FR2947914A1 - Wire guided torpedo combating method for boat, involves providing shape including zero directivity to radiation diagram of acoustic masking signal, and orienting zero directivity for reducing jamming of sonar of boat through buoy - Google Patents

Abstract

The method involves emitting an acoustic masking signal by using a buoy (102) of a boat (101), and providing a shape including zero directivity to a radiation diagram (105) of the acoustic masking signal. The zero directivity is oriented for reducing jamming of sonar (109) of the boat through the buoy. Emission of the acoustic masking signal is triggered when the buoy is at a distance (D) from an assembly of a linear acoustic antenna (103) and the boat such that the assembly is contained in an angular sector centered on the zero, where the sector is formed by half-lines (107, 108). An independent claim is also included for a buoy for jamming a wire guided torpedo launched against a boat.

Description

The present invention relates to methods of countermeasures that make it possible to fight against wire-guided torpedoes launched by a submarine against a ship. It also relates to the buoys that are used to implement such a method. It is known to combat the torpedoes launched by a submarine against a surface vessel to use, when these torpedoes are acoustically self-guided, jammers or lures dropped by the attacked vessel. These lures consist for example of buoys which include an acoustic transmitter for emitting in water acoustic signals similar to those of the attacked building. The torpedo is then attracted by these lures and either explodes in contact with them, or exhausts the power supply of its engine by navigating between the different lures. To cover the two techniques quite close to jamming and deception, we will use the generic term "masking". There are now new types of torpedoes that are guided from the launching submarine by a wire that runs behind the torpedo and connects it to the submarine. The submarine follows with her sonar the building to be attacked as well as the torpedo, and corrects the trajectory of this one so that it always goes towards the boat, in spite of maneuvers of this one. Obviously, in the latter case, the torpedo decoy system no longer allows to divert it directly from its purpose because the submarine has significant processing means, to discriminate the boat from these lures. One solution would then be to use sonobuoys that are particularly designed to directly jam the submarine's sonar (s). To obtain the best efficiency of such a jammer, it is attempted to drop it into the sea so that it is placed between the boat and the submarine to mask the signals coming from the boat by those coming from the decoy. . For this it is better to know, at least approximately, the position of the submarine. This position can be determined using sonars of the boat, mainly with hull sonars, and possibly with passive towed sonars, such as linear antenna for example, when the submarine is quite "noisy". In fact, most often the boat spots the presence of the submarine by first detecting the arrival of the torpedo with its passive sonars and then tries to locate it using (as little as possible for reasons of discretion) his sonar assets.

It is clear that in this case the decoys will scramble sonars as well as those of the submarine, which decreases the efficiency of the system. To overcome this drawback, the invention proposes a wire-guided anti-torpedo countermeasure method for a boat, of the type consisting in dropping a buoy for emitting an acoustic masking signal, mainly characterized in that the Radiation diagram of this masking signal a shape having at least one directional zero and that this zero is oriented to reduce the jamming of sonars of the boat by the buoy.

According to another characteristic, the radiation pattern is in the form of a cardioid. According to another characteristic, the boat tows a linear acoustic antenna and the emission of the acoustic signal of the masking is triggered when the buoy is sufficiently far away from the boat / linear acoustic antenna assembly so that this assembly is contained inside the boat. an angular sector centered on the directivity zero and in which the intensity of the masking signal is sufficiently reduced so as not to hinder the reception of the other signals by the boat and the linear acoustic antenna.

According to another characteristic, it triggers the emission with a reduced intensity of the masking acoustic signal during the dropping of the buoy and that it controls the increase of this intensity as the buoy moves away from the boat . According to another characteristic, the orientation of the radiation pattern is controlled remotely from the boat.

According to another characteristic, this remote control is done by transmission to the buoy of the field of this buoy relative to the boat and the magnetic north and by detecting the orientation of the buoy relative to the magnetic north with the help of a compass included in this buoy. According to another characteristic, this control of the orientation of the radiation pattern is effected by initial control of a complete rotation of this diagram, by detecting the orientation of the latter when the level of reception of the masking signal by the boat is minimal and frozing the orientation on that corresponding to this minimum level. According to another characteristic, it is also ordered to start and possibly stop the emission of the masking signal from the boat.

