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 in ter 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] 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 the assembly 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.

[0003] The position of the assembly of NO 20161708 on a net to be cleaned is determined through use of GPS. The assembly is provided with receivers, which may recei ve information from transmitters of the GPS system in order to calculate the position of the assembly relative to the net to be cleaned. As the accuracy of GPS is typically considered to be in the order of meters, it will be difficult to controllably navigate the assembly of NO 20161708 across the net without crossing the same patch twice or without missing a patch.

[0004] It is an aim of the present disclosure to provide a subsea assembly that may navigate across a submerged net of a fish pen with a higher accuracy than what may be obtained using GPS.

Summary of the present disclosure

[0005] A first aspect of the present disclosure provides a subsea assembly for adhering to and navigating across 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 parallelly oriented belt assemblies, and a camera, and 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, 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 adheres to the net, where at least one of the first subsea unit and the second subsea unit further comprises a cleaning means for cleaning the net, and where at least one of the first subsea unit and the second subsea unit further comprises an on-board computer configured to receive image data from the camera as the subsea assembly moves across the net, and to determine the position of the subsea assembly on the net based on the image data.

[0006] According to an embodiment of the disclosure the second subsea unit further comprises a background element, and the camera and the background element are arranged such that they face each other when the subsea assembly adheres to the net.

[0007] According to another embodiment of the disclosure the first subsea unit and/or second subsea unit further comprises a light source.

[0008] According to yet another embodiment of the disclosure the light source is integrated in the background element.

[0009] According to yet another embodiment of the disclosure the camera is a line camera.

[0010] According to another embodiment of the disclosure at least one of the first subsea unit and the second subsea unit further comprises a cleaning means for cleaning the net.

[0011] According to yet another embodiment of the disclosure at least one of the first subsea unit and the second subsea unit further comprises one or more of an oxygen sensor, a temperature sensor, a salinity sensor, a C02-sensor, a conductivity sensor, a flow sensor and a water clarity sensor.

[0012] The first aspect of the disclosure also provides a method for determining the position of a subsea assembly on a submerged net, the method comprising the steps of moving a subsea assembly across the net while the subsea assembly adheres to the net, collecting image data from a camera of the subsea assembly as the subsea assembly adheres to and moves across the net, and determining, from the image data, the position of the subsea assembly on the net. [0013] A second aspect of the disclosure provides a subsea assembly for adhering to and navigating across 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 parallelly oriented belt assemblies, and a driving unit comprising a motor, 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, 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 adheres to the net, where at least one of the first subsea unit and the second subsea unit further comprises a cleaning means for cleaning the net, where at least one of the first subsea unit and the second subsea unit further comprises an orientation sensor, and where at least one of the first subsea unit and the second subsea unit further comprises an On-board computer configured to receive motion data from the driving unit and orientation data from the orientation sensor, and to determine the position of the subsea assembly on the net based on the motion data and orientation data.

[0014] According to an embodiment of the disclosure the motor is a stepper motor or a servo motor.

[0015] According to another embodiment of the disclosure the orientation sensor comprises one or more of a compass, a gyroscope, an accelerometer or a gravity sensor.

[0016] According to yet another embodiment of the disclosure at least one of the first subsea unit and the second subsea unit further comprises a cleaning means for cleaning the net.

[0017] According to yet another embodi ment of the disclosure at least one of the first subsea unit and the second subsea unit further comprises one or more of an oxygen sensor, a temperature sensor, a salinity sensor, a CO2-sensor, a conductivity sensor, a flow sensor and a water clarity sensor.

[0018] The second aspect of the disclosure also provides a method for determining the position of a subsea assembly on a submerged net, the method comprising the steps of moving the subsea assembly across the net while the subsea assembly adheres to the net, collecting motion data from a driving unit of the subsea assembly as the subsea assembly adheres to and moves across the net, collecting orientation data from an orientation sensor of the subsea assembly as the subsea assembly adheres to and moves across the net and determining, from the motion data and orientation data, the position of the subsea assembly on the net.

[0019] A third aspect of the disclosure provided use of a subsea assembly according to any embodiment of either aspect of the disclosure for cleaning a submerged net.

