Relocation system and process

Abstract

Relocation system and method A relocation method is proposed, including underwater relocation, comprising: receiving prior detection information relating to objects detected by a detection sonar (10) in a surveillance area in the water, determining secondary detection information relating to objects detected by a relocation sonar (200), carried by the identification device, during its movement towards one of the target objects of interest detected by the detection sonar;- the determination of an error correction vector between the position of the target object of interest estimated by the detection sonar (10) and that estimated by the relocation sonar (200), based on the prior and secondary detection information, - the correction of the position of the target object of interest estimated by the relocation sonar (200), by applying the position error correction vector, and - the control of the movement of the identification device (20) towards the target object of interest using the corrected position. Figure for the abstract: figure 9;

Description

Title of the invention: Relocation system and method technical field

[0001] The invention relates generally to detection systems and in particular to a device and method of relocation, especially underwater, using a sonar system.

[0002] Sonar systems are used in the field of underwater acoustics to detect and locate objects underwater.

[0003] Sonar systems can be used by various surveillance infrastructures, for example for the detection of submarines or objects placed on the seabed, or in the field of archaeology (for example underwater and submarine archaeology).

[0004] Sonar systems are equipped with antennas to transmit and / or receive signals. Processing the signals received by the sonar system makes it possible to detect the presence of objects or to form images of the seabed on which objects can be detected.

[0005] For example, in a surveillance system used to perform an area surveillance mission using sonar, the sonar may implement a first phase (detection phase) consisting of detecting one or more objects of interest (for example, a threatening object) from the sonar images, thus providing a set of detection data. This detection data is generally in the form of geographically projected images and includes the position of each object of interest. The position of the object of interest may be affected by a positioning error inherent in the sonar system and its operator.

[0006] In a second phase, the surveillance system must verify whether the detected object is indeed an object of interest (for example, whether it constitutes a threat) and, if so, implement appropriate actions (for example, neutralizing the threat) using another robotic underwater system or divers who must then locate the geographical position of the detected object.

[0007] However, robotic underwater systems (such as a remotely operated underwater vehicle, or ROV) or divers must rely on sometimes imprecise position information to effectively locate the detected object in turbid waters and on cluttered seabeds. Indeed, in the case of a seabed cluttered with multiple objects around the detected object, for example, it is sometimes difficult to locate the object's position within the circle of uncertainty provided by the sonar in the first phase of detection.

[0008] This results in a fairly long search time for the detected object (which is critical in the case where the detected object is a threat) and a risk of error on the ocean floor due to the positioning error intrinsic to the sonar system which carried out the first phase of detection and localization, or even a risk of error in the object found if the bottom is cluttered.

[0009] Various localization solutions are known in the terrestrial domain, as described, for example, in EP2932182. In particular, known detection solutions applicable to terrestrial environments use a GNSS system to position a detected object. However, a GNSS (Global Navigation Satellite System) cannot be used directly underwater (the frequencies used do not penetrate water). When a sonar (towed sonar, for example) or an underwater relocation system (such as an autonomous underwater vehicle, or AUV) establishes the position of an echo to be classified on the ocean floor, it uses its onboard attitude control or inertial measurement unit to locate that echo. These units are more accurate the more accurate the data supplied to them.For example, in the case of an AUV, the GNSS data collected at the surface drifts throughout the descent phase and over time, while in the case of towed sonar, the GNSS position data is relayed to a lever arm established by acoustic positioning. In the case of surface-mounted sonars, which could benefit from being directly coupled to the GNSS system, their positioning performance is degraded due to the distance to the seabed (for a side-scan sonar, an error in measuring yaw or the speed of sound in water leads to a positioning error).

[0010] There is therefore a need for an improved underwater detection system and method. General definition of the invention

[0011] To this end, a monitoring system is proposed, configured to monitor the presence of objects in water within a surveillance zone. The monitoring system comprises a detection sonar and a mobile identification device in water. The detection sonar is capable of detecting the presence of a set of objects in the surveillance zone, the set comprising at least one object of interest and one or more auxiliary objects. The detection sonar is capable of determining preliminary detection information comprising, for each detected object of interest, at least the position of the object of interest, referred to as the starting position, and a reference image corresponding to a sonar image taken by the detection sonar that includes the objects detected by the detection sonar. The detection sonar is capable of transmitting the preliminary detection information to the identification device.

[0012] The identification device is configured to move towards at least one target object of interest among the objects of interest, in response to the receipt of prior detection information, the identification device comprising a relocation sonar configured to detect objects in the surveillance area, the sector of the relocation sonar being initially directed towards the starting position of the target object of interest, which provides secondary detection information relating to the objects detected by the relocation sonar.

