A device and a method for crowding and conveying out marine organisms

Abstract

A device and a method for crowding and discharge of marine organisms from a tank (12) are described. The device comprises a horizontally arranged crowding grate (16) which is arranged for vertical movement in the tank (12), and which consists of at least two rotatable crowding grate units (17) with respectively open portions (17a) and grate portions (17b). When the grate (16) is lowered into the tank, the open portions (17a) in at least two crowding grate units (17) are mutually overlapping, such that fish can pass through the grate (16). When the grate is in a lower inactive position, the crowding grate units (17) are rotated such that the grate portions (17b) form a continuous perforated grate that is impenetrable to fish. By the grate (16) being raised from the lower position, the fish is crowded upwards in the tank (12) and is preferably led via a central channel (16a) and an extraction arrangement (14) out of the tank (12).

Description

[0001] A device and a method for crowding and conveying out marine organisms

[0002] DESCRIPTION

[0003] Field of invention

[0004] The present invention relates to a device and a method for crowding and discharge of marine organisms, such as fish, in a liquid in a tank. Preferably, the tank is circular, such as a rearing tank for marine organisms, but other shapes, such as rectangular, square or hexagonal, may also occur.

[0005] Background of the invention

[0006] With the environmental challenges one has today with the farming of marine species in open net pens at sea, more and more of the production will have to take place in closed tanks. Requirements for increased production and yield mean that the tanks become larger and larger, and in order to utilise these to the maximum, fish must be moved from one tank to another tank as the fish or the marine organism grows. The water, i.e. the liquid in which the marine organism resides, is valuable, and one cannot allow oneself to crowd and move fish by emptying such large tanks. The water must therefore be transferred together with the fish to a new tank, while the liquid levels in the tanks are preferably maintained. Moving fish becomes an increasingly important part of the operating method at a fish farm as the facilities become larger and larger, since one wishes to utilise the tank volumes maximally for production, and thereby have as much biomass as possible at all times in the tank. Moving marine organisms, such as fish, can be divided into two steps. First, the fish is crowded together to a suitable location in the tank, before moving or transferring the fish to another tank. The crowding itself is a critical operation, as it triggers stress reactions in the fish. This leads to increased oxygen consumption and excretion of carbon dioxide. This is a great strain on the fish. The fish then typically seeks down into the tank. This is an instinct that most fish species have. It is therefore important to take this into account in the design of mechanisms for crowding and leading the fish out of the tank.

[0007] Description of the prior art

[0008] Various solutions exist today for crowding fish, where the fish is led into a pipe system that takes it further out of the tank. For net pens at sea, crowding nets that gather the fish in bags, where it is sucked up and into a fish pump, are much used. This type of crowding system inflicts much stress on the fish and entails high mortality. In closed tanks, various methods are used, i.e. everything from draining out the water to various forms of crowdingbulkheads that press the fish into an ever smaller sector from which it is pumped out. The best solutions crowd the fish down towards the bottom and suck it out through a hole in the tank wall. A typical example of this is shown in patent application PCT / N02021 / 050275 and in NO324024.

[0009] MMC Tendos AS describes in NO324024 a solution for crowding fish in cylindrical tanks, primarily intended for use in well boats that transport fish. The solution is based on upwardly projecting profiles being mounted on or near the bottom of the tank, and on a grate formed in approximately the same shape as the tank being led down towards these upwardly projecting profiles. When the grate has come down to the level of these upwardly projecting profiles, one of the upwardly projecting profiles is rotated around the centre of the tank and presses the fish into a small sector. The opening out of the tank is in the tank wall in this sector, and the fish is finally pressed out through the opening in the tank wall for transfer to a new container.

[0010] This solution has drawbacks, especially in tanks where the fish is to reside for a somewhat longer time, and where it is also to be fed. The upwardly projecting profiles at the bottom will affect the flow pattern in the tank, and sedimentation of fish faeces and feed residues will occur around these profiles. This is a major drawback in tanks where large quantities of fish are to be produced. At the same time, it is a drawback that the fish is taken out through a hole in the tank wall down at the bottom, as this is often cast into the ground and thus difficult to clean, so that it easily becomes a trap for stagnant water that can develop hydrogen sulphide, which is highly toxic to the fish.

