DEVICE AND METHOD FOR DETECTING AND LOCATED UNDERWATER OBJECTS

Description

[0001] The present invention relates to the field of detection and location, using one or more sonars, of submerged or floating objects between two waters such as moored mines and drifting mines.

[0002] A moored mine is a positively buoyant mine, submerged or floating in midwater. It is connected by a cable, called a mooring, to a mooring resting on the seabed, called a toad. It is automatically triggered when a surface ship or submarine comes into contact with it or passes nearby. Often used extensively, they represent a serious threat to maritime forces and commercial maritime traffic. There is therefore a real need to detect, locate, and destroy them.

[0003] Apart from the sonars (acronym for sound navigation and ranging in English terminology) of minehunters, the vast majority of existing sonars for detecting moored and drifting mines are forward-looking sonars (also called Mine and Obstacle Avoidance Sonar in English terminology or MOAS), installed under the hull of surface ships which are high-value platforms (also called High Value Unit in English terminology or HVU). The sonar's essential mission is the self-protection of the HVU and, for this purpose, must detect shallow-diving mines at a great distance in front of the ship, in order to give it time to execute an evasive maneuver, including when it is launched at full speed, for example during a transit.

[0004] The detection geometry, which is very horizontal due to the low immersion of the sonar and the mines, is a challenge, particularly in rough seas. Indeed, this geometry is very unfavorable for sound propagation, the almost horizontal orientation of the rays leading to considerable losses by absorption, due in particular to bubbles in rough seas, which can lead to extinction of the emitted signal.

[0005] These constraints lead to complicated and expensive sonars, which is not desirable for mine hunting drone sonars. Indeed, these drones are intended to spend a substantial amount of time in minefields to detect and neutralize mines and not just avoid them like an HVU. The needs are therefore different. For a drone, the self-protection function, although essential, remains secondary to the main mission of detecting mines on the bottom but also in the entire water column (sonars allowing such detections are generally called Volume Search Sonar or VSS in English terminology).

[0006] As an illustration, patent application US 2020 / 0333787 describes the implementation of an electronically scanned MOAS on a surface drone. The solution is identical to that proposed for HVUs, with the drawbacks described above.

[0007] US Patent No. 5,506,812 describes a side-viewing VSS, called a TVSS (Toroidal Volume Search Sonar). It uses a cylindrical transmitting and receiving antenna mounted on a towed fish, which insonifies in a single ping (i.e., a single transmit / receive cycle) a toroidal area of 3 degrees in bearing (called along-track in English terminology) and 360 degrees in elevation (called across-track in English terminology), scanning a large cylindrical volume around the fish's path as it moves forward. This geometry is effective for detection due to the exclusion of reverberations from the surface or bottom interfaces of most range gates in the water column where mines are searched. Even very low index targets can then be detected. However, TVSS is complicated and therefore expensive.

[0008] International application WO9603662A2 describes an underwater vehicle comprising a lower sonar for mapping the seabed and an upper sonar for mapping ice.

[0009] French patent application FR 3 010 799 describes a system for detecting and locating submerged underwater objects floating between two waters, comprising a mechanical scanning sonar making it possible to detect underwater objects having returned sonar echoes following the emission of an acoustic pulse by the sonar.

[0010] The present invention aims to overcome the drawbacks of the prior art by providing a system offering high resolution in deposits and allowing the detection of mines close to the surface. Statement of the invention

[0011] To address at least one of the problems mentioned above, an underwater vehicle is thus proposed provided with at least a first sonar and a second sonar, for the detection of underwater objects, the at least a first sonar being a sonar whose angular coverage in elevation is between 45 and 240 degrees, is oriented towards the surface when the underwater vehicle is in the phase of detecting an underwater object and whose angular coverage in bearing is less than 10 degrees to obtain measurements in a plane, all the measurements of a plane being obtained in one transmission / reception cycle, the at least a first sonar allowing the detection of underwater objects located at a depth less than that of the underwater vehicle, the underwater vehicle being characterized in that the second sonar is configured to detect underwater objects located at a depth greater than that of the underwater vehicle,and in that the underwater vehicle further comprises correlation means for correlating data from said at least one first sonar and said second sonar, an underwater object being identified and located according to a correlation result. The at least one sonar is for example a scanning sonar, the scanning of which is carried out by the movement of the underwater vehicle.,

[0012] Such a solution is more efficient than the known solutions of the prior art as presented above and costs less to implement.