[0013] The identification device further includes a relocation unit configured to:

[0014] - determine a position error correction vector between the starting position of the target object of interest estimated by the detection sonar and the position of the target object of interest estimated by the relocation sonar, from the prior detection information and the secondary detection information;

[0015] - apply the position error correction vector to correct at least the position of the target object of interest estimated by the relocation sonar, the movement of the identification device towards the target object of interest being controlled using the corrected position of the target object of interest.

[0016] In one embodiment, the relocation unit may include an association module configured to determine pairs associating an object detected by the detection sonar and an object detected by the identification device, the position correction vector determination module being configured to determine a position error correction vector from the pairs.

[0017] In certain aspects, the identification device may include an imaging unit configured to generate a consolidated representation comprising the reference image including the objects detected by the detection sonar, and superimposed on the reference image, the sonar sector of the relocation sonar and the objects detected by the relocation sonar.

[0018] In embodiments, the association module can be configured to determine the pairs by applying a translation to the sonar image of the relocation sonar in the consolidated representation, according to a criterion based on the distances between the objects.

[0019] The position error correction vector determination module can be configured to determine the position error correction vector by iterating through the different determined association pairs and determining for each pair a candidate correction vector corresponding to the position translation from one element of the pair to the other, the position error correction vector determination module being configured to select the candidate correction vector which minimizes the quadratic sum or a criterion for minimizing the distances between each element of each pair.

[0020] In one embodiment, the association module may use an 'Iterative Closest Point' type association technique.

[0021] Alternatively, the position error correction vector determination module can be configured to apply an image processing technique to the consolidated representation and a cost function to determine the position error correction vector.

[0022] In certain aspects, the identification device may include an absolute localization system having a maximum positioning error less than the range of the relocation sonar.

[0023] In some embodiments, the identification device may be a remotely controlled underwater robot.

[0024] A monitoring method configured to monitor the presence of objects in a monitoring zone in water is further proposed, implemented in a mobile identification device. The method advantageously comprises the steps of:

[0025] - receive prior detection information relating to detected objects by a detection sonar in the surveillance area comprising at least one object of interest and one or more auxiliary objects, the prior detection information comprising for each object of interest detected, at least the position of the object of interest, called the starting position, and a reference image corresponding to a sonar image taken by the detection sonar comprising the objects detected by the detection sonar;

[0026] - determine secondary detection information relating to detected objects by a relocation sonar carried by the identification device during its movement towards a target object of interest among the objects of interest;

[0027] the process comprising one or more iterations of the following steps:

[0028] - determine a position error correction vector between the starting position of the target object of interest estimated by the detection sonar and the position of the target object of interest estimated by the relocation sonar, from the prior detection information and the secondary detection information;

[0029] - correct at least the position of the target object of interest estimated by the sonar of relocation, by applying the position error correction vector,

[0030] - control the movement of the identification device towards the target object of interest by using the corrected position of the target object of interest.

[0031] The embodiments of the invention thus allow for improved relocation of objects detected in the first phase of detection by minimizing the risk of error and improving the relocation time of the detected object. Brief Description of the Figures

[0032] Other features, details and advantages of the invention will become apparent from the description given with reference to the accompanying drawings provided by way of example, which represent, respectively:

[0033] [Fig-1] - Fig. 1 represents a monitoring system according to modes of realization.

[0034] [Fig.2] - Fig.2 illustrates an example of a representation of the reference image extracted in the first phase of detection.

[0035] [Fig.3] - Fig.3 represents the structure of the relocation unit, according to methods of implementation.

[0036] [Fig.4] - Fig.4 represents the structure of the relocation unit, according to other methods of implementation.

[0037] [Fig. 5] - Fig. 5 illustrates the navigation of the identification device towards an object of interest according to an example of implementation.

[0038] [Fig.6] - The [Fig.6] illustrates a phase of the relocation of the target objects of interest.

[0039] [Fig.7] - Fig.7 illustrates another phase of the relocation of objects of interest targets.

[0040] [Fig.8] - The [Fig.8] illustrates yet another phase of the relocation of the target objects of interest.

[0041] [Fig.9] - Fig.9 is a flowchart representing the relocation process object implemented by the identification device, according to embodiment modes.

[0042] [Fig. 10] - The [Fig. 10] represents an example of the progression of an ROV-type identification device towards a target object of interest. Detailed description of the request

[0043] Fig. 1 schematically represents an example of an environment in which certain embodiments of the invention can be implemented.

[0044] Embodiments of the invention provide a monitoring system 100 (also called an object relocation system) configured to monitor the presence of objects, in a monitoring area, in water, such as for example in a marine environment.

[0045] The surveillance system includes a detection sonar 10 and an identification device 20 (also called a 'relocation device').

[0046] The detection sonar 10 may be part of a pre-detection data acquisition system (not shown).