[0011] PCT application PCT / N 02023 / 000002 describes a solution where a crowding grate is moved from an inactive position at the bottom of the tank, and where this vertical movement upwards in the tank will crowd together fish located on the upper side of the crowding grate. The applicant's patent application N020240046 describes a solution where a framework with a number of panels is lowered into the tank. The lowering is done such that at least one of the panels is not arranged in the framework, i.e. such that a passage is formed in the framework that allows the fish to swim through. When the framework is to be pushed upwards, in order to crowd the fish upwards in the tank, all the panels cover the framework completely, so that only water, and not fish, can penetrate through the framework.

[0012] Object of the invention

[0013] It is an object of the present invention to provide an improvement or alternative solution to the solution shown in N020240046.The object of the invention is to provide a system (a device and a method) for moving a crowding grate from a position above the liquid level in the tank down towards the bottom of the tank, so that the crowding grate is positioned beneath the fish residing in the tank. Furthermore, it is an object of the invention that this is carried out in a gentle manner, and preferably more gently than with known methods and devices. It is an object that the fish's natural reaction pattern is taken into account in that it seeks down towards the bottom when it is frightened.

[0014] It is also an object of the invention that there are no penetrations in the tank wall below the water level. The patent applicant has various patents and patent applications related to closed tank solutions, where, among other things, the importance of having clean, smooth internal surfaces in the tank is emphasised, i.e. without objects that disturb the flow pattern and create sedimentation of particles. A clean cylindrical tank without installations on the internal surfaces, which provides good tank hydraulics, is therefore of great importance for efficient farming in closed tanks.

[0015] Likewise, the arrangement that crowds the fish must be reliable and easy to handle, as crowding and moving fish is something that happens often. The solution should also be able to be operated while the water is circulating in the tank. The water velocity in the tank can typically be around 0.5 m / s. This can give large forces on objects that are to crowd the fish.

[0016] Summary of the invention

[0017] The solution for which a patent is sought consists of a horizontally arranged crowding grate (16), in the form of a perforated lid, which can move up and down around a central column (18) in a rearing tank (12). The grate must be positioned in an inactive position at the bottom of the tank, and with the present invention this can be done even when there is fish present in the tank. The crowding grate is perforated such that water flows through it and is sucked out beneath the grate and into the central column (18). This will ensure that there is no sedimentation of particles beneath the grate. Fish that die will settle on top of the grate, and will at regular intervals be sucked towards the central column, into it and out of the facility. When the fish is to be crowded and led out of the tank, the crowding grate (16) is moved from its inactive position at the bottom of the tank and vertically upwards. An extraction arrangement (14) can be lowered into the tank and positioned in the centre just above the crowding grate (16). The fish is crowded to this position and led via the extraction arrangement (14) out of the tank, and transferred to a new tank. Preferably, the extraction arrangement (14) is connected to a siphon that leads the fish out of the tank.The principle underlying the present invention is that the crowding grate (16) comprises at least two crowding grate units (17), and that each of these comprises portions that are open (17a) and portions that are equipped with a grate (17b). When two such crowding grate units (17) are rotated relative to each other, a configuration can be established where grate portions (17b) cover the entire tank area, so that fish cannot swim through the grate. This configuration is used when the crowding grate units (17) are moved upwards in the tank and crowd the fish to a new location.

[0018] Furthermore, the two crowding grate units (17) can be set such that at least one open portion (17a) lies over each other, i.e. such that the fish can move through the two crowding grate units (17). This configuration is used when the crowding grate units are lowered into the tank to an inactive position. The crowding grate and crowding grate units can thus be lowered into the tank at the same time as there is fish in the tank, because the fish can move through open portions (17a).

[0019] The present invention thus relates, in a first aspect, to a device for crowding and discharge of marine organisms from a tank, comprising a horizontally arranged crowding grate which is arranged for vertical movement in the tank, characterised in that the crowding grate comprises at least two rotatable crowding grate units, where each crowding grate unit comprises at least one open portion and at least one grate portion, and that the crowding grate units are arranged for rotation relative to each other between:

[0020] - a first configuration where open portions in at least two crowding grate units are mutually overlapping such that fish can pass through the crowding grate, and

[0021] - a second configuration where grate portions together form a perforated grate that is impenetrable to fish.

