FR2804215A1 - Geographic acoustic transmitter search/positioning system includes position measuring acoustic receiver time scale references using allowing incidence timing and recorder/ remote operation output - Google Patents

Abstract

The search and positioning of acoustic transmitter system has an acoustic source in the sea. The system has a processing section and position measuring (19) section with an acoustic receiver (11-15) receiving transmitted signals from immersed objects in time scale references (18) allowing timing of acoustic signal incidence. There is a recorder (45) or remote transmission of the output signals. An Independent claim is also included for search and geographic positioning method.

Description

 METHOD AND DEVICE FOR SEARCHING AND LOCATING IRREGULAR OBJECTS SUCH AS BLACK AIRCRAFT BOXES <I> 9. The present invention relates to a method and a device for searching and locating in geographical coordinates of one or more objects equipped with acoustic transmitters underwater and resting on the sea floor. Applies in many areas, including the location of objects such as flight recorders damaged aircraft at sea, submerged munitions, containers loaded with dangerous substances lost at sea, ...

<I> 2. TECHNICAL FIELD The technical field of the invention is that of the immersed object search means using ultrasonic waves.

3. State of the Art- <I> Disadvantages - Limitations </ I> Various systems for searching and locating an underwater object, which use acoustic signals in particular, are already known.

A first solution exploits images of the seabed as made using a side sonar towed by a ship. This method, although it allows the localization of submarine forms and obstacles, is not exploitable for the localization of an acoustic source which alone makes it possible to identify the object to be searched among a multitude of echoes.

A second solution is described in US 5,570,323 A which presents a navigation device for a submarine plunger allowing it to join an acoustic transmitter operating in interrogation / response mode. Datasonics, Cataumet, Massachusetts, USA, manufactures equipment for the same purpose; but purely directional, such as the portable equipment for diver bearing the reference DPL-275. These materials, if they prove of a precious help during the recovery phase of the immersed object, do not allow the research on a large extent, nor the location in geographical coordinates. The result is sometimes lengthy and perilous operations for the human lives of the teams involved in the mission of recovery of the aforementioned objects.

Finally, in special circumstances, it may be necessary to use means normally reserved for military use. In many circumstances, the detection or classification sonar of a mine hunter is used. In similar circumstances, the Canadian Navy was forced to use, in early September 1998, the passive sonar of an inhabited submarine to search for flight recorders of an aircraft lost at sea south of Halifax. This heavy means, if it allows the search, does not allow, with the necessary precision, the localization in absolute geographical coordinates of the searched object (s). <I> 4. Problem </ I> posed Generally speaking, the problem posed consists in allowing the search and location in geographical coordinates of one or more acoustic transmitters, having a time base, not necessarily stabilized, nor synchronous with that of acoustic receivers. On an operational level, the means used must be easy and quick to implement over a vast extent sometimes difficult to access. They must be compatible with all kinds of research methods used (ships, helicopters, maritime patrol aircraft, submarine robots, ...) and if possible inexpensive.

The invention particularly relates to a device and a method providing a solution to this problem.

5. The device according to the invention.

The device for searching and locating one or more immersed objects placed on the bottom and transmitting acoustic signals according to the invention is remarkable in that it comprises at least, on the one hand, a treatment station and, on the other hand, measuring equipment provided with at least one means enabling its location, for example in three-dimensional geographic coordinates, of an acoustic receiver compatible with the signals emitted by said immersed object or objects, of a reference of time scale for dating the instants of detection of acoustic signals and a means of recording or remote transmission. According to another characteristic arrangement of the device of the invention, said processing means is programmed to exploit said information in order to enable the location of the transmitter or emitters of said objects immersed in geographical coordinates on the basis of the information from the measurement equipment or devices. .

According to another characteristic arrangement, the device of the invention may be supplemented by auxiliary measuring equipment, placed at the bottom of the sea or surface-stabilized, comprising an acoustic receiver, a time scale reference and a recording means. or teletransmission.

6. The process according to the invention

This method of searching and locating immersed acoustic sources is notably remarkable in that it comprises the following operations: One or more measuring equipment of the device of the invention is deployed on the search area from an air or naval means such as a maritime patrol aircraft, a helicopter, a ship, a submarine inhabited or not, so that, carried by the current, the wind, the tide, the equipment drifts while covering as much as possible the search zone (alternatively, in the absence of natural drift movement, the measurement equipment can be towed or self-propelled) - At least one memory is stored for transmission to the treatment station, at least the instants of detection of the acoustic signals and the position information of said equipment, - is collected at the level of the processing means of the device of the invention, the information s previously memorized, - The information thus acquired is processed in order to determine the position or positions of the sources of acoustic emissions.

