Submarine exploration system with a fleet of drones

Abstract

The present invention relates to a submarine exploration system (1) comprising a master submarine drone (2) designed to move autonomously according to a predetermined navigation plan (E) and equipped with a communication module (C) for transmitting communication signals, and a number of follower submarine drones (31, 32, 33, 34, 35, 36), each equipped with at least one magnetic field detection system (D) and each follower drone further equipped with a communication module (C) for receiving communication signals from the master drone, wherein the master drone is designed to transmit navigation instructions (I) to the follower drones, each follower drone being designed to move autonomously in response to the movement instructions such that its movements are slaved to those of the master drone.

Description

[Technical field]

[0001] The present invention relates to the field of submarine exploration, more precisely to the exploration of the deep sea floor using a fleet of submarine drones.

[0002] The deep sea floor contains sites of important mining potential. Indeed, hydrothermal activity in the region of ocean ridges has contributed to the creation of hydrothermal sites such as polymetallic sulfide nodules that are rich in metals, especially zinc, silica, copper and lead, and generally enriched in gold and silver.

[0003] Despite their potential, these sites have not yet been exploited. On the one hand, the depths at which these sites are located, exceeding 800 m, and in fact exceeding 4000 m, mean that traditional techniques of submarine exploration are inadequate. On the other hand, the small dimensions of these sites, with a radius of 10 to 500 meters, in relation to the extremely wide range of ocean surfaces where they can be found, complicate the exploration of said surface to identify them. Finally, not all these sites can be exploited. In fact, some sites are called inactive, i.e., cold and estimated to have low biodiversity, while others are called active, i.e., hot and with oases of life. It goes without saying that, in order to preserve the marine ecological environment, active sites must be excluded from any selfish exploitation. However, current techniques for site discovery are essentially based on the detection of hydrothermal plumes present in the water column, which are only associated with active sites and are therefore not effective in locating inactive sites.

[0004] There is therefore a need for a solution for the exploration of the deep seabed that is effective, rapid and allows for the detection of active and inactive sites in order to identify sites with mineral potential.

[0005] In the field of submarine exploration, a known solution is to use several autonomous submarine drones, also called AUVs (Autonomous Underwater Vehicles), equipped with sensors that allow to detect possible sites of minerals, the drones forming a fleet covering the seabed. These drones, capable of moving autonomously according to a given navigation plan, have the drawback of being very costly, in particular on the one hand due to the precision of the navigation systems they use and on the other hand due to the large number of on-board sensors. However, to allow an effective exploration of the seabed, it is necessary to use a large number of drones, each of which covers a part of the surface to be explored, in order to reduce the exploration time. These limitations therefore make an effective, fast and low-cost exploration of the deep seabed impossible. Moreover, the on-board sensors of said drones do not allow to detect inactive sites.

[0006] The present invention is within this context and aims to overcome the identified problems by proposing a solution for the exploration of the deep seabed that meets the requirements of speed, effectiveness and detection of active and inactive sites while maintaining reasonable exploration costs.

[0007] To this end, the present invention comprises: a. a master submarine drone configured to move autonomously according to a predetermined navigation plan and equipped with a communication module for transmitting communication signals; b. A submarine exploration system comprising: a plurality of follower submarine drones, each comprising at least one magnetic field detection system, each follower drone further comprising a communications module for receiving communications signals from the master drone.

[0008] According to the present invention, a master drone is configured to transmit navigation instructions to follower drones, and each follower drone is configured to move autonomously in response to the movement instructions such that its movement is enslaved to the movement of the master drone.

[0009] It is therefore understood that only the master drone requires accurate navigation equipment to move according to its flight plan, and the follower drones are limited to following the master drone in its movements. The equipment of the follower drones can therefore be simplified, reducing their cost. In addition, it has been found that hydrothermal sites with mineral potential such as sulfide nodules have significant magnetic signatures with submarine magnetic anomalies, the peak-to-peak amplitudes of which can exceed hundreds to thousands of nanoteslas. Moreover, the magnetic signatures persist even after hydrothermal activity has ceased, as is the case for inactive sites. Due to this persistence, the use of magnetic field detection systems in the follower drones thus makes it possible to detect magnetic anomalies that may be active sites as well as inactive sites. The master drone can further be equipped with other types of sensors that, following the detection of the magnetic anomaly, make it possible to characterize the source of the magnetic anomaly and, in particular, to distinguish whether it is an active or inactive site.

[0010] "Submarine drone" means any type of vehicle capable of autonomous movement underwater.