[0022] In one embodiment, the perforated crowding grate is arranged to be moved vertically between a lower inactive position at the bottom of the tank and an upper position, and in that grate portions in the second configuration form a continuous perforated grate that extends between the wall of the tank and a central column.

[0023] In one embodiment, the crowding grate units are circular-sector-shaped and comprise a ring-shaped framework that encloses an inner opening adapted to a central column and an outer opening adapted to the wall of the tank, and where several alternately distributed open portions and grate portions are arranged in each crowding grate unit, where the grate portions in the second configuration form a unified perforated grate that leads fish towards a central channel with an extraction arrangement.In one embodiment, a flexible sealing element is arranged between the tank wall and the crowding grate, and / or between the central column and the crowding grate.

[0024] In one embodiment, the flexible sealing element is a flexible hose arranged for pressurisation with liquid.

[0025] In one embodiment, the crowding grate is movably attached to vertical guides along the tank wall and / or central column.

[0026] In one embodiment, the crowding grate unit and / or crowding grate is attached with ropes, cables or wires to a lifting arrangement arranged above the tank.

[0027] In one embodiment, the assembly of the crowding grate comprises a central channel arranged to lead fish towards a position above an extraction arrangement.

[0028] In one embodiment, the channel comprises at least one recess.

[0029] In one embodiment, the extraction arrangement is arranged in said channel or recess. In one embodiment, the extraction arrangement is connected to a siphon.

[0030] In one embodiment, grate portions are a perforated net, grate or grid material with openings adapted to the size of the marine organisms.

[0031] In one embodiment, the crowding grate is inclined from the outer edge of the tank towards the centre such that fish is led towards the extraction arrangement when the grate is moved upwards.

[0032] In one embodiment, the extraction arrangement comprises a flexible pipe run.

[0033] In one embodiment, the device is characterised in that the stress level and / or position of the marine organisms is monitored and used as a control parameter for raising the crowding grate.

[0034] In one embodiment, the monitoring comprises visual and / or acoustic methods, including camera, hydrophone and / or radar.

[0035] In a second aspect, the present invention relates to a method for crowding marine organisms in a tank, characterised in that a horizontally arranged crowding grate, comprising at least two rotatable crowding grate units with respectively open portions and grate portions, is brought from a storage position above the liquid level to a lower inactive position in the tank, where the crowding grate units upon lowering are set in a first configuration where open portions are mutually overlapping such that fish can pass through the crowding grate, that the crowding grate units after positioning are rotated to a second configuration where grate portions together form a perforated grate that is impenetrable tofish, and that the crowding grate is then moved upwards in the tank such that fish is crowded to the upper part of the tank.

[0036] In one embodiment, the grate portions in the second configuration form a continuous perforated grate that extends between the wall of the tank and a central column.

[0037] In one embodiment, fish is led into a central channel and led out of the tank via an extraction arrangement.

[0038] In one embodiment, the extraction arrangement is driven by a siphon and / or a pump. In one embodiment, the crowding grate slopes towards the centre such that fish is led towards the central column.

[0039] In one embodiment, the method is characterised in that the stress level and / or position of the marine organisms is monitored and used as a control parameter for raising the crowding grate.

[0040] In one embodiment, the monitoring is carried out with visual and / or acoustic sensors.

[0041] Description of the figures

[0042] Preferred embodiments of the invention shall in the following be described in more detail with reference to the accompanying figures, where:

[0043] • Figures 1-7 show the figures from Norwegian patent application N020240046, which illustrate an alternative embodiment where a framework with panels is lowered into the tank, where panels in downward movement leave openings that the fish can swim through, and where the panels in the lower position are assembled to form a perforated surface for crowding by upward movement.

[0044] • Figure 8 schematically shows a tank (12) for farming marine organisms, and two crowding grate units (17), each of which has open portions (17a) and closed grate portions (17b), and which can be introduced into the tank (12).

[0045] • Figure 9 schematically shows the same tank (12) as in figure 8, but where the two crowding grate units (17) have moved to a lower inactive position. The fish stands in the tank above the lowered crowding grate units (17). The figure shows the crowding grate units (17), which in this embodiment are identical, partly rotated relative to each other, such that there are still some open portions (17a) and some portions closed off for the fish (17b).