According to another characteristic, it also controls from the boat the acoustic emission level of the masking signal. According to another characteristic, the control of the shape of the diagram is furthermore controlled from the boat. According to another characteristic, the temporal and frequency characteristics of the masking signal are also controlled from the boat. According to another characteristic, the noise radiated by the boat is received on board the buoy and the acoustic signal of the masking is modified so that it resembles that emitted by the boat, thereby giving the buoy the characteristics of deception. . According to another characteristic, a copy of the masking acoustic signal emitted by the buoy is also produced and this copy is used to process the sonar reception signals of the boat in order to eliminate in these reception signals the influence of the acoustic masking signal. 30 issued by the buoy. According to another characteristic, it emits masking signals adapted to the sonar of a submarine for wire guide the torpedo to decoy. The invention further proposes a buoy for the implementation of this method, mainly characterized in that it comprises a body suspended by a rope to a float, an antenna located on the float to receive the radio control signals from of the boat, means for generating the electrical signals representing the masking signal and control signals for the orientation of the radiation pattern, and at least one antenna for transmitting the masking acoustic signals under the control of the electrical signals representing them, wherein the antenna comprises three sets of acoustic transducers located at the top of an equilateral triangle and wherein the control signals of the orientation of the radiation pattern make it possible to apply the electrical signals to the transducers with delays determining twelve separate directions for the directivity zero; these twelve directions corresponding to the three sides and to the three heights of the triangle each taken in both directions.

According to another characteristic, the body further comprises fins forming an anti-gyratory system for stabilizing the orientation of the directivity zero in a bearing. Other features and advantages of the invention will become clear in the following description, given by way of non-limiting example with reference to the appended figures which represent: FIG. 1: the schematic diagram of the protection of the boat against signals jamming the buoy; - Figure 2: a schematic sectional view of a jamming buoy; FIG. 3 is a schematic perspective view of the transducers of the acoustic antenna of the buoy; FIG. 4 is a diagrammatic top plan view of these same transducers; and FIG. 5 is a diagram of the electronic orientation members of the acoustic emission cardioid. According to the invention, when the boat chased by a submarine detects with its sonar the firing of a torpedo directed against it, it throws into the sea in the direction of the submarine an interfering buoy designed in such a way that it scrambles the sonars of the submarine without disturbing those of the boat. For this, and taking into account the usual characteristics of the different sonars used by the boats and the submarines, the emission diagram of this buoy will present a zero of directivity which will be maintained directed towards the boat. Given the current specifications of the various acoustic systems of the submarines, this zero directivity will preferably be in a frequency band of at least two octaves typically ranging between 1 and 10 kHz, the angular sector of the lobe corresponding to this zero will have an opening of about 40 and the attenuation will be at least -20 dB inside this lobe. FIG. 1 schematically represents the respective situations of the buoy, the boat and the linear acoustic antenna that it is towing. The boat 101 therefore tows at the end of a cable 102 a linear acoustic antenna 103 and the assembly remains substantially aligned on a straight line when the boat does not maneuver. The jamming buoy 104 which was dropped by the boat 101 is located at a distance D on a perpendicular to this trajectory of the boat. This buoy emits acoustic scrambling signals intended to disturb the sonars of the submarine (not shown) which launched the torpedo, itself not shown. The emission diagram 105 of these signals has a zero of directivity corresponding to a hole 106 whose attenuation at 20 dB is delimited by the half-lines 107 and 108. The buoy 104 comprises means which make it possible to orient this zero towards the direction of the boat assembly 101 / linear acoustic antenna 103, such that this assembly is included in the sector delimited by the half-lines 107 and 108.

In fact, in addition to the acoustic linear antenna 103, the boat 101 often comprises one or more sonars represented in the figure by the circle 109 and it is desirable that the buoy not interfere with the linear acoustic antenna or sonars of the boat. This respective position of course depends on the distance D away from the buoy and its position relative to the median between the front end of the boat and the rear end of the linear acoustic antenna. Indeed, the position shown in the figure is a special case where the buoy is substantially on the median, but this position evolves course depending on the movements of the boat, which tends to maneuver to avoid the torpedo. The means which make it possible to orient the zero 106 thus take into account these respective positions. Moreover, in a first variant, the buoy is started up only when it is sufficiently far from the boat, so that the boat assembly plus linear acoustic antenna is well understood in the angular sector 1071108, which can take a some time depending on the method of launching the buoy, that it was thrown simply overboard or that it was propelled remotely by auxiliary means such as a rocket.