[0020] Other advantageous features will be apparent from the accompanying claims.

Brief description of the drawings

[0021] In order to make the present disclosure more readily understandable, the description that follows will refer to accompanying drawings, in which:

[0022] Figure la is a schematic representation of a subsea assembly according to the present disclosure where the second subsea unit comprises a background element,

[0023] Figure lb is a schematic representation of the subsea assembly where one subsea unit is illustrated as partly transparent in order to visualise belt assemblies of the two subsea units adjoining each other,

[0024] Figure 2a is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a camera,

[0025] Figure 2b is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a line camera,

[0026] Figure 3 is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a light source,

[0027] Figure 4 is a schematic representation of a subsea assembly according to the present disclosure where the second subsea unit comprises a background element having an integrated light source,

[0028] Figure 5a is a schematic representation of a subsea assembly according to the present disclosure where the first subsea comprises a line camera,

[0029] 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,

[0030] Figure 6 is a representation of an image on a net captured by a line camera of a subsea assembly according to the present disclosure,

[0031] Figure 7a is a schematic representation of a subsea assembly according to the present disclosure where the first subsea unit comprises a line camera that spans the whole width of the first subsea unit, [0032] Figure 7b is a schematic representation of a subsea assembly according to the present disclosure where the background element comprises a plurality of LE Ds arranged in a line that spans the whole width of the second subsea unit,

[0033] Figure 8 is a schematic illustration of a subsea unit, illustrated with a transparent base, where the subsea unit comprises a driving unit, an orientation sensor and an on-board computer,

[0034] Figure 9 is a schematic representation of how the relative position of a subsea assembly may be determined based on knowledge of the distance travelled and the orientation of the subsea assembly during said travel,

[0035] Figure 10 is a schematic illustration of a subsea unit comprising an oxygen sensor, a temperature sensor, a salinity sensor, a CO2-sensor, a conductivity sensor, a flow sensor and a water clarity sensor.

Detailed description of the present disclosure

[0036] 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.

[0037] 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.

[0038] The present disclosure provides a subsea assembly 100 for adhering to and navigating across 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 figures la and lb, each provided with at least two parallel ly oriented belt assemblies 150. The first subsea unit 110 and second subsea unit 120 may according to any embodiment of the disclosure each be provided with two parallelly oriented belt assemblies 150. The various embodiments of the present disclosure will be described and illustrated for an 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 disclosure wilt appreciate, however, that each embodiment of the present disclosure may be generalized such that at least one of the first subsea unit 110 and the second subsea unit 120 is/are provided with more than two parallelly oriented belt assemblies 150.

[0039] 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 figures 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 a battery, and a motor, optionally provided in the hub of any one or more wheel of the belt assembly 150. Figure 8 schematically illustrates a subsea unit 110,120, illustrated with a transparent base, where the subsea unit 110,120 comprises a driving unit 380.

[0040] Each belt assembly 150 of the subsea units 110,120 may, as schematically illustrated in figures la and lb, be arranged such that the ground pad 165 of the track 160 of each belt assembly 150 protrudes a non-zero distance from the underside of the relevant 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.

[0041] The first subsea unit 110 and second subsea unit 120 may, as schematically illustrated in figures la and lb) be arranged on opposite sides of a net 130. 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 adjoin 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 partly transparent for illustrative purposes. A person skilled in the art with knowledge of the present disclosure will appreciate that a net 130 may be present between any two ground pads 165 described as adjoining in the above context. Figures 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 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, a ground pad 165 of the track 160 of a belt assembly 150 of the second subsea unit 120.

[0042] The track 160 of each belt assembly 150 is, as schematically illustrated in figure lb, provided with magnets 210. The magnets 210 are provided 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. 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. The subsea assembly 100 may thus, due to this attractive force, and the resulting frictional force, adhere to the net 130 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 of those in the first track 160. 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 polarities, but where the tracks 160 of the two subsea units are adjoining each other with a relative shift such that magnets 210 of opposite polarities are adjoining/attracting one another. The latter configuration may be utilized to counteract skidding of the tracks 160.