[0046] • Figure 10 schematically shows the same solution as in figure 9, but where the two crowding grate units (17) are now rotated further relative to each other such that thetwo crowding grate units (17) together form a “tight” perforated grate, i.e. such that only liquid can pass through the grate portions (17b). The crowding grate (16) is now ready to be able to be lifted from this inactive position upwards in the tank (12), and thereby also crowd fish upwards in the tank.

[0047] • Figure 11 shows the crowding grate (16) in an upper position, i.e. after it has crowded the fish upwards and out of the tank (12).

[0048] Detailed description of preferred embodiments of the invention

[0049] As described in PCT / N02023 / 000002, a crowding grate is used that is raised from a lowered inactive position at the bottom of a rearing tank in order to crowd (concentrate) fish in an upper part of the tank. The problem with this solution is that one cannot position the crowding grate to the inactive lower position at the same time as there are marine organisms in the tank. The crowding grate must be placed in the tank before the tank is filled with fish.

[0050] Furthermore, N020240046 describes a solution where a framework with loose panels can be lowered into a rearing tank. The panels are lowered detached from the framework, such that there are openings in the framework that the fish can swim through. When the framework is in its lower position, the panels are assembled with the framework, and a grate is then established that is impenetrable to the fish, but which the liquid can flow through. When this framework is moved upwards in the tank, the fish will also be crowded upwards. The present invention solves the problem in N020240046 with loose panels that must be brought together with the framework at the bottom of the tank. The solution provided consists in that at least two crowding grate units (17) are used, and that each of these has closed grate portions (17b) and open portions (17a), so that the two units can be lowered into the tank (12) with open portions (17a) arranged over each other (i.e. such that fish can pass). When the crowding grate units (17) are in the lower portion of the tank (12), they are rotated relative to each other such that the grate portions (17b) fill the entire area, i.e. such that the crowding grate units (17) together form a perforated grate that covers the entire inner circumference of the rearing tank and is impenetrable to fish.

[0051] Figure 8 shows a tank (12), such as a rearing tank for farming marine organisms, for example fish. The figure also shows two crowding grate units (17), each of which comprises open portions (17a) and grate portions (17b) consisting of a grate or a net material. The grate portions (17b) are here called closed portions, because they are impenetrable to the marine organisms, while the open portions (17a) are open to both fish and water.One does not wish to have crowding grates permanently installed at the bottom of the tank (12) due to the risk of accumulation of sludge, as well as a disturbing effect on the water flow in the tank (12). The crowding grate units (17) are therefore in a parked position above the water level so that one has a clean and smooth tank (12) where the fish resides. The crowding grate (16) can typically hang beneath walkways or similar structures.

[0052] The challenge is to get the crowding grate units (17) themselves down beneath the fish before crowding the fish upwards. This is solved in that the crowding grate units (17) in principle consist of two types of portions: open portions (17a), where both fish and liquid penetrate through, and closed grate portions (17b), where only liquid penetrates through. The framework for the crowding grate (16) forms a structure that has an inner circle that will enclose the central column (18), and an outer circle that will be adapted to the shape of the circumference in the tank (12) within the walls (12a). There are large openings (17a) in the grate units (17) that the fish can swim through when the grate is lowered from the storage position and down into the tank.

[0053] Figure 9 shows how the frame and the two crowding grate units (17) are now lowered down to the lower inactive position. The marine organisms have now moved to be in a position above the crowding grate units (17). The figure shows that the two crowding grate units (17) are rotated somewhat relative to each other, such that one or more open portions (17a) are established. The fish can swim through these open portions (17a) when the crowding grate units (17) are lowered down to the lower inactive position.

[0054] Figure 10 shows how the crowding grate units (17) have been rotated relative to each other such that there are now no open portions (17a) lying over each other. The entire grate (16) is closed with respect to fish and now consists only of closed grate portions (17b). The crowding grate units (17) are in figure 10 arranged down in the tank (12) (in inactive position) and are now ready to be able to be raised upwards in the tank (12). The fish cannot penetrate through the crowding grate units (17) in this configuration, and the fish will be crowded upwards in the tank as the crowding grate units are raised.

[0055] Figure 11 shows the crowding grate units (17) after they have been raised to an upper position. The fish has now been crowded upwards, and out of the tank (12), typically via an extraction arrangement (14).

