Indirect measurements of the water depth using a vessel's speed and wave pattern

Abstract

There is provided a method of measuring a depth of a body of water, the method comprising: moving a watercraft across the surface of the body of water (S100); and whilst moving: recording a speed of the watercraft (S200); and recording a wavelength of a transverse wave portion of a wave pattern generated by the watercraft (S300); and determining the depth of the body of water based on the speed of the watercraft and the wavelength of the transverse wave portion (S400).

Description

[0001] INDIRECT MEASUREMENTS OF THE WATER DEPTH USING A VESSEL'S SPEED AND WAVE PATTERN

[0002] FIELD

[0003] The present disclosure relates to a method for determining the depth of a body of water, such as a canal or other navigable inland waterway, using the speed of, and wave pattern created by, a watercraft moving through the body of water. The present disclosure also relates to a computing device and computer program product configured to carry out the method.

[0004] BACKGROUND

[0005] The depth of a body of water is key in determining the efficiency of a vessel moving through the water. At very small water depths, the power requirements grow exponentially. Therefore, knowledge of the water depth is important in ensuring optimum operation. For canals and other navigable inland waterways in particular, the cross- sectional area of the body of water also determines the maximum speed a watercraft can achieve. Continuous monitoring of the water depth is also important to prevent runaway sedimentation that can prevent navigability altogether. Knowing the depth of a body of water can also be vital to ensure that there is sufficient depth for safe navigation of vessels.

[0006] The majority of depth measurements carried out are performed using echo sounders. Echo sounders have a number of drawbacks, including the cost to purchase, retrofit and the requirement for extensive data transfer and analysis. In addition, sound waves are only partially reflected by sedimentation (e.g. mud) layers, and consequentially many international ports define the water depth as the location where the mud density reaches 1 ,200 kg / m3, rather than the position that any solids in the seabed cause reflections in the echo sounder (McAnally et al., 2016). Inland waterways operators are often micro-businesses or small charities that cannot afford the substantial cost of installing and using echo sounders.

[0007] In the UK alone there are over 80,000 inland watercraft, and an estimated 2,000 miles of inland waterways that are non-navigable due to insufficient water depth, and at present there is no up to date bathymetric survey of the UK’s inland waterways.

[0008] It would be beneficial to have a simple, cost-effective method of measuring water depth that does not require retrofitting of expensive electronic equipment, and that can be performed without specialist training or knowledge. SUMMARY

[0009] Various aspects of the present invention are defined in the independent claims. Some preferred features are defined in the dependent claims.

[0010] According to a first aspect of the present disclosure there is provided a method of measuring a depth of a body of water, the method comprising: moving a watercraft in or across the surface of the body of water; and whilst moving: recording a speed of the watercraft; and recording a wavelength of a transverse wave portion of a wave pattern generated by the watercraft; and determining the depth of the body of water based on the speed of the watercraft and the wavelength.

[0011] By using the speed of a watercraft moving through a body of water and the wavelength of a transverse wave portion of the wave pattern generated by the movement to determine the depth of the water, there is no requirement for expensive, difficult to use sensors or equipment to be installed or present on or in the watercraft.

[0012] Reduced cost and ease of such a measurement method means that measurements can be carried out without any expert training and / or equipment. This results in more measurements and more reliable measurements in particular being carried out, providing substantially more data to allow tracking of the status (e.g. sedimentation) of the body of water. A trend of values over time of a particular body of water can then be established. This allows limited resources (time, money, personnel etc.) to be efficiently distributed to the areas which are most in need of maintenance, repair and the like.

[0013] More reliable and simpler measurements also allow a user of a watercraft to regularly check the depth of a body of water as they move through, along or across the surface of it to ensure that the depth is sufficient for the watercraft.

[0014] The body of water may be an inland, coastal or open waterway; a waterway being any navigable body of water. In particular, the body of water may be a canal, river, firth, lake, loch or the like.

[0015] The watercraft may be a boat, ship, kayak, canoe, board or any other waterborne vessel having a propulsive capability; whether by sail, oar, paddle or engine. In particular, the watercraft may be a canal boat or barge.