[0043] The subsea assembly may according to the present disclosure move across a net by means of the belt assemblies of the first subsea unit and the 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 magnetically 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 a motor, gear system, watertight 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. 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 at least one 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 a driving unit generally may be considered as the collection of any one or more of a motor, battery, shafts, gears, etc. necessary for enabling propulsion of a belt assembly.

[0044] The subsea assembly 100 may, as illustrated in figures 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 the 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 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.

[0045] The subsea assembly may according to any embodiment of the present disclosure be dimensioned according to the net. A typical extension of the subsea assembly may be between 80 cm and 200 cm, alternatively between 50 cm and 100 cm. The extension of the subsea assembly is according to a specific embodiment of the present disclosure less than 150 cm.

[0046] 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 to clean a seine, net cage, a water permeable sheet, water impermeable sheet or similar. Other examples are watertight tarpaulin, perforated tarpaulin, or similar.

[0047] The subsea assembly 100 is according to the present disclosure suitable for navigating across a submerged net 130. In order to enable the latter, the first subsea unit 110 is in a fist aspect of the present disclosure provided with a camera 229, while at least one of the first subsea unit 110 and the second subsea unit 120 is provided with an on-board computer 382. As the subsea assembly 100 moves across the net 130, the camera 229 of the first subsea unit 110 may acquire image data and output the image data to the on-board computer 382. The on-board computer 382 may then analyse the received image data in order to determine the position of the subsea assembly 100 on the net 130. The camera 229 may for example capture image data continuously as the subsea assembly 100 moves across the net 130. The on-board computer 382 may then combine all or at least a part of the image data into a joint file, e.g,, an image, as the on-board computer 382 receives the image data from the camera 229 before analysing the image in order to determine the position of the subsea assembly 100 on the net 130. Figure 2a schematically illustrates a first subsea unit 120 comprising a camera 229, while figure 8 schematically illustrates a figure comprising an on-board computer 382.

[0048] The determination of the position of the subsea assembly on the net may, as a way of example, be performed by identifying a number and relative position of grid cells of the net in the image data or image. The relative position of the subsea assembly on the net may then be determined using knowledge of the size of each grid cell of the mesh of the net, The relative position of the subsea assembly on the net may alternatively be given by two integer values that determine the position of the subsea assembly on the net by employing the mesh of the net as a coordinate system.

[0049] In another example, the on-board computer may analyse an image generated from the image data in order to determine a number of stands along two nonparallel directions in the image. The two directions may in this example be chosen to each be perpendicular to a longitudinal stand direction of the net. By counting the number along the two non-parallel directions in the image, the direction and distance travelled by the subsea assembly during the acquisition of the image may be calculated. The latter enables the relative location of the subsea assembly to be determined.

[0050] It will be appreciated by a person skilled in the art with knowledge of the present disclosure that the position of the subsea assembly on the net may be determined in a number of ways. Various image analysis methods may here be utilized to analyse the net depicted as the subsea assembly moves across the net in order to determine the relative position of the subsea assembly on the net. The on-board computer may thus generally be considered as configured to receive image data from the camera and to determine the position of the subsea assembly on the net based on the image data.

[0051] The first subsea unit 110 is according to an embodiment of the disclosure provided with a camera 229. The latter is schematically illustrated in figures 2a and 5a. The camera 229 may be considered as arranged on the side of the first subsea unit 110 that faces the net 130 under operation of the subsea assembly 100.

[0052] As a way of example to understand how the subsea assembly can manoeuvre around on a net and know its own position reference can be made to scanners, in particular sheet fed scanners. In a sheet fed scanner the scanning source is moving whilst the lights source, background and image sensor is stationary. As the sheet fed scanners scans paper which is not transparent the image sensor and the light source are oriented on the reading side of the paper and a setup of mirrors which reflects the reading side is reflected via mirrors to the image sensor. Sheet feeding mechanisms including rotating rollers feeds the paper forward in a constant speed passing the light source and moving forward to a sheet output tray. The sheet fed scanners typically includes a single line or few lines of image sensors - sensor pixels. Effectively providing one-dimension which eventually will build up a two-dimensional image. The second dimension results from the motion of the scanning source (paper) imaged. Two-dimensional images are acquired line by line (or few lines ) by successive single-line scans (few lines scans) while the scanning source (paper) moves (perpendicularly) past the line of pixels in the image sensor.