[0013] According to particular embodiments, the at least one sonar is provided with a longitudinal transmission antenna oriented along the axis of the underwater vehicle, allowing broadband transmission.

[0014] Still according to particular embodiments, the at least one sonar is provided with a linear or curved transverse receiving antenna.

[0015] Still according to particular embodiments, the cover is oriented forward in a longitudinal vertical plane of the underwater vehicle, at an angle of between 5 and 25 degrees when the underwater vehicle is in the phase of detecting an underwater object. The at least one sonar may in particular be scanning in a longitudinal vertical plane of the underwater vehicle, said scanning in a longitudinal vertical plane of the underwater vehicle being controlled independently of the advance of the underwater vehicle.

[0016] Still according to particular embodiments, the at least one sonar is a multibeam sonar.

[0017] Still according to particular embodiments, the at least one sonar is a side-scan sonar. It may in particular be a synthetic antenna sonar. It may have colored emission.

[0018] Still according to particular embodiments, the at least one sonar consists of a plurality of sonars.

[0019] Still according to particular embodiments, the second sonar may in particular be a synthetic antenna sonar.

[0020] Still according to particular embodiments, the machine is autonomous.

[0021] The invention also relates to a method for detecting an underwater object, by an underwater vehicle provided with at least a first sonar and a second sonar, the method comprising the emission, by the at least a first sonar, of an acoustic signal towards the surface according to an angular coverage in elevation of between 45 and 240 degrees and an angular coverage in bearing of less than 10 degrees, the acquisition of acoustic signals in return from the signal emitted towards the surface, to obtain measurements in a plane, all the measurements of a plane being obtained in one transmission / reception cycle, the method being characterized in that it further comprises the emission, by the second sonar, of an acoustic signal towards the bottom, the acquisition of acoustic signals in return from the signal emitted towards the bottom and the processing of the acquired signals to detect and locate an underwater object located at a depth less than that of the underwater vehicle,said processing comprising a correlation of data obtained by processing the signals acquired in return from the signals emitted towards the surface and towards the bottom. Such a method allows effective detection of underwater objects, in particular underwater objects located close to the surface.,

[0022] According to particular embodiments, the acoustic signal is emitted forward in a longitudinal vertical plane of the underwater vehicle, at an angle of between 5 and 25 degrees. Brief description of the drawings

[0023] Other features, details and advantages of the invention will become apparent from the detailed description below. This is purely illustrative and should be read in conjunction with the attached drawings, in which: Fig. 1 [ Fig. 1 ] illustrates an example of an underwater vehicle, seen from the side, provided with several sonars, according to embodiments of the invention; Fig. 2 [ Fig. 2] illustrates the underwater vehicle shown on the figure 1 , seen from the front; Fig. 3 [ Fig. 3 ] schematically illustrates a second example of configuration of an underwater vehicle, seen from the front, according to embodiments of the invention; Fig. 4 [ Fig. 4 ] illustrates an example of steps to identify a correlation between data from different sonars to identify a particular object; and Fig. 5 [ Fig. 5 ] represents a schematic block diagram of an information processing device for implementing steps for processing data from sonars, for example the steps illustrated in the figure 4 . Detailed description

[0024] The inventors determined that when choosing an underwater vehicle such as a towed fish or a variable immersion drone, navigating near the seabed, it is not useful to implement a detection sonar in a water column (i.e. a VSS type sonar) covering 360 degrees in elevation but only a part of the hemisphere above the underwater vehicle, for example the 180 degrees of the hemisphere above the underwater vehicle, the hemisphere located below the underwater vehicle being better covered by a bottom imaging sonar, for example a synthetic array sonar (or SAS). Indeed, the latter allows the detection of bottom mines and short-moored mines (whose immersion is greater than or equal to that of the underwater vehicle), with performances much superior to known VSS type solutions.Furthermore, by combining float detection with a sonar covering part of the hemisphere above the underwater vehicle and the toad, or possibly the mooring line, with the bottom imaging sonar, excellent classification and localization of long mooring mines (whose immersion is less than that of the underwater vehicle) can be performed. In addition, a choice of a commercially available sonar for bathymetry or structural inspection then becomes possible for the VSS, considerably reducing the costs of the underwater detection vehicle.