In a second variant, the buoy is started from its release, with a reduced acoustic emission level so as not to disturb the sonars of the boat too much. This level of emission is gradually increased as the buoy moves away from the boat. The buoy as shown diagrammatically in FIG. 2 comprises a body 201 suspended by a rope 202 from a float 203. This float itself supports an antenna 204 which makes it possible to transmit to the buoy via the rope 202 information received. electromagnetically from the boat 101. The body of the buoy is composed of a resistant portion 205 which comprises a power supply unit 206 and a set of electronic members 207. This portion 205 is surmounted by a portion 208 of material acoustically transparent. Inside this part 208 are fixed acoustic emission antennas 209 and 210 which bathe in a neutral and insulating liquid to maintain the compartment in equipression The assembly is surmounted by an anti-giratory system 211, formed here pallets, which prevents the body 201 to rotate on its vertical axis, or at least not to perform such a rotational movement at a sufficiently low speed that can be taken into account and compensated by the processing members transmission signals. The rope 202 maintains the body of the buoy at a suitable immersion for luring the submarine in a known manner. When the buoy is released, the power unit 206 is activated, for example under the effect of the sea water that fills, a battery specially adapted for this purpose. The electronic circuits 207 then listen for the radio signals received by the antenna 204, and, in the case where the first variant mentioned above is used, when the buoy is sufficiently far from the boat, the An operator located on the boat who appreciates this distance transmits by radio a command to activate the acoustic transmitters contained in the buoy. This procedure can optionally be implemented automatically. The acoustic signals thus emitted are in particular received by the sonars of the boat 101. Until then there is no reason for the buoy to be exactly oriented so that the propagation trough is directed in the right direction. In addition, the level of attenuation obtained in this hollow is sufficient not to interfere with sonars son of the boat, but it remains nevertheless high enough for these signals are clearly received by them. These signals being studied to scramble the sonars of the submarine nevertheless have characteristics that are known in the boat, which allows to locate with sufficient accuracy the location of the buoy when it begins to emit. If necessary, still in the context of the first variant, if the distance is not sufficient the operator can emit a signal for stopping the acoustic emission and resume it after a sufficient time for the distance between the boat and the buoy has reached a suitable value. The relative locations of the boat and the buoy relative to each other being thus determined, it is easy from the means of navigation of the boat, the compass for example, to determine the orientation to be given to the diagram. transmission 105 of the buoy so that the entire boat 101 / towed linear acoustic antenna 103 is contained in the attenuation lobe of this diagram determined by the half-lines 107 and 108, according to Figure 1.

This orientation is then communicated to the buoy, still by radio, via the antenna 204, either via an operator, or by automatic means. The buoy itself comprises means for determining its orientation in space, a terrestrial induction compass for example, and the knowledge of this orientation and the orientation to be given to the pit of the directivity diagram allows a simple way of determining the rotation to be made to this directivity diagram so that it takes the necessary orientation not to interfere with the sonar of the boat 101. This rotation being thus determined, it is communicated to the means which make it possible to orient the diagram of acoustic emission and whose operation provides the desired effect. The system a priori the simplest would be to provide a motor for orienting the antennas 209 and 210. However such a system would be fragile and relatively expensive. Insofar as this orientation requires only a relatively small precision, the invention proposes to use, preferably, an electronic switching system of the transducer elements of the antenna to thereby electronically orient the directivity diagram thereof. . It could thus be for special needs, instead of trying to put the towed linear boat / antenna assembly in the attenuation area of the radiation pattern, more specifically orienting the precise direction of the attenuation hole to the sonar 109 of the beam. or to the towed acoustic linear antenna 103, deliberately sacrificing interference attenuation to the other detection system.