[0047] The detection sonar 10 is configured to determine prior detection information relating to objects detected in the surveillance area, the detected objects including at least one object of interest. The prior detection information includes, for each detected object of interest, at least the starting position of the object of interest estimated by the detection sonar 10 and a reference image corresponding to a geolocated sonar image taken by the detection sonar 10, representing a portion of the surveillance area including the object of interest and the auxiliary objects detected in the vicinity of the object of interest.

[0048] The reference image can be a geolocated image representing the seabed when the monitoring area is a maritime area.

[0049] The detection sonar 10 is configured to transmit prior detection information to the identification device 20.

[0050] The identification device 20 is a mobile device (such as a vehicle) capable of moving through the water to approach at least one object of interest, referred to as the target object of interest, in order to identify it and / or take action. The identification device 20 includes a relocation sonar 200 configured to determine secondary relocation information relating to objects detected by the relocation sonar 200 in the surveillance area, during the movement of the identification device 20. The sonar sector of the relocation sonar 200 is initially directed towards the starting position of the target object of interest provided by the prior detection information.

[0051] The identification device 20 may also include an absolute localization system 201 enabling it to move towards the area of ​​the target object of interest with a maximum uncertainty less than the range of the relocation sonar.

[0052] The absolute localization system 201 advantageously has a maximum positioning error less than the range of the relocation sonar 200 which equips the identification device 20, which allows the identification device to approach a contact of interest by moving with the localization system, so that the positioning error does not prevent the object of interest from being present in the sonar image taken by the detection sonar 200.

[0053] Advantageously, the identification device 20 is capable of heading towards a target object of interest by relocating the target object of interest from prior detection information, secondary relocation information detected by the relocation sonar 200, and known relative position data between reference objects, among the auxiliary objects detected around the object of interest, these reference objects forming a constellation around the target object of interest.

[0054] Landmarks (also called "landmarks" in English) are fixed landmarks positioned on the seabed whose position is known (stored in a database of the device 20), with an uncertainty intrinsic to the detection system that was used to determine this position beforehand (this detection system may be a system separate from the detection sonar 10). In embodiments of the invention, constellations formed of reference objects (comprising at least one reference object) and an object of interest are used to enable the relocation of an object of interest previously detected by the detection sonar 10.

[0055] The constellation of reference objects is advantageously used to locate the object of interest by matching the constellation in the reference image with the constellation in the sonar image of the identification device 20 (sonar image of the relocation sonar 200). If no reference objects are present around the object of interest, then relocation does not require the use of a constellation.

[0056] The detection sonar 10 can be mounted on a carrier such as, for example, a naval vessel or a submarine capable of being submerged in water. The detection sonar 10 can, for example, be a towed sonar or one installed on an autonomous underwater vehicle (AUV).

[0057] The detection sonar 10 is configured to emit sound pulses and receive in response waves reflected from the bottom and underwater objects, which enables image formation and object detection.

[0058] The 100 surveillance system can be used in various fields of application, such as, for example and without limitation, in the field of target detection for detecting threats, in the field of marine biology and ecology (for example, for analyzing aquatic pollution), or in the field of archaeology (for example, underwater and submarine archaeology), etc. In such fields, it may be useful or required to approach detected objects of interest to identify them, or to implement an intervention action at the level of the target object of interest, depending on the field of application of the invention (an action may be, for example, image capture, video recording, measurement taking, target neutralization, etc.).

[0059] The detection sonar 10 and the relocation sonar 200 can be active sonars. An active sonar comprises a transmitter and a receiver. The transmitter and receiver comprise a set of transducers configured to emit and / or receive sound waves.

[0060] During transmission, the sonar transmitter transducers are capable of emitting pulses in a given direction. During reception, the conversion of acoustic data (pressure of the incident acoustic wave) into electrical data (output voltage) is performed by one or more transducers.

[0061] A sonar receiver is configured to listen for reflected echoes in response to sonar emissions, in a given frequency band (expressed in Hz), with a given hydrophonic sensitivity (designated by 'Sh' and expressed in decibels dB) and a given processing gain (expressed in dB) of the received signals, which enables object detection.

[0062] A sonar receiver is further configured to locate detected objects. To locate a detected object, a sonar receiver locates the echoes in direction (or 'bearing') by means of its spatial directivity (in dB) obtained by temporal channel formation, and estimates the distance (in meters m) of the echoes from the echo delay time (in seconds s) for a sonar in active mode.

[0063] The detection sonar 10 and the relocation sonar 200 can be capable of forming a sonar image representing the scene detected by the sonar.

[0064] The detection sonar 10 is thus used in a first phase of detection to detect objects of interest and auxiliary objects around the objects of interest, and to determine the preliminary detection information (for each object of interest, the starting position of the object of interest estimated by the detection sonar 10 and the associated geolocated reference image). The first phase of detection may also include object classification to determine whether a detected object is an object of interest (the first phase of detection is then also called the 'DCL phase' for 'Detection, Classification, Localization').