In cases where only one measuring equipment would be used, a method of treatment is described below. A mathematical resolution of the problem posed: namely, the calculation of the coordinates in latitude and longitude of the emitters, becomes possible from then on, that for each of them, it was possible to determine - the own recurrence of emission of its acoustic signals with great precision, if the latter is stable, or failing that, the time between each emission by using the auxiliary measuring equipment.

- The time offset of the time base specific to each transmitter with respect to the time base of the receivers located in the measuring equipment.

With regard to the recurrence of emissions, a first method consists in holding a buoy equipped with measurement equipment in an acoustic signal reception zone. The time differences separating the instants of reception of the acoustic signals then measure, without error and directly, the recurrence of the submarine transmitters. Alternatively, it is possible to overcome this constraint by an analytical method using a series of measurements.

The proposed technique allows a discrimination in the reception of the signals coming from the different emitters, even if they transmit at the same frequency, since the duration of the acoustic emissions is generally short compared with the recurrences of the emissions. It follows a high probability of non-recovery spatio-temporal pulses. The detection instants evolve almost continuously as a function of the drift of the measuring equipment, it will be easy to isolate areas of non-recovery of the signals and consequently of certain identification of their origin.

Assuming that only one measuring equipment is used, consider the triplets (Xi, j, Yi, j, Ti, j) corresponding to the position and the date of reception of an acoustic signal from the transmitter " J ".

If we call Rj the recurrence of the emissions of the transmitter "j" and Dj, its clock offset, the emission times are given by the formula Emi, i = njxRj + Dj In which "nj" represents the number of emission of the source with respect to a reference time. Since the range of the transmitters is generally less than 1500 m, the signals will be detected at most within one second of their emission. It is therefore easy to associate a reception instant with a given transmission.

The buoy-emitter distance is then given by the formula Distancei, j = (Ti, j-Emi, i) x (sound speed in the water), considering that the object to be located is placed on the bottom, its Z immersion, can be considered equal to the value given by the reading of the probes on a nautical chart of the zone; It can be refined as soon as a first position of the source has been given.

The Oblique distances Equipment-Object, Doi, j, can be reduced to the horizontal, Dhi, j, by application of the theorem of Pythagoras (Dhi, j2 = Do;, j2 - z2).

For a set of "i" triplets, (Xi, j, Yi, j, Ti, j), the computation of the XY coordinates of the source is carried out by any method (eg: iterative method of "Least Squares" type ). For example, we search for the pair of coordinates (Xo-Yo) which minimizes the expression Sigma = (Distance, measured j - Distance, calculated j) 2 The summation being extended to a set of measuring points.

Sigma is then calculated for different values of clock shift Dj, over a range framing predictable variations in the recurrence of emissions.

The desired offset value, Dj, is the value that minimizes Sigma. At this minimum also corresponds the desired pair Xo-Yo.

In the case where several measuring equipment would be used simultaneously, the applicable location calculations would be so-called hyperbolic or pseudo-circular algorithms. They are based on the minimization of a cost function by an iterative numerical method known as the gradient. The purpose of the auxiliary measuring equipment is to reduce the number of unknowns per transmitter at 3: X, Y and the transmitter's clock offset at a given time in relation to the time reference used in the equipment of the transmitter. measurement, this reference being able, for example, to be the absolute GPS time. <I> 7. <I> Innovative Solution <i> and Benefits. </ I>

The result of the aforementioned provisions, is a new method and a new device for searching and locating one or more immersed objects using one or more measuring equipment and a processing station. The main features of the invention relate to # The architecture of the system, composed of a processing station and measuring equipment, as defined above, and its implementation method, # The choice and the nature of the electronic modules implanted in the measurement equipment or its external environment, # the choice of the information acquired therein and possibly stored, # the device implementation conditions, # the digital techniques implemented at the processing station.

Of these characteristics, the following advantages of the device and the method of the invention are apparent compared to the known systems # They allow the search over a large area, # They do not require the intervention of divers, # They locate the or acoustic sources in absolute geographic coordinates with great precision, # The fact of having precise absolute coordinates allows the eventual recovery of the objects thus localized by simplified independent means, easy to implement and in a very short time.

