Relocation system and method

Abstract

The invention relates to a relocation method, in particular an underwater relocation method, comprising: - receiving prior detection information relating to objects detected by a detection sonar (10) in a water-based monitoring zone; - determining secondary detection information relating to objects detected by a relocation sonar (200), carried by the identification device, as it moves towards one of the target objects of interest detected by the detection sonar; - determining an error correction vector between the position of the target object of interest as estimated by the detection sonar (10) and that as estimated by the relocation sonar (200) on the basis of the prior and secondary detection information; - correcting the position of the target object of interest as estimated by the relocation sonar (200) by applying the position error correction vector; and - controlling the movement of the identification device (20) so that it moves towards the target object of interest using the corrected position.

Description

[0001] DESCRIPTION

[0002] TITLE: Relocation System and Process

[0003] Technical field

[0004] The invention relates generally to detection systems and in particular to a device and a method for relocation, in particular underwater, using a sonar system.

[0005] Sonar systems are used in the field of underwater acoustics to detect and locate objects underwater.

[0006] Sonar systems can be used by various surveillance infrastructures, for example for the detection of submarines or objects on the seabed, or in the field of archaeology (e.g. underwater and subaquatic archaeology).

[0007] Sonar systems are equipped with antennas to transmit and / or receive signals. The processing of 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 it is possible to detect objects.

[0008] For example, in a surveillance system used to carry out a surveillance mission of an area using a sonar, the sonar may implement a first phase (first detection) consisting of detecting one or more objects of interest (for example a threatening object) from the sonar images, which provides 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 to the sonar system and its carrier.

[0009] 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 necessary, implement appropriate actions (for example, neutralization of the threat) using another robotic underwater system or divers who must then find the geographical position of the detected object.

[0010] However, underwater robotic systems (such as a ROV or Remotely Operated Vehicle) or divers must rely on sometimes imprecise position information to efficiently find 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 find the position of the detected object within the circle of uncertainty given by the sonar in the first detection phase.

[0011] 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 having carried out the first phase of detection and localization, or even a risk of error in the object found if the bottom is cluttered. Different 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 system ("Global Navigation Satellite Systems") cannot be used directly underwater (the frequencies used do not pass through water).When a sonar (e.g., towed sonar) 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 unit or inertial unit to locate this echo. These units are all the more precise as the data supplied to them is precise. In the case of an AUV, for example, the GNSS data collected at the surface have drifted throughout the descent phase and with the elapsed time, and in the case of towed sonar, the GNSS position data are relayed to a lever arm established by positioning acoustics.In the case of surface-borne sonars, which could benefit from the advantage of being coupled directly to the GNSS system, their positioning performance is degraded due to the distance to the bottom (for a side-scan sonar, an error in measuring the yaw or the speed of sound in the water leads to a positioning error).

[0012] There is thus a need for an improved underwater detection system and method. General definition of the invention

[0013] For this purpose, a surveillance system is provided configured to monitor the presence of objects, in a surveillance zone, in the water, the surveillance system comprising a detection sonar and a mobile identification device in the 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 prior detection information comprising, for each detected object of interest, 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. The detection sonar is capable of transmitting the prior detection information to the identification device.

[0014] The identification device is configured to move toward at least one target object of interest among the objects of interest, in response to receiving the 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 toward the starting position of the target object of interest, thereby providing secondary detection information relating to the objects detected by the relocation sonar.

[0015] The identification device further comprises a relocation unit configured to 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; 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 some 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 may be configured to determine the pairs by applying a translation to the sonar image of the relocation sonar in the consolidated representation, based on a criterion based on the distances between the objects.

[0019] The position error correction vector determination module may be configured to determine the position error correction vector by traversing the various 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 that 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 may 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 some aspects, the identification device may include an absolute location system having a maximum positioning error less than the range of the relocation sonar.

[0023] In embodiments, the identification device may be a remotely controlled underwater robot. Further provided is a monitoring method configured to monitor the presence of objects, in a monitoring area in the water, implemented in a mobile identification device. The method advantageously comprises the steps of: receiving prior detection information relating to objects detected by a detection sonar in the monitoring area comprising at least one object of interest and one or more auxiliary objects, the prior detection information comprising for each detected object of interest, 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;determining secondary detection information relating to objects detected by a relocation sonar carried by the identification device during its movement towards a target object of interest among the objects of interest; the method comprising one or more iterations of the following steps: determining 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; correcting at least the position of the target object of interest estimated by the relocation sonar, by applying the position error correction vector, controlling the movement of the identification device towards the target object of interest using the corrected position of the target object of interest.;

[0024] The embodiments of the invention thus allow improved relocation of the objects detected in the first detection phase by minimizing the risk of error and improving the relocation time of the detected object.

