Technical field

The present disclosure relates to the field of maintenance of fish pens.

Background

[0001] Biofouling of fish pens is a major issue in the fish farming industry. Algae and other biological compounds contaminate the nets of fish pens, which causes inter alia reduced health for the fish, reduced oxygen supply to the fish pen, and increased difficulty in inspecting wear of the fish pen. Several approaches have been employed in order to address biofouling related issues, including hoisting and pressure cleaning the nets, as well as the employment of separate underwater remotely operated vehicles (ROVs) that clean the net while submerged.

[0002] In order to clean a net of a fish pen of biofouling it is beneficial to acquire knowledge of the type and amount of biofouling that has accumulated on the net. Knowledge of the type and amount of biofouling may thus be used in order to determine the type of cleaning method for removing said biofouling.

[0003] NO 20161708 describes an assembly for carrying out a cleaning operation on a net, where the assembly comprises a first unit and a second unit configured to be positioned on opposite sides of the net to be cleaned. The first and second units of adhere to one another and to the net to be cleaned by magnetic attraction and move across the net while cleaning the net using a cleaning system, such as a steam unit, an ultrasound unit, a high-pressure washing unit, or a water suction unit. The assembly of NO 20161708 does however not comprise any means for analysing the net.

[0004] It is an aim of the present disclosure to provide an assembly for imaging and cleaning a submerged net of a fish pen.

Summary of the present disclosure

[0005] A first aspect of the present disclosure provides a subsea assembly for imaging and cleaning a submerged net, the subsea assembly comprising a first subsea unit for being positioned on a first side of the net, the first subsea unit comprising at least two pa rallelly oriented belt assemblies, and a camera, a second subsea unit for being positioned on a second side of the net opposite to the first subsea unit, the second subsea unit comprising at least two parallelly oriented belt assemblies, and a background element, where the first subsea unit and/or the second subsea unit further comprises a cleaning means for cleaning the net, where each belt assembly comprises a track provided with magnets for generating an attractive force between the belt assemblies of the first subsea unit and the belt assemblies of the second subsea unit such that the subsea assembly adhere to the net, and where the camera and the background element are arranged such that they face each other when the subsea assembly adhere to the net, and where the background element is shaped to provide a fixed homogeneous background for the camera, in the same manner as a cover for a flatbed scanner, when the camera captures images.

[0006] According to an embodiment of the present disclosure the first subsea unit and/or second subsea unit further comprises a light source.

[0007] According to another embodiment of the present disclosure the light source is integrated in the background element.

[0008] According to yet another embodiment of the present disclosure the camera is a line camera.

[0009] According to yet another embodiment of the present disclosure the light source has an elongated shape or where the light source comprises a plurality of LEDs arranged in a line.

[0010] According to yet another embodiment of the present disclosure the background element comprises a Lambertian surface.

[0011] According to yet another embodiment of the present disclosure the light source is configured to flash.

[0012] According to yet another embodiment of the present disclosure the first subsea unit further comprises a filter arranged in front of the camera.

[0013] According to yet another embodiment of the present disclosure the camera comprises a spectrometer.

[0014] According to yet another embodiment of the present disclosure the background element comprises a plane surface.

[0015] According to yet another embodiment of the present disclosure each belt assembly comprises a track, a rear road wheel, a middle road wheel and a front road wheel, and each road wheel is provided with a suspension.

[0016] A second aspect of the present disclosure provides use of a subsea assembly according for imaging and cleaning a net or a sheet of a fish pen. [0017] A second aspect of the present disclosure provides a method for imaging and cleaning a submerged net of a fish pen, comprising the steps of: providing a subsea assembly, positioning the first subsea unit on a first side of the net, positioning the second subsea unit on a second side of the net opposite to the first subsea unit, driving the subsea assembly across the net, imaging the submerged net of a fish pen using the camera of the first subsea unit, and cleaning the submerged net of a fish pen using the cleaning means of the first subsea unit and/or second subsea unit.

[0018] In an embodiment of the present disclosure the first subsea unit is positioned on the side of the net facing into the fish pen and the second subsea unit is positioned on the side of the net facing out from the fish pen.

[0019] Other advantageous features will be apparent from the accompanying claims.

