accordance with the present invention, there is provided a submarine detection buoy, comprising a float connected to antenna means, emission and supply means which are connected by way of an assembly for mechanical connection, mechanical stabilisation and electrical current connection to a non-magnetic electronic housing containing means for processing, multiplexing and measuring orientation, the housing being connected to a detector unit, which is in turn connected mechanically to a ballast means, the detector unit comprising an omnidirectional magnetic-resonance probe, the means for measuring the orientation of the housing comprising means for measuring the three components of the terrestrial magnetic field with respect to the housing, and rigid connecting means being provided between the housing and the detector unit.

If the probe is a nuclear magnetic-resonance type probe, the means for measuring the orientation further comprise means for measuring the orientation of gravity with respect to the housing.

According to one embodiment of the present invention, the rigid connecting means are extendible and non-magnetic.

According to another embodiment of the present invention, the extendible means comprise means mounted so as to slide with the housing means and blocking means for blocking the means which are mounted to slide in the open position.

According to a further embodiment of the present invention, the means for measuring orientation comprise a directional magnetometer and two inclinometers.

According to yet another embodiment of the present invention, the means for providing a signal HF for the magnetometer and means for energising such means are disposed in a second housing disposed between the detector unit and the ballast.

According to another embodiment of the present invention, the electronic housing includes a high-accuracy frequency reference.

Thanks to the special arrangement of the housing with respect to the detector, to the choice of materials, the choice of electronic systems disposed in the housing and to their arrangement, and to the choice of means for measuring the orientation, it is possible, in accordance with the present invention, to use a magnetic-resonance magnetometer to achieve detection sensitivities of the order of some which is several orders of magnitude greater than the performances of magnetic devices known from prior airborne devices.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, wherein:-Fig.1 is a schematic representation of the principle components of a submarine hydrophone buoy in

accordance with the prior art;

Fig.2 is a schematic representation of the principle components of a magnetic detection submarine buoy in accordance with the present invention; Fig.3 shows a different arrangement of the lower part of a magnetic detection buoy in accordance with the present invention; Fig.4 shows by way of example the arrangement of the principle electronic circuits disposed in the lower part of a magnetic detection buoy according to the present invention; Fig.5 is a schematic sectional view of a method of attaching the electronic case/magnetic detector unit according to one embodiment of the present invention; and Fig.6 is a schematic sectional view of another method of attaching the electronic case/magnetic detector unit according to an embodiment of the present invention.

Fig.l is a very schematic representation of the principle components of a conventional submarine hydrophone buoy. Starting from the surface of the water, this buoy comprises a float 1, in which is contained and from which emerges a VHF antenna 2. A module 3 is fixed to the lower part of the buoy and comprises systems for inflating and possibly scuttling the buoy, an electronic VHF emission system and a supply battery, for example a battery which can be activated by sea water. The module 3 is connected by a bifilar connection 4, which acts as an electric transmission and mechanical support line and which may, for example, have a length of several tens of metres to several hundreds of metres, to a hydrodynamic module 5 which stabilises an electronic case 6 and a detector 7 which are connected thereto.

The hydrodynamic system 5 comprises in particular a cable unwinder for the above-mentioned cable 4, a bjfjlar connection between the lower circuits 6 and 7 and the circuit 3 to ensure transmission of the battery supply coming from the circuit 3 towards the electronic circuits of the case 6 and the rise of measured data from the lower part to the upper part.

The hydrodynamic stabilisatiori system typically comprises an elastic cable connected to a horizontal disc for damping the pounding movements of the swell, and a vertical panel intended to reduce rotational movements.

The lower part comprises, for example, an electronic housing or case provided with panels which unfold to reduce the effect of rotational stress, an amplitude and phase modulator for electrical signals which allows all the signals to be emitted from the detector unit to the emission system 3 on the bifilar cable 4, and possibly a magnetic course detector such as a magnetic compass, which acts as a directional marker if the detector unit 7 comprises directional hydrophones. It will be noted that this system of measurement comprising a compass allows only one measurement of the magnetic course in the horizontal plane with respect to magnetic north and in general does not have a high level of precision, given that directional hydrophones themselves do not have a very high degree of precision in the azimuth.

In certain embodiments of the prior art, the

hydrophones 7 are not in one unit with the electronic case 6, but are connected thereto by elastic connections 8. Finally, a ballast means 9 establishes tension in the cables.