[0025] Brief Description of Figures

[0026] Other characteristics, details and advantages of the invention will emerge from reading the description given with reference to the appended drawings given by way of example and which represent, respectively:

[0027] [Fig.1] - Figure 1 represents a monitoring system according to embodiments.

[0028] [Fig.2] - Figure 2 illustrates an example representation of the reference image extracted in the first detection phase.

[0029] [Fig.3] - Figure 3 represents the structure of the relocation unit, according to embodiments.

[0030] [Fig.4] - Figure 4 represents the structure of the relocation unit, according to other embodiments.

[0031] [Fig.5] - Figure 5 illustrates the navigation of the identification device towards an object of interest according to an exemplary embodiment.

[0032] [Fig.6] - Figure 6 illustrates one phase of the relocation of target objects of interest.

[0033] [Fig.7] - Figure 7 illustrates another phase of the relocation of target objects of interest. [Fig.8] - Figure 8 illustrates yet another phase of the relocation of target objects of interest.

[0034] [Fig.9] - Figure 9 is a flowchart representing the object relocation method implemented by the identification device, according to embodiments.

[0035] [Fig.10] - Figure 10 represents an example of progression of an ROV type identification device towards a target object of interest.

[0036] Detailed description of the request

[0037] Figure 1 schematically represents an example of an environment in which certain embodiments of the invention can be implemented.

[0038] Embodiments of the invention provide a surveillance system 100 (also referred to as an object relocation system) configured to monitor the presence of objects, in a surveillance area, in water, such as in a maritime environment.

[0039] The surveillance system comprises a detection sonar 10 and an identification device 20 (also called a 'relocation device').

[0040] The detection sonar 10 may be part of a pre-detection data acquisition system (not shown).

[0041] The detection sonar 10 is configured to determine prior detection information relating to objects detected in the surveillance area, the detected objects comprising at least one object of interest. The prior detection information comprises at least, for each detected object of interest, 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 comprising the object of interest and the auxiliary objects detected in the vicinity of the object of interest.

[0042] The reference image can be a geolocated image representing the seabed when the monitoring area is a maritime zone.

[0043] The detection sonar 10 is configured to transmit the prior detection information to the identification device 20.

[0044] The identification device 20 is a mobile device (such as a vehicle) capable of moving in the water to approach at least one object of interest, called the target object of interest, to identify it and / or implement an action. The identification device 20 comprises a relocation sonar 200 configured to determine secondary relocation information relating to objects detected by the relocation sonar 200 in the surveillance zone, 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.

[0045] The identification device 20 may also comprise an absolute location system 201 enabling it to steer towards the area of ​​the target object of interest with a maximum uncertainty less than the range of the relocation sonar. The absolute location system 201 advantageously has a maximum positioning error less than the range of the relocation sonar 200 which equips the identification device 20, which enables the identification device to approach a contact of interest by steering with the location 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.

[0046] Advantageously, the identification device 20 is able to move towards a target object of interest by performing a relocation of the target object of interest from the prior detection information, the 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.

[0047] The landmark objects (also called "landmarks" or "beams" in English) are fixed landmark objects positioned on the seabed whose position is known (stored in a database of the device 20), with an uncertainty intrinsic to the detection system which was used to determine this position beforehand (this detection system being able to be a system distinct from the detection sonar 10). In the embodiments of the invention, the constellations formed of landmark objects (comprising at least one landmark object) and an object of interest are used to allow the relocation of an object of interest previously detected by the detection sonar 10.

[0048] The constellation of landmark objects is advantageously used to find 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 landmark object is present around the object of interest, then the relocation does not require any use of a constellation.

[0049] The detection sonar 10 may be arranged on a carrier such as, for example, a naval vessel or a submarine capable of being submerged in water. The detection sonar 10 may, for example, be a towed sonar or installed on an autonomous underwater vehicle (AUV).

[0050] The detection sonar 10 is configured to emit sound pulses and receive in response waves reflected from the bottom and from underwater objects, thereby enabling image formation and object detection.