Brief description of the drawings

[0020] In order to make the present disclosure more readily understandable, the description that follows will refer to accompanying drawings, in which:

[0021] Figure la is a schematic representation of a subsea assembly according to the present disclosure where the second subsea unit comprises a background unit,

[0022] Figure lb is a schematic representation of the subsea assembly where one subsea unit is illustrated as transparent in order to visualise belt assemblies of the two subsea units adjoining each other,

[0023] Figure 2 is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a camera,

[0024] Figure 3 is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a light source,

[0025] Figure 4 is a schematic representation of a subsea assembly according to the present disclosure where the second subsea unit comprises a background unit having an integrated light source,

[0026] Figure 5a is a schematic representation of a subsea assembly according to the present disclosure where the first subsea comprises a line camera,

[0027] Figure 5b is a schematic representation of a subsea assembly according to the present disclosure where the background element comprises a plurality of LEDs arranged in a line,

[0028] Figure 6 is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a filter arranged in front of the camera, [0029] Figure 7 is a schematic representation of a belt assembly where each road wheel and at least one damper wheel are provided with suspension,

[0030] Figure 8 is a representation of an image that may be captured by a line camera of a net,

[0031] Figure 9a is a schematic representation of a subsea assembly according to the present disclosure where the first subsea comprises a line camera that spans the whole width of the first cleaning unit, and

[0032] Figure 9b is a schematic representation of a subsea assembly according to the present disclosure where the background element comprises a plurality of LEDs arranged in a line that spans the whole width of the second cleaning unit.

Detailed description of the present disclosure

[0033] In the following, general embodiments as well as particular exemplary embodiments of the present disclosure will be described. References will be made to the accompanying drawings. It shall be noted, however, that the drawings are exemplary embodiments only, and that other features and embodiments may well be within the scope of the present disclosure as claimed.

[0034] Unless otherwise defined, all terms of art, notations and other scientific terms or terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this disclosure pertains. Certain terms of art, notations, and other scientific terms or terminology may, however, find a definition in the field of continuous track propulsion systems, or they may be defined specifically as indicated below.

[0035] The present disclosure provides a subsea assembly 100 for cleaning and imaging a submerged net 130, e.g. that of a fish pen. The subsea assembly 100 according to the present disclosure comprises a first subsea unit 110 for being positioned on a first side of the net 130 and a second subsea unit 120 for being positioned on a second side of the net 130, opposite to the first subsea unit 110. The first subsea unit 110 and second subsea unit 120 are, as schematically illustrated in figure la and lb, each provided with at least two parallelly oriented belt assemblies 150. The first subsea unit 110 and second subsea unit 120 may according to any embodiment of the invention each be provided with two parallelly oriented belt assemblies 150. The various embodiments of the present disclosure will be described and illustrated for the example where the first subsea unit 110 and second subsea unit 120 are each provided with two parallelly oriented belt assemblies 150. A person skilled in the art with knowledge of the present invention will appreciate, however, that each embodiment of the present disclosure will be enabled also when the first subsea unit 110 and/or second subsea unit 120 are each provided with more than two parallelly oriented belt assemblies 150.

[0036] A belt assembly 150 may in the context of the present disclosure be understood by a person skilled in the art as the collection of wheels, track 160, bearings, supports, etc. necessary to enable continuous track propulsion of the subsea units, and hence the subsea assembly 100. Each belt assembly 150 may as schematically illustrated in figure la and lb for example comprise a rear road wheel 170, optionally one or more middle road wheels 180, a front road wheel 190 and a track 160. Additional elements such as bearings, fastening mechanisms etc., may be provided in a variety of ways as will be appreciated by a person skilled in the art with knowledge of the present disclosure. The terms "front", "middle" and "rear" may here be defined relative to the driving direction 220 of the subsea assembly 100. However, as the driving direction 220 may be reversed, said terms are largely used herein to refer to the relative position of the road wheels 170,180,190, meaning in practice that any middle road wheel 180 is placed between the front road wheel 190 and the rear road wheel 170. A belt assembly 150, or more generally a subsea unit 110,120, may further be considered as comprising a driving unit 380 for enabling the belt assembly to provide continuous track propulsion for the subsea unit 110,120 to which it belongs. A driving unit 380 may for example comprise such as a battery, and a conventional motor or a motor in the hub of any one or more wheel of the belt assembly 150.