[0025] According to particular embodiments, it is thus proposed to use a sonar, preferably multi-beam, oriented towards the surface of the sea (i.e. towards any point on the surface, preferably towards the zenith of the underwater vehicle or nearby) when the underwater vehicle is used for the purpose of detecting and locating an underwater object (i.e. when it is in the detection phase), which emits a wideband code, for example according to a bandwidth of between 60 and 80 KHz, with a longitudinal antenna oriented along the axis of movement of the underwater vehicle, thus forming at least one beam that is thin in bearing and wide in elevation (for example of the order of 2 degrees in bearing and 180 degrees in elevation, which can be noted 2 x 180).The received signal is preferably received using a transversely oriented antenna, preferably a curved antenna, forming a plurality of fine beams in elevation (for example of the order of 2 degrees) thus allowing, by intersection of the transmission and reception beams, the location in elevation-bearing-distance of any object in a cylindrical volume whose base is defined by the arc of the circle of the transmission beam and the axis by the rail along which the vehicle is moving.

[0026] The use of very fine beams in the deposit, as well as the high distance resolution, makes it possible to detect and locate drifting mines in the surface reverberation in excellent conditions (the detection problem is formally identical to that of detecting a bottom mine in the bottom reverberation). According to these embodiments, all the measurements made in a ping (i.e. in a transmission / reception cycle) belong to a volume (or a swath) which can be similar to a plane, for example a swath perpendicular or substantially perpendicular to the movement of the underwater vehicle. The measurements of different planes are made at different times, by scanning, by the advancement of the underwater vehicle, and all the measurements of the same plane are made in a single ping.It is noted here that a transmission / reception cycle corresponds to one or more transmissions carried out at a given instant and to the reception of the signal(s) transmitted at that instant.

[0027] The underwater vehicle may be an autonomous vehicle, for example an underwater drone, a remotely operated vehicle or a vehicle towed by a surface vessel, autonomous or not, such as a towed fish.

[0028] There figure 1schematically illustrates an example of an underwater vehicle 100, for example an underwater drone, equipped with sonars, seen from the side. As illustrated, the underwater vehicle 100 here comprises a first sonar 105 such as a scanning sonar, with side vision, mounted in the upper part of the vehicle 100, or zenith sonar, allowing the detection and location of objects, in particular moored mines or drifting mines, for example the mine 150, in the part of a water column located between the vehicle 100 and the surface of the water. Examples of characteristics of such a sonar are described below. According to the example illustrated in the figure 1, the craft 100 further comprises a second sonar 110 such as a side-view scanning sonar, mounted in the lower part of the craft 100 and allowing the detection and location of objects, in particular mooring lines and moored mine toads, for example the mooring line 155 and the toad 160, in the part of a water column located between the craft 100 and the bottom of the water. The sonar 110 is, for example, a synthetic antenna sonar. It can also ensure the detection of bottom mines, and more generally of any object of comparable index placed on the bottom, as well as the detection of moored mines whose float is at an immersion greater than or equal to that of the underwater craft 100. Similarly, still by way of example, the craft 100 here comprises a frontal avoidance sonar 115.

[0029] There figure 2 schematically illustrates the underwater vehicle 100 shown in the figure 1 , seen from the front.

[0030] The upper sonar 105 here comprises a longitudinal transmission antenna allowing broadband transmission in a swath transverse to the road. The transmission sector is advantageously offset, for example by an angle θ D from 5 to 20 degrees forward, to avoid a nadir return. According to embodiments, the emission sector is narrow in bearing, forming for example an angle θ L between 1 and 4 degrees, to ensure, in combination with the broadband, good detection performance in the surface reverberation volume, and wide in elevation to provide good volumetric coverage. The emission angle in elevation, noted θ T , is preferably between less than 90 degrees and more than 180 degrees, for example an angle between 45 and 240 degrees. This angle defines the sonar intercept, equal to I h xI v Or 2A h xI v (Or I h Or 2A h is the horizontal intercept and I vis the vertical intercept), as described with reference to the figure 2 , and therefore, taking into account the speed of the underwater vehicle, the volumetric coverage of the sonar. The upper sonar 105 is for example a multibeam sonar, also known as MBES type sonar (multibeam echosounder in English terminology), generally used for bathymetry applications, or a side-scan sonar, also known as SSS type sonar (side-scan sonar in English terminology), generally used for imaging applications.

[0031] The top sonar 105 further comprises a transverse receiving antenna. It may be linear or, advantageously, curved to cover a receiving angle greater than 180 degrees and maximize the vertical intercept (such that the vertical intercept I v be greater than or equal to the water height Iabove the underwater vehicle), forming a plurality of elevation channels, allowing both better detection and elevation localization of echoes.