[0011] Advantageously, the communication modules of the master and follower drones are acoustic communication modules. In other words, the data transmitted by the communication modules of each of the master and follower drones is encoded, for example, by frequency modulation of the acoustic signal transmitted by said communication modules. If applicable, the master drone may be configured to periodically transmit navigation instructions to all follower drones, each of which is configured to move according to the last received instruction until a subsequent instruction is received. The periodicity of the transmission of navigation instructions by the master drone over a short period, for example, 6 seconds, makes it possible to ensure that the movement of the follower drones is slaved to the movement of the master drone over a short distance, for example, over a distance of less than 15 meters, thereby preventing overdriving and thus improving the robustness of the system.

[0012] Advantageously, the master drone is configured to periodically determine the steering heading and the formation geometry of the follower drones from the flight plan, and each navigation command is transmitted by the master drone to all follower drones including the steering heading and said formation geometry. When applicable, each follower drone is configured to move in a direction according to the steering heading upon receiving each navigation command until a subsequent navigation command is received, and to determine and adopt a position relative to the master drone according to the formation geometry. For example, a given flight plan may define a plan of navigation lines and a formation geometry suitable for exploration of a given zone under conditions associated with the master and follower drones, and the master drone is configured to determine the steering heading from the plan of navigation lines and by its own position on the plan of navigation lines. "Formation geometry" means a set of relative positions of master and follower drones, which may include, for example, for each follower drone, its spatial position relative to the master drone, i.e., left or right, front or back, as well as the lateral distance separating the follower drone from the master drone.

[0013] According to an example, the formation geometry may consist of a comb-shaped formation of master and slave drones, centered on the master drone, with follower drones distributed on either side of the master drone and regularly spaced apart by 100 m. In this formation, it is understood that the master and follower drones move progressively and simultaneously, following parallel lines as defined in the navigation line plan of the operation plan, following the transmission and reception of navigation commands, while adhering to the formation geometry defined by the master drone. The movement is performed, for example, at an operational altitude of 100 m above the seabed, and at a navigation speed of 3 to 4 knots. This recognition strategy represents a good compromise between the detection objectives and the need for effectiveness and speed.

[0014] According to an example, the master drone and each follower drone are equipped with a memory, each of which has a plurality of formation geometries loaded therein, each of which is associated with a formation code that identifies the geometry. If applicable, the navigation instructions transmitted by the master drone include the formation code that identifies the formation geometry determined by the master drone, and each follower drone is configured to determine its relative position with respect to the master drone by selecting the formation geometry that is loaded in its memory and associated with the transmitted formation code.

[0015] In an embodiment of the invention, each follower drone comprises a navigation system configured to determine its position at a given moment and to move from said determined position according to navigation commands received from the master drone. The follower drone may in particular be configured to move from said determined position according to a steering orientation and in a manner that maintains its relative position to the master drone as defined in the formation geometry of the navigation commands transmitted by the master drone. For example, the navigation system may comprise an instrument for measuring the attitude of the follower drone at a given moment, in particular an attitude unit of MEMS (Micro Electro Mechanical System) type, which makes it possible to obtain information about the rolling and pitching of the follower drone, and a magnetometer that makes it possible to obtain the magnetic orientation of the follower drone. The position of the follower drone at a given moment can thus be estimated from its attitude measured by said measuring instrument, by the navigation system according to the navigation commands received, and from the last position estimated. This type of system performing "dead reckoning" navigation offers a satisfactory compromise between the accuracy of the estimation of the position of the follower drone and the cost of the navigation system.

[0016] Advantageously, the navigation system of each follower drone is configured to determine the altitude of the follower drone relative to the seabed at a given moment, and each follower drone is configured to move while maintaining a constant altitude relative to the seabed. It is therefore understood that the follower drone is autonomous with respect to its altitude. In the opposite case, a complete enslavement of the movement of the follower drone, including with respect to its altitude, could lead to collisions with local changes in the seabed that are not taken into account by the operation plan in the area of ​​the master drone. The autonomy of the follower drone with respect to altitude therefore allows these local changes to be taken into account.

[0017] The communication module of each follower drone is preferably configured to transmit a signal to the master drone that includes the determined position of the follower drone.

[0018] Advantageously, the communication module of each follower drone is configured to transmit a signal including the determined position of the follower drone and the operation state of the follower drone to the master drone, and the master drone is configured to determine the piloting orientation and the formation geometry from the operation state of the follower drone. For example, each follower drone is configured to determine its operation state, i.e., a viable state or a fault state. If applicable, in the event of a fault, each follower drone can be configured to leave the formation and rejoin the base. Advantageously, upon receiving a signal including the fault state of the follower drone, the master drone can be configured to determine a new formation geometry suitable for the follower drone in a viable state.