[0037] Each belt assembly 150 of the subsea units 110,120 may, as illustrated in figure la and lb, be arranged such that the ground pad 165 of the track 160 protrudes a non-zero distance from the underside of a subsea unit 110,120. The ground pad 165 of each belt assembly 150 of the first subsea unit 110 may thus in other words be said to protrude a nonzero distance from the underside of the first subsea unit 110, while the ground pad 165 of each belt assembly 150 of the second subsea unit 120 may be said to protrude a nonzero distance from the underside of the second subsea unit 120. A person skilled in the art with knowledge of the present disclosure will appreciate that the ground pad 165 of any belt assembly 150 may be interpreted as the part of a track 160 that lies between any two road wheels. A ground pad 165 may thus be considered as a part of a track 160. The ground pad 165 of any track 160 may according to the present disclosure be considered as planar, or at least essentially planar, where "essentially planar" may be interpreted as meaning for example that the ground pad 165 of any belt assembly 150 may be tilted by < 10 degrees, or be at least in part wavy, e.g. due to the track 160 not being completely tight.

[0038] The first subsea unit 110 and second subsea unit 120 may, as schematically illustrated in figure la and lb, be arranged on opposite sides of the net 130 to be cleaned. The first subsea unit 110 and second subsea unit 120 may be aligned relative to one another such that the at least two belt assemblies 150 of the first cleaning 110 unit are aligned with and adjoins separate belt assemblies 150 of the second subsea unit 120. The ground pad 165 of each respective track 160 of each belt assembly 150 of the first subsea unit 110 may, as schematically illustrated in figure lb, be positioned such that each said ground pad 165 adjoins the ground pad 165 of the track 130 of separate belt assemblies 150 of the second subsea unit 120. Note that in figure lb one of the subsea units 110,120 of the subsea assembly 100 is schematically illustrated as transparent for illustrative purposes. A person skilled in the art with knowledge of the present disclosure will appreciate that a net 130 to be cleaned may be present between any two ground pads 165 described as adjoining in the above context. Figure la and lb illustrate an example where the first subsea unit 110 and second subsea unit 120 are positioned on opposite sides of a net 130 to be cleaned such that the ground pad 165 of the track 160 of each belt assembly 150 of the first cleaning 110 unit adjoins, via the net 130 to be cleaned, a ground pad 165 of the track 160 of a belt assembly 150 of the second subsea unit 120.

[0039] The track 160 of each belt assembly 150 is, as schematically illustrated in figure lb, provided with magnets 210. The magnets 210 are provided in order to generate an attractive force between the belt assemblies 150 of the first subsea unit 110 and the belt assemblies 150 of the second subsea unit 120 such that the subsea assembly 100 may adhere to a net 130 to be cleaned. A track 160 of a belt assembly 150 of the first subsea unit 110 may as a way of example comprise magnets 210 with a first polarity, while a track 160 of a belt assembly 150 of the second subsea unit 120 may comprise magnets 210 with a second polarity, opposite to the first polarity. When the tracks 160 of said at least two belt assemblies 150 are positioned such that they adjoin, an attractive force will occur between them such that a frictional force will be obtained between each subsea unit 110,120 and the net 130 to be cleaned. The subsea assembly 100 may thus due to this attractive force, and the resulting frictional force, adhere to the net 130 to be cleaned such that the two subsea units 110,120 may maintain a position on the net 130 relative to one another. A person skilled in the art with knowledge of the present disclosure will appreciate that there are numerous degrees of freedom in the configuration of the magnets 210 in each track 160. The magnets 210 in two, first and second, adjoining tracks 160 may, as a way of example, be such that all the magnets 210 of the first track 160 have the same polarity, while all the magnets 210 in the second track 160, adjoining the first track 160, have the opposite polarity. Another example is that the magnets 210 in two adjoining tracks 160 may be such that any two adjacent magnets 210 in any one track 160 have opposite polarity, but where the tracks 160 of the two subsea units are adjoining with a shift such that magnets 210 of opposite polarity are adjoining/attracting one another. The latter configuration may be utilized in order to counteract skidding of the tracks 160.