In addition, # The device can be deployed quickly on the search area by any airborne or naval means, # II makes it possible to locate objects immersed in spaces not accessible from the surface with light equipment, easy to implement for years. small launchers.

Another advantage of the invention is related to the fact that the measuring equipment, if it is for example a buoy or a free underwater vehicle, has an excellent signal-to-noise ratio. This would not be the case of a means deployed from a ship (propeller noise, cavitation, ...). This results in increased detection distances.

In addition, since the acoustic detection system is completely passive (without emission), it does not interfere with other research operations using other acoustic means (lateral sonars, ...).

Similarly, if the search area is particularly large, an almost unlimited number of measurement devices can be deployed, allowing faster relocation. Finally, measurement equipment may be retrieved for redeployment to a particular area of interest; in particular in order to refine the measures.

8. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, and advantages will become more apparent from the following description and accompanying drawings in which - Figure 1 is a schematic view illustrating a search area.

FIG. 2 is a schematic view showing the search technique used in the method of the invention.

FIG. 3 is a schematic view of an exemplary configuration of a measuring equipment.

FIG. 4 is a schematic view of an exemplary conformation of a treatment station.

FIG. 5 is a synoptic view of a first exemplary embodiment of a measuring equipment.

FIG. 6 is a diagrammatic view illustrating a first example of implementation of the device and the method of location by free gear (surface reference).

- Figure 7 is a schematic view showing a measuring equipment consisting of a buoy drifting in front of the desired transmitter.

FIG. 8 is a schematic view showing an example of tracing the detection instants as a function of time. FIG. 9 is a diagrammatic view illustrating another example of implementation of the device and method of location by free machine (reference background).

- Figure 10 is a synoptic view of a second measuring equipment, intended to be installed on an underwater vehicle.

FIG. 11 is a synoptic view of an exemplary configuration of an auxiliary measurement equipment.

Reference is made to the said drawings to describe interesting examples, although not limiting, of embodiment of the device and implementation of the method of the invention.

9. Description of a preferred embodiment of the device of the invention. According to a preferred embodiment of the invention, the measuring equipment or each measurement equipment consists of a drifting buoy, 7 (FIG. 3) in which the locating device is a GPS satellite receiver 19 (FIG. 5). preferably operating in differential mode, the acoustic receiver consists of a pre-amplification circuit 12 of a hydrophone signal 11, a narrow-band filter 13, an integrator circuit 14 and a circuit 15. The clock signal used is the clock signal 18 delivered at 1 Hz by the GPS receiver card 19. This signal is delivered with an absolute precision of 10 -6 seconds The line or link 16 is used to freeze a counting register 17 whose content is transferred by a link 26 to a central unit 21. An output 23 of the central unit is used by a radio transceiver 22 to transmit to the processing station 8 (FIG. From the measurement equipment in particular, the position data from the line 25 and the times of reception of the acoustic signals referenced to the clock signal 18 from the GPS receiver. Alternatively, this information can be saved in the memory 45. Differential correction messages received by radio are retransmitted to the GPS receiver using the links 20 and 24.

A radio transceiver 22 makes it possible to transmit the position of the buoy and the instants of detection on the buoy of the signals coming from the acoustic emitter (s) 33 integral with the desired objects 2, towards a heading 3.

On board the star (FIG. 4) is the processing station 8. The radio modem or teletransmitter 9 (FIG. 4) makes it possible to receive messages from buoys for recording and processing. A mass storage medium reader 10 makes it possible to reread the information that would have been stored on board the buoy or buoys.

Figure 7 shows a drifting buoy 39 traveling in front of the desired transmitter 33 resting on the seabed in a path 37. The circle 38 indicates the practical range of detection by the buoy of the desired transmitter. The detection times of the drifting buoy emissions, reduced to one-second cycles, are represented by the trace 40 of FIG.

It is conceivable that the measuring equipment consists of a drifting surface material, that is to say, animated by a natural movement of drift due to sea currents, wind or tide; it can also, if necessary, in the absence of such a movement, be towed, anchored or self-propelled.

The measuring equipment may be a free underwater or wired subsea gear, as indicated below.

Auxiliary measuring equipment whose mimic is shown in Figure 11, can be placed on the seabed and located at a distance of detection of the desired transmitter. It allows the memorization 45 of the detection instants of the signals coming from the desired acoustic emitter or emitters. This auxiliary measurement equipment comprises a hydrophone 11, a preamplifier 12, a filter 13, an integrator 14, a detector 15, a clock 44, a central unit 21 and a memory 45.