[0056] The solution according to the invention can consist of two or more crowding grate units (17). For example, one can have a magazine with several crowding grate units (17), and one can for example move a large number of crowding grate units down into the lower portion of the tank (12) at the same time. This presupposes that one has rotated the crowding grate units (17) relative to each other such that they all have openings (17a) in the same sector. Theycan then for example be pushed up with two crowding grate units (17) at a time, which will be sufficient if they have equally large open and closed portions, and if these can be arranged such that two crowding grate units (17) will form a completely closed perforated crowding grate (16) when it is pushed upwards in the tank (12).

[0057] Together with the crowding grate units (17), an extraction arrangement (14) can be arranged, as described in PCT / N02023 / 000002. When the crowding grate (16) is to crowd the fish in order to transfer the fish to a new tank, the crowding grate units (17) are moved upwards at the same time as the extraction arrangement (14) is also moved upwards. The extraction arrangement (14) therefore has a flexible pipe line, for example a hose (14a). The crowding grate units (17) are permeable to liquid, i.e. the water in which the fish resides flows freely through the crowding grate units (17). The openings in the grate portions (17b) of the crowding grate units are sufficiently small that the marine organisms cannot move from one side of the crowding grate units (17) to the other. When the crowding grate units (17) have two open portions (17a) lying over each other, i.e. the configuration they have when they are lowered down into the tank (12), the crowding grate units (17) are also permeable to fish, i.e. the fish can move from a position beneath the crowding grate units (17) to a position above the crowding grate units (17) as the crowding grate is lowered into the tank.

[0058] The crowding grate (16) can be attached to the tank wall (12a) and / or the outer side of the central column (18) via guides on the tank wall (12a) and central column (18) respectively. These guides can be in the form of slots, in which pins on the grate are led vertically up and down. Alternatively, the crowding grate (16) and / or the crowding grate units (17) are attached with wires or cables (16c) that are used to lower and raise the crowding grate (16) and the crowding grate units (17).

[0059] In a preferred embodiment, the crowding grate (16) is arranged vertically higher at the outer periphery than at the centre, such that the grate is positioned sloping in towards the centre of the tank (12). This will cause the fish, during crowding, to be led towards the centre. The crowding grate units (17) preferably consist of an outer ring and an inner ring, where the outer ring lies higher than the inner. When the grate is raised in the tank (12), the fish will be able to feel threatened, seek down towards the grate and be led towards the centre and in towards the intake of the flexible pipe, i.e. to the extraction arrangement (14), and be led up and out of the tank (12). This design also means that when the crowding grate (16) comes all the way up, the last remainder of fish will be drawn towards the centre and into the channel (16a) and sucked up.In a preferred embodiment, the extraction arrangement (14) is connected to a siphon, such that the siphon principle is used to lead the fish out of the tank (12). Alternatively, or in combination, one can suck the fish out of the tank by means of a pump. Preferably, the crowding grate units (17), near the centre, are equipped with a circular channel (16a). The fish will during crowding be led towards, and seek down into, this channel (16a). Preferably, the channel (16a) is equipped with one or more recesses (16b), and the extraction arrangement (14) is preferably arranged in one or more of these recesses (16b).

[0060] With this solution, one has achieved that one can lead the fish gently out of a tank, and optionally over to a new tank, by raising the crowding grate units (17) in the tank (12). The crowding will result in the fish gathering just above the crowding grate units (17) and in the centre of the tank (12). It is then led via channel (16a), and preferably recesses (16b), to the extraction arrangement (14) which leads the fish out of the tank (12). Since the solution is very gentle to the fish, it will be particularly relevant in tanks (12) where the fish is to stand for shorter periods, e.g. as a slaughter tank.

[0061] A further embodiment of the invention can comprise only one crowding frame, for example the uppermost one shown in the figures, with a battery of panels that lie as in a magazine over each other, where the uppermost frame is rotated and pulls out one element at a time from the magazine, until the entire circumference of the crowding grate (16) is covered.

Claims

CLAIMS1. A device (10) for crowding and discharge of marine organisms from a tank (12), comprising a horizontally arranged crowding grate (16) which is arranged for vertical movement in the tank (12), characterised in that the crowding grate (16) comprises at least two rotatable crowding grate units (17), where each crowding grate unit (17) comprises at least one open portion (17a) and at least one grate portion (17b), and that the crowding grate units (17) are arranged for rotation relative to each other between:- a first configuration where open portions (17a) in at least two crowding grate units (17) are mutually overlapping such that fish can pass through the crowding grate (16), and - a second configuration where grate portions (17b) together form a perforated grate that is impenetrable to fish.