[0016] The depth of the body of water is the distance measured downward between the surface of the body of water and the base, bottom or bed of the body of water along a line substantially perpendicular to the surface.

[0017] The watercraft moving in or across the surface of the body of water may be at least partially submerged, e.g. shallowly submerged such that the movement of the watercraft in or across the surface of the body of water generates a wave pattern according to the present disclosure. The speed of the watercraft moving across the surface of the body of water may be measured as the speed of the watercraft relative to the surface of the water; commonly referred to in the field as the Speed Through Water (STW). In a body of moving water e.g. a current or tidal drift, the STW may be different to the speed of the water craft over the base, bottom or bed of the body of water; commonly referred to in the field as the Speed Over Ground (SOG). This difference may be measured and corrected for where it produces a substantial source of error in the recorded speed.

[0018] A wave pattern is the pattern created on the surface of a body of water by a watercraft moving across the surface of the body of water. The transverse wave portion of the wave pattern is the portion of the pattern comprising a series of transverse waves. A transverse wave is a wave that extends, e.g. whose oscillations are, substantially in the direction of the wave's advance i.e. substantially in the direction of movement of the watercraft moving through the body of water. The wavelength of a transverse wave of a wave pattern can be measured as the distance between two adjacent crests.

[0019] Determining the depth of the body of water may be further based on an algorithm relating depth to the speed and the wavelength. The algorithm may comprise a dispersion relation between the speed and the wavelength.

[0020] In shallow water i.e. water of such depth that surface waves are affected by bottom topography, the depth of a body of water can be determined using the speed of a watercraft moving through the body of water and the wavelength of a transverse wave portion of a wave pattern generated by the watercraft.

[0021] Alternatively, the depth may be determined using a look up table or graph or the like relating the transverse wave portion wavelength and speed to the depth. The look up table or graph values may be predetermined using the dispersion relation or any other suitable relationship.

[0022] Recording the speed may comprise recording the speed and determining whether the recorded speed is within an expected speed range. The recording of the speed may be rejected and / or repeated if the recorded speed is outside an expected speed range.

[0023] By checking the recorded speed against an expected speed range, measurement and / or data entry errors can be immediately identified and rejected from the dataset. As the potential error is immediately identified, the measurement can also be repeated. This minimises erroneous speed calculations, increasing the accuracy and reliability of the resulting depth calculation.

[0024] The expected speed range may be based on a maximum theoretical speed of the watercraft. The maximum theoretical speed may be the rated or expected top speed of the watercraft, the expected top speed of the watercraft in the particular body of water, a manually entered expected maximum or the like and / or based on historical speed recordings.

[0025] The speed may be recorded using a satellite positioning sensor such as a GPS sensor, or a satellite positioning sensor using any other suitable satellite positioning system such as Galileo, GLONASS, BeiDou and / or the like. The speed may be based on the flow of the body of water e.g. the current or tidal flow of the body of water.

[0026] Using a satellite positioning sensor to provide changes in location data over time to allow the speed to be recorded provides a more accurate measurement of speed over the ground, resulting in a more accurate calculation of depth. As aforementioned, the flow of the body of water may or may not introduce a significant error into the speed measurement which can be corrected for. Many available watercraft already include a satellite positioning sensor and a sensor allowing the flow of the body of water they are moving in to be measured in order to aide navigation. In other examples, a satellite positioning sensor in a user device such as a smartphone or tablet could be used to determine the speed. This data can be further utilised in the depth calculation.

[0027] Recording the wavelength may comprise capturing one or more images of the wave pattern generated by the watercraft. The captured image may be used to determine the wavelength of the transverse wave portion of the wave pattern. For example, the method may be implemented by or using an app or other program on a user device or other computer device. The one or more images may be captured or received by the user device or other computing device. The app or other program may be executable to process the one or more images to determine the wavelength of the transverse wave portion of the wave pattern shown in the one or more images, e.g. using object or pattern recognition, a suitably trained Al model or the like. The image processing may be performed locally on the user device or may be performed remotely at a remote computing resource, or distributed between local and remote processing.

[0028] Advantageously, using image capture techniques allows a more accurate and reliable measurement of the wavelength. If the captured image(s) are stored they can be reanalysed and / or viewed at a later period of time allowing the measurement to be repeated and / or manually reviewed / verified.