[0051] The surveillance system 100 can be used in different fields of application such as, for example and without limitations, in the field of target detection to detect threats, in the field of underwater biology and ecology (for example to analyze aquatic pollution), or in the field of archaeology (for example underwater and sub-marine 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 target object of interest depending on the field of application of the invention (an action may be, for example, capturing images, taking videos, taking measurements, a target neutralization action, etc.)

[0052] The detection sonar 10 and the relocation sonar 200 may be active sonars. An active sonar includes a transmitter and a receiver. The transmitter and receiver include a set of transducers configured to transmit and / or receive sound waves.

[0053] When transmitting, the sonar transmitter's transducers are capable of emitting pulses in a given direction. When receiving, the conversion of acoustic data (pressure of the incident acoustic wave) into electrical data (output voltage) is carried out by one or more transducers.

[0054] A sonar receiver is configured to listen for echoes reflected in response to sonar emissions, in a given frequency band (expressed in Hz), with a given hydrophonic sensitivity (designated 'Sh' and expressed in decibels dB) and a given processing gain (expressed in dB) of the received signals, which allows object detection.

[0055] A sonar receiver is further configured to locate detected objects. To perform a location of 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 to estimate the distance (in meters m) of the echoes from the delay time (in seconds s) of the echo for a sonar in active mode.

[0056] The detection sonar 10 and the relocation sonar 200 may be capable of forming a sonar image representing the scene detected by the sonar.

[0057] The detection sonar 10 is thus used in a first phase of the detection to detect objects of interest and auxiliary objects around the objects of interest, and to determine the prior detection information (for each object of interest, starting position of the object of interest estimated by the detection sonar 10 and associated geolocated reference image). The first detection phase may further comprise an object classification making it possible to determine whether a detected object is an object of interest (the first detection phase is then also called 'DCL phase' for 'Detection Classification, Localization').

[0058] The monitoring system 100 may further comprise a control unit 18 configured to control the operation of the identification device 20 and / or transmit commands to communication equipment fitted to 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 comprise a display device (not shown) comprising a graphical interface in which a representation of the reference images provided by the detection sonar 10, of the sonar image detected by the relocation sonar 200 or a consolidated representation of these two images may 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, a keyboard, a touch input device, a voice-activated 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 notably capable of modifying the display on the graphical interface based on commands entered into the control unit 18 by means of the input devices or based on the detection carried out by the detection sonar 10 and / or the relocation sonar 200.

[0059] The identification device 20 may be robotic and / or automated. The identification device 20 may be controlled remotely by the operator via the control unit 18.

[0060] 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.

[0061] 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 may be, for example and without limitation, a remotely operated underwater vehicle ROV which may be equipped with the relocation sonar 200. The identification device 20 may be entirely implemented in the relocation sonar 200 (the identification device 20 then coincides with the relocation sonar 200) when the relocation sonar 200 is a portable sonar carried by a diver (for example, a clearance diver).

[0062] The identification device 200 may be connected to the same carrier as the detection sonar 10. The carrier of the detection sonar 10 may be, for example, an autonomous surface vessel (USV, acronym for the corresponding English expression “Unmanned Surface Vehicle”). The identification device 200 may, for example, be connected by a cable to the carrier (as in the case of an ROV).

[0063] In the first detection phase, the detection sonar 10 is configured to insonify the surveillance area in order to detect objects in the surveillance area (i.e., emit acoustic waves in the surveillance area). After each emission, the detection sonar 10 can remain on standby (or listening) for a sufficient time to receive the echoes of the detected objects (e.g., targets) present in the surveillance area. The detection sonar 10 can then process the received echoes in order to detect the objects in the surveillance area, perform a classification to identify objects of interest, the other detected objects being auxiliary objects, and to estimate the position of each object of interest (called the starting position).The detection sonar 10 may use a classification technique to characterize the 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.

[0064] The detection sonar 10 is not limited to the use of a detection technique using the echoes directly. In embodiments, the detection sonar 10 can be configured to generate high-resolution images of the bottom, and to use them to detect and classify objects on the bottom from their echo and also their shadows. In such embodiments, the detection sonar 10 can be configured to classify the 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 SAS (Synthetic aperture sonar) side-scan sonar.