[0065] The monitoring system 100 may further include a control unit 18 configured to control the operation of the identification device 20 and / or transmit commands to communication equipment worn by a diver, when the identification device 20 is directly implemented by the relocation sonar 200 worn by such a diver. The control unit 18 may also control the operation of the detection sonar 10. The monitoring system 100 may further include a display device (not shown) comprising a graphical interface in which a representation of the reference images provided by the detection sonar 10, the sonar image detected by the relocation sonar 200, or a consolidated representation of these two images, can be displayed during the first detection phase and / or in the second relocation phase. The display device may be connected to the control unit 18.The monitoring system 100 may also include one or more input / output devices (such as a mouse, keyboard, touch input device, voice input device, or any equivalent form of input) that can be used by an operator to enter commands into the control unit 18. The control device 18 is particularly capable of changing the display on the graphical interface according to commands entered into the control unit 18 by means of the devices. of capture or according to the detection carried out by the detection sonar 10 and / or the relocation sonar 200.

[0066] The identification device 20 can be robotic and / or automated. The identification device 20 can be remotely controlled by the operator via the control unit 18.

[0067] The control unit 18 may be located in an operational center such as a surface vessel or a submarine. The control unit 18 may, for example and without limitation, be located at the level of the carrier of the detection sonar 10.

[0068] The identification device 20 is capable of moving towards one or more target objects of interest based on relocation information calculated for the target object of interest. The identification device 20 can be, for example and without limitation, a remotely operated underwater vehicle (ROV) that can be equipped with the relocation sonar 200. The identification device 20 can be fully integrated into the relocation sonar 200 (the identification device 20 then coincides with the relocation sonar 200) when the relocation sonar 200 is a handheld sonar worn by a diver (for example, a mine clearance diver).

[0069] The identification device 200 can be connected to the same carrier as the detection sonar 10. The carrier of the detection sonar 10 can be, for example, an autonomous surface vessel (USV, acronym for the corresponding Anglo-Saxon expression "Unmanned Surface Vehicle"). The identification device 200 can, for example, be connected by a cable to the carrier (as in the case of an ROV).

[0070] In the first detection phase, the detection sonar 10 is configured to insonify the surveillance area in order to detect objects within the surveillance area (i.e., to emit acoustic waves within the surveillance area). After each emission, the detection sonar 10 can remain on standby (or listening) for a sufficient time to receive echoes from the detected objects (e.g., targets) present in the surveillance area. The detection sonar 10 can then process the received echoes to detect objects within the surveillance area, perform a classification to identify objects of interest (the other detected objects being auxiliary objects), and estimate the position of each object of interest (called the starting position).The detection sonar 10 can use a classification technique to characterize detected objects in order to classify them into the category of objects of interest or into the category of auxiliary objects, and a positioning technique to estimate the positions of the objects of interest.

[0071] The detection sonar 10 is not limited to the use of a detection technique directly using echoes. In some embodiments, the detection sonar 10 can be configured to generate high-resolution images of the seabed and to use them to detect and classify objects on the seabed based on their echoes and also of their shadows. In such embodiments, the detection sonar 10 can be configured to classify detected objects using the dimensions of the echoes, their shadows, and / or their shapes. In such embodiments exploiting the high-resolution images produced, the detection sonar 10 can be, by way of non-limiting example, a side-scanning SAS (Synthetic aperture sonar).

[0072] Since the detection sonar 10 is submerged, its absolute position can only be calculated indirectly, from a GNSS position measured before its dive (in the case of an AUV) and maintained during the dive by an inertial system (or a system combining an inertial system and a DVL acoustic sensor, acronym for "Doppler Velocity Log" meaning Doppler velocity recorder), or from an acoustic localization measurement between a surface vehicle located by a GNSS system and the detection sonar 10. In these cases, the absolute positioning of the detection sonar is known with a non-negligible uncertainty which depends on the performance of its localization system.To this absolute positioning error of the detection sonar 10, there is added an uncertainty in the relative positioning of the objects detected by the detection sonar with respect to it (related to the uncertainty on the speed of sound and the uncertainty on the azimuth of the sonar channels formed by the detection sonar 10).

[0073] Advantageously, embodiments of the invention allow relocation of target objects of interest and guidance of the identification device 20 towards these objects despite such uncertainties of absolute positions.

[0074] The objects of interest and auxiliary objects thus detected can then be located on the sonar data of the detection sonar 10.

[0075] In embodiments where the detection sonar uses a sonar image for detection, the detection sonar 10 can be configured to geographically project sonar images of the seabed detected by the detection sonar 10 into the surveillance area and perform detections of objects of interest and auxiliary objects from a sonar image. The sonar image used for detecting an object of interest is a geolocated image, also called a 'geolocated reference image'. It represents the detected scene (seabed when the invention is implemented in a marine environment) around an object of interest (the step of extracting a geolocated image around each object of interest).