Such a buoy is generally designed to be dropped from an aeroplane or helicopter. To do this, it must b able to be folded up and placed in a container.

This is the reason for the provision of the cable unwinder in the hydrodynamic block 5 and the flexible connections 8 between the lower electronic case and the acoustic detector 7.

On the other hand, these conventional acoustic buoys are optimised to reduce the acoustic noise which they are capable of generating, but not to be non-magnetic.

Fig.2 is a general representation of the structure of a magnetometric buoy in accordance with the present invention. The buoy shown in Fig.2 also comprises the float 1, antenna 2, upper electronic case 3, bifilar connection 4, hydrodynamic system 5 and ballast 9 of

the acoustic system of the prior art. The main

difference between the present invention and the prior art is that these elements are optimised to be non-magnetic insofar as their material is concerned, and they are disposed so that the internal electric

currents do not generate any field in the probe.

The lower part of the present buoy includes a magnetic-resonance detector 10 such as a magnetometer of the electronic pumping type (nuclear magnetic resonance) or of the optical pumping type (electronic magnetic resonance), for example by solid laser. Such detectors are known in the art and various types of nuclear magnetic-resonance magnetometers are described, for example, in French Patent Applications 1 447 226, 2 098 624 and 2 583 887. Such an apparatus comprises at least two fluid gauges contained in flasks, the flasks being disposed in a resonant cavity excited to a very high frequency. The detector comprises windings around these flasks for taking off and reinserting a signal at a Larmor frequency defined on the one hand by the intensity of the magnetic field in which the probe is dipped and, on the other hand, by the gyromagnetic ratio of the particles or molecules of the fluids contained in the flasks possessing a spin and a magnetic moment.

Thus, a supply BF and a supply HF must be provided for the magnetic-resonance probe, wherein, in accordance with the state of the art, the supply HF must have a power of the magnitude of watts. This means that it is not acceptable for the oscillator HF to be supplied by the battery contained in the upper part 3 of the buoy, in particular because of the over-large attenuation which would be caused by the wires and because of the magnetic fields which would be caused by the circulation of an increased current in the supply wires.

Thus, in accordance with one aspect of the present invention, a supply means is provided, such as a battery, which can be energised by sea water, which means is disposed in the lower part of the buoy, for example in the electronic case 11 which also comprises the generator HF.

On the other hand, in order to have sufficient detection opportunity, the magnetic detector must have a relative sensitivity of the order of several i08.

Such a sensitivity is not currently sought within the framework of conventionally used magnetic-resonance -9-.

magnetometers. These magnetic resonance probes, which are used for example in aeroplanes or in "birds" attached to aeroplanes or helicopters, are connected to processing means in the aeroplane and are not connected to the probe itself. If it is desired to achieve a sensitivity of the order of 1o_8, a number of extremely important data should be dispatched from the probe. In order to solve this problem, in accordance with one aspect of the present invention, a high-precision frequency meter provided in the electronic case 11, is connected to a quartz stabilized oscillator, which itself has a precision of the order of O_8, and is intended to calculate the frequency of the nuclear oscillator of the magnetic resonance probe having a sensitivity which is several io8 lower and allowing minimisation of the rate of emission of the data from the magnetic field or the storage of these data, thus making it possible for transmission to be improved, or possibly made redundant.

Furthermore, while a probe of the magnetic-resonance magnetometer type is conventionally considered as being an omnidirectional sensor, if this probe is utilised to the limits of its sensitivity, that is to say with a precision of the order of several i08, it can be seen that it is advisable to carry out directionality error corrections. To do this, the present invention provides for precision measurement of the orientation of the unit 10 containing the magnetic-resonance magnetic detector.

This system for measuring the orientation, which is disposed in the case 11, comprises, for example, a triaxial magnetometer which provides the direction of

the terrestrial magnetic field with respect to the

case and, furthermore, in the case of a nuclear io magnetic-resonance magnometer, a system for measuring the direction of the field of gravity with respect to the case, comprising, for example, two inclinometers (such as potentiometric pendulums). These direction measurement sensors cannot be disposed in the unit 10 comprising the magnetic-resonance detector, in order to prevent any magnetic perturbation, and are disposed in the case 11. Consequently, it is advisable to have precise knowledge of the position of the case 11 with respect to the position of the detector unit 10. To do this, the present invention provides for connecting the case 10 to the unit 11 by rigid means.