10. First Particular Embodiment - Case of an Underwater Vehicle According to a particular embodiment (FIG. 6) intended to locate emitters in the deep sea, since the buoys on the surface are no longer able to detect the signals from the searched transmitter or emitters, a free or wired device 27 is used to intercept the acoustic signals from the transmitters within range of the latter. Buoys 28, 29, 30 are used to locate and guide the craft during navigation. The heading 31 receives the messages transmitted by the locator buoys of the underwater vehicle, themselves positioned by receiving the signals received from the positioning satellites 32. A time reference 34 on board the craft is used to dating of the moments of reception of the acoustic signals coming from the searched transmitters 33. The reference of time 34 is set on a standard clock serving as reference to the whole system, either before the immersion of the machine, or during its recovery. Auxiliary equipment 35 is deposited on the bottom remote detection of signals emitted by the object to be relocated. It is used to determine the time between the transmissions of signals from the searched objects.

Figure 10 shows a block diagram of the on-board measurement equipment aboard the underwater vehicle. Equipment 43 allows the location of the machine in a landmark. An acoustic modem 42 makes it possible to signal to the surface that the vehicle detects or not the desired acoustic transmitters. The clock 44 is set to a standard clock, that of the time reference of the GPS for example, and is used to date the instants of detection of the signals from the transmitters to locate.

Alternatively to a locating means using buoys located on the surface, Figure 9 shows a locating means using tags 41 located at the bottom of the sea.

11. Second Particular Embodiment - Use of Communication Satellites Alternatively, to the radio modem fitted to the measurement buoys, it is possible to use low-orbiting satellite communication means, such as ORBCOMM or IRIDIUM, in order to transmit to a large extent. distance the information emitted by the buoys 28; and this without maintaining airborne or naval means on the area.

In this case, the teletransmission equipment between the measuring equipment and the treatment station uses a communication satellite.

12. Third Particular Embodiment-Use of a Digital Detector Alternatively to the use of an analog signal 13, 14, 15, the detection means could be constituted by the combination of a digital analog converter and a digital signal processing circuit (DSP).

In this case, the acoustic reception of the measurement equipment uses digital signal processing processors and an analog / digital signal conversion chain from the hydrophone.

<I> 13. Description of a </ I> mode <I> of preferential </ I> implementation <I> of the method of </ I> <I> the invention. </ I>

Advantageously, the method according to the invention, when used in shallow waters, comprises the following operations: The location of the search area (FIG. 1) is investigated by the search for all the indices easily detectable to the human eye, such as wreckage debris. , especially if it is a plane damaged at sea, or kerosene stains drifting on the surface. In this zone, the desired acoustic emitters (2) are located.

A helicopter 6 (Figure 2), or any other means, arrives on the search area, and successively releases one or more buoys 4 upstream of the current, (marine current or current created by the winds or the tides), preferably in staggered. The buoys drift on the search area. One of them perceives the signals emitted by the acoustic transmitter of the searched object 5 when it reaches within reach of the acoustic transmitter. Throughout the duration of the contact with the acoustic transmitter, the buoy (s) 4 transmits (ent) to the helicopter 6, or any other support, their positions and the instants of detection on each buoy acoustic signals. At the processing station 8 (FIG. 4), these messages received by the teletransmitter 9 are recorded for processing. At the end of the loss of acoustic contact, all the recorded data is processed by the processing station, in accordance with one of the methods indicated above, in order to restore the position in longitude and latitude of the transmitters sought. The mass memory reader (10) is used to receive any data that would have been stored locally on board the measuring equipment. The recordings of the acoustic signals and the positions of the measuring buoys can be carried out on board an aircraft, or a naval or land means, and processed on board, real time or deferred.

14. First Particular Mode of Implementation of the Deep Seabed Method A first embodiment makes it possible to apply the method, as long as the desired objects are situated in deep waters, (FIG. 6). In this case, the buoys remain out of range of the signals of the acoustic emitters of the desired objects. The measuring equipment is then a submarine mobile inhabited or not 27, perfectly located by an external tracking device consisting of either relay buoys 28, 29 and 30 or underwater beacons 41. The information is then preferentially recorded at edge of the free craft (underwater mobile 27). The dates then refer to a synchronized stabilized clock before immersion or after returning to the surface of the submarine with the time base of the tracking device. This synchronization operation is necessary to form the quadruplets (X;, j, Y; j, Z; j, T; j) which associate with a dating of the instant of arrival of the acoustic signal on the measuring equipment, a position in space.