[0076] The first detection phase thus makes it possible to obtain preliminary detection information including:

[0077] The list of objects of interest (e.g., suspicious objects or objects constituting a potential threat) that need to be approached (e.g., to inspect them), each object of interest being associated with position data representing the estimated absolute position (or starting position) of the object of interest, associated with a positioning uncertainty;

[0078] For each object of interest, the geolocated reference image around the object of interest (an image of the seabed, for example). These images may show other auxiliary objects around the object of interest if such objects were detected in the first phase of detection.

[0079] In one embodiment, the prior detection information can be determined by a detection sonar 10 independent of the identification device 200 (controlled by a separate control unit and mounted on an independent carrier).

[0080] The information obtained at the end of the first detection phase is then used by the identification device 20. The identification device 20 may include a relocation unit 202 configured to determine relocation information for each target object of interest (i.e. which must be approached by the identification device 20), the identification device 20 being configured to move towards the target object of interest using the relocation information.

[0081] Figure 2 illustrates an example of a representation of the reference image 101 extracted in the first phase of detection. The reference image 101 includes a detected object of interest 102 and auxiliary objects 104 in the vicinity of the object of interest.

[0082] In the second phase, called the relocation phase, the identification device 200 receives, from the detection sonar 10, the prior detection information A, acquired during the first detection phase including at least the geolocated reference image Iref{, the prior positions Pi of the different objects of interest and the positioning uncertainties associated with the positions Pi.

[0083] The preliminary detection information A1 may include additional information such as the positions of the detected auxiliary objects.

[0084] The preliminary detection information Aj can be stored by the identification device 20 in a storage memory. A display of this stored information can be generated on a control screen embedded in the identification device 20.

[0085] For example, if the identification device 20 is an ROV, the geolocated reference image Ireft and the prior positions Pi of the different objects of interest can be stored by the identification device 20 and a display of this stored information can be generated on a control screen on board the identification device 20 (pilot screen) and connected to the relocation sonar 200.

[0086] In another example, if the identification device 20 is a diver and the relocation sonar 200 equipping the identification device 20 is a handheld sonar, the geolocated reference image Iref and the prior positions Pi} of the various objects of interest Oj can be stored by the relocation sonar 200 and a display of this information can be generated on an on-board control screen directly on the portable sonar 200 (in this case the identification device 20 corresponds to the portable relocation sonar 200).

[0087] The relocation sonar 200 equipping the identification device 20 may be of a different type than the detection sonar 10 used in the DCL phase. The detection sonar 10 may be, for example, a side-scan sonar, a synthetic aperture side-scan sonar, a hull-frontal sonar, or any other sonar capable of generating images of the seabed. The relocation sonar 200 of the identification device 20 may be, for example and without limitation, a multibeam front-end sonar, or any other sonar.

[0088] The identification device 20 may include an imaging unit 203 configured to generate a consolidated representation R comprising the geolocated reference image Pef} determined in the DCL phase, and received from the detection sonar 10, and superimposed on the geolocated reference image lref}, data from the secondary detection information A2 determined by the relocation sonar 200 and comprising:

[0089] Points representing the objects O'j detected by the relocation sonar 200 of the identification device 20, in the relocation phase, these points being positioned on the reference image at the level of their estimated positions P'j;

[0090] The secondary sonar image hec2 obtained with the relocation sonar 200 of the identification device 20 by projecting it onto the reference image h-efi at its estimated position; the display can be generated with a sufficient degree of transparency to make visible the rendering of the reference image L-ef cn below the auxiliary sonar image Pee..

[0091] Thus, the secondary detection information A2 can include the information P'j determined for the different objects O'j detected by the relocation sonar 200 and the auxiliary sonar image Isec2 obtained with the relocation sonar 200 on which the different detected objects O'j are positioned.

[0092] The imaging unit 203 can further generate a display of the contour of the sonar sector of the relocation sonar 200 and of the position of the identification device 20 on the displayed reference image Pef.

[0093] Advantageously, the relocation unit 202 is capable of using the received preliminary detection information A1, the secondary detection information A2 detected by the relocation sonar 200, and the identification of at least one reference object among the detected objects (also called landmarks) having known position information to guide the identification device 20 to one or more selected target objects of interest, minimizing the risk of positioning error and thus optimizing the time required to approach an object of interest. The reference objects can, for example, rocks present on the seabed, whose initial position is determined during prior detection and of which we have their positions and the associated position uncertainty.

[0094] Fig. 3 represents the structure of the relocation unit 202 according to one embodiment.

[0095] The relocation unit 202 includes a position error correction vector determination module 2022 configured to determine a position error correction vector (also called a 'recalibration vector'), from the prior detection information A1 received from the detection sonar 10, the secondary detection information A2 detected by the relocation sonar, and the known position of at least two reference objects identified among the detected objects and present both on the reference image Iref[ and on the image Isec2 of the relocation sonar 200.