[0040] The subsea assembly may according to the present disclosure move across a net to be cleaned by means of the belt assemblies of the first and second subsea unit. The adhesion to the net obtained by the magnetic attraction between adjoining tracks of the two subsea units will result in a grip for the subsea assembly such that movement is enabled. Said grip may thus be termed a magnetic induced grip. A person skilled in the art with knowledge of the present disclosure will appreciate that each belt assembly of the subsea assembly may operate as a continuous track vehicle propulsion system that is configured to operate under water, i.e. where each belt assembly is provided with one or more of an engine, gear system, water tight gaskets, power supply, etc. The subsea units may generally be provided with other parts necessary for allowing the subsea assembly to move across a net to be cleaned. A person skilled in the art with knowledge of the present disclosure will appreciate that such parts may comprise e.g. watertight housing, transmitter, receiver, lighting device, battery, etc. At least one of the first subsea unit and the second subsea unit may as a way of example comprise a driving unit, where the driving unit comprises an electric motor and a battery. The electric motor may here be connected to one or more of the wheels of a belt assembly of the first subsea unit and/or the second subsea unit via for example a shaft or another suitable power transfer mechanism. In another example the first subsea unit and the second subsea unit may each comprise a driving unit as described above. A person skilled in the art with knowledge of the present disclosure will appreciate that there are several options for how to drive the belt assemblies of the subsea units. [0041] The subsea assembly 100 may, as illustrated in figure la and lb be provided with cleaning means 140 for cleaning a submerged net 130. Both or either of the first subsea unit 110 and second subsea unit 120 may be provided with cleaning means 140. Cleaning means 140 may according to the present disclosure be any suitable means for cleaning a net 130. As a way of example, the subsea assembly 100 may be provided with one or more brushes, e.g. a rotating brush. The one or more brushes may be provided on only one of the subsea units 110,120 or alternatively be distributed between the two subsea units 110,120. A brush may brush against the net in order to clean the net of unwanted substances such a biofouling. In another example the cleaning means 140 may comprise a water-based cleaning means 140, such as a pressure cleaner. In yet another example the cleaning means 140 may comprise one or more friction surfaces, such as a scrub or stationary brush, suitable for cleaning a net by being moved across the net 130.

[0042] The first subsea unit 110 may as schematically illustrated in figure 2 be provided with a camera 230, while the second subsea 120 unit may, as schematically illustrated in figure la be provided with a background element 240. Alternatively, the other way around. The camera 230 and the background element 240 are arranged such that they face each other when the subsea assembly 100 adhere to the net 130. The camera 230 and background element 240 may thus respectively be considered as arranged on the side of the first subsea unit 110 and second subsea unit 120 that face the net 130 to be cleaned under operation of the subsea assembly 100. The camera 230 and background element 240 may as a way of example be positioned between two parallelly oriented belt assemblies 150 of the first subsea unit 110 and second subsea unit 120 respectively. The camera 230 may more specifically be positioned between two parallelly oriented belt assemblies 150 of the first subsea unit 110, while the background element 240 may cover at least a part of the area between the two parallelly oriented belt assemblies 150 of the second subsea unit 120. In a particular embodiment of the disclosure the first subsea unit 110 may be provided with a camera 230 and a background element 240, while the second subsea 120 unit may be provided with a camera 230 and a background element 240.

[0043] Technically, this arrangement has a parallel in flatbed scanners/copiers where you have one side with scanner elements and lighting and an opposite side with a contrast element, preferably flat white. What is to be scanned is arranged between the surfaces of the plate, the scanner element moves line by line so that the entire object to be scanned is scanned. In the invention, the object to be scanned is a net, while the "scanner" itself, the first subsea unit, moves relative to the net (knot by knot) together with the second subsea unit with the background element. The background element provides a uniform background that the scanning software can use as a reference point for determining the positions and/or the state of the net being scanned.

[0044] A background element may generally in the context of the present invention be considered as an element shaped to provide a fixed homogeneous background for the camera when the latter captures an image. Generally, the background element may be shaped according to the type of camera used such that an image of the background element results in an image with no or at least limited contrast.

[0045] The camera and background element in the subsea assembly may be used for example in order to identify biofouling on the net to be cleaned. Knowledge of the presence of biofouling may further be used in order to determine whether to activate or how to control the cleaning means of the subsea assembly. In the event where the cleaning means comprises rotatable brushes, knowledge of the presence of biofouling, or amount of biofouling, on the net to be cleaned may for example be used in order to determine the velocity of the rotating brush or the force in which the brush is applied towards the net to be cleaned. The first subsea unit and/or the second subsea unit may for example be provided with a moving mechanism for adjusting the position of the cleaning means. The moving mechanism may for example be a linear motor or a hydraulic moving mechanism, for example configured to a move a rotating or stationary brush in a direction perpendicular to the net to be cleaned.