[0019] In practice, in the event of a failure of a follower drone, the exploration of the area explored by the formation of drones includes a recording gap corresponding to the zone not yet explored by the failed follower drone. To overcome this gap, the master drone may determine a new flight plan, i.e. a new plan of the navigation line and / or a new formation geometry. For example, in the case of a failure of a failed drone in a comb-shaped formation geometry, the master drone may determine a new formation geometry in which a viable follower drone located at the end of the comb takes the place of the failed follower drone, and a new navigation line plan in which the navigation line is narrowed. The new flight plan may be selected from a plurality of flight plans stored in the memory of the master drone, for example, depending on the operational state of the follower drone, each flight plan being associated with a given number of viable follower drones.

[0020] Advantageously, the communication module of each follower drone may be configured to receive echoes of signals transmitted by the communication module of the follower drone to the master drone and reflected by the master drone, and to determine from said echoes the relative distance separating the follower drone from the master drone. If applicable, the navigation system of the follower drone is configured to determine said position of the follower drone at said given moment by the determined relative distance. Thus, the follower drone determines its relative distance from the master drone by echo localization of the master drone by the signals transmitted by the follower drone.

[0021] Thus, the navigation system of each follower drone can alternately function in a navigation mode called "dead reckoning", according to which it estimates its position at a given moment from its last estimated position using only its attitude and the navigation instructions received, and in a mode called "convergence", according to which the relative distance from the master drone, which occurs with each transmission of a signal by the communication module, is integrated into the determination of the position at the given moment. This integration makes it possible to correct drifts that may occur during the dead reckoning navigation mode and may result in deviations in the relative positioning of the follower drone with respect to the master drone. For example, the relative distance to the master drone determined by echolocation can be used in the determination of the position at the given moment by comparing it with the relative distance fixed by the formation geometry determined by the master drone. In case of drift, the follower drone can correct its movement to move according to a steering heading, regaining its relative position with respect to the master drone as defined in the formation geometry of the navigation instructions received from the master drone.

[0022] In an embodiment of the invention, the master drone comprises a navigation system configured to determine the position of the master drone at a given moment and a memory in which a flight plan is loaded, the master drone being configured to move from its determined position according to the flight plan loaded in its memory. If applicable, the accuracy of the navigation system of the master drone is higher than the accuracy of the navigation systems of the follower drones. For example, the navigation system of the master drone may comprise an inertial unit of the FOG type (Fiber Optic Gyroscope) and comprises a data processing module that receives information from an acoustic positioning system such as a DVL (Doppler Velocity Log) and integrates, for example, an algorithm of the Kalman filter type.

[0023] Advantageously, the master drone comprises multiple systems of different types for characterizing the seabed. Where applicable, each follower drone comprises a single system for characterizing the seabed formed by said magnetic field detection system. The follower drone is therefore called single-sensor and the master drone is called multi-sensor. For example, the master drone may comprise at least two systems for characterizing the seabed selected from the following non-limiting list of systems: a magnetic field detection system, a bathymetric mapping system (such as a multi-beam bathymetry), an acoustic imaging system (such as a lateral scanning sonar), an object detection system (such as a camera), and a system for measuring physical or chemical hydrodynamic parameters. In this way, when detecting a magnetic anomaly by the magnetic field detection system of the follower drone, and optionally of the master drone, the master drone may be able to distinguish, by the system for characterizing the seabed that it contains, the type of source of the magnetic anomaly, in particular whether it is an active or inactive hydrothermal site with mineral potential.

[0024] In an embodiment of the invention, the magnetic field detection system of each follower drone comprises a magnetic field sensor capable of measuring the magnetic field in the vicinity of the follower drone. If applicable, the system according to the invention may comprise a data processing module configured to extract from the measured magnetic field a value independent of the values ​​of the ambient magnetic field and the magnetic field of the follower drone itself, and to detect magnetic anomalies based on said value. If applicable, the magnetic field sensor may be what is known as a three-component vector magnetometer, comprising three magnetometers arranged at 90° to each other. This type of magnetometer allows to be free from the influence of some of the parasitic magnetic fields generated by the follower drone.

[0025] Advantageously, the data processing module is configured to correct the measured total magnetic field to extract said value, the correction being made based on the movement attitude of the follower drone, i.e. its rolling, its pitching and its orientation, as well as on the surrounding local geomagnetic field. In fact, it has been observed that the magnetic field measured by the magnetic field sensor is the sum of the magnetic anomalies present locally in the area of ​​the seabed, the surrounding geomagnetic field and the parasitic magnetic field associated with the follower drone, i.e. the induced and permanent magnetic fields. However, the induced and permanent magnetic fields generated by the follower drone depend on the movement attitude of the follower drone. As the follower drone is equipped with a navigation system, the data processing module of the magnetic field detection system can thus recover data related to the movement attitude of the follower drone at each moment, from which the induced and permanent magnetic fields can be determined, for example, by determining the coefficients of the magnetic susceptibility tensor and the residual magnetization vector of the follower drone. For example, the value can be extracted by the following correction operation:

[0026] [Formula 1] A=H mes -(H i +H p )-F, where A represents the extracted value and H mes is the magnetic field measured by the magnetic field sensor, H i is the induced magnetic field of the follower drone, H p is the permanent magnetic field of the follower drone, and F is the local ambient Earth magnetic field.