[0053] Based on the idea of sheet fed scanners where the scanning source is moving relative to the housing of the light source and image sensor it is provided a navigation system for a subsea assembly where the scanning source is fixed, and the light source and image sensor is moving relative to the scanning source - the net.

[0054] The subsea assembly may comprise a first subsea unit which comprises the image detector and a second subsea unit which comprises a light source. The first subsea unit and the second subsea unit adheres to each other using magnetic forces. The scanning source, the net, is arranged between the first subsea unit and the second subsea unit. The first subsea unit and the second subsea unit may crawl on the net, thereby providing a relative movement between the scanning source and the light source and the image sensor(s). To improve scanning qual ity of the scanning source - the net, the light source side can be provided with a background, such as a plate. The plate may be white as is common for the plates provided as background in flatbed scanners and copy machines. [0055] The image sensor can be an array of CCD's or CIS'. CIS may replace the CCD array, mirrors, filters, lamp and lens with rows of red, green and blue light emitting diodes (LEDs).

[0056] Stray light is prevented from entering in space between the first subsea unit and the second subsea unit. As in a camera, the dark conditions between the first subsea unit and the second subsea unit allow the light source to control the amount of light reflected on the net 130 surface. The light shined on the source to be scanned then reflects back into the machine and is reflected onto the image sensors by a series of mirrors. In a scanner the area which is scanned is divided into x,y coordinates which eventually is transformed into pixels. When the subsea assembly travels over a net it scans the net 130 between the first and the second subsea unit. A net 130 can be characterised by a grid pattern, the grid pattern may be stored in the memories of an onboard computer 382 or on remote computers. By knowing the mesh size and Scanning and counting the number of meshes passed by the subsea assembly 100, the subsea assembly may in a precise manner determine its own position on the net 130. The mesh of the net 130 can be compared with pixels.

[0057] Figures 2b schematically illustrates an embodiment of the disclosure where the camera is a line camera 230. The line camera 230 may as a way of 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 230 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 that is captured per pass of the subsea assembly 100. As a way of example, a line camera 230 may be configured to span the full width of the first subsea unit 110. The latter may be obtained by placing the line camera 230 in front of, or behind, the parallelly oriented belt assemblies 150 of the first subsea unit 110. Figure 7a schematically illustrates a first subsea unit provided with a line camera 230, where the line camera 230 is configured to span the full width of the first subsea unit 110. Figure 7b is a schematic representation of a subsea assembly according to the present disclosure where the background element 240 comprises a plurality of LEDs arranged in a line that spans the whole width of the second subsea unit 120.

[0058] The camera may according to the disclosure be used to capture image data in the form of a plurality of images of the net as the subsea assembly adheres to and moves across the net. The image data may be captured continuously, and the capture rate may for example be set according to a desired resolution and the speed in which the subsea assembly moves across the net. The image data captured by the camera may further be communicated to the onboard computer for the on-board computer to generate a combined image of a portion of the submerged net based on the received image data. The on-board computer may subsequently determine the position of the subsea assembly on the net based on the image. By providing the subsea assembly with a camera it is possible to obtain a short distance between the camera and the net, a distance that due to the magnetic adhesion of the subsea assembly to the net will be fixed over time. Using a camera in combination with the subsea assembly according to this disclosure has been found to result in images with a high contrast and resolution. Figure 6 shows an example of a two-dimensional image of a net of a fish pen obtained using a line camera configured to capture images with a resolution of 300 DPI.

[0059] Analysing the image data from the camera using an on-board computer rather than communicating it to the shore for analysis has the advantage that less data has to be transferred from the subsea assembly relative to a situation where the image data were analysed in an onshore server, separate computing unit or similar. The need for bandwidth between the subsea assembly and any onshore server, separate computing unit or similar is then reduced. It will be appreciated, however, that the image data from the camera does not have to be analysed using an on-board computer of the subsea assembly. Although being less practical, the image data from the camera may be analysed by an onshore server, separate computing unit or similar.