[0065] 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, an acronym for “Doppler Velocity Log” meaning Doppler speed recorder), or from an acoustic location 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 significant uncertainty which depends on the performance of its location system.In addition to this absolute positioning error of the detection sonar 10, there is an uncertainty in the relative positioning of the objects detected by the detection sonar in relation to the latter (linked to the uncertainty in the speed of sound and to the uncertainty in the azimuth of the sonar paths formed by the detection sonar 10).

[0066] Advantageously, the embodiments of the invention allow relocation of the target objects of interest and guidance of the identification device 20 towards these objects despite such absolute position uncertainties.

[0067] The objects of interest and auxiliary objects thus detected can then be located on the sonar data from the detection sonar 10.

[0068] In the 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, in the surveillance zone and perform the detections of objects of interest and auxiliary objects from a sonar image. The sonar image used for the detection of 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 maritime environment) around an object of interest (step of extracting a geolocated image around each object of interest).

[0069] The first detection phase thus makes it possible to obtain preliminary detection information including:

[0070] The list of objects of interest (e.g. suspicious objects or objects constituting a potential threat) that need to be approached (e.g. for inspection), 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; For each object of interest, the geolocated reference image around the object of interest (e.g. an image of the seabed). These images may show other auxiliary objects, around the object of interest, if such objects were detected in the first detection phase.

[0071] In one embodiment, the prior detection information may 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).

[0072] The information obtained at the end of the first detection phase is then used by the identification device 20. The identification device 20 may comprise 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.

[0073] Figure 2 illustrates an example representation of the reference image 101 extracted in the first detection phase. The reference image 101 comprises a detected object of interest 102 and auxiliary objects 104 in the vicinity of the object of interest.

[0074] In the second phase, called the relocation phase, the identification device 200 receives, from the detection sonar 10, the prior detection information > acquired during the first detection phase comprising at least the reference geolocated image I refi , the prior positions P i of the various objects of interest O i t and the positioning uncertainties associated with the P positions i .

[0075] The prior detection information T)1 may include additional information such as the positions of the detected auxiliary objects.

[0076] The prior detection information D1 may be stored by the identification device 20 in a storage memory. A display of this stored information may be generated on a control screen embedded in the identification device 20.

[0077] For example, if the identification device 20 is an ROV, the reference geolocated image I refi and the prior positions P ti of the various objects of interest O t 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.

[0078] In another example, if the identification device 20 is a diver and the relocation sonar 200 equipping the identification device 20 is a portable sonar, the reference geolocated image I refi and the prior positions P i of the various objects of interest O tcan be stored by the relocation sonar 200 and a display of this information can be generated on a control screen directly on the portable sonar 200 (in this case the identification device 20 corresponds to the portable relocation sonar 200).

[0079] The relocation sonar 200 equipping the identification device 20 may be of a different type from the detection sonar 10 which was 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-front sonar, or any other sonar capable of generating images of the bottom. The relocation sonar 200 of the identification device 20 may be, for example and without limitation, a multi-beam front-scan sonar, or any other sonar.

[0080] The identification device 20 may comprise an imaging unit 203 configured to generate a consolidated representation R comprising the geolocated reference image I refi determined in the DCL phase, and received from the detection sonar 10, and superimposed on the geolocated reference image I refi , data from the secondary detection information T>2 determined by the relocation sonar 200 and comprising:

[0081] 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 their estimated positions P'j;

[0082] Secondary sonar image I seC2 obtained with the relocation sonar 200 of the identification device 20 by projecting it onto the reference image I refiat its estimated position; the display can be generated with a sufficient degree of transparency to make the rendering of the Z reference image visible reA below the auxiliary sonar image I seC2 .

[0083] Thus, the secondary detection information Z>2 can include the information P'j determined for the different objects O'j detected by the relocation sonar 200 and the auxiliary sonar image l seC2 obtained with the 200 relocation sonar on which the various detected O'j objects are positioned.

[0084] The imaging unit 203 can further generate a display of the contour of the sonar sector of the relocation sonar 200 and the position of the identification device 20 on the reference image I refi displayed.

[0085] Advantageously, the relocation unit 202 is able to use the prior detection information T received, the secondary detection information T>2 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 towards one or more chosen target objects of interest, minimizing the risk of position error and thus optimizing the time required to approach an object of interest. The reference objects may for example be rocks present on the seabed, the initial position of which is determined during the prior detection and of which their positions and the associated position uncertainty are available.