[0029] The one or more images may be captured using an image capture device, such as the image capture device of the user device, a digital camera or the like. The one or more image capture devices may be arranged to capture one or more images of the wave pattern from different perspectives / locations. Image capture may be performed using one or more image capture devices with one or more lenses / sensors etc. At least one of the captured images may be reference measurement, and there may be a plurality of captured images allowing depth measurement etc.

[0030] Recording the wavelength may additionally / alternatively comprise determining a wave vector cut-off value based on the speed of the watercraft and the wavelength of a transverse wave portion of the wave pattern and determining a maximum theoretical wave vector cut-off value based on the speed of the watercraft. A difference between the maximum theoretical wave vector cut-off value and the determined wave vector cut-off value may be determined. The recording of the wavelength may be rejected and / or repeated if the determined difference is greater than a maximum expected difference.

[0031] In deep water i.e. water of such depth that surface waves are not affected by bottom topography, the wave vector cut-off value of a wave pattern generated by a watercraft moving across the surface of a body of water can be determined based on the speed of the watercraft. If the difference between the recorded wave vector cut-off value and this maximum theoretical wave vector cut-off value in deep water is greater than expected it indicates that there has been an erroneous measurement and / or recording of the transverse wavelength.

[0032] By checking the difference between the recorded and theoretical wave vector cut-off values, measurement and / or data entry errors can be immediately identified and rejected from the dataset. As the potential error is immediately identified, the measurement can also be repeated. This minimises erroneous wavelength calculations, increasing the accuracy and reliability of the resulting depth calculation.

[0033] The maximum theoretical wave vector cut-off value may be the wave vector cutoff value which would be calculated for the watercraft moving in deep water at the recorded speed. The maximum expected difference may be a predetermined proportion or percentage of the maximum theoretical wave vector cut-off value. The predetermined proportion or percentage may be based on the typical operating conditions of the watercraft in the body of water. “Deep water” may be defined by a pre-determined or otherwise specified depth.

[0034] The method may further comprise determining a speed and / or direction of a current of the body of water. The depth of the body of water may be determined based on the speed, the wavelength and the speed and / or direction of the current.

[0035] According to a second aspect of the present disclosure, there is provided a computing device comprising a processor, the processor configured to: record the speed of a watercraft moving across the surface of a body of water; record the wavelength of a transverse wave portion of a wave pattern generated by the watercraft; and determine the depth of the body of water based on the speed of the wavecraft and the wavelength of a transverse wave portion.

[0036] The computing device may be a mobile phone or other portable personal computing device.

[0037] Many portable computing devices already have a number of sensors and / or processing capabilities e.g. satellite positioning sensor, accelerometer, communications module and / or multiple image capture devices. As most people will already own such a device the disclosed method may be carried out without needing to purchase or install additional expensive equipment onto a watercraft in order to determine the depth of a body of water.

[0038] Determining the depth of the body of water may be further based on the dispersion relation between the speed and the wavelength.

[0039] The computing device may further comprise one or more image collection devices. Recording the wavelength may comprise: capturing one or more images of the wave pattern using the one or more image devices; and determining the wavelength of the transverse wave portion of the wave pattern using the image. The computing device may be configured to determining the wavelength of the transverse wave portion of the wave pattern from the image using object or pattern recognition, a suitable trained Al model or the like.

[0040] The one or more image capture devices may be arranged to capture one or more images of the wave pattern from different perspectives / locations.

[0041] The computing may further comprise a satellite positioning sensor, such as a satellite positioning sensor. Recording the speed may comprise using the satellite positioning sensor to record the speed.

[0042] The processor may be further configured to determine whether the determined depth of the body of water is below a threshold. The threshold may be based on the minimum depth of water required for the watercraft to float, which may be the minimum depth of water required for the watercraft to float plus a set or pre-set margin. The computing device may be further configured to alert a user of the computing device when the depth of the body of water is below the threshold.

[0043] By alerting the user of an insufficient depth of water below a threshold it may be possible to avoid the watercraft coming into contact with the base, bottom or bed of the body of water. This may occur where the depth of the body of water is less than expected due to sedimentation, erroneous reporting or the like.