On the other hand the characteristics of the acoustic signal emitted by the buoy can be modified on command of the operator located on the boat so as to improve the jamming. This improvement can be done in different ways, for example by changing the orientation of the emission diagram with respect to the best position not to interfere with the sonars of the boat, or by controlling the modification in both amplitude and frequency of the transmitted signal, to best adapt it to the sonars of the submarine to maximize the effect of jamming. Finally, since the characteristics of the jamming signal are known as described above, the invention also proposes to improve the efficiency of the reduction of jamming of the sonars of the boat by using means making it possible to subtract those signals electronically. interfering with sonar reception signals from the boat. In these ways the effect of jamming of the boat, which is never totally nil as discussed above, is best reduced.

The essential elements of the jammer contained in the buoy are therefore on the one hand the emission antenna acoustic interference signals, and secondly the means of controlling the zero directivity to the desired direction.

With regard to the transmitting antenna, the invention proposes, as shown in FIG. 4, to use triplets of acoustic transmitters 401, 402, 403 located at the three vertices of an equilateral triangle. This arrangement makes it possible to obtain, by supplying these emitters with properly phase-shifted or delayed signals, any desired transmission direction, but to make it simpler and taking advantage of the fact that the attenuation lobe is wide enough, the The invention proposes to limit itself to twelve emission diagrams in the form of cardioids, the propagation zeros of which are located in twelve different directions each spaced 30 ° apart. Six of these cardioids are formed by feeding the three emitters in known manner by signals suitably offset in time. The zeros of these cardioids are then located in the directions corresponding to the heights of the triangle formed by these emitters, ie in FIG. 4 the six directions ranging from 1.2 - 3 to 2-3, 1. The figures in FIG. In FIG. 4, the bold numbers correspond to the numbers of the in-phase transmitters, and the lean digits to the numbers of the transmitters whose signal is delayed compared with that of the transmitters in phase. The other six cardioids are formed by feeding there also by signals properly out of phase or shifted the transmitters two by two, the third transmitter is not powered. The zeros of the obtained cardioids are then located in directions corresponding to the sides of the triangle, ie in FIG. 4 the directions ranging from 1-3 to 2-3. For this purpose, for example, a device similar to that shown diagrammatically in FIG. 5 is used in which the signal S (t) is transmitted directly to one of the transducers, after digital-to-analog conversion in a converter 501 and amplification of power in a stage 502. This same signal S (t) is shifted by a duration equal to T1 or T2 in a shift device 503, then converted into analog, shifted by a value of 7t in a phase-shifter 504, and finally transmitted, after amplification in the power stage, either to the other two transducers of the triplet, or to only one of these two other transducers. The values of these delays obtained by offset are equal for the pairwise operation at Ti = d / c, and for triplet operation at T2 = d / c. cosine (71/6). In these formulas, d is the distance between two consecutive transducers and c is the speed of sound in the water. However, to obtain a cardioid in a band of 70 frequencies ranging from f1 to f2, the distance d between the phase centers of the transducers used must not exceed half the wavelength (2./2 ) at the highest frequency f2. However, to avoid obtaining "image" zeros in the diagram, the invention proposes to limit d to a value equal to a14. Under these conditions, in order to be able to cover a sufficient frequency band, it is necessary to use several triplets of transmitters each optimized for a more restricted frequency band than the total band. This arrangement also makes it possible to minimize the size of the diameter of the body of the buoy. Thus, to cover the three octaves extending from 1 kHz to 9 kHz, a first triplet 401, 402, 403 will be used to cover the 1 kHz / 3 kHz band, and a second smaller triplet 411, 412, 413 may be used. cover the 3 kHz / 9 kHz band. These triplets will preferably be placed one above the other so as not to interfere acoustically and to take up a minimum of room in the buoy body, as shown in FIG. 3. As described above, The control of the zero direction of the cardioid can be achieved in the most efficient manner by sending to the buoy by the radio channel information on its bearing relative to the ship and with respect to the magnetic north, which therefore gives directly the location of the boat relative to the buoy and relative to the magnetic north. By bringing these indications closer to those of a compass contained in the buoy and which itself gives the direction of the magnetic north, we thus obtain the direction to give to the zero of the cardioid, which makes it possible to choose among the twelve directions possible that which is closest to the direction thus determined and thus select, for example from a table contained in a memory, the different delays to be applied to the signals emitted by the transducers of the antenna.