[0046] The use of a background element in the second subsea unit has been found to be beneficial as the background element provides a fixed background for the camera of the first subsea unit. The net to be imaged by the camera will during operation of the subsea assembly be present between the camera and the background element, thus enabling the camera to image the net to be cleaned using the background element as a fixed background. Multiple images of the net to be cleaned may thus be compared without having to consider various lighting conditions that for example may occur if one where to image a net using the open sea as a background. The open sea will for example give a lighting effect in a captured image dependent on the depth of the subsea assembly during the capture of the image. The fixed background provided by the background element has further been found to enable high resolution images to be captured by the camera. The latter is useful for detecting holes in the net, wear of the net, and particularly early signs of wear of the net. Early signs of wear allow for example maintenance to be conducted prior to a hole developing in the net, thereby hindering for example the fish escaping the fish pen. Figure 8 shows an example of an image of a fish pen obtained using a line camera configured to capture images with a resolution of 300 DPI and using a plane surface as a background element.

[0047] The background element 240 may as schematically illustrated in figure la comprise a plane surface, which may as a way of example be oriented in parallel with the ground pad 165 of the tracks 160 of the belt assemblies 150 of the second subsea unit 120. A plane background element 240 may generally be arranged such that it is parallel with the net 130 to be cleaned during operation of the subsea assembly. It will be appreciated by a person skilled in the art with knowledge of the present disclosure that the background element 240 in this embodiment doesn't have to be perfectly in parallel with the net 130 to be cleaned during operation of the subsea assembly 100. A plane background element 240 may generally be arranged such that it is within 10 degrees or 5 degrees of being in parallel with the net 130 to be cleaned during operation of the subsea assembly. A background element 240 comprising a plane surface may as a way of example be a plate, for example a metal plate, a plastic plate, polymer plate or a composite plate.

[0048] The background element may generally comprise a Lambertian surface, where the Lambertian surface is facing the camera of the first subsea unit during operation. A Lambertian surface has been found to be beneficial for imaging certain types of net, as the Lambertian surface contributes for example to eliminate unwanted specular reflections from stray light sources being captured by the camera. A Lambertian surface may be considered herein as any surface that offers at least 80 % diffuse scattering, at least 90 % diffuse scattering or alternatively at least 95 % diffuse scattering. An example of a material that may be used in the background element in order to provide a Lambertian surface is fluoropolymers, e.g. in the form of a compressed PTFE powder.

[0049] The first subsea unit 110 and/or the second subsea unit 120 may as schematically illustrated in figure 3 further comprises one or more light sources 250. The presence of a light source 250 in at least one of the first subsea unit 110 and the second subsea unit 120 has/have been found to be beneficial in order to illuminate the net 130 to be imaged by the camera 250. As the first subsea unit 110 and the second subsea unit 120 are facing each other during operation of the subsea assembly 100, with limited light from the ambient, a light source 250 may be present for example next to the camera 230 on the first subsea unit 110 in order to illuminate the net 130 to be imaged. A light source 250 may additionally or alternatively be provided on the second subsea unit 120, for example facing the camera 230 of the first subsea unit 110 when the subsea assembly 100 adhere to the net 130 to be cleaned.

[0050] The light source may in any embodiment of the present disclosure be a light source configured to illuminate white light. Other colours may alternatively be used, for example in order to enhance contrast between the net to be imaged and any biofouling, or other substances of interest that may be present on the net. The light source may in any embodiment of the present disclosure comprise at least one LED.

[0051] The light source 250 may as schematically illustrated in figure 4 be integrated in the background element 240. Integration in the background element 240 enables for example bright field images to be captured by the camera 230, allowing for a high contrast of the net. The background element 240 may as a way of example comprise an array of light sources 250 such as LEDs 270. The background element 240 may in a particular embodiment be configured to generate Kohler illumination, i.e. even illumination, ensuring that the light source 250 does not appear in images captured by the camera 230. Kohler illumination may for example be achieved at least in part by providing a diffuse transmitter in front of an array of light sources 250 such as LEDs 270. It will be appreciated by a person skilled in the art with knowledge of the present disclosure that perfect Kohler illumination may generally be difficult to obtain. Kohler illumination may thus in the context of the present disclosure be considered as illumination illuminating the field of view of the camera with a relative intensity variation of maximum 15 % or alternatively maximum 5 %.