15. Second particular mode of implementation of the method - Case of recording acoustic signals on board an aircraft.

When the search area is located a great distance from the land, a maritime patrol aircraft may be used to deploy measurement equipment and record all acoustic signals and buoy positions transmitted in parallel with a vessel on board. common time base. Thus the same treatments are applicable, either on board the plane or on the ground, on his return.

<I> 16. Fields of use </ I> concerned <I> by the invention </ I> The present invention is particularly applicable to the search and location of objects immersed voluntarily or not such as # Flight recorders d aircraft, # oceanographic measuring equipment, # exercise or combat mines, # submarine robots, # contraband packages; In general, any object with an acoustic transmitter.

Claims (1)

CLAIMS 1. - Device for searching and locating one or more submarine acoustic transmitter objects (2) resting at the bottom of the sea, characterized in that it comprises at least one treatment station (8) and equipment measuring device (7) provided with at least one means for locating it (19), an acoustic receiver (11-12-13-14-15) compatible with the signals emitted by the at least one immersed object, a time scale reference (18) for dating the detection instants of the acoustic signals and a recording means (45) or remote transmission means (22). 2. - Device according to claim 1, characterized in that it comprises an auxiliary measuring equipment (35), located on the sea floor or stabilized in geographical coordinates on the surface, consisting of an acoustic receiver compatible with the signals emitted by the immersed emitter object or objects, a time scale reference for dating the instants of detection of acoustic signals and a means of recording or remote transmission. 3. - Device according to claim 1, characterized in that it comprises a plurality of measuring equipment, which can be used for different periods of time or used simultaneously. 4. - Device according to any one of claims 1 to 3, characterized in that the location equipment integrated in the measuring equipment uses satellites. 5. - Device according to any one of claims 1 to 4, characterized in that the teletransmission equipment between the measuring equipment and the processing station uses a communication satellite or any other means of digital data exchange . 6. - Device according to any one of claims 1 to 5, characterized in that the acoustic receiver of the measuring equipment uses digital signal processing processors and an analog / digital conversion chain of the signal from the hydrophone. 7. - Device according to any one of claims 1 to 6, characterized in that the detection-dating device (14, 15) is deported to an air, sea or land. 8. - Device according to any one of claims 1 to 7, characterized in that the means for recording acoustic signals and / or buoy positions is deported on board an aircraft, a naval or land means . 9. - Device according to any one of claims 1 to 8, characterized in that the measuring equipment is constituted by floating equipment drifting, towed, anchored or self-propelled. 10. - Device according to any one of claims 1 to 9, characterized in that the measuring equipment is a free underwater vehicle or wire (27). 11. - Device according to any one of claims 1 to 10, characterized in that the locating means of the underwater measurement equipment is associated with a set of buoys located on the surface (28, 29, 30). 12. - Device according to any one of claims 1 to 10, characterized in that the locating means of the measuring equipment is a set of beacons arranged at the bottom of the sea (41). 13. - Method for searching and locating in geographic coordinates of one or more underwater acoustic transmitters using one or more measuring equipment and a treatment station characterized in that it comprises the following operations - It deploys, on the search area, one or more measuring equipment (7) each having at least one means for locating it (19), an acoustic receiver (11-12-13-14-15) compatible with the signals emitted by the at least one immersed object, and a time reference (18) for dating the instants of detection of the acoustic signals; At least one memory for transmission to the treatment station is recorded in at least one memory, at least the instants of detection of the acoustic signals and the information of the positions of the equipment at the said detection instants; the information previously stored, - The information thus acquired is processed in order to determine the position or positions of the sources of acoustic emissions. 14. - Method according to claim 13 characterized in that it comprises the deployment operations and possibly recovery of the measurement equipment or from an aircraft, or from a naval means, or from a submarine inhabited or not. 15. - Method according to one of claims 13 or 14 characterized in that it comprises the deployment on the bottom or on the surface of a stabilized auxiliary measuring equipment in geographic position. 16. - Method according to any one of claims 13 to 15 characterized in that the recordings of the acoustic signals and the positions of the measuring buoys are carried on board an aircraft, a naval or land means and processed on board said means in real time or deferred.