This servo therefore operates in open loop. Embedding a compass in a buoy may however have some disadvantages in terms of complication and cost of this buoy. According to a variant, the invention therefore proposes to operate in a closed loop the control of the direction of the hollow of the cardioid.

For this purpose at the beginning of the operations the system contained in the boat controls by radio a complete rotation of the cardioid emission according to the twelve successive directions. The reception sonar (s) of the boat then detect the signals emitted by the buoy, if necessary by controlling the emission of a specific code, and the reception level is memorized for each of the directions. At the end of this phase, the system selects the direction corresponding to the lowest reception level, that is to say in fact at the best orientation of the zero of the cardioid. It then transmits to the buoy a command to select this direction for further operations. As seen above, the buoy is provided with hydrodynamic means that allow it in principle not to rotate around its axis of rotation, except perhaps for a very slow drift. Under these conditions the direction thus selected can be used for a long enough time, and if the drift becomes too large, taking into account in particular changes in the boat, the system will transmit, when the level of reception of the jamming signal has crossed a determined threshold, an order of change of the direction of zero of the cardioid. As the evolutions are slow, the determination of the next direction to be used can be carried out by successive approximations by successively testing the reception levels on the two directions which frame that which was previously chosen. Most often one of these two directions corresponds to an increase in the level of reception and the other to a decrease, and then one will choose of course that corresponding to a decrease. If, however, the level of reception increases for both directions, it is not necessary to make a change. In addition, given that the evolutions of the boat should be preponderant compared to changes in the orientation of the buoy, and that the respective positions of the boat and the buoy are known with a certain accuracy, it is also possible to use a likelihood and continuity criterion making it possible to directly obtain the most probable direction, or even to make a switch a priori while knowing substantially the evolution of the buoy's field relative to the ship. In the above description, the case of a radio link between the boat and the buoy has been provided, which has the advantage of being able to transmit the control signals for a very short time, making it possible to limit the risks of detection as much as possible. The invention extends, however, to the case where these control signals are transmitted acoustically, which may be useful in certain cases, for example in the case where the ship to be protected is a submarine which can hardly use the radio channel. The messages transmitted from the boat to the buoy are not necessarily limited to the orientation of the jamming cardioid, but may also include other control signals such as an on-off signal acoustic emission, possibly a shape control of the emission diagram allowing in particular a finer orientation than the twelve directions 25 seen above, and possibly an emitted acoustic signal type control allowing for example the choice of operation between jamming and decoy. In order to adjust the shape of the radiation pattern, which may be useful in the case for example where the location of the submarine to be jammed with sufficient precision is known, it is possible to predict, in known manner, other values of delays and phase shifts than those described above for the signals emitted by the transducers of the transmitting antenna, which also allows the fine orientation of the second variant embodiment.

These values will then for example be listed in a table stored in the buoy's electronic system and whose addresses will be selected from the control signals received. Methods for modulating a transmission pattern from certain delay and phase values of elementary signals are well known in the art. To modify the type of acoustic signal, which may be useful in the case where it has been possible to determine the characteristics of the acoustic receivers to be jammed in the submarine, or if it is found that the interference is ineffective for example, because it does not affect the behavior of the torpedo to be deflected, it is possible, for example, to use signal characteristics recorded in a memory. These characteristics can be directly a noise recorded in this memory, or parameters such as the level and / or the frequency making it possible to vary the emission obtained from a noise generator and to choose between the deception and the jamming. Alternatively, the invention also proposes to provide the buoy means for receiving acoustic signals, a hydrophone for example, which can be advantageously directed towards the boat to protect. In this way it is possible to receive the noise radiated by this boat and to modify the noise emitted by the buoy so that these characteristics correspond as exactly as possible to those of the noise of the boat. The simplest is to amplify the noise thus received and re-emit it with sufficient power to cover the direct noise emitted from the boat. It is also possible to receive the sound of the boat on the acoustic antenna towed by it and retransmit this signal to the buoy by the radio link. This characteristic, combined with the fact that the buoy is in principle interposed between the boat and the submarine to scramble, allows to decoy the latter effectively. The buoy then behaves not only as a jammer but as a decoy. Finally, as already mentioned above, another important improvement is to develop on board the boat to protect, upstream of electronic processing performed, a copy of the signal emitted by the jammer. By carrying out a subtraction (in the broadest sense) of this copy of the sonar track signals of this boat, it is thus possible to very effectively reject the jamming noise emitted by the buoy and which is nevertheless received by the boat despite the orientation of the boat. zero of the cardioid.