[0032] It is observed here that the implementation of a side-looking sonar results in a lack of coverage in a cylinder around the route. This lack can be covered by the use of a front-looking sonar, for example the front-looking avoidance sonar 115.

[0033] The 105 top sonar is, for example, a sonar from the WBMS family of the Norbit company (Norbit is a brand), for example, a WBMS STX sonar. These sonars have an elevation aperture of up to 210 degrees in a single ping, a bearing aperture of 1 degree at a frequency of 400 kHz and 2 degrees at 200 kHz, with a range greater than 150 meters at a frequency of 400 kHz and 350 meters at 200 kHz. They offer a bandwidth greater than 60 kHz with a noise level of 220 dB at a frequency of 400 kHz and 214 dB at 200 kHz. The WBMS STX sonar has programmable transmission, allowing for transmission sector depointing and pitch stabilization.

[0034] There figure 3 schematically illustrates a second example of configuration of an underwater vehicle 300, seen from the front, according to embodiments of the invention. Like the underwater vehicle 100 illustrated in the Figures 1 and 2, the underwater vehicle 300 here comprises a first sonar 305, mounted in the upper part of the vehicle 300 and allowing the detection of objects, in particular moored mines or drifting mines, in the part of a water column located between the vehicle 300 and the surface of the water. Similarly, the vehicle 300 further comprises a second sonar 310 mounted in the lower part of the vehicle 300 and allowing the detection of objects, in particular moored mine toads, in the part of a water column located between the vehicle 300 and the bottom of the water. Again, the sonar 310 is, for example, a synthetic antenna sonar. Likewise, still by way of example, the vehicle 300 here comprises a frontal avoidance sonar.

[0035] The upper sonar 305 is for example an SSS type sonar consisting of two sonars. As illustrated, the elevation emission angle, noted θ' T , results from the combination of the emission angle of each of the two sonars, noted θ 1T And θ 2T .Again, it is preferably between less than 90 degrees and more than 180 degrees, for example between 45 and 240 degrees. The two sonars constituting the upper sonar 305 may be, for example, side-scan sonars, in particular synthetic antenna sonars.

[0036] The implementation of a top sonar and a bottom sonar makes it possible to detect in a single pass bottom mines, moored mines and drifting mines with the exception of a blind volume close to the nadir of the underwater vehicle. This blind volume can be filled, in a known manner, by the association of two successive rails, each rail covering the blind volume of the other rail.

[0037] According to particular embodiments, the upper sonar is electronically scanned in a longitudinal vertical plane of the underwater vehicle, thus making it possible to depoint the transmission beam, for example to compensate for the pitching of the underwater vehicle and ensure optimal coverage of the volume despite trim errors. In an extension of this variant, the sonar is colored emission (the emitted signal comprises several distinct frequencies) in bearing also allowing compensation for the yaw of the platform and increasing the number of detection opportunities. The sonar emits in the same recurrence, several pulses in disjoint sub-bands covering an interval in a longitudinal vertical plane of the underwater vehicle.According to a particular example given for illustration purposes, a bandwidth of 80kHz is divided into 5 sub-bands of 16kHz each, which are emitted in the sectors 90 degrees + 2 degrees, 90 degrees + 1 degree, 90 degrees, 90 degrees - 1 degree, 90 degrees - 2 degrees in a longitudinal vertical plane of the underwater vehicle, which makes it possible to cover a sector of 6 degrees without loss of resolution, this being fixed at 2 degrees. The multiple echoes of a target can then be the subject of incoherent tracking and integration, using the navigation of the underwater vehicle or even micro-navigation in the case where the underwater vehicle is equipped with a synthetic antenna sonar.Incoherent integration allows to reduce the natural fluctuations of the echoes of both the targets and the medium (especially surface reverberation), and thus to flatten the tails of the probability distribution of the corresponding amplitudes and thus to increase the probability of detection and reduce false alarms.

[0038] According to particular embodiments, the underwater vehicle comprises a processing unit which receives data from the upper and lower sonars to identify a correlation between this data with respect to predetermined models, for example to establish a correlation between data likely to represent a moored mine with data likely to represent a moored or a toad, allowing an excellent classification of the moored mine.

[0039] There figure 4illustrates steps of such embodiments. As illustrated, a first step here aims to obtain data from the upper sonar (step 400). In a following step (step 405), the data obtained are processed, for example to reduce noise, and compared to data representative of searched objects, for example data representative of moored mines, stored in a database 410, to determine whether the data obtained are likely to characterize a searched object. A confidence level can be associated with each potentially identified object. The position of the potentially identified objects is preferably determined.