[0044] The computing device may further comprise a network communications module configured to communicate over a network at least one of: the location of the watercraft, the speed of the watercraft, the wavelength of the transverse wave portion of the wave pattern generated by the watercraft, the determined depth.

[0045] Communicating the recorded and / or determined values to a central location provides substantially more data to allow tracking of the status (e.g. sedimentation) of the body of water. A trend of values over time of a particular body of water communicated from a plurality of watercraft moving across the particular body of water can then be established. This allows limited resources (time, money, personnel etc.) to be efficiently distributed to the areas which are most in need of maintenance, repair and the like.

[0046] According to a third aspect of the present disclosure, there is provided a computer program product configured such that, when executed by the computing device of the second aspect, causes the device to perform the method of the first aspect.

[0047] The computer program product may be a mobile phone application.

[0048] The individual features and / or combinations of features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either separately and individually, alone or in combination with any other defined feature, in any other aspect or embodiment of the invention.

[0049] Furthermore, the present invention is intended to cover apparatus configured to perform any feature described herein in relation to a method and / or a method of using or producing, using or manufacturing any apparatus feature described herein.

[0050] Where appropriate any of the optional features described above in relation to one of the aspects of the disclosure may be applied to another one of the aspects of the disclosure.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052] These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0053] Figure 1 is a plan view of a watercraft moving across the surface of a body of water;

[0054] Figure 2 is a flowchart of a method of measuring a depth of a body of water;

[0055] Figure 3 is a flowchart of a method of recording the speed of a watercraft;

[0056] Figure 4 is a flowchart of a method of recording the transverse wavelength of a wave pattern

[0057] Figure 5 is a schematic overview of a computing device which may be used in the method of Figure 2.

[0058] DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 shows a plan view 1 of a watercraft 2 moving across the surface of a body of water and the pattern of waves created by the motion of the watercraft 2 through the water. The wave pattern of Figure 1 is typical for a watercraft 2 moving at low to moderate speeds through a shallow body of water i.e. water of such depth that surface waves are affected by bottom topography. The direction of motion of the watercraft 2 is indicated by arrow 9.

[0059] Each curved line in the wave pattern indicates the position of a crest of a wave. The wave pattern can be split into two distinct portions, the divergent wave portion 4 and the transverse wave portion 6. The divergent wave portion 4 comprises waves having a crest which extends generally parallel to the direction of motion 9 of the watercraft 2. The transverse wave portion 6 comprises waves having a crest which extends substantially perpendicular to the direction of motion 9 of the watercraft 2. The distance between the crest of a wave of the wave pattern and the crest of an adjacent wave of the wave pattern is the wavelength A of the wave at that particular position. The wavelength A of the wave in the transverse wave portion 6 is referred to as the transverse wavelength.

[0060] The physical properties of waves are governed by dispersion, the fact that a wave’s speed depends on its length. In deep water i.e. water of such depth that surface waves are not affected by bottom topography, the dispersion relation takes the form of: )2= ^ / C (1) where is the wave frequency, g is the gravitational acceleration, and k is the angular wave vector of the wave, describing how many oscillations it completes per unit of distance, and is related to the wavelength A by: k = 2n / A (2)

[0061] In shallow water, the dispersion relation is modified due to bottom topography (e.g. the base, bottom or bed of the body of water) and takes the form of: a>2= gk tanh(kh) (3) where h is the water depth i.e. the distance measured downward between the surface of the body of water and the base, bottom or bed of the body of water along a line substantially perpendicular to the surface. The angular wave vector k can be used to determine the wavelength A at any angle relative to the track of a watercraft e.g. relative to the direction of travel 9 of the watercraft 2. Using the dispersion relation allows a cut-off value kc, equivalent to the maximum transverse wavelength Ayto be defined; wavelengths larger than the cut-off value correspond to the near-field disturbance produced by the watercraft 2 moving across the surface of the body of water, while smaller wavelengths can be found within the wave system at an angle to the direction of travel 9. In Figure 1 , block 8 indicates the area of the wave pattern where k = kci.e. where transverse wavelength Ayis at a maximum limit. In deep water the cut-off value kcdepends only on the speed V of the watercraft 2, related by the equation: kc= 9 / V2(4) whilst in shallow water the cut-off value kcdepends on both the speed V of the watercraft 2 and the depth h of the body of water which the watercraft 2 is moving across, related by the equation:

[0062] V2k — gkctanh( / cc / i) = 0 (5)

[0063] Using this relationship, the depth h of the body of water can be determined if the speed V of the watercraft 2 and the cut-off value kc(based on the transverse wavelength Ay) is known or can be estimated. This allows an estimate of the depth h of the body of water to be determined without requiring any specialist expensive and / or complex sensors or equipment to be installed or present on or in the watercraft.