[0027] If applicable, the data processing module of the magnetic field detection system may be configured to detect a magnetic anomaly if the extracted value is greater than a predefined threshold.

[0028] If desired, the data processing module may be mounted on one, some or indeed each of the follower drones. In a variant, the data processing module may be external to the drones of the system according to the invention.

[0029] According to an embodiment of the present invention, the acoustic communication modules of the master and follower drones are configured to transmit communication signals over the same communication channel. If applicable, the communication modules of the master and follower drones are configured to multiplex communication signals transmitted by the master and follower drones on the communication channel. If necessary, the communication modules of the master and follower drones can be configured to temporally multiplex communication signals transmitted by the master and follower drones on the communication channel. If applicable, the communication modules of the master and follower drones can be configured to transmit acoustic signals modulated at the same carrier frequency or the same frequency band.

[0030] Preferably, the communication modules of the master and follower drones are configured to periodically transmit data frames together, and each of the communication modules is configured to transmit a communication signal during at least one period of the data frame attributed to it. In other words, the communication modules take turns accessing the communication channel according to a time division multiple access (TDMA) technique.

[0031] Advantageously, the communication module of the master drone is configured to transmit navigation instructions to all follower drones in the first period of the data frame. It is thus understood that one single command, i.e. a code related to steering orientation and formation geometry, established based on the flight plan of the master drone, is transmitted to all follower drones. If necessary, the communication module of the master drone is configured to transmit multiple navigation instructions to all follower drones in multiple separate periods of the data frame, with only some communication modules of the follower drones configured to transmit signals to the master drone in periods of data frames located between the first and second consecutive periods of data frames attributed to the master drone. If applicable, other communication modules of the follower drones are configured to transmit signals to the master drone in periods of data frames located between the second and third consecutive periods of data frames attributed to the master drone. This feature makes it possible to accelerate the transmission of navigation instructions to the follower drones, thereby reducing drift during movement.

[0032] Advantageously, the communication module of each of the follower drones is configured to transmit, during the period of the data frame attributed to it, a signal to the master drone including an item of information on its position. Preferably, the communication module of each of the follower drones is configured to transmit, during the period attributed to it, a signal to the master drone including an item of information on its position and an item of information on its operating state.

[0033] Preferably, the communication modules of the master and follower drones are configured such that a guard period separates two consecutive periods attributable to the communication modules.

[0034] Again advantageously, the communication module of the master drone is configured to transmit an item of status information of the submarine exploration system to the remote control unit during the final period of the data frame.

[0035] According to an embodiment of the present invention, the communication modules of the master and follower drones are configured such that the duration of the period attributed to the communication modules is the same for all communication modules, such that the period of the transmission of navigation instructions by the master drone corresponds to each movement of the follower drone being less than a predetermined threshold distance. For example, the duration of the period for transmitting navigation instructions is fixed, so that the follower drone can move at a speed of 3.5 knots over a distance of up to 15 meters following the heading given by the master drone.

[0036] According to an embodiment of the present invention, each follower drone comprises a body with a front compartment isolated from the rest of the body, each follower drone comprises a propulsion system, a battery, and a magnetic field detection system disposed in the front compartment, the propulsion system and the battery disposed in the body outside the front compartment. Thus, the influence of the induced and permanent magnetic fields of the propulsion system and the battery on the magnetic field detection system is limited.

[0037] Advantageously, the body is formed from a rear compartment, a central compartment and a front compartment, each compartment being isolated from the others, the propulsion system being located in the rear compartment and the battery being located in the central compartment.

[0038] If applicable, the follower drone's acoustic communication module and / or navigation system are located in the forward compartment.

[0039] The invention also relates to a method of submarine exploration implemented by a submarine exploration system according to the invention, said method advantageously comprising the following steps: a. Selection of at least one predefined flight plan by the master drone; b. Autonomous movement of the master drone according to the selected flight plan; c. The master drone issues navigation commands to the follower drones based on the selected flight plan; d. Autonomous movement of each of the follower drones according to the received navigation commands.

[0040] Optionally, the method may include a step of transmitting, by each of the follower drones, a signal to the master drone including at least one item of information regarding its operational status, and a reconfiguration step in which, if the master drone receives from a follower drone a signal including an item of information indicating a failure of said follower drone, the master drone selects a new flight plan depending on the remaining feasible drones.

[0041] Advantageously, the method may include a step of echo localization of the master drone, performed by each of the follower drones using a transmission signal comprising at least one item of information related to its operating state, and a step of correcting the movement of the follower drone by its relative distance to the master drone obtained during the echo localization step.