[0060] The first subsea unit 110 may as schematically illustrated in figure 2 be provided with a camera 229, while the second subsea 120 unit may, as schematically illustrated in figure la be provided with a background element 240. The camera 229 and the background element 240 may be arranged such that they face each other when the subsea assembly 100 adhere to the net 130. The camera 229 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 under operation of the subsea assembly 100. The camera 229 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 229 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 229 and a background element 240; while the second subsea 120 unit may be provided with a camera 229 and a background element 240.

[0061] A background element may generally in the context of the present disclosure be considered as an element shaped to provide a fi xed 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.

[0062] 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 line camera will during operation of the subsea assembly be present between the line camera and the background element, thus enabling the camera to image the net using the background element as a fixed background. Multiple images of the net 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.

Figure 6 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. A light source may generally be arranged such that it illuminates the field of view of the camera.

[0063] The background element 240 may as schematically illustrated in figure ia 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 during operation of the subsea assembly 100. 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 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 during operation of the subsea assembly 100. 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.

[0064] 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. 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 229 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 of the first subsea unit 110 when the subsea assembly 100 adhere to the net 130.

[0065] The light source may in any embodiment of the present disclosure be a light source configured to radiate white light. Other colours may alternatively be used, for example 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.

[0066] 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, 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. 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 %.

[0067] 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, hence allowing for sampling of a linear segment of the net 130 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 230 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. The latter will allow any part of the elongate light source 250 and/or the light source 250 comprising a plurality of LEDs 270 arranged in a line to be arranged facing into the line camera 230 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 7 be integrated in the background element 240.

[0068] 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.

[0069] The first aspect of the disclosure provides in a particular example a method for determining the position of a subsea assembly on a submerged net. The method comprises moving a subsea assembly across the net while the subsea assembly adheres to the net, while the subsea assembly collects image data from a camera of the subsea assembly . The position of the subsea assembly on the net is then determined based on the image data.

[0070] The subsea assembly may according to a second aspect of the present disclosure navigate across a submerged net using an alternative approach to that described for the first aspect of the present disclosure. The alternative approach is based on a principle where the position of the subsea assembly is determined from knowledge of the direction of motion and the distance travelled by the subsea assembly across the net. This aspect of the disclosure is described more in detail below.

[0071] Figure 8 schematically illustrates as an embodiment of the disclosure where the first subsea unit 110 comprises driving 380 unit comprising a motor and where at least one of the first subsea unit 110 and the second subsea unit 120 further comprises an orientation sensor 400. The driving unit 380 may for example output information regarding the length travelled by one or both belt assemblies 150 of the first subsea unit 110, and consequently also the length travelled subsea assembly as a whole. Information regarding the length travelled by the subsea assembly may be combined with information regarding the orientation of the subsea assembly during said travel in order to determine a relative position of the subsea assembly after completion of the travel. Relative position herein means a position relative to a starting position.

[0072] Figure 9 schematically illustrates an example of an operation of a subsea assembly 100 where a path travelled by the subsea assembly 100 is determined from information regarding the length travelled by the subsea assembly 100 and information regarding the orientation of the subsea assembly 100 during said travel. The driving unit outputs in this example that the subsea assembly 100 has travelled a distance a without turning, while the orientation sensor 400 outputs that the subsea assembly 100 has maintained an orientation 0 during the duration in which the subsea assembly 100 travelled the distance a. Relative to a starting position, it may then be determined, for example by the on-board computer 382, that the subsea assembly 100 has travelled a distance a-Cos(θ) in the horizontal x-direction and a distance a-Sin(0) in the vertical y-direction. The final position of the subsea assembly 100, assuming a starting position A person skilled in the art with knowledge of the present disclosure will appreciate that the above approach may be made more general in order to account for the subsea assembly 100 performing turning operations etc. The position of the subsea assembly 100 relative to a starting position may be determined based on a sum of several calculations like the one above, e.g., based on a pre-programed path.

[0073] A driving unit may, as mentioned above, generally be considered herein as the collection of any one or more of a motor, battery, shafts, gears, etc. necessary for enabling propulsion Of a belt assembly. The motor may for example be a stepper motor Or a Servo motor, optionally provided as hub motor in one of the drive wheels of one or more of the belt assemblies of the subsea assembly . Use of a stepper motor or servo motor is preferred, as these types of motors enables a precise control of angular or linear position, velocity and acceleration of the motor.