[0064] Figure 2 is a flowchart illustrating a method 10 of measuring a depth of a body of water according to an example embodiment of the present disclosure. Figures 3 and 4 illustrate example techniques for carrying out steps of method 10, however any other suitable technique may be used.

[0065] Referring to Figure 2, at step S100 a watercraft moves across the surface of a body of water. Alternatively, the watercraft may move at or partially / fully below the surface of the body of water such that a wave pattern may be observed by a user or observer of the watercraft. The user of the watercraft may be on or in the watercraft or may operate the watercraft remotely.

[0066] At step S200 the speed of the watercraft is recorded. The speed may be recorded using standard speed recording equipment commonly installed on or in watercraft or alternatively using a standalone device located on or in the watercraft e.g. the satellite positioning sensor of a smart phone of a user of the watercraft. Referring to Figure 3, a method of improving the accuracy and reliability of the step of recording the speed of the watercraft S200 is illustrated. At step S210 the speed of the watercraft is measured by any suitable method such as those detailed above.

[0067] At step S220 the range of expected speeds is determined. A minimum speed of the range of expected speeds may be Omph or substantially Omph or a value within the expected noise range of the device or method being used to measure the speed. A maximum speed of the range of expected speeds may be based on the type or location of the body of water e.g. a regulatory speed limit or maximum expected speed in a particular body of water. Alternatively, the maximum speed may be based on the type of watercraft e.g. the rated / expected maximum theoretical speed of the watercraft. The minimum and maximum speeds of the range of expected speeds may be manually set or automatically determined based on characteristics of the watercraft, body of water and / or method of speed measurement.

[0068] At step S230 the measured speed is compared with the range of expected speeds. If the measured speed is within the range of expected speeds the measurement is accepted at step S240 and submitted at step S250. Submitting the accepted recorded speed may comprise storing the recorded speed to memory on a local computing device, transmitting the recorded speed to a remote database or manually recording the speed for entry onto a database at a later time.

[0069] If the measured speed is not within the range of expected speeds the measurement is rejected at step S260. Rejecting the recorded speed may comprise discarding the recorded speed or storing the recorded speed marked as rejected such that it is not used to calculate the depth of the body of water and / or is not included in any cumulative analysis exercises. At step S270 the measurement step S210 may be repeated. When a recorded speed is rejected the method S200 may be repeated once, twice or a suitable number of times. Successive rejected recorded speeds may indicate a fault in the measurement method, an error in the determined expected speed range or an actual speed outside the expected speed range of the watercraft and / or body of water, and the fault may be flagged, such as by being highlighted to a user collecting the measurements and / or a system operator. Optionally further assistance or guidance on taking measurements may be offered, e.g. electronically on a user device of the user. The assistance could depend on the error, e.g. depending on whether the calculated speed was below the minimum cut-off or above the maximum cut-off.

[0070] The method illustrated in Figure 3 may be employed at or immediately after the speed is measured, e.g. in real-time or near real time or on the fly. Alternatively / additionally the method may be applied at a post processing step to a database of recorded speeds and associated watercraft / body of water characteristics. By checking the recorded speed against an expected speed range, measurement and / or data entry errors can be immediately identified and rejected from the dataset. As the potential error may be immediately identified, the measurement can also be repeated. This minimises erroneous speed measurements, increasing the accuracy and reliability of the resulting depth calculation.