[0042] Optionally, the method may include measuring the local magnetic field carried by each of the follower drones, extracting from each measured magnetic field a value that is independent of the surrounding magnetic field and the own magnetic field of the follower drone that measured it, and detecting magnetic anomalies from the extracted values.

[0043] The present invention also relates to a submarine exploration system comprising a master submarine drone and a number of follower submarine drones whose movements are slaved to those of the master drone, each of the master and follower drones comprising an acoustic communication module for transmitting communication signals on the same communication channel, the communication modules of the master and follower drones being configured such that the communication signals transmitted by the master and follower drones on said communication channel are multiplexed.

[0044] Indeed, electromagnetic waves prove difficult to propagate underwater, especially at the expected exploration depths. It is therefore preferable to foresee acoustic communication means between the drones. However, insofar as it is necessary to establish uplinks and downlinks between the master drone and each of the follower drones, it is important to provide a solution that allows each of said links to be established in a simple and reliable manner, without interfering with the others. It is therefore understood that the multiplexing of the acoustic communication signals transmitted by the communication modules of the drones of the system according to the invention makes it possible to easily and reliably establish communication between the drones on the same channel, and thus a quasi-simultaneous enslavement of the movements of all the follower drones to those of the master drone.

[0045] The present invention also relates to a method for communication between a master drone and a number of follower drones of a submarine exploration system according to the present invention.

[0046] The present invention also relates to a submarine exploration system comprising a master submarine drone and a number of follower submarine drones whose movements are slaved to those of the master drone, each follower drone comprising a propulsion system, a battery and a magnetic field detection system, the magnetic field detection system being disposed within a forward compartment and the propulsion system and the battery being disposed within the body outside the forward compartment.

[0047] Thanks to the present invention, by separating the various elements of the follower drone in magnetically isolated compartments, it is possible to minimize the influence of the various magnetic field sources, in particular the battery and motor elements, on the detection of magnetic anomalies by the detection system of each follower drone. [Brief description of the drawings]

[0048] The present invention will now be described with reference to an embodiment based on the accompanying drawings, which are given purely as examples and without limiting the scope of the invention.

[0049] [Figure 1] 1 is a partial schematic diagram of a submarine exploration system in accordance with an embodiment of the present invention. [Diagram 2] [Figure 1] shows a method of submarine exploration performed by the submarine exploration system. [Diagram 3] [Figure 1] shows a method of communication between the master and follower drones of the submarine exploration system. [Figure 4] [Figure 1] shows the movement of the master drone and one of the follower drones of the submarine exploration system. [Diagram 5] 1 shows various steps of a method for detecting magnetic anomalies implemented by the submarine exploration system of [Figure 1]. [Figure 6] FIG. 2 is a cross-sectional view of the follower drone of the submarine exploration system of [Figure 1].

[0050] In the following description, elements that are identical in terms of structure or function are provided with the same reference signs in different figures, unless otherwise specified.

[0051] FIG. 1 is a perspective view of a submarine exploration system 1 according to an embodiment of the present invention.

[0052] The system 1 comprises a master submarine drone 2 and a number of follower submarine drones 31-36. The drones 2 and 31-36 are submarine drones capable of moving autonomously. Each of the drones of the master 2 and the followers 31-36 is equipped with a communication module C for transmitting and receiving signals from a magnetic field detection system D capable of measuring magnetic fields and from a navigation system N configured to determine the position of the drone at a given moment. Furthermore, and in contrast to the follower drones 31-36, the master drone 2 comprises a number of systems for characterizing the seabed, including a bathymetric mapping system in the form of a multi-beam bathymetry MBS and an acoustic imaging system in the form of a lateral scanning sonar LSS. The master drone 2 is therefore multi-sensor and the follower drones 31-36 are single-sensor.

[0053] The navigation system N of each of the follower drones 31-36 comprises an attitude unit of MEMS type, capable of determining the rolling and pitching of the follower drone. Furthermore, the magnetic field detection system D of each follower drone provides the navigation system N with a magnetic orientation. In a variant, it is possible to provide each follower drone with a second magnetic field detection system for providing said magnetic orientation, in which case the magnetic field detection system D is dedicated to the measurement of the magnetic field. The navigation system N of the master drone 2 comprises an inertial unit of FOG type, and a data processing module for position data, which receives information provided by an acoustic positioning system, such as a DVL (Doppler Velocity Log), and integrates an algorithm of Kalman filter type. The accuracy of the navigation system of the master drone 2 is therefore much higher than the accuracy of each of the navigation systems of the follower drones 31-36.