[0040] Similarly, data from the bottom sonar are obtained (step 415). In a subsequent step (step 420), the data obtained from the bottom sonar are processed, for example to reduce noise, and compared with data representative of searched objects, for example data representative of a mooring line, a toad or a bottom mine, stored in a database 425 to determine whether the data obtained are likely to characterize a searched object. The position of the potentially identified objects is preferably determined.

[0041] In a following step (step 430), a correlation is carried out between the objects potentially identified from the data obtained from the upper sonar and the objects potentially identified from the data obtained from the lower sonar from references stored in a database 435. Thus, for example, if data obtained from the upper sonar are potentially identified as representative of a mooring mine and if data obtained from the lower sonar are potentially identified as representative of a toad, the confidence level associated with the identification of each of these objects can be incremented.Conversely, if, for example, data obtained from the top sonar are potentially identified as representative of a moored mine and if data obtained from the bottom sonar are potentially identified as representative of a bottom mine, there is no need to modify the level of confidence associated with the identification of each of these objects. The relative position of the potentially identified objects, for example the relative position of a moored mine and a toad, is also preferably used to modify the level of confidence associated with the identification of each of these objects.

[0042] It is observed herein that the databases 410, 425 and 435 may be separate databases or may constitute one or more databases.

[0043] There Figure 5represents a schematic block diagram of an information processing device 500 for implementing steps described previously, in particular steps described with reference to the figure 4 . According to the illustrated example, the information processing device 500 comprises two parts, a first part 500-1 which can be implemented in an underwater vehicle according to the invention and a second part 500-2 belonging here to a remote system, for example a surface ship. Data, for example data from sonars, processed or unprocessed, can be exchanged between the parts 500-1 and 500-2 using a wired connection or wireless communication means.

[0044] As illustrated, the device 500 may comprise a memory 505 for storing instructions enabling the implementation of the method, the data from the received backscattered signal, and temporary data for carrying out the different steps of a method as described previously.

[0045] The device may further comprise a 510 circuit. This circuit may be, for example: a processor capable of interpreting instructions in the form of a computer program, or an electronic card whose steps of the method of the invention are described in the silicon, or even a programmable electronic chip, such as an FPGA chip (for "Field-Programmable Gate Array" in English), a SOC (for "System On Chip" in English), a GPU (for "Graphics Processing Unit" in English), or an ASIC (for "Application Specific Integrated Circuit" in English).

[0046] SOCs, or systems on chips, are embedded systems that integrate all the components of an electronic system into a single chip. An ASIC is a specialized electronic circuit that combines custom features for a given application. ASICs are typically configured during manufacturing and can only be simulated by the user. Field-Programmable Gate Arrays (FPGAs) are electronic circuits that can be reconfigured by the user.

[0047] The device 500 may comprise an input interface 515, for example for receiving data from one or more sonars and an output interface 520, for example for transmitting this data, processed or unprocessed, and / or identifiers of potentially identified objects.

[0048] Furthermore, the device may comprise, to allow easy interaction with a user and to display detection results, a screen 525 and a keyboard 530. Of course, the keyboard is optional, particularly in the context of a computer in the form of a touch pad, for example. As illustrated, the screen and / or the keyboard are preferably remote.

[0049] Depending on the embodiment, the portion 500-1 of the device 500 may be a computer, an electronic component, or another apparatus comprising a processor operably coupled to a memory, as well as, depending on the embodiment selected, a data storage unit, and other associated hardware elements such as a network interface and a media reader for reading and writing to a removable storage medium (not shown in the figure). The removable storage medium may be, for example, a memory card.

[0050] Depending on the embodiment, the memory, data storage unit, or removable storage medium contains instructions that, when executed by the control circuit 510, cause the control circuit 510 to perform or control the input interface 515, output interface 520, data storage in the memory 505, and / or data processing portions according to one or more embodiments of the proposed method.

[0051] It is observed here that while all the steps may be implemented in a device of the underwater vehicle, some steps may be implemented in the underwater vehicle while other steps are implemented in a remote device. Thus, for example, the correlation between objects potentially identified from the data obtained from the upper sonar and objects potentially identified from the data obtained from the lower sonar may be performed in a device of a surface vessel receiving an identification of the potentially detected objects.

[0052] Of course, the present invention is not limited to the embodiments described above as examples. It extends to other variants.