In contrast to the State of the art as described with respect to Fig.1, in which, in order to simplify the foldable property of the buoy assembly, the connection is provided by elastic means, rigid means must be provided whilst still preserving the

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extendible nature. Some embodiments of such a system are described below with reference to Figs. 5 and 6.

Once the orientation of the probe and, possibly, its rotational speed, are known, a processing device corrects the directionality and, possibly, the effects of speed, as a function of connection factors stored prior to the immersion of the buoy.

Fig.3 shows a variant of the embodiment of the lower part of the buoy described above and illustrated in Fig.2. In this embodiment, the detector 10 is connected to a case 12 which contains only part of the elements of the case 11, in particular the means for measuring orientation. In contrast, another case 13, which is disposed between the detector unit 10 and the ballast 9, contains the supply generator HF for the probe and a battery for supplying power of the order of watts for several hours. This allows the source 1-IF and the battery of the sensor unit to be moved further away and magnetic perturbations to be avoided. In this case, the unit 12 may be supplied from the battery contained in the electronic case 3 of the upper part connected to the float 1 or from its own supply source.

By way of example of an embodiment of the present invention, Fig.4 is a schematic representation of the electronic circuits contained in the case 11 of Fig.2. This electronic case is of cylindrical shape and may comprise stabilisation vanes. Inside the case, which is supplied by a bifilar connection (not shown), there is an arrangement of printed circuit boards and electronic units, each of which fulfils the various functions, known in themselves, described above. In this arrangement:- (a) the upper board 20 may correspond to a supply; (b) the following board 21 may correspond to an electronic adaptation, emission and acquisition circuit; (c) the following board 22 may correspond to a microprocessor circuit connected to a frequency meter for calculating the Larmor frequency of the magnetic resonance oscillator precisely and possibly to effect a first numerical processing (filtering) of it, and to handle the acquisitions of the signals issued by the sensors and the transfer of these data by time multiplexing of the digitised and serialised signals; (d) the following board 23 may correspond to electronic circuits for processing the signals provided by the inclinometers; (e) the following board 24 may correspond to an electronic circuit HF for supplying the probe; (f) the following boards 25 and 26 may correspond to circuits intended for the electronic processing of signals BF from the probe (amplification, filtering);

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(g) the unit 27 may correspond to a quartz oscillator, preferably having a thermostat, which is used together with the above-mentioned frequency meter (board 22); (h) the unit 28 may correspond to a triaxial directional magnetometer which allows the orientation of the terrestrial magnetic field to be established; and (i) units 30 and 31 may correspond to inclinonieters.

Fig.5 shows an example of an expandible rigid connection between the detector unit 10 and the electronic case 11. This connection comprises a cylinder 40 made of a non-magnetic material, for example an epoxy resin reinforced by glass fibres.

This cylinder is provided with three longitudinal grooves or slots 41, 42 and 43, which are disposed at l2O'' from one another, contrary to what is shown in the drawing, in which, for reasons of simplification, two grooves are disposed diametrically, the base of the electronic case 11 comprises three splines 44, 45, 46 which engage respectively in grooves 41, 42 and 43, which have a V-shaped end. When the buoy is folded, the base of the case 11 rests on the upper surface of the detector unit 10. In the position shown, when the buoy is folded under the weight of the case 10 and the ballast 9, the splines 44, 45, 46 move into abutment against the V at the top of the grooves 41, 42, 43 and are blocked in this position by the support plates 47, 48, 49 mounted on the cylinder 40, which have a long portion having a slight inclination and a short portion having a greater inclination from the upper side to prevent the electronic case 11 descending again towards the detector unit 10. Of course, this constitutes only one example of an expandible rigid mounting; other systems, for example a column system, may be envisaged.

Fig.6 is a partial view of another embodiment of an expandible rigid connection between the detector unit 10 and the cylindrical case 11. Elements which are the same as those in Fig.l have been given the same reference numerals. Thus, Fig.6 also includes the case 11, the cylinder 40, the groove 41 and the spline 44. The spline 44 contains a piston 50 which is urged outwardly by a spring 51 so that it engages in a recess 52in the inside surface of the cylinder when said cylinder is in the open position. Fig.6 also shows means for holding the spring in its extended position, which means comprise a fusible wire 53, which is fused by a current supplied by a battery 54 when contacts 55 and 56 provided on the spline 44 and in the groove 41 of the cylinder 40 respectively come into contact.