[0074] The motor may generally be provided with a sensor that provides a signal that represent the position of the motor. The signal may thus comprise information regarding the length travelled by belt assembly powered by the motor. Said signal may herein be termed as motion data or alternatively be considered as representing motion data. The motion data may then be considered as comprising information regarding the position of the motor and thus the length travelled by belt assembly powered by the motor. It will be appreciated by a person skilled in the art with knowledge of the present disclosure that the sensor alternatively provides a signal that generally represents the length travelled by belt assembly. The sensor does not need to provide a signal that represent the position of the motor but may alternatively provide a signal that represents the position of an axel, a drive wheel, or another component of the driving unit that represents the length travelled by a belt assembly powered by the motor. The sensor may comprise one or more of a synchro, resistive potentiometer, PID- controller, rotary encoder, etc.

[0075] The orientation of the subsea assembly on the net may according to the present disclosure be determined through employment of a suitable orientation sensor 400. An orientation sensor 400 may for example comprise one or more of a compass, a gyroscope, an accelerometer and a gravity sensor. A person skilled in the art with knowledge of the present disclosure will appreciate that the orientation sensor may comprise several individual sensors, e.g., sensors that detects orientation in different spatial directions. As a way of example, an orientation sensor 400 may comprise a combination of a compass and a gravity sensor. The net 130 to be cleaned may generally according to the present disclosure be approximated as a 2D structure, optionally at least in part with periodic boundary conditions. The orientation Sensor may thus in a particular example be configured to gi ve the orientation of the subsea assembly i n two directions.

Second Aspect of the present invention

[0076] The subsea assembly may according to the second aspect of the present disclosure differ from the first aspect of the present disclosure i.a. in that the subsea assembly according to the second aspect of the present disclosure does not need to be provided with a camera. It will be appreciated, however, that the first aspect of the present disclosure may be combined with the second aspect of the present disclosure. The two aspects of the present disclosure may in other words be employed simultaneously, for example in order to improve accuracy of the position of the subsea assembly on the net 130, as the two may act as backups for each other. The subsea assembly of the second aspect may thus be provided with a camera, an on-board computer, an orientation sensor and a driving unit configured to output motion data.

[0077] The second aspect of the disclosure provides in a particular example a method for determining the position of a subsea assembly on a submerged net 130. The method comprises the steps of moving a subsea assembly across the net while the subsea assembly adheres to the net 130, collecting motion data from a driving unit 380 of the subsea assembly as the subsea assembly adheres to and moves across the net 130, and collecting orientation data from an orientation sensor of the subsea assembly as the subsea assembly adheres to and moves across the net 130. The method further comprises a step of determining, from the motion data and orientation data, the position of the subsea assembly on the net 130. The latter step may be performed by an on-board computer or by a computer or similar that is located at a remote location from the subsea assembly.

[0078] The position of the subsea assembly may in any embodiment of either aspect of the present disclosure be employed in order to determine a future path of the subsea assembly across the net. Information regarding the position of the subsea assembly on the net 130 may for example be communicated to a separate navigation system that is configured to control any driving unit or driving units of the subsea assembly to steer the subsea assembly in a desired direction. The navigation system may for example also store location history for where the subsea assembly 100, 1000 have been in the past. The latter may be beneficial to combine with an analysis of the net 130 as the subsea assembly moves across the net 130. Images of the net 130 may thus be paired with location data that indicate where on the net 130 said image was captures, hence allowing for surveillance of the net over time. The latter may further allow for properties of the net to be monitored over time, which for example include monitoring of wear of the net over time. It will be appreciated by a person skilled in the art with knowledge of the present disclosure that a navigation System may comprise the necessary components for example for performing one or more of analysing position data, controlling one or more driving units of the subsea assembly to move the subsea assembly along a predetermined route, etc. The on-board computer in the latter context may be the same or a different on-board computer from that described previously. It will also be appreciated that the term a navigation system in the above context is a generic term, and that a person skilled in the art with knowledge of the present disclosure will know how to implement such a system. The subsea assembly may thus according to any embodiment of the present disclosure comprise a navigation system configured to receive information regarding the position of the subsea assembly on the net 130 and be configured control any number of driving units of the subsea assembly such that the subsea assembly moves across the net according to a predete rm i ned path .