[0096] The relocation unit 202 may include a position correction module 2024 configured to apply the position error correction vector determined to correct the estimated position of each object detected by the relocation sonar 200 in the sonar image of the relocation sonar by a translation corresponding to the position correction vector, which allows the entire image and objects to be relocated relative to the position of the objects in the first detection phase (pre-detection).

[0097] For each target object of interest, the constellation of objects including the target object of interest and the set of reference objects (among the auxiliary objects) in the vicinity of the target object of interest in the relocation image Isec^est is compared to the constellation of objects formed by the target object of interest and the set of reference objects in the reference image Ireq produced in the first phase of detection, using a comparison technique.

[0098] The identification device 20 may further include a controller 205 capable of controlling the movement of the identification device 20 towards the target object of interest using the position corrected by the position correction module 2024 (the corrected position is the position of the target object of interest estimated by the identification device 20, after correction by applying the calculated position error correction vector). The identification device 20 is equipped with positioning means (e.g., inertial system, DVL sensor, acoustic positioning means, etc.) to move relative to the object of interest from the corrected position.

[0099] During the movement of the identification device 20 towards an object of interest to be identified, the positioning error correction module 2022 can reiterate The position correction is performed dynamically several times until the object of interest is reached, thus avoiding drift.

[0100] In one embodiment, the relocation unit 202 may include an association unit configured 2020 to determine pairs associating an object detected by the detection sonar 10 and an object detected by the identification device 200 using the prior detection information A1 received and the secondary detection information A2 detected by the relocation sonar 200 (for example in the consolidated representation R. The position error correction vector determination module 2022 is then configured to determine the position error correction vector from the association pairs.

[0101] An association pair can correspond to the same object, one element of the pair corresponding to the object detected by the detection sonar 10 and the other element of the pair then corresponding to the same object detected by the relocation sonar 200. However, it is not essential that the target object of interest be part of the pairs formed (for example if it is not detected by the relocation sonar).

[0102] According to one aspect, the association module 2020 can be configured to determine association pairs by applying a translation to the sonar image of the relocation sonar 200 in the consolidated R representation, the translation being carried out in such a way as to minimize the sums of distances between pairs of objects.

[0103] In one embodiment, the pairing method may use the ICP transformation method, for "Iterative Closest Point," as described, for example, in Paul J. Besl and N.D. McKay, "A Method for Registration of 3-D Shapes," IEEE Trans. on Pattern Analysis and Machine Intelligence, Los Alamitos, CA, USA, IEEE Computer Society, vol. 14, no. 2, 1992, or any other similar pairing method. The ICP transformation method is a method that allows two sets of point clouds to be matched in order to iteratively minimize the distances between these points. Those skilled in the art will readily understand that the invention is not limited to the ICP pairing technique and encompasses any pairing technique that allows for the estimation of a translation and a rotation between two sets of points.

[0104] In one embodiment, the position error correction vector determination module can be configured to determine the position error correction vector by traversing the different determined association pairs and determining for each pair a candidate correction vector corresponding to the position translation of one element of the pair to the other, the position error correction vector determination module being configured to select the candidate correction vector that minimizes the quadratic sum or any other criterion for minimizing the distances between each element of each pair.

[0105] Alternatively, instead of using pairwise associations, the correction vector determination module 2022 may include an image processing module 2021 configured to apply an image processing technique (also called "image registration") to the consolidated representation and a cost function to determine the position error correction vector as illustrated in [Fig.4].

[0106] Figure 5 illustrates the navigation of the identification device 20 towards an object of interest 502 according to an exemplary embodiment. Figure 5 shows more specifically the extracted sonar image 501 around the object of interest 502, the auxiliary objects 504 around the object, and the position of the identification device 20. The dashed arrow 505 represents the trajectory of the identification device 20 towards an object of interest 502.

[0107] The relocation sonar 200 of the identification device 20 can be activated when the identification device 20 comes into proximity with the object of interest (502 in the [Fig.5]), or before.

[0108] When the identification device 20 approaches the object of interest (502 in Figure 5), the relocation sonar 200 is active and the objects O'j (504) visible on the sonar image of the relocation sonar 200 can be detected by any suitable method, such as an automatic detection method that may be based on artificial intelligence. The identification device 20 can also locate the detected objects Orj visible on the sonar image of the relocation sonar 200, based on the location of the identification device 20 and its relative position within the sonar image of the relocation sonar 200.

[0109] Figures 6, 7 and 8 illustrate different phases of the relocation of the target objects of interest. These figures show successive views of the consolidated representation 600 generated by the imaging unit 203, in one embodiment, corresponding to the sonar image obtained with the relocation sonar 200 of the identification device 20 at different successive times t0, ti and t2 (with t0 <ti<t2).

