Towed sensor array

Abstract

A towed sensor array comprises a plurality of sensors 202 (e.g. acoustic, magnetic or electric field, pressure, temperature, motion, location, light) spatially separated along an axial direction. A first layer 240 at least partially enclosing the plurality of sensors is formed of a structure resistant to deformation in a radial direction of the array. A second layer 206 at least partially enclosing the first layer, comprises a structure resistant to deformation along the axial direction of the array formed of a plurality of fibres e.g. synthetic polymers braided and / or twisted together around the first layer. A third fluid insulating layer 208 encloses the second layer. A fluid to provide buoyancy is disposed within the array. The first layer may be helical and formed by additive manufacturing or injection moulding. The third layer may be extruded.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a towed sensor array and a method of manufacturing a towed sensor array. BACKGROUND

[0002] Towed sensor arrays may be deployed with respect to a vehicle, such as a vessel on or under water, to detect changes in the surrounding environment. As a result of being towed through a medium, such as water, towed sensor arrays may experience forces, such as drag, that may cause portions of the towed sensor array to be subject to stress or strain. Moreover, during, or prior to a deployment phase, a towed sensor array may also be subjected to stress or strain, for example, as a result of handling. Such stresses and strains may cause a towed sensor array to be deformed or damaged, which may result in sub-optimum sensing by the towed sensor array. SUMMARY OF INVENTION

[0003] According to the present disclosure, there is provided a towed sensor array comprising: a plurality of sensors spatially separated along an axial direction of the towed sensor array; a first layer at least partially enclosing the plurality of sensors, wherein the first layer is formed of a structure resistant to deformation in a radial direction of the array; a second layer at least partially enclosing the first layer, wherein the second layer comprises a structure resistant to deformation along the axial direction of the array formed of a plurality of fibres braided and / or twisted together around the first layer; a third layer enclosing the second layer, wherein the third layer is a fluid insulating layer; and a fluid disposed therewithin.

[0004] In one example, at least one of the first layer, second layer and third layer extends unbroken along an axial extent of the towed sensor array within which the plurality of sensors of the array are disposed.

[0005] In one example, the at least one of the respective first, second and third layers have a length (for example a continuous or unbroken length) of at least 50 metres along the axial direction of the towed sensor array, and may for example have a length of at least 200 metres along the axial direction of the towed sensor array.

[0006] In one example, the structure resistant to deformation along the axial direction of the array of the second layer formed of the plurality of fibres braided and / or twisted together, is a load distributing structure.

[0007] In one example, the structure of the second layer resistant to deformation along the axial direction of the array and formed of the plurality of fibres braided and / or twisted together is configured to internally balance torque.

[0008] In one example, the plurality of fibres twisted together around the first layer comprises an equal number of fibres twisted in opposite directions around the first layer.

[0009] In one example, the second layer comprises synthetic fibres. For example, the synthetic fibres may comprise one or more synthetic polymers.

[0010] In one example, the second layer comprises one or more synthetic polymers, wherein the synthetic polymers comprise one of an aromatic polyamide and / or an aromatic polyester.

[0011] In one example, the second layer comprises one or more synthetic polymers, wherein the synthetic polymers comprise Kevlar, Twaron, and / or Vectran.

[0012] In one example, the plurality of fibres of the second layer comprises a number of fibres that is variable along the axial direction of the towed sensor array.

[0013] In one example, a portion of the second layer proximate to a leading end of the towed sensor array comprises a larger number of fibres than a portion of the second layer proximate to a trailing end of the towed sensor array.

[0014] In one example, the first layer is flexible to off-axis deformation of the towed sensor array, for example, bending of the array.

[0015] In one example, the first layer is formed of a resiliently compressible structure, and / or a structure comprising a plurality of rigid members.

[0016] In one example, the structure of the first layer is helical, for example it is a coil.

[0017] In one example, the first layer comprises a material suitable for additive manufacturing or injection molding.

[0018] In one example, the first layer comprises a carbon-fibre or composite thereof.

[0019] In one example, the first layer comprises a polyamide, such as Nylon.

[0020] In one example, the third layer comprises a material that prevents fluid permeation therethrough, for example, the third layer is a fluid impermeable layer.

[0021] In one example, the third layer comprises a plastic, such as polyurethane, PU, or more particularly, a thermoplastic, such as polyvinyl chloride, PVC, polyethylene, PE, or thermoplastic polyurethane, TPU.

[0022] In one example, the fluid disposed within the towed sensor array is a buoyancy providing fluid.

[0023] In one example, the fluid disposed within the towed sensor array is a liquid with a density less than water (e.g., fresh water or salt water), such as a hydrocarbon liquid.

[0024] In one example, the fluid disposed within the towed sensor array is an aviation fuel, such as kerosene.

[0025] In one example, an inner surface of the third layer comprises an interference structure. For example, a structure that is configured to increase friction between the inner surface of the third layer and an outer surface of the second layer.

[0026] In one example, an inner surface of the third layer comprises an interference structure that interlocks with the outer surface of the second layer, for example the interference structure of the third layer and the outer surface of the second may form an interlocking structure comprising corresponding recesses and protrusions formed at overlapping regions of the inner surface of the third layer and the outer surface of the second layer.

[0027] In one example, each of the plurality of sensors of the towed sensor array are configured to provide measurements of, or detect changes in, one or more of: acoustic waves, magnetic fields, electric fields, pressure, temperature, motion, location, orientation and incident light. For example, the plurality of sensors comprises one or more of: acoustic sensors, magnetic field sensors, electric field sensors, pressure sensors, temperature sensors, motion sensors, location sensors, orientation sensors and light sensors.

[0028] In one example, each of the plurality of sensors of the towed sensor array are regularly or irregularly spaced along the axial direction of the towed sensor array.