[0053] Depending on the embodiment selected, certain acts, actions, events, or functions of each of the methods described herein may be performed or occur in a different order than they were described, or may be added, merged, or may not be performed or occur, as the case may be. In addition, in some embodiments, certain acts, actions, or events are performed or occur concurrently and not successively.

[0054] Although described through a number of detailed exemplary embodiments, the proposed device and method include various variations, modifications and improvements that will be apparent to those skilled in the art, it being understood that these various variations, modifications and improvements are within the scope of the invention, as defined by the following claims. In addition, various aspects and features described above may be implemented together, or separately, or substituted for each other, and all of the various combinations and subcombinations of the aspects and features are within the scope of the invention. Furthermore, some systems and equipment described above may not incorporate all of the modules and functions described for the preferred embodiments.

Claims

1. An underwater vehicle (100, 300) provided with at least a first sonar (105, 305) and a second sonar (110, 310), for the detection of underwater objects, the at least one first sonar (105, 305) being a sonar whose angular coverage in elevation is comprised between 45 and 240 degrees, is oriented towards the surface when the underwater vehicle (100, 300) is in the detection phase of an underwater object and whose angular coverage in bearing is less than 10 degrees to obtain measurements in a plane, all the measurements of a plane being obtained in one emission / reception cycle, the at least one first sonar (105, 305) allowing the detection of underwater objects located at a depth less than that of the underwater vehicle (100, 300), the underwater vehicle (100, 300) being characterized in that the second sonar (110, 310) is configured to detect underwater objects located at a depth greater than that of the underwater vehicle (100, 300), the underwater vehicle (100, 300) further comprises correlation means for correlating data from said at least first sonar (105, 305) and said second sonar (110, 310), an underwater object being identified and located according to a correlation result.

2. The vehicle according to claim 1, according to which the at least one first sonar (105, 305) is provided with a longitudinal emission antenna oriented along the axis of the underwater vehicle (100, 300), allowing broadband emission.

3. The vehicle according to claim 1 or 2, according to which the at least one first sonar (105, 305) is provided with a linear or curved transverse reception antenna.

4. The vehicle according to any one of claims 1 to 3, according to which the cover is oriented forward in a longitudinal vertical plane of the underwater vehicle (100, 300), at an angle comprised between 5 and 25 degrees when the underwater vehicle (100, 300) is in the detection phase of an underwater object.

5. The vehicle according to claim 4, according to which the at least one first sonar (105, 305) is with a scanning in a longitudinal vertical plane of the underwater vehicle (100, 300), said scanning in a longitudinal vertical plane of the underwater vehicle (100, 300) being controlled independently of the advance of the underwater vehicle (100, 300).

6. The vehicle according to any one of claims 1 to 5, according to which the at least one first sonar (105, 305) is a multibeam sonar.

7. The vehicle according to any one of claims 1 to 5, according to which the at least one first sonar (105, 305) is a side sonar.

8. The vehicle according to claim 7, according to which the at least one first sonar (105, 305) is a synthetic antenna sonar.

9. The vehicle according to claim 7 or claim 8 according to which the at least one first sonar (105, 305) has coloured emission.

10. The vehicle according to any one of claims 1 to 9, according to which the at least one first sonar (105, 305) is made up of a plurality of sonars.

11. The vehicle according to any one of claims 1 to 10 according to which the second sonar (110, 310) is a synthetic antenna sonar.

12. The vehicle according to any one of the preceding claims, according to which the vehicle is autonomous.

13. A method for detecting an underwater object, by an underwater vehicle (100, 300) provided with at least a first sonar (105, 305) and a second sonar (110, 310), the method comprising - the emission, by the at least one first sonar, of an acoustic signal towards the surface according to an angular coverage in elevation comprised between 45 and 240 degrees and an angular coverage in bearing less than 10 degrees, - the acquisition of acoustic signals in return of the signal emitted towards the surface, to obtain measurements in a plane, all the measurements of a plane being obtained in one emission / reception cycle, the method being characterized in that it further comprises - the emission, by the second sonar (110, 310), of an acoustic signal towards the seabed, - the acquisition of acoustic signals in return of the signal emitted towards the seabed and - the processing of the acquired signals to detect and locate an underwater object located at a depth less than that of the underwater vehicle (100, 300), said processing comprising a correlation of data obtained by processing the acquired signals in return for the signals emitted towards the surface and towards the seabed.

14. The method according to claim 13, according to which the acoustic signal emitted towards the surface is emitted forward in a longitudinal vertical plane of the underwater vehicle (100, 300), at an angle comprised between 5 and 25 degrees.