[0071] Referring again to Figure 2, at step S300 the transverse wavelength of the wave pattern is recorded. In the example of Figure 1 the transverse wavelength Ayis the distance between two adjacent crests in area 8. The measurement of the transverse wavelength may be an estimated measurement by a user or observer of the watercraft. Alternatively, the measurement may be calculated from one or more images captured by one or more image capture devices. The one or more images may be captured from a plurality of positions and / or perspectives. The one or more images may include a reference measurement means e.g. a reference scale or card. In this way the transverse wavelength can be recorded more accurately providing a more reliable measurement. In other examples, the images can be analysed using a suitable technique, such as pattern recognition or using machine learning models to determine the transverse wavelength from the images. Although a more reliable measurement is preferred, absolute accuracy of the wavelength measurement is not essential to the depth measurement method as many bodies of water are subject to continuous sedimentation and erosion which would quickly invalidate highly accurate results within days of the measurement being carried out.

[0072] Referring to Figure 4, a method of improving the accuracy and reliability of the step of recording the transverse wavelength S300 is illustrated. At step S310 the transverse wavelength of the watercraft is measured by any suitable method such as those detailed above.

[0073] At step S320 a difference between a cut-off value kccalculated based on the measured speed and transverse wavelength, and a maximum theoretical cut-off value kccalculated based on the measured speed only is determined. The maximum theoretical cut-off value kcis the cut-off value which would be expected were the watercraft to move at the recorded speed through ‘deep’ water. This calculation is detailed above with reference to Figure 1 .

[0074] At step S330 the calculated difference is compared to a maximum expected difference. If the calculated difference is less than the maximum expected difference the recorded transverse wavelength is accepted at step S340 and submitted at step S350. Submitting the accepted recorded transverse wavelength may comprise storing the recorded transverse wavelength to memory on a local computing device, transmitting the recorded transverse wavelength to a remote database or manually recording the recorded transverse wavelength for entry onto a database at a later time.

[0075] If the calculated difference is not less than the maximum expected difference the recorded transverse wavelength is rejected at step S360. Rejecting the recorded transverse wavelength may comprise discarding the recorded transverse wavelength or storing the recorded transverse wavelength marked as rejected such that it is not used to calculate the depth of the body of water and / or is not included in any cumulative analysis exercises. At step S370 the measurement step S310 may be repeated. When a recorded transverse wavelength is rejected the method S300 may be repeated once, twice or a suitable number of times. Successive rejected recorded transverse wavelengths may indicate a fault in the measurement method, an error in the expected maximum difference or another anomaly in the recorded transverse wavelength such as interference from a second watercraft or an unexpected obstacle on the bed of the body of water at the time the measurement was taken. Again, any rejection may be flagged to the user and / or system operator and optionally assistance may be offered.

[0076] The method illustrated in Figure 4 may be employed at or immediately after the transverse wavelength is measured, e.g. in real time or near real time or on the fly. Alternatively / additionally the method may be applied at a post processing step to a database of recorded transverse wavelengths and relevant recorded speeds. By verifying the plausibility of the recorded transverse wavelength, measurement and / or data entry errors can be immediately identified and rejected from the dataset. As the potential error may be immediately identified, the measurement can also be repeated. This minimises erroneous transverse wavelength measurements, increasing the accuracy and reliability of the resulting depth calculation.

[0077] Referring again to Figure 2, at step S400 the depth of the water is determined based on the recorded speed of the watercraft and the recorded transverse wavelength of the wave pattern created by the watercraft moving across the body of water. The depth may be calculated based on the dispersion relation, e.g. as discussed above. The depth may be determined locally and / or in real time as the watercraft moves across the body of water. Alternatively, the depth may be determined using a look up table or graph or the like relating the transverse wave portion wavelength and speed to the depth. The look up table or graph values may be predetermined using the dispersion relation or any other suitable relationship. The use of look up tables or graph values, may speed up or simplify processing.

[0078] Alternatively, the recorded speed, recorded transverse wavelength and relevant characteristics of the watercraft and / or the body of water may be transmitted in real time, or at the end of a predetermined period of movement, to a remote device which will determine the depth of the body of water. In some examples when the determination of depth is carried out in real time (locally or remotely), the user or observer of the watercraft will be alerted if the determined depth is below a threshold e.g. a minimum depth required for the watercraft to safely and / or efficiently operate.