[0086] Figure 3 shows the structure of the relocation unit 202 according to one embodiment.

[0087] The relocation unit 202 comprises a position error correction vector determination module 2022 configured to determine a position error correction vector (also called 'registration vector'), from the prior detection information T>1 received from the detection sonar 10, the secondary detection information D2 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 I ref and on image I seC2 of the 200 relocation sonar.

[0088] The relocation unit 202 may comprise a position correction module 2024 configured to apply the determined position error correction vector 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, thereby relocating all of the images and objects relative to the position of the objects in the first detection phase (pre-detection).

[0089] For each target object of interest, the object constellation comprising the target object of interest and the set of landmark objects (among the auxiliary objects) in the vicinity of the target object of interest in the relocation image I seC2 is compared to the constellation of objects formed by the target object of interest and the set of landmark objects in the reference image I refiproduced in the first detection phase, using a comparison technique.

[0090] The identification device 20 may further comprise 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 (for example inertial system, DVL sensor, acoustic positioning means, etc.) for moving relative to the object of interest, from the corrected position.

[0091] During the movement of the identification device 20 towards an object of interest to be identified, the positioning error correction module 2022 can repeat the position correction several times dynamically until reaching the object of interest, which makes it possible to avoid drift.

[0092] In one embodiment, the relocation unit 202 may comprise a configured association unit 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 received and the secondary detection information ï>2detected 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.

[0093] An association pair may 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). According to one aspect, the association module 2020 may be configured to determine the association pairs by applying a translation to the sonar image of the relocation sonar 200 in the consolidated representation R, the translation being carried out so as to minimize the sums of distances between the pairs of objects.

[0094] In one embodiment, the pairwise association 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 association method. The ICP transformation method is a method for matching two sets of point clouds 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 association technique and encompasses any association technique that allows for estimating a translation and a rotation between two sets of points.

[0095] In one embodiment, the position error correction vector determination module may be configured to determine the position error correction vector by traversing the various 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 that minimizes the quadratic sum or any other criterion for minimizing the distances between each element of each pair.

[0096] 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.

[0097] 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 precisely the extracted sonar image 501 around the object of interest 502, auxiliary objects 504 around the object and the position of the identification device 20. The dotted arrow 505 represents the trajectory of the identification device 20 towards an object of interest 502.

[0098] The relocation sonar 200 of the identification device 20 may be activated when the identification device 20 arrives in proximity to the object of interest (502 in FIG. 5), or before.

[0099] When the identification device 20 arrives in proximity to the object of interest (502 in FIG. 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 which can be based on artificial intelligence. The identification device 20 can additionally perform a localization of the detected objects O'j visible on the sonar image of the relocation sonar 200, from the location of the identification device 20 and the position relative to the identification device 20 in the sonar image of the relocation sonar 200.

[0100] 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 an exemplary embodiment, corresponding to the sonar image obtained with the relocation sonar 200 of the identification device 20 at different successive times to, ti and tz (with to <ti<tz).

[0101] As shown in Figures 6, 7 and 8, the consolidated representation 600 includes the reference image 601 (I ref ) obtained in the DCL phase with the detection sonar 10, the objects 602 (O detected by the detection sonar 10 (each represented by a point), an object of interest 603 detected by the detection sonar 10, the objects 604 (O' y) detected by the identification device 20 (each represented by the sign '+') and projected at their estimated positions, the point 20 representing the position of the identification device, and the sonar sector 606 of the identification device 20.

[0102] The 2020 association module can determine association pairs, denoted O t -> O' J t between an object O'j detected (604 in figures 6 to 8) on the sonar image of the identification device 20 and an object O t (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.

[0103] Figure 8 shows the translation performed by applying the position error correction vector. In the example of Figure 8 the translation performed brings the objects of the same pairs back to approximately the same position.

[0104] Figure 9 is a flowchart showing the object relocation method implemented by the identification device 200, according to embodiments.

[0105] 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.

[0106] Steps 901 (moving the identification device 20 toward the target object of interest) to 906 (applying the position error correction vector) may be repeated until the identification device 20 is close enough to the target object of interest (e.g., suspicious contact) to perform an action that is assigned to the identification device 20 (e.g., an action of identification using a camera, or an action of neutralizing the target object of interest by depositing or applying an explosive charge to the target object of interest).