[0054] The communication modules C of the drones of the master 2 and the followers 31-36 are acoustic communication modules, which allow the drones to exchange data in the form of modulated acoustic signals transmitted by said communication modules on the same communication channel, i.e. on the same wavelength. Moreover, the acoustic signals transmitted by the drones of the master 2 and the followers 31-36 on said communication channel are temporally multiplexed, so that the communication modules C access the communication channel in turn according to a time division multiple access technique, and thus each of the drones transmits an acoustic signal in at least one period of the periodic data frame attributed to it.

[0055] [Figure 2] is a plan view of a method for submarine exploration of an exploration zone Z implemented by the exploration system 1, [Figure 3] shows a method of communication between the master drone 2 and the follower drones 31-36 during the exploration, as well as the data frame F moving within the communication channel thus formed between the drones, and [Figure 4] shows an example of enslaving the movements of one of the follower drones 31 to the movements of the master drone 2.

[0056] Prior to exploration, multiple formation geometries are loaded into the memory of each of the drones of the master 2 and the followers 31-36. Each formation geometry describes, for a given number of follower drones, and for each of said follower drones, its spatial position relative to the master drone 2, i.e. whether it should be positioned to the left, right, in front or behind the master drone 2, and the lateral distance that separates said follower drone from the master drone 2. Again, prior to exploration, the master drone selects an operation plan E, i.e. a given formation geometry GF, and a navigation line plan PL associated with said formation geometry GF and suitable for the intended exploration zone Z. Each line of the line plan PL thus defines the movement of the drones in the exploration zone Z (solid lines for the master drone 2 and dotted lines for the follower drones 31-36 in [Figure 2]). As depicted in [Figure 2], the formation geometry GF defined in the selected flight plan E corresponds to a comb-shaped formation centered on the master drone 2, with follower drones distributed on either side of the master drone 2 and regularly spaced at 100 m intervals.

[0057] The master drone 2 is configured to move autonomously according to its own line in the flight plan E and the navigation line plan PL with the aid of the navigation system N. During its movement along the flight plan E, the master drone 2 periodically transmits, for example every 6 seconds, via its communication module C to all follower drones 31-36 a navigation command I including a steering heading Cm determined from the flight plan E, as well as a code identifying a formation geometry GF defined in the selected flight plan E. Thus, multiple navigation commands I are transmitted to all follower drones in multiple periods of the data frame F.

[0058] Upon receiving the navigation command I by the communication module C, each follower drone 31-36 determines its relative position to the master drone 2 by selecting the formation geometry loaded into its memory and associated with the code included in the navigation command I. Thus, each follower drone 31-36 moves in an autonomous manner according to the steering orientation and the position of the follower drone estimated by its navigation system N, while maintaining its relative position to the master drone 2, according to the received navigation command I, until a subsequent navigation command is received. More specifically, each follower drone 31-36 employs a navigation mode called "dead reckoning", which estimates its position P1-P6 according to its movement, determined by its magnetic orientation measured by the magnetic field detection system and its attitude measured by the attitude unit, based on the last estimated position. Thus, the follower drone moves towards a new position determined by its estimated position and by the steering orientation Cm included in the navigation command I, and in a manner of maintaining its relative position to the master drone 2 defined by the formation geometry GF.

[0059] As shown in [Figure 4], the dead reckoning navigation mode introduces drift in the movement of each follower drone (exemplified by follower drone 31) due to the positioning uncertainty introduced by the estimation of positions P1-P6. In other words, the positioning uncertainty (represented by circle IP in [Figure 4]) increases over time and can lead, on the one hand, to deviations of the follower drone 31 relative to its line of navigation in the line plan PL, and, on the other hand, to differences between the actual lateral distance d1 between the master drone 2 and the follower drone 31 and the distance fixed to the formation geometry GF.

[0060] Each follower drone 31-36 transmits to the master drone 2, during the period in the data frame F due to it, a signal S1-S6 containing its estimated position P1-P6, as well as its operational state E1-E6, i.e. ready or fault state. To overcome the drift of the movement of the follower drone mentioned above, the communication module C of each follower drone receives an echo S1' of the signal S1 reflected by the master drone 2 and determines from said echo the actual relative distance d1 that separates the follower drone from the master drone. In this way, the follower drone 31 goes from the dead reckoning navigation mode to a navigation mode called "convergence", in which said relative distance d1 determined by echo localization is integrated into the determination of the position of the follower drone by the navigation system N and into the movement of the follower drone. On the one hand, this determined relative distance d1 allows to reduce the positioning uncertainty. On the other hand, a comparison between the actual relative distance d1 and the distance fixed to the formation geometry GF allows the follower drone 31 to regain its navigation line and thus comply with the formation geometry GF.

[0061] In the described example, the navigation instructions I sent by the master drone 2 lack instructions regarding the altitude to follow. Furthermore, the navigation system N of each follower drone 31-36 includes an altimeter configured to determine the altitude of the follower drone relative to the seabed at a given moment, and each follower drone is configured to move while maintaining a constant altitude relative to the seabed.