[0079] While the steps of the method of measuring a depth of a body of water are shown and described in a particular order, it should be understood that this does not imply that these steps must be carried out in this order, or that all steps are always required. While some steps should be performed sequentially (for example, the watercraft must be moving S100 before a measurement of speed or transverse wavelength is recorded S200, S300 respectively), other steps may be performed in any order. In particular, recording the speed of the watercraft S200 and recording the transverse wavelength S300 may be performed in any order including simultaneously. In some examples the step of recording the speed of the watercraft may be omitted e.g. in successive measurements where a constant speed is maintained.

[0080] Method steps of the invention can be performed by one or more programmable processors executing a computer program to perform functions of the invention by operating on input data and generating output. Method steps can also be performed by special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit) or other customised circuitry. Processors suitable for the execution of a computer program include CPUs and microprocessors, and any one or more processors. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g. EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry, such as a manycore vision processing unit, such as e.g. the Intel Movidius Neural Compute Stick, or an inferencing engine, such as e.g. Google Coral or nVidia Jetson Nano.

[0081] Figure 5 is a block diagram illustrating a computing device 1000 for measuring a depth of a body of water according to an example embodiment of the present disclosure. Referring to Figure 5, the computing device 1000 comprises a processor 1100, an image capture device 1200, a satellite positioning sensor 1300, a storage device 1400, and a network module 1500. The computing device may be a mobile phone, digital camera or alternatively the elements of the computing device may be distributed locally or remotely from the watercraft.

[0082] The processor 1100 may be used when the computing device 1000 perform computations or calculations and / or to record data relevant to those computation or calculations e.g. measure speed or transverse wavelength. For example, the processor 1100 may include a microprocessor, an application processor (AP), a central processing unit (CPU), a digital signal processor (DSP), a graphic processing unit (GPU), or the like. Although Figure 5 illustrates that the computing device 1000 includes one processor 1100, the invention is not considered limited as such. For example, the computing device 1000 may include a plurality of processors. In addition, the processor 1100 may include cache memories to increase computation capacity.

[0083] The image capture device 1200 is configured to capture images of the wave pattern created by a watercraft moving across a body of water. The image capture device 1200 may be integrated into or fixed onto the watercraft, integrated into the computing device 1000 or held by the user or observer of the watercraft. The image capture device 1200 may be a digital camera integrated into the computing device 1000, however the image capture device may take other forms.

[0084] The satellite positioning sensor 1300 may be used to determine the geographical location of the depth measurement and / or may be used to measure the speed of the watercraft moving across the body of water.

[0085] The storage device 1400, which may be for example a storage medium, may include any non-transitory computer-readable storage medium used to provide commands and / or data to the computing device 1000. For example, the non-transitory computer-readable storage medium may include a volatile memory such as a static random access memory (SRAM), a dynamic random access memory (DRAM), or the like, and a nonvolatile memory such as a flash memory, a magnetic random access memory (MRAM), a phase-change random access memory (PRAM), a resistive random access memory (RRAM), or the like. The non-transitory computer-readable storage medium may be inserted into the computing device 1000, may be integrated in the computing device 1000, or alternatively may be coupled to the computing device 1000 through a communication medium such as the network module 1500 which may be a physical link and / or a wireless link. The storage device 1400 may store data, which is to be processed by the processor 1100, or data obtained through processing by the processor 1100. The computing device 1000 may perform steps of the method 10 according to the example embodiments described with reference to Figure 2. For example, the processor 1100, satellite positioning sensor 1300 and image capture device 1200 that are included in the computing device 1000 may perform steps S200, S300 and S400 in Figure 2. In addition, the computing device may also comprise the control system for the watercraft such that the computing device 1000 may perform, directly or indirectly, step S100 in Figure 2.

[0086] Although various examples are described above, variation to the configuration of the computing device 1000 is possible. For example, with the use of multiple capture devices 1200 having a lateral separation a more accurate measurement of transverse wavelength may be achieved.