[0052] The camera 230 may as schematically illustrated in figure 5a be a line camera 260. A line camera 260 may for example span between two parallelly oriented belt assemblies 150 of the first subsea unit 110, and optionally be arranged perpendicularly to two parallelly oriented belt assemblies 150 of the first subsea unit 110. A line camera 260 may generally be arranged perpendicularly to the driving direction of the subsea assembly 100, which may be beneficial in order to optimize how much of the net to be cleaned that is captured per pass of the subsea assembly 100. As a way of example, a line camera 260 may be configured to span the full width of the first subsea unit 110. The latter may be obtained by placing the line camera in front of, or behind, the parallelly oriented belt assemblies 150 of the first subsea unit 110. In the latter example, the background element 240 will thus be positioned in front of, or behind, the parallelly oriented belt assemblies 150 of the second subsea unit 110 such that it is aligned opposite the line camera 260 of the first subsea unit 110. The latter is schematically illustrated in figure 9.

[0053] Figure 5b schematically illustrates an embodiment of the present disclosure where the light source 250 has an elongated shape, or where the light source 250 comprises a plurality of LEDs 270 arranged in a line. Either configuration may optionally be arranged perpendicularly to the driving direction of the subsea assembly 100. The elongate shape may in other words be elongate in the direction perpendicularly to the driving direction of the subsea assembly 100, or the line of LEDs may be arranged in the direction perpendicularly to the driving direction of the subsea assembly 100. An elongate light source 250 and/or a light source 250 comprising a plurality of LEDs 270 arranged in a line has been found to be beneficial in order to save power in the subsea assembly 100. Such a light source 250 may be used to selectively illuminate a section of the net 130 to be cleaned, hence allowing for sampling of a linear segment of the net 130 to be cleaned per time. An elongate light source 250 and/or a light source 250 comprising a plurality of LEDs 270 arranged in a line may for example be combined with the use of a line camera 260 where the elongate light source 250 and/or the light source 250 comprising a plurality of LEDs 270 arranged in a line may be aligned with the line camera 230, e.g. such that any part of the elongate light source 250 and/or the light source 250 comprising a plurality of LEDs 270 arranged in a line is arranged facing into the line camera 260 when the subsea assembly 100 is being operated. The use of an elongate light source 250 and/or a light source 250 comprising a plurality of LEDs 270 arranged in a line may in the latter case optimize power consumption, as a limited amount of light will be wasted for illuminating parts of the net 130 not being imaged by the line camera 230. An elongate light source 250 and/or a light source 250 comprising a plurality of LEDs 270 arranged in a line may as schematically illustrated in figure 5 and 9 be integrated in the background element 240. [0054] The light source may according to any embodiment of the present disclosure be configured to flash or alternatively be configured to pulsate. A light source configured to flash or configured to pulsate may be used to reduce the power consumption of the subsea assembly, as the light source may be synchronized with the capture rate of the camera. A camera having a capture rate of 1 fps may thus only need illumination once per second, allowing the light source to be off or idle for the rest of the time. A person skilled in the art with knowledge of the present disclosure will appreciate how to obtain a light source that is configured to flash or at least be configured to pulsate. The light source, or a control unit for the light source may for example be provided with necessary capacitors sufficiently sized in order to power the light source.

[0055] Figure 6 schematically illustrates an embodiment of the present disclosure where the second subsea unit 120 further comprises a filter 280 arranged in front of the camera 230. A filter 280 may for example be used in order to filter out the colour of the net 130 to be cleaned in order to enhance contrast with for example biofouling on the net 130. A filter 280 may alternatively be used in order to filter out the colour of the surrounding water. As a way of example, the filter 280 may be a band-stop filter or a band pass filter. A red-stop filter may for example be used if the net to be cleaned is red. Biofouling or other substances of interest on the red net 130 having any other colour than red may thus more easily be detected.

[0056] Instead of, or additionally to using a filter, the camera may comprise a spectrometer. A spectrometer may here be used in order to obtain images of the net to be cleaned based on selected wavelengths of interest. The effects of using a spectrometer may be considered similar to using a filter but has the additional advantage that more information may be obtained by any one image relative to what may be obtained using for example a normal image sensor like a charge- coupled device in combination with a filter.

[0057] When used to clean the net of a fish pen, the first subsea unit may in a particular embodiment of the present disclosure be positioned on the side of the net facing into the fish pen, while the second subsea unit may be positioned on the side of the net facing out from the fish pen. As obstacles such as ropes and rope knots are typically positioned on the outer surface of the fish pen, it is beneficial to image the net of the fish pen from the inside of the fish pen. The camera may thus in this embodiment be positioned on the side of the net facing into the fish pen, thus allowing for a shorter and more permanent distance between the camera and the net to be cleaned relative to what would have been possible if the camera was provided on the subsea unit positioned on the side of the net facing out from the fish pen.