[0062] In the example of [Fig. 1], the drone 32 is damaged and therefore transmits a signal S2 during that period including its position P2 and an operational state E2 indicating a fault. Following the transmission of the signal S2, the drone 32 is no longer in a condition to continue the exploration and leaves the exploration zone Z, for example to rejoin the base. Upon receiving the signal S2 indicating the fault state E2 of the follower drone 32, the master drone selects a new flight plan E, which defines a new formation geometry GF suitable for the remaining follower drones 31 and 33-36. In the illustrated example, the follower drone 36 replaces the follower drone 32 and thus takes its position. In order to maintain a homogeneous exploration of the exploration zone Z, the master drone 2 further determines a new plan PL of the navigation line. The master drone 2 therefore performs a reconfiguration of the drone fleet.

[0063] As illustrated in FIG. 4, a guard period G separates the successive transmissions of signals by the master 2 and follower drones 31-36 in the data frame F. Furthermore, note that the periods attributable to the follower drones 31-36 are distributed among the various periods attributable to the master drone 2.

[0064] Finally, in the last period of data frame F, the master drone 2 transmits an item of status information E of the submarine exploration system to a remote control unit located, for example, on a boat on the surface of the exploration zone Z.

[0065] The duration of the periods attributable to the communication modules C of the drones of the master 2 and the followers 31-36 is identical for all these communication modules. Moreover, the duration of the transmission of the navigation command I by the master drone is such that the movement of each of the follower drones 31-36 between two successive navigation commands is substantially equal to 15 meters according to a speed of 3.5 knots. Thus, the follower drones 31-36 are found to move according to an elementary movement of 15 meters according to the flight plan E, which makes it possible to achieve a precise enslavement of the trajectories of the follower drones 31-36 to the trajectory of the master drone 2, while ensuring the robustness of the exploration system 1 in case of drift or failure of one of the follower drones.

[0066] Each magnetic field detection system D of the master 2 and follower drones 31-36 comprises a magnetic field sensor of a form known as a three-component vector magnetometer, with three directional magnetometers arranged at 90° to each other, each capable of measuring the magnetic field in the vicinity of the drone. Thus, in a first graph G1, [Figure 4] shows an example of measurements of the three components of the magnetic field obtained by each of the directional magnetometers of one of the follower drones 31-36 during exploration of zone Z.

[0067] The exploration system 1 comprises a data processing module (not shown), which is external to the drones 2 and 31-36, and which is configured to calculate a total magnetic field from the measurements of the three components of the magnetic field shown in graph G1, which is shown in a second graph G2.

[0068] The data processing module recovers from the navigation system N during the exploration data on the movement of the follower drone during the exploration of the zone Z, in particular its orientation shown in the third graph G3, and its rolling and pitching shown in the fourth graph G4. Furthermore, the data processing module determines the magnetic susceptibility tensor of the follower drone, for example by means of a magnetic data set, referred to as the calibration data set, as well as the residual magnetization vector. From this set of data, the data processing module corrects the total magnetic field of graph G2 in order to remove therefrom the induced and permanent magnetic fields as well as the ambient magnetic fields, in order to extract therefrom the values ​​shown in graph G5. It should be noted that on said graph G5 the extracted values ​​represent the variations corresponding to the magnetic anomaly A in the exploration zone. Furthermore, the data collected by the systems for characterizing the seabed (MBS and LSS) of the master drone make it possible to characterize the source of the magnetic anomaly A, in particular to determine whether it is an inactive hydrothermal site with mineral potential.

[0069] Finally, [Figure 5] is a cross-sectional view of one of the follower drones 31, it being understood that the structure of all follower drones 31-36 is identical. Drone 31 comprises a body 4 formed from a rear compartment 41, a central compartment 42, and a front compartment 43. Each compartment is isolated from the others.

[0070] The follower drone 31 comprises a propulsion system 5 arranged in a rear compartment 41 and a battery 6 arranged in a central compartment 42. The magnetic field detection system D, the acoustic communication module C and the navigation system N are arranged in a front compartment 43, thereby limiting the influence of the induced and permanent magnetic fields of the propulsion system and the battery on the magnetic field detection system D.

[0071] The above description clearly explains how the invention makes it possible to achieve the objectives it sets for itself, in particular by proposing a submarine exploration system made up of a fleet of submarine drones with an autonomous master drone and follower drones whose movements are slaved to those of the master drone. The described system thus allows a fast and effective exploration of the deep seabed, making it possible to detect and distinguish active sites from inactive ones, so that exploration costs are controlled.

[0072] In any case, the present invention is not limited to the embodiments specifically described in this document, but in particular extends to all equivalent means and any technically possible combinations of said means. In particular, it is possible to envisage other types of formations of master and follower drones. It is also possible to envisage the use of other types of methods for communication between master and follower drones other than TDMA, or indeed the use of internal structures of follower drones different from those described.