2. A device according to claim 1, characterised in that the perforated crowding grate (16) is arranged to be moved vertically between a lower inactive position at the bottom of the tank (12) and an upper position, and in that grate portions (17b) in the second configuration form a continuous perforated grate that extends between the wall of the tank (12a) and a central column (18).

3. A device according to claim 1, characterised in that the crowding grate units (17) are circular-sector-shaped and comprise a ring-shaped framework that encloses an inner opening adapted to a central column (18) and an outer opening adapted to the wall of the tank (12a), and where several alternately distributed open portions (17a) and grate portions (17b) are arranged in each crowding grate unit (17), where the grate portions (17b) in the second configuration form a unified perforated grate that leads fish towards a central channel (16a) with an extraction arrangement (14).

4. A device according to any one of claims 1-3, characterised in that a flexible sealing element is arranged between the tank wall (12a) and the crowding grate (16), and / or between the central column (18) and the crowding grate (16).

5. A device according to claim 4, characterised in that the flexible sealing element is a flexible hose arranged for pressurisation with liquid.

6. A device according to any one of claims 1-5, characterised in that the crowding grate (16) is movably attached to vertical guides along the tank wall (12a) and / or central column (18).

7. A device according to any one of claims 1-6, characterised in that the crowding grate unit (17) and / or crowding grate (16) is attached with ropes, cables or wires (16c) to a lifting arrangement arranged above the tank (12).

8. A device according to any one of claims 1-7, characterised in that the assembly of the crowding grate (16) comprises a central channel (16a) arranged to lead fish towards a position above an extraction arrangement (14).

9. A device according to claim 8, characterised in that the channel (16a) comprises at least one recess (16b).

10. A device according to one of claims 8 or 9, characterised in that the extraction arrangement (14) is arranged in said channel (16a) or recess (16b).

11. A device according to any one of claims 1-10, characterised in that the extraction arrangement (14) is connected to a siphon.

12. A device according to any one of claims 1-11, characterised in that grate portions (17b) are a perforated net, grate or grid material with openings adapted to the size of the marine organisms.

13. A device according to any one of claims 1-12, characterised in that the crowding grate (16) is sloping from the outer edge of the tank towards the centre such that fish is led towards the extraction arrangement (14) when the grate is moved upwards.

14. A device according to any one of claims 1-13, characterised in that the extraction arrangement (14) comprises a flexible pipe run (14a).

15. A device according to any one of claims 1-14, characterised in that the stress level and / or position of the marine organisms is monitored and used as a control parameter for raising the crowding grate (16).

16. A device according to claim 15, characterised in that the monitoring comprises visual and / or acoustic methods, including camera, hydrophone and / or radar.

17. A method for crowding marine organisms in a tank (12), characterised in that a horizontally arranged crowding grate (16), comprising at least two rotatablecrowding grate units (17) with respectively open portions (17a) and grate portions (17b), is brought from a storage position above the liquid level to a lower inactive position in the tank (12), where the crowding grate units (17) upon lowering are set in a first configuration where open portions (17a) are mutually overlapping such that fish can pass through the crowding grate (16), that the crowding grate units (17) after positioning are rotated to a second configuration where grate portions (17b) together form a perforated grate that is impenetrable to fish, and that the crowding grate (16) is then moved upwards in the tank (12) such that fish is crowded to the upper part of the tank.

18. A method according to claim 17, characterised in that the grate portions (17b) in the second configuration form a continuous perforated grate that extends between the wall of the tank (12a) and a central column (18).

19. A method according to claim 17 or 18, characterised in that fish is led into a central channel (16a) and led out of the tank (12) via an extraction arrangement (14).

20. A method according to claim 19, characterised in that the extraction arrangement (14) is driven by a siphon and / or a pump.21 .A method according to any one of claims 17-20, characterised in that the crowding grate (16) slopes in towards the centre such that fish is led towards the central column (18).

22. A method according to any one of claims 17-21, characterised in that the stress level and / or position of the marine organisms is monitored and used as a control parameter for raising the crowding grate (16).

23. A method according to claim 22, characterised in that the monitoring is carried out with visual and / or acoustic sensors.

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