[0110] As shown in Figures 6, 7 and 8, the consolidated representation 600 comprises the reference image 601 (Iref) obtained in the DCL phase with the detection sonar 10, the objects 602 (^1) detected by the detection sonar 10 (each represented by a point), an object of interest 603 detected by detection sonar 10, objects 604 ( detected by identification device 20 (each represented by the '+' sign) and projected at their estimated positions, point 20 representing the position of the identification device, and sonar sector 606 of identification device 20.

[0111] The association module 2020 can determine association pairs, denoted O; O'j, between an object O'j detected (604 in Figures 6 to 8) on the sonar image of the identification device 20 and an object <7, (602 in Figures 6 to 8) detected on the reference image in the DCL phase. The association pairs are represented by an arrow going from an object O'j to an object O in Figures 7 and 8.

[0112] Figure 8 shows the translation performed by applying the position error correction vector. In the example in Figure 8, the translation brings the objects of the same pairs back to approximately the same position.

[0113] The [Fig.9] is a flowchart representing the object relocation process implemented by the identification device 200, according to embodiments.

[0114] All positions of objects or geolocated images detected by the detection sonar 10 are associated with an uncertainty, which can be recalculated when these positions are updated.

[0115] Steps 901 (moving the identification device 20 towards the target object of interest) to 906 (applying the position error correction vector) can be repeated until the identification device 20 is close enough to the target object of interest (e.g., suspect contact) to perform an action that is assigned to the identification device 20 (e.g., an identification action using a camera, or an action to neutralize the target object of interest by depositing or applying an explosive charge to the target object of interest).

[0116] In step 900, the preliminary detection information (or data) from the detection sonar 10 (which may more generally be part of an acquisition system) is transmitted to the identification device 20, for example via a direct communication link or by radio. The identification device 20 can then store this information in a memory space.

[0117] The preliminary detection information includes, for each object of interest, the position of the object of interest estimated by the detection sonar, the geolocated reference image and may include the position of auxiliary objects detected in the vicinity of the object of interest.

[0118] In step 901, for each target object of interest among the objects of interest detected by the detection sonar 10, the identification device 20, which includes an absolute positioning system 201 (inertial and / or acoustic, for example), moves to an absolute position close to the target object of interest. As used here, the term "close" means at a distance greater than the sum of the absolute positioning uncertainty of the identification device 20 and the absolute positioning uncertainty of the target object of interest (for example, a suspect object), and at a distance less than the maximum range of the relocation sonar 200. When this Step 901 is repeated, the absolute position of the target object of interest is modified by the position error correction vector and its positioning uncertainty is reduced.

[0119] In step 902, the identification device 20 uses the relocation sonar 200 to acquire an image of the seabed over a sonar sector directed forward of the identification device 20. The relocation sonar 200 is switched on (i.e. activated) to acquire secondary detection information, record the corresponding sonar image, and acquire the corresponding position of the identification device 20. Step 902 thus corresponds to the detection of sonar data by the relocation sonar.

[0120] In step 903, objects are detected in the sonar image produced by the relocation sonar 200, for example, by using an automatic detection method capable of extracting objects from the image by applying appropriate image processing (e.g., thresholding) or artificial intelligence algorithms trained to detect objects in this type of image. The objects detected by the relocation sonar 200 are then located by calculating or estimating their relative position with respect to the relocation sonar (distance and azimuth) and adding to this the absolute position of the identification device carrying the relocation sonar. Step 903 thus provides a set of secondary detection information D2 corresponding to the objects detected by the relocation sonar 200.

[0121] In step 904, an association step is implemented to determine association pairs (object pairing) between the objects detected by the detection sonar 10 and the relocation sonar 200, based on the prior detection information and the secondary detection information D2. In this phase, the detected objects from D] (objects from the reference image) and the detected objects from D2 (objects detected in the sonar image of the relocation sonar 200) are compared. Various association techniques can be used, the constraint being that the relative positions of the objects in the reference image are preserved in the image of the relocation sonar 200.

[0122] In step 905, the position error correction vector (or 'relocation vector') is determined to correct the position error between the starting position of the target object of interest estimated by the detection sonar 10 and the position of the object of interest estimated by the relocation sonar 200. The position error correction vector can be calculated as the average of the position error vectors of the pairs of objects associated in step 904.

[0123] In step 906, the position error correction vector is applied to correct the position of the target object of interest, estimated by the relocation sonar 200 and can can also be applied to correct the position of other objects detected by the relocation sonar 200, estimated by the latter.

[0124] Step 901 is then repeated using the recalibrated (or corrected) position of the target object of interest to control the movement of the identification device 20 towards the target object of interest.

[0125] Fig. 10 represents an example of the progression of an ROV-type identification device 20 towards a target object of interest 603 using the detected auxiliary objects 604 in the vicinity of the target object of interest 603.

[0126] In [Fig. 10], the relocation sonar 200 has a given search sector (in degrees) and resolution (in cm).