[0058] The subsea assembly may according to the present disclosure be dimensioned according to the net to be cleaned. A typical extension of the subsea assembly is between 80 cm and 200 cm. The extension of the subsea assembly is according to a specific embodiment of the present disclosure less than 150 cm.

[0059] Each road wheel 170,180,190 may, as schematically illustrated in figure 7, provided with a suspension 200. The suspension 200 for each road wheel 170,180,190 may be configured for shifting the position of said road wheel 170,180,190 in a direction at least in part perpendicular to a driving direction 220 of the subsea assembly. An example of such a distance is less than 10 centimetres, or more specifically a distance of between 3 and 5 centimetres. The suspension 200 of the road wheels 170,180,190 aims inter alia to enable the subsea assembly to traverse obstacles of the net to be cleaned, such as ropes, knots or similar. The combination of the road wheel suspension 200 and the presence of three road wheels 170,180,190 means that any two adjoining tracks 160 may retain magnetic attraction even when the subsea assembly is traversing an obstacle. As a way of example one can assume a subsea assembly according to the present disclosure traversing a rope of the net to be cleaned. As the subsea assembly drives across the rope, the front road wheels 190 of each pair of adjoining tracks 160 will be displaced away from one another and the magnetic attraction between the part of the ground pad 165 between the front road wheel 190 and middle road wheel 180 of the pair of adjoining tracks 160 will be strongly reduced. A subsea assembly having only two road wheels would in such an instance likely lose its magnet-induced grip on the net to be cleaned and consequently fall of the net. The subsea assembly according to the present disclosure would on the contrary maintain its magnet induced grip on the net, as the part of the ground pad 165 between the middle road wheel 180 and read road wheel 170 would still be adjoining, such that sufficient magnetic attraction may be maintained. Following the same example, the subsea assembly will upon continuing its traversing of said rope move relative to the rope such that the front road wheels 190 once again are brought in contact with each other, but where the middle road wheels 180 subsequently are displaced from their default position using their respective suspension 200. At such a position the subsea assembly according to the present disclosure may maintain its adhesion to the net to be cleaned due to the magnet attraction between the ground pad 165 around the front road wheels 190 and the rear road wheels 170. The subsea assembly will upon continuing its traversing of said rope, move relative to the rope such that the middle road wheels 180 once again are brought in contact with each other, but where the rear road wheels 170 subsequently are displaced from their default position using their respective suspension 200. The latter situation is equivalent to the situation where the front road wheels 190 were displaced.

[0060] Figure lb and 7 schematically illustrate an embodiment of the present disclosure where each belt assembly 150 further comprises a damper wheel 225. Said damper wheel 225 may typically be positioned at a non-zero distance from the ground pad 165 of the belt assembly 150 to which it belongs. The latter location may here be in a direction perpendicular to the driving direction 220 of said belt assembly 150. A damper wheel 225 may be utilized in order to compensate for any strain in a track 160 caused when the subsea assembly traverses an obstacle that causes one of its road wheels 170,180,190 to be displaced from their nondamped position. A road wheel 170,180,190 being displaced as a consequence of the subsea assembly traversing an obstacle will result in the relevant track 160 having to conform to the shape of the object that is being traversed. Instead of the track 160 becoming strained due to the displacement of a road wheel

170.180.190, the damper wheel 225 may instead compensate for the shift in position of the road wheel 170,180,190, i.e. compensate for the resulting strain in the track 160 by being itself displaced. Each damper wheel 225 may thus in other words be provided with a suspension 200 for shifting the position of said damper wheel 225 in order to compensate for a shift in position of a road wheel

170.180.190. As a way of example, if a road wheel 170,180,190 of a belt assembly 150 is displaced in a direction perpendicular to the driving direction 220 of said belt assembly 150, a damper wheel 225 of that belt assembly may be displaced in the opposite direction of the displaced road wheel 170,180,190 in order to compensate for the increased length requirement on the track 160 due to the belt having to conform to the shape of the object that is being traversed. A typical object that needs to be traversed may as previously mentioned be a rope or a knot, which for example could have a diameter or extension of 3-5 centimetres. Each road wheel 170,180,190 may thus be provided with a suspension 200 for shifting the position of said road wheel 170,180,190 a distance of at least 3-5 centimetres in a direction at least in part perpendicular to a driving direction 220 of the subsea assembly. Each damper wheel 225 may consequently be provided with a suspension 200 for shifting the position of said damper wheel 225 a distance of 3-5 centimetres. In general, any road wheel 170,180,190 may be provided with a suspension 200 for shifting the position of said road wheel 170,180,190 a distance of up to 10 centimetres in a direction at least in part perpendicular to a driving direction 220 of the subsea assembly. A suspension 200 may generally be any suitable suspension 200. Examples of suitable suspensions 200 are spring-based suspension and hydraulic suspension.