[0107] In step 900, the prior 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 by a direct communication link or by radio. The identification device 20 can then store them in a memory space. The prior detection information D- comprises, for each object of interest, the position of the object of interest estimated by the detection sonar, the geolocated reference image and may comprise the position of the auxiliary objects detected in the vicinity of the object of interest.

[0108] 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 comprises an absolute positioning system 201 (inertial and / or acoustic for example), heads towards an absolute position in the vicinity of the target object of interest. As used herein, the term "in the vicinity" 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 suspicious 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.

[0109] In step 902, the identification device 20 uses the relocation sonar 200 to acquire an image of the seabed on a sonar sector directed towards the front of the identification device 20. The relocation sonar 200 is started (i.e. activated) to acquire the 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 the sonar data by the relocation sonar.

[0110] 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 the objects from the image by applying suitable image processing (for example of the thresholding type) or artificial intelligence algorithms trained to detect objects on 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 by adding thereto the absolute position of the identification device which carries the relocation sonar. Step 903 thus provides a set of secondary detection information D2 corresponding to the objects detected by the relocation sonar 200.

[0111] 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 from the prior detection information D ± and secondary detection information D2. In this phase, the detected objects from (objects of the reference image) and the detected objects from D2 (objects detected in the sonar image of the relocation sonar 200). Various association techniques can be used, the constraint being that the relative positions of the objects of the reference image between them are preserved in the image of the relocation sonar 200.

[0112] In step 905, the position error correction vector (or 'registration 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.

[0113] 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 also be applied to correct the position of the other objects detected by the relocation sonar 200, estimated by the latter.

[0114] 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.

[0115] Figure 10 shows an example of 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.

[0116] In Figure 10, the relocation sonar 200 has a given search sector (in degrees) and resolution (in cm).

[0117] The relative distance between the identification device 20 and the target object of interest 603 changes from 150 m, to 40 m, then to 20 m.

[0118] Sector A is an expansion of the area

[0119] Those skilled in the art will understand that the system or subsystems according to embodiments of the invention may be implemented in various ways by hardware, software, or a combination of hardware and software, including in the form of program code that may be distributed as a program product, in various forms. In particular, the program code may be distributed using computer-readable media, which may include computer-readable storage media and communication media. The methods described in the present disclosure may be implemented, in particular, in the form of computer program instructions executable by one or more processors in a computer computing device. These computer program instructions may also be stored in a computer-readable medium.

[0120] Furthermore, the invention is not limited to the embodiments described above as a non-limiting example. It encompasses all the variant embodiments which may be envisaged by those skilled in the art.

Claims

CLAIMS 1. Surveillance system configured to monitor the presence of objects, in a surveillance zone, in the water, the surveillance system comprising a detection sonar (10) and an identification device (20) mobile in the water, characterized in that: the detection sonar (10) is capable of detecting the presence of a set of objects in the surveillance zone, 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 detected object of interest, 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 (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 receiving said prior detection information, the identification device comprising a relocation sonar (200) configured to detect objects in the monitoring 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:, - determining 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), from the prior detection information and the secondary detection information, - applying 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 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 sonar of detection (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. The system of claim 2, wherein the position error correction vector determination module is configured to determine the position error correction vector by traversing the various 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 criterion for minimizing the distances between each element of each pair.

6. System according to claim 5, in which the association module uses an 'Iterative Closest Point' type association technique.

7. The system of claim 3, wherein the position error correction vector determination module (2022) is configured to apply an image processing technique to the consolidated representation and a cost function to determine the position error correction vector.

8. The system of claim 1, wherein the identification device comprises an absolute location system (201) having a maximum positioning error less than the range of the relocation sonar (200).

9. System according to one of the preceding claims, in which the identification device is a remotely controlled underwater robot.

10. A monitoring method configured to monitor the presence of objects, in a monitoring area in water, implemented in a mobile identification device (20), characterized in that the method comprises the steps of: receiving prior detection information relating to objects detected by a detection sonar (10) in the monitoring area comprising at least one object of interest and one or more auxiliary objects, the prior detection information comprising for each detected object of interest, 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 (10) comprising the objects detected by the detection sonar (10),determining 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 method comprising one or more iterations of the following steps:, - determining 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), from the prior detection information and the secondary detection information, - correcting at least the position of the target object of interest estimated by the relocation sonar (200), by applying the position error correction vector, - controlling 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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