The buoy described above comprises one single detector. In order to carry out differential measurements or target localisation, multiple-detector buoys may be used. For example, for vertical differential measurements, it would be possible to connect at least two detector/case units to one another. It would also be possible to connect at least two floats carrying probes in accordance with the invention, wherein only one of the floats carries the electronic circuits of the upper part (3) mentioned above.

Other variants of the invention will be clear to a person skilled in the art. For example, it would be possible to provide means for storing data and not sending them to the antenna until an interrogation signal is received. In the same way, various means could be used to reinforce the non-magnetic nature of the elements of the buoy.

Claims

CLAIMS1. A submarine detection buoy, comprising a float connected to antenna means, emission and supply means which are connected by way of an assembly for mechanical connection, mechanical stabilisation and electrical current connection to a non-magnetic electronic housing containing means for processing, multiplexing and measuring orientation, the housing being connected to a detector unit, which is in turn io connected mechanically to a ballast means, the detector unit comprising an omnidirectional magnetic-resonance probe, the means for measuring the orientation of the housing comprising means for measuring the three components of the terrestrial magnetic field with respect to the housing, and rigid connecting means being provided between the housing and the detector unit.
2. A buoy as claimed in claim 1, wherein the means for measuring the orientation further comprise means for measuring the orientation of gravity with respect to the housing.
3. A buoy as claimed in claim 1, wherein the rigid connecting means are extendible and non-magnetic.
4. A buoy as claimed in claim 3, wherein the extendible means comprise means mounted so as to slide with the housing means and blocking means for blocking the means which are mounted to slide in the open position.
5. A buoy as claimed in claim 1, wherein the means for measuring orientation comprise a triaxial directional magnetometer.
6. A buoy as claimed in claim 2, wherein the means for measuring the orientation comprise two inclinonieters.
7. A buoy as claimed in claim 1, wherein means for providing a signal HF for the magnetometer and means for supplying said means are disposed in a second housing disposed between the detector unit and the ballast means.
8. A buoy as claimed in claim 1, wherein the electronic case comprises high-accuracy means for measuring frequency, comprising a microprocessor and a frequency meter connected to a quartz oscillator.
9. A submarine magnetic detection buoy, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 1%Amendments to the claims have been filed as follows 1. A submarine detection buoy, comprising a float, an antenna carried by the float, emission means and an electrical supply means supported by the float, with the emission means coupled to the antenna, the emission and supply means being connected electrically and mechanically to a non-magnetic electronics case by way of a means which provides stabilization of the buoy with respect to its orientation in the water, the electronics case containing means for processing data and multiplexing such data for onward transmission via the antenna, and the case being connected by rigid means to a detector unit which comprises an * oznni-directjonal magnetic resonance probe and which is, in turn, connected mechanically to a ballast means, the electronics case also containing an orientation measuring means for measuring the orientation of the case, and thence that of the detector unit, and comprising a means for measuring the three components of the terrest�al magnetic field with respect to the case.2. A buoy as claimed in claim 1, wherein the omni-direction magnetic resonance probe is a nuclear magnetic resonance probe and the means for measuring the orientation further comprise means for measuring the orientation of gravity with respect to the electronics case. q3. A buoy as claimed in claim 1, wherein the rigid connecting means between the electronics case and the detector unit are extendible and non-magnetic.4. A buoy as claimed in claim 3, wherein the extendible means comprise an expansion unit coupled to the detector unit and adapted to slide relative to the electronics case, and a locking means for locking the expansion unit relative to the electronics case in a fully expanded condition of the extendible means.5. A buoy as claimed in claim 1, wherein the means for measuring orientation comprise a triaxia].directional magnetometer.6. A buoy as claimed in claim 2, wherein the means for measuring the orientation comprise two inclinometers.7. A buoy as claimed in claim 5, wherein means for providing a signal HF for the magnetometer and means for supplying said means are disposed in a second housing disposed between the detector unit and the ballast means.8. A buoy as claimed in claim 1, wherein the electronics case contains a high-accuracy, frequency measuring means comprising a microprocessor and a frequency meter connected to a quartz oscillator.9. A submarine magnetic detection buoy, substantially as hereinbefore described with reference to and as illustrated in Figs. 2 to 6 of the accompanring drawings.