[0087] To provide for interaction with a user, the method 10 of Figure 2 can be implemented on a computing device having a screen, e.g., a CRT (cathode ray tube), plasma, LED (light emitting diode) or LCD (liquid crystal display), or OLED (organic LED) monitor, or a projector, e.g. a projection system based on LCD, or on a DLP (digital light processing) array, or on a LCOS (liquid crystal on silicon) chip, for displaying information to the user and an input device, e.g., a keyboard, touch screen, a mouse, a trackball, a pedal, and the like by which the user can provide input to the computer. Other kinds of devices can be used, for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. Input can be either voluntary (i.e. , the user deliberately provides the input), or involuntary (i.e. a measuring device measures image quality, to trigger the input when the image quality is sufficient for the measurement).

[0088] As such, while certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms and modifications as would fall within the scope of the invention.

Claims

CLAIMS:

1. A method of measuring a depth of a body of water, the method comprising: moving a watercraft across the surface of the body of water; and whilst moving: recording a speed of the watercraft; and recording a wavelength of a transverse wave portion of a wave pattern generated by the watercraft; and determining the depth of the body of water based on the speed of the watercraft and the wavelength of the transverse wave portion.

2. The method of any preceding claim wherein determining the depth of the body of water is further based on a dispersion relation between the speed and the wavelength.

3. The method of claim 1 or claim 2 wherein recording the speed comprises: recording the speed; determining whether the recorded speed is within an expected speed range; and rejecting and / or repeating the recording of the speed if the recorded speed is not within the expected speed range.

4. The method of claim 3 wherein the expected speed range is based on a maximum theoretical speed of the watercraft.

5. The method of any preceding claim wherein the speed is recorded using a satellite positioning sensor and / or is based on the current or tidal flow of the body of water.

6. The method of any preceding claim wherein recording the wavelength comprises: capturing one or more images of the wave pattern generated by the watercraft; and determining the wavelength of the transverse wave portion of the wave pattern using at least one of the one or more images.

7. The method of any preceding claim wherein recording the wavelength comprises:determining a recorded wave vector cut-off value based on the speed of the watercraft and the wavelength of a transverse wave portion of the wave pattern; determining a maximum theoretical wave vector cut-off value based on the speed of the watercraft; determining a difference between the maximum theoretical wave vector cut-off value and the recorded wave vector cut-off value; and rejecting and / or repeating the recording of the wavelength if the difference is greater than a maximum expected difference.

8. The method of claim 7 wherein the maximum theoretical wave vector cut-off value is the wave vector cut-off value which would be recorded in deep water at the recorded speed and / or wherein the maximum expected difference is 1 % of the maximum theoretical wave vector cut-off value.

9. The method of any preceding claim wherein the body of water is a canal or other navigable inland waterway.

10. The method of any preceding claim further comprising determining a speed and / or direction of a current of the body of water; and determining the depth of the body of water based on the speed, the wavelength and the speed and / or direction of the current.11 . A computing device comprising a processor, the processor configured to: record the speed of a watercraft moving across the surface of a body of water; record the wavelength of a transverse wave portion of a wave pattern generated by the watercraft; and determine the depth of the body of water based on the speed of the watercraft and the wavelength of the transverse portion.

12. The computing device of claim 11 wherein determining the depth of the body of water is further based on the dispersion relation between the speed and the wavelength.

13. The computing device of claim 11 or claim 12 further comprising one or more image collection devices and wherein recording the wavelength comprises:capturing one or more images of the wave pattern using the one or more image devices; and determining the wavelength of the transverse wave portion of the wave pattern using the one or more images.

14. The computing device of any one of claims 11 to 13 further comprising a satellite positioning sensor and wherein recording the speed comprises using the satellite positioning sensor to record the speed.

15. The computing device of any one of claims 11 to 14 wherein the processor is further configured to determine whether the determined depth of the body of water is below a threshold.

16. The computing device of claim 15 wherein the threshold is based on the minimum depth of water required for the watercraft to float.

17. The computing device of claim 15 or 16 further configured to alert a user of the computing device when the depth of the body of water is below the threshold.

18. The computing device of any one of claims 11 to 17 further comprising a network communications module configured to communicate over a network at least one of:- the location of the watercraft- the speed- the wavelength- the determined depth19. A computer program product configured such that, when executed by the computing device of claim 11 , or any claim dependent thereon, causes the apparatus to perform the method of claim 1.

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