Claims (16)

REVENDICATIONS1. A wire-guided anti-torpedo counter-measurement method for a boat (101), of the type consisting in dropping a buoy (102) making it possible to emit an acoustic masking signal, characterized in that the radiation diagram (105) is given ) of this masking signal a shape having at least one directional zero (106) and that this zero is oriented to reduce the jamming sonars (109) of the boat by the buoy. 2. Method according to claim 1, characterized in that the radiation pattern (105) is shaped cardioid. 3. Method according to any one of claims 1 and 2, wherein the boat (101) tows a linear acoustic antenna (103), characterized in that it triggers the emission of the acoustic signal masking when the buoy ( 102) is sufficiently far away (D) from the boat / linear acoustic antenna assembly (101, 103) for this assembly to be contained within an angular sector (107, 108) centered on the directivity zero (106) and wherein the intensity of the masking signal is sufficiently reduced so as not to impede the reception of the other signals by the boat and the linear acoustic antenna. 4. Method according to any one of claims 1 and 2, characterized in that it initiates the emission with a reduced intensity of the masking acoustic signal during the dropping of the buoy and that one controls the increase of this intensity as the buoy moves away from the boat. 5. Method according to any one of claims 1 to 4, characterized in that the orientation of the radiation pattern (105) is controlled remotely from the boat (101). 6. Method according to claim 5, characterized in that this remote control is by transmission to the buoy (102) of the deposit 35 of the buoy relative to the boat and the magnetic north and by detecting the orientation of the buoy by magnetic north ratio using a compass included in this buoy. 7. Method according to claim 6, characterized in that this control of the orientation of the radiation pattern (105) is effected by initial control of a complete rotation of this diagram, by detecting the orientation thereof. when the level of reception of the masking signal by the boat (101) is minimal and by setting the orientation to that corresponding to this minimum level. 8. Method according to any one of claims 5 to 7, characterized in that it also controls the start and possibly the stopping of the emission of the masking signal from the boat (101). 9. Method according to any one of claims 5 to 8, characterized in that it also controls from the boat (101) the acoustic emission level of the masking signal. 20 10. Method according to any one of claims 5 to 9, characterized in that it also controls from the boat (101) the setting of the shape of the diagram. 11. Method according to any one of claims 5 to 10, characterized in that one further controls from the boat (101) the time and frequency characteristics of the masking signal. 12. Method according to any one of claims 1 to 11, characterized in that the noise radiated by the boat (101) is received on board the buoy (102) and that the acoustic signal of the boat is modified. masking so that it looks like the one emitted by the boat, thus giving the buoy lure characteristics. 13. Method according to any one of claims 1 to 12, characterized in that a copy of the masking acoustic signal emitted by the buoy (102) is also produced and that this copy is used to process the signals. receiving the sonars (109, 103) of the boat (101) to eliminate in these reception signals the influence of the acoustic signal masking emitted by the buoy. 14. A method according to any one of claims 1 to 13, characterized in that one transmits masking signals adapted to the sonars of a submarine for wire guide the torpedo to decoy. 10 15. Buoy for implementing the method according to any one of claims 1 to 14, characterized in that it comprises a body (201) suspended by a rope (202) to a float (203), an antenna ( 204) on the float for receiving the radio control signals from the boat (101), means (207) for generating electrical signals representing the masking signal and control signals for the orientation of the radiation pattern, and at least one antenna (209, 210) for transmitting the acoustic masking signals under the control of the electrical signals representing them, wherein the antenna comprises three sets of acoustic transducers (401, 403) located at the top of a triangle equilateral and in which the control signals of the orientation of the radiation pattern make it possible to apply the electrical signals to the transducers with delays making it possible to determine twelve distinct directions for the directivity zero (106); these twelve directions corresponding to the three sides and to the three heights of the triangle each taken in both directions. 16. Buoy according to claim 15, characterized in that the body (201) further comprises fins (211) forming an anti-gravitational system for stabilizing the orientation of the directivity zero. 30