Claims

1. A submarine exploration system (1), comprising: a. a master submarine drone (2) configured to move autonomously according to a predefined navigation plan (E) and comprising at least two seabed characterization systems and a communication module (C) for transmitting communication signals; b. a plurality of follower submarine drones (31, 32, 33, 34, 35, 36), each of which comprises at least one magnetic field sensor (D) capable of measuring a magnetic field in the vicinity of said follower submarine drone, and each of which further comprises a communication module (C) for receiving communication signals from said master submarine drone; A submarine exploration system (1), comprising: c) a submarine exploration system (1), wherein the master submarine drone is configured to transmit navigation instructions (I) to the follower submarine drones, each follower submarine drone configured to move autonomously in response to the navigation instructions such that its movement is enslaved to the movement of the master submarine drone.

2. The submarine exploration system (1) according to claim 1, wherein the communication modules (C) of the master submarine drone (2) and the follower submarine drones (31, 32, 33, 34, 35, 36) are acoustic communication modules.

3. A submarine exploration system (1) as described in claim 1 or claim 2, wherein the master submarine drone (2) is configured to periodically transmit navigation commands (I) to all of the follower submarine drones (31, 32, 33, 34, 35, 36), each follower submarine drone being configured to move according to the last received command until a subsequent command is received.

4. 4. The submarine exploration system (1) of claim 3, wherein the master submarine drone (2) is configured to periodically determine a steering heading (Cm) and a formation geometry (GF) of the follower submarine drones (31, 32, 33, 34, 35, 36) from an operation plan (E), each navigation command (I) transmitted by the master submarine drone to all of the follower submarine drones (31, 32, 33, 34, 35, 36) includes the steering heading and the formation geometry, and each follower submarine drone is configured, upon receiving each navigation command, to move in a direction according to the steering heading and to determine and adopt a relative position (d1) with respect to the master submarine drone in accordance with the formation geometry until a subsequent navigation command is received.

5. A submarine exploration system (1) as described in claim 4, wherein each follower submarine drone (31, 32, 33, 34, 35, 36) comprises a navigation system (N) configured to determine a position (P1, P2, P3, P4, P5, P6) of the follower submarine drone at a given moment and to move from said determined position in response to navigation commands (I) received from the master submarine drone (2).

6. A submarine exploration system (1) as described in claim 5, wherein the navigation system (N) of each follower submarine drone (31, 32, 33, 34, 35, 36) is configured to determine the altitude of the follower submarine drone relative to the seabed at a given moment, and each follower submarine drone is configured to move while maintaining a constant altitude relative to the seabed.

7. A submarine exploration system (1) as described in claim 5 or claim 6, wherein the communication module (C) of each follower submarine drone (31, 32, 33, 34, 35, 36) is configured to transmit to the master submarine drone (2) signals (S1, S2, S3, S4, S5, S6) including the determined position (P1, P2, P3, P4, P5, P6) of the follower submarine drone.

8. A submarine exploration system (1) as described in claim 7 in combination with claim 4, wherein the communication module (C) of each follower submarine drone (31, 32, 33, 34, 35, 36) is configured to transmit to the master submarine drone (2) signals (S1, S2, S3, S4, S5, S6) including the determined position (P1, P2, P3, P4, P5, P6) of the follower submarine drone and the operating states (E1, E2, E3, E4, E5, E6) of the follower submarine drone, and the master submarine drone is configured to determine the steering heading (Cm) and the formation geometry (GF) from the operating states of the follower submarine drones.

9. A submarine exploration system (1) as described in claim 7 or claim 8, wherein the communication module (C) of each follower submarine drone (31, 32, 33, 34, 35, 36) is configured to receive an echo (S1') of the signal (S1) transmitted by the communication module (C) of the follower submarine drone to the master submarine drone (2) and reflected by the master submarine drone, and to determine from the echo the relative distance (d1) separating the follower submarine drone from the master submarine drone, and wherein the navigation system (N) of the follower submarine drone is configured to determine the position (P1, P2, P3, P4, P5, P6) of the follower submarine drone at the given moment by the determined relative distance.

10. A submarine exploration system (1) as described in any one of claims 1 to 9, wherein the master submarine drone (2) includes multiple systems (MBS, LSS) of different types for characterizing the seabed.

11. A submarine exploration system (1) as described in any one of claims 1 to 10, comprising a data processing module configured to extract from the measured magnetic field a value independent of the values ​​of the ambient magnetic field and the magnetic field of the follower submarine drone itself, and to detect magnetic anomalies (A) based on said value.

12. A method of submarine detection implemented by a submarine detection system (1) according to any one of claims 1 to 11.

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