[0079] As an alternative to providing the subsea assembly with a navigation system as described above, the subsea assembly may in any embodiment of either aspect of the disclosure be remotely controlled by an operator. The Operator may, based on knowledge of the position of the subsea assembly steer the subsea assembly across a desired route, for example in order to clean the net or in order to employ the subsea assembly for analysing the net.

[0080] The subsea assembly may in any embodiment of either aspect of the present disclosure be provided with any one or more of an oxygen sensor, a temperature sensor, a salinity sensor, a CO2-sensor, a conductivity sensor, a flow sensor and a water clarity sensor. Readings from any one or more of said sensors may be combined with data representing the position of the subsea assembly on the net in order to provide knowledge of the conditions at various positions along the net. Figure 10 Is a schematic illustration of a subsea assembly 1000 comprising two subsea unit 1010,1020 comprising an oxygen sensor 410, a temperature sensor 420, a salinity sensor 430, a CO2-sensor 440, a conductivity sensor 450, a flow sensor 460 and a water clarity sensor 470.

An exemplary embodiment of the present invention

[0081] An exemplary embodiment of the present invention will now be described with reference to figure 11.

[0082] Figure 11 shows a section of an upper second subsea unit 1120. The upper second subsea unit includes a light source array 1170.

[0083] Figure 11 also shows a section of a lower first subsea unit 1110, The section of the lower first subsea unit 1110 comprises an image Sensor array 1130, The image sensor array 1130 faces the light source array 1170. The image sensor array may be a CCD-array or several CCD-arrays or CIS-arrays.

[0084] In figure the light source 1170 and image sensor 1130 are elongate and facing each other throughout its lengths.

[0085] The scanning source - the net 130 is arranged between the image sensor array 1130 and the light source array 1170, The driving direction 220 is known as well as the driving speed of the lower first subsea unit 1110 and the second upper subsea unit 1120, hence the output of the image sensor array can be processed by a computer and the data can be decoded into x.y positioning coordinates.

[0086] Other advantageous features will be apparent from the accompanying claims. [0087] Reference list

CCD Charge Coupled Device

CIS Contact image sensor

LED Light emitting diodes

100 Subsea assembly

110 First subsea unit

120 second subsea unit

130 Net

140 Cleaning means

150 Belt assemblies 160 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.

165 Ground pad

170 A rear road wheel

180 One or more middle road wheels

190 Front road wheel

210 Magnets

220 Driving direction

229 A camera

230 A line camera

240 Background element.

250 One or more light sources

270 LED array(s) arranged in at least one row arranged facing into the line camera 230

380 A driving unit

382 On-board computer

400 Orientation sensor.

410 Oxygen sensor

420 T e mpe ra tu re se n so r

430 Salinity sensor

440 C02-sensor

450 Conductivity sensor

460 Flow sensor

470 Water clarity sensor

1000 Subsea assembly of any embodiment, i.e. comprising camera system (scanning devices) for navigation, navigation systems including orientation sensors, or remote navigation where the subsea assembly comprises sensors providing environmental data mapped with positioning data to a computer.

1010 A first subsea unit of a subsea assembly 1000. 1020 A second subsea unit of a subsea assembly 1000.

1100 A subsea assembly comprising a first subsea unit 1110 and a second subsea unit 1120, where both units adheres to a net 130 in-between the first subsea unit 1110 and the second subsea unit 1120.

1110 A first subsea unit according to an exemplary embodiment of the present invention. The first subsea unit 1110 comprises an image sensor array 1130.

1120 A second subsea unit according to an exemplary embodiment Of the present invention. The seceond subsea unit 1120 comprises a light source array 1170.

1130 Image sensor array, such as an array of CCD's or several parallel arrays of CCD's or an array of SIC's or several parallel array of SIC's.

1170 Light source array, such as LEDs, Xenon lights or other lights source array.