[0061] The subsea assembly may according to any embodiment of the present disclosure be configured to traverse obstacles of a given size. As a way of example, the subsea assembly may be configured to traverse an obstacle such as a rope or a rope knot. In order for the subsea assembly to not loose adhesion to the net to be cleaned upon traversing an obstacle, the road wheels of each belt assembly may be spaced apart depending on the dimension of the obstacle to be traversed. In one embodiment of the present disclosure the road wheels of each individual belt assembly may be separated by a distance of at least 3-5 centimetres. The latter distance is here measured between the surface of two adjacent road wheels. The road wheels of each individual belt assembly may generally be separated by a distance longer than 5 centimetres. It will be appreciated by a person skilled in the art that the upper limit for the spacing between two adjacent road wheels of the same belt assembly is determined by for example the obstacle that it is desirable to traverse, and/or for example the dimension and weight of the subsea assembly. A distance between two adjacent road wheels of at least 3-5 centimetres, alternatively 5 - 10 centimetres, is considered adequate for most fish pen. Such a distance will allow the subsea assembly to traverse ropes and rope knots without having two adjacent road wheels of the same belt assembly being displaced by the rope.

[0062] Any belt assembly 150 may, as illustrated in figure lb and 7, further comprise any number of drive wheels 320, damping wheels 225, road wheels, idlers and/or tightener wheels 340. As a way of example, any belt assembly may be provided by a driving wheel 320, i.e. a wheel that supplies driving power to the track 160. Any road wheel or damper wheel 225 may in any relevant embodiments of the present disclosure be a driving wheel 320. A person skilled in the art would appreciate that the subsea assembly according to the present disclosure may comprise any number of additional wheels, e.g. dependent on the exact size and shape of the belt assemblies 150. A tightener wheel 340 may for example be provided to form the previously described driving edge 245 or trailing edge 255. In a particular embodiment of the present disclosure, each belt assembly 150 may further comprise an additional middle road wheel 180. An additional middle road wheel 180 may contribute to increase the attraction between two adjoining belt assemblies 150 when the subsea assembly traverses an obstacle. An additional middle road wheel 180 may contribute to ensuring a plane surface of the ground pad 165 of two adjoining tracks 160 being in contact during the traversing of said obstacle. The size of each wheel of the subsea assembly will generally depend on the size of each subsea unit. The size of each wheel may typically be dimensioned according to the type of track used, for example such that the track may run across the wheels without experiencing too great a curvature. In a particular embodiment of the present disclosure each wheel of each belt assembly has a diameter in the range of 60 mm to 120 mm. Such a diameter has been found to be preferable when the track is made from silicone, rubber or plastic. Any wheel of a belt assembly that is positioned farthest to the front or back along the driving direction of a belt assembly will typically inflict the largest curvature on the track. These farthermost wheels may thus have a diameter that is larger than that of any road wheels appurtenant to the same belt assembly, e.g. in the range from 10% - 250% larger, in particularly in the range from 50% - 100 % larger. Any one or both of the farthermost wheels may for example be a driving wheel 320.

[0063] The track of any belt assembly of the subsea assembly may according to any embodiment of the present disclosure be made at least in part from rubber, plastic or silicone. A person skilled in the art will appreciate that the track may be made from other materials than those listed explicitly herein. The track may for example be made from a combination of materials, e.g. a combination of those mentioned above.

[0064] It will be appreciated that the subsea assembly according to any embodiment of the present disclosure is not limited to cleaning a net. The subsea assembly may according to any embodiment of the present disclosure alternatively be used in order to clean a seine, net cage, a water permeable sheet, water impermeable sheet or similar. Other examples are watertight tarpaulin, perforated tarpaulin, or similar.

[0065] Other advantageous features will be apparent from the accompanying claims.