[0127] The relative distance between the identification device 20 and the target object of interest 603 decreases from 150m to 40m, then to 20m.

[0128] Sector A is an extension of the area

[0129] Those skilled in the art will understand that the system or subsystems according to embodiments of the invention can be implemented in various ways by hardware, software, or a combination of hardware and software, in particular in the form of program code that can be distributed as a program product in various forms. In particular, the program code can be distributed using computer-readable media, which may include computer-readable storage media and communication media. The methods described herein can, in particular, be implemented in the form of computer program instructions executable by one or more processors in a computer system. These computer program instructions can also be stored in computer-readable media.

[0130] Furthermore, the invention is not limited to the embodiments described above by way of non-limiting example. It encompasses all the variant embodiments that could be envisaged by a person skilled in the art.

Claims

1. Demands A surveillance system configured to monitor the presence of objects in water within a surveillance zone, the surveillance system comprising a detection sonar (10) and a mobile identification device (20) in water, characterized in that: - the detection sonar (10) is capable of detecting the presence of a set of objects in the surveillance area, said set comprising at least one object of interest and one or more auxiliary objects, said detection sonar being capable of determining prior detection information comprising, for each object of interest detected, at least the position of the object of interest, referred to as the starting position, and a reference image corresponding to a sonar image taken by the detection sonar comprising the objects detected by the detection sonar (10), the detection sonar being capable of transmitting the prior detection information to the identification device (20), - the identification device (20) is configured to move towards at least one target object of interest among said objects of interest, in response to the receipt of said prior detection information, the identification device comprising a relocation sonar (200) configured to detect objects in the surveillance area, the sector of the relocation sonar being initially directed towards the starting position of the target object of interest, which provides secondary detection information relating to the objects detected by the relocation sonar, the identification device further comprising a relocation unit (202) configured to: - determine a position error correction vector between the starting position of the target object of interest estimated by the detection sonar (10) and the position of the target object of interest estimated by the relocation sonar (200), based on the prior detection information and the secondary detection information, - apply the position error correction vector to correct at least the position of the target object of interest estimated by the relocation sonar (200), the movement of the identification device (20) towards the target object of interest being controlled using the corrected position of the target object of interest.

2. System according to claim 1, wherein the relocation unit (202) comprises an association module (2020) configured to determine pairs associating an object detected by the detection sonar and an object detected by the identification device (200), the position correction vector determination module (2022) being configured to determine a position error correction vector from said pairs.

3. System according to any one of the preceding claims, wherein the identification device (20) comprises an imaging unit (203) configured to generate a consolidated representation comprising the reference image including the objects detected by the detection sonar (10), and superimposed on the reference image, the sonar sector of the relocation sonar (200) and the objects detected by the relocation sonar (200).

4. System according to claims 2 and 3, wherein the association module (2020) is configured to determine the pairs by applying a translation to the sonar image of the relocation sonar in the consolidated representation, according to a criterion based on the distances between the objects.

5. System according to claim 2, wherein the position error correction vector determination module is configured to determine the position error correction vector by traversing the different determined association pairs and determining for each pair a candidate correction vector corresponding to the position translation from one element of the pair to the other, the position error correction vector determination module (2022) being configured to select the candidate correction vector that minimizes the quadratic sum or a distance minimization criterion between each element of each pair.

6. A system according to claim 5, wherein the association module uses an 'Iterative Closest Point' type association technique.

7. System according to claim 3, wherein the position error correction vector determination module (2022)

8.

9.

10. is configured to apply an image processing technique to the consolidated representation and a cost function to determine the position error correction vector. System according to claim 1, wherein the identification device comprises an absolute localization system (201) having a maximum positioning error less than the range of the relocation sonar (200). A system according to any one of the preceding claims, wherein the identification device is a remotely controlled underwater robot. A monitoring method configured to monitor the presence of objects in a surveillance zone in water, implemented in a mobile identification device (20), characterized in that the method comprises the steps of: - receive prior detection information relating to objects detected by a detection sonar (10) in the surveillance area comprising at least one object of interest and one or more auxiliary objects, the prior detection information comprising for each object of interest detected, at least the position of the object of interest, referred to as the starting position, and a reference image corresponding to a sonar image taken by the detection sonar (10) comprising the objects detected by the detection sonar (10), - determine secondary detection information relating to objects detected by a relocation sonar (200) carried by the identification device (20) during its movement towards a target object of interest among said objects of interest; the process comprising one or more iterations of the following steps: - determine a position error correction vector between the starting position of the target object of interest estimated by the detection sonar (10) and the position of the target object of interest estimated by the relocation sonar (200), based on the prior detection information and the secondary detection information, - correct at least the position of the target object of interest estimated by the relocation sonar (200), by applying the position error correction vector, - control the movement of the identification device (20) towards the target object of interest using the corrected position of the target object of interest.

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