[0029] In one example, each of the plurality of sensors of the towed sensor array are spaced apart by a respective distance based on a sampling parameter of a signal to be detected.

[0030] It should be understood that the examples of the towed sensor array described above may be combined in any combination where feasible.

[0031] According to another aspect of the present disclosure, there is provided a method of manufacturing a towed sensor array. The method of manufacturing a towed sensor array comprising: providing a plurality of sensors spatially separated along an axial direction of the towed sensor array; providing a first layer at least partially enclosing the plurality of sensors, wherein the first layer is formed of a structure resistant to deformation in a radial direction of the array; providing a second layer at least partially enclosing the first layer, wherein the second layer comprises a structure resistant to deformation along the axial direction of the array formed of a plurality of fibres braided and / or twisted together around the first layer; providing a third layer enclosing the second layer, wherein the third layer is a fluid insulating layer; and providing a fluid disposed therewithin.

[0032] In one example, providing the first layer comprises winding the first layer around the plurality of sensors.

[0033] In one example, providing the first layer comprises providing segments of the first layer to the plurality of sensors, and optionally further comprises coupling respective segments of the first layer provided to the plurality of sensors.

[0034] In one example, providing the first layer comprises forming the first layer by an additive manufacturing process, or by an injection molding process.

[0035] In one example, the plurality of fibres are braided and / or twisted directly around the first layer provided to the plurality of sensors.

[0036] In one example, providing the third layer comprises extruding a third layer material on to the second layer.

[0037] In one example, providing the plurality of sensors comprises spatially separating at least a subset of the plurality of sensors at respective distances along the axial direction of the towed sensor array based on at least one characteristic of a signal to be detected.

[0038] It should be understood that the method examples described above may be combined in any combination where feasible. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Various features of the present disclosure will be apparent from the detailed description which follows, taken in conjunction with the accompanying drawings, which together illustrate features of the present disclosure, and wherein:

[0040] FIG. 1 is a schematic diagram of functional blocks of an example towed sensor array according to the disclosure.

[0041] FIG. 2 is a schematic diagram of an example towed sensor array according to the disclosure.

[0042] FIG. 3 is a schematic diagram of another example towed sensor array according to the disclosure.

[0043] FIG. 4 is a schematic diagram of a radial cross-section of an example towed sensor array according to the disclosure.

[0044] FIG. 5 is a schematic diagram of a magnified view of a partial radial cross-section of an example towed sensor array according to the disclosure.

[0045] FIG. 6 is a schematic diagram of an example towed sensor array towing configuration according to the disclosure.

[0046] FIG. 7 is a flow chart illustrating an example method of manufacturing a towed sensor array.

[0047] FIG. 8 is a flow chart illustrating an example method of manufacturing a towed sensor array comprising winding a first layer around a plurality of sensors.

[0048] FIG. 9 is a flow chart illustrating an example method of manufacturing a towed sensor array comprising braiding and / or twisting a plurality of fibres around a first layer.

[0049] FIG. 10 is a flow chart illustrating an example method of manufacturing a towed sensor array comprising extruding a third layer. DETAILED DESCRIPTION

[0050] Towed sensor arrays are commonly implemented as sensor arrays attached via a cable, or other means, to a vehicle that tows the sensor array along behind it. In some cases, the towed sensor array is towed through water behind a vessel that is either on the surface of the water, or is under the water, such as a submersible or a submarine. Such vessels may be directly human operated or may be Remote Operated Vehicles (ROVs).

[0051] The sensors of the towed sensor array may be used to sense changes in the surrounding, e.g., underwater, environment, and may, for example, be acoustic sensors used for sonar, or any other type of sensor that provides information about an underwater environment. For example, the sensors may be configured to detect communication signals, detect the presence of other underwater bodies, perform seismic analysis of the seabed to investigate potential offshore oil and gas resources, or may be configured to perform scientific studies of environments hosting marine life etc. The sensors of the towed sensor array may additionally, or alternatively, provide information on at least one of the location, orientation (e.g., pitch and / or roll) and heading of the array itself.

[0052] As the signals to be detected by the sensors are often expected to be weak, for example due to having inherently low amplitudes, or due to attenuation over the path lengths the signals are expected to traverse between a signal source and the array, the sensors of the array are required to be sensitive to an incident signal. In practice, the sensitivity of the sensors may be significantly impacted by the specific configuration of the array during a sensing event.

[0053] For example, the sensors of the towed sensor array are commonly protected from water ingress by a water impermeable outer layer that is applied to the sensor array. This water impermeable outer layer may have a given overall shape or form when the array is at rest. For example the outer layer may have a uniform thickness along the length of the array when the array is at rest. However, as the towed sensor array is towed through the water, the array may experience drag, e.g., hydrodynamic drag, which may exert a strain on the protective outer layer. This may result in the outer layer being deformed. For example, this may result in an overall redistribution of the outer layer material along a length of the array, which may change the overall shape, or form of the outer layer. In some cases, as a result of the drag force experienced during towing, the outer layer may be stretched in some regions and compressed in other regions. In some cases, the initially uniform thickness of the outer layer may be changed, for example, the outer layer may become thinner at a first position, e.g., at a leading end of the array, and thicker at a second position along the portion of the towed sensor array, e.g., at a trailing end of the array. In some cases the structure of the outer layer material may be changed from an initial state as a result of the drag. For example, the outer layer may be stretched (e.g., necked down) at the first region, and compressed (e.g., rucked up) at the second portion, which changes the form of the outer layer. Redistribution of the outer layer material (i.e., a change in the overall shape or form of the outer layer) may result in changes to the flow of the medium in which the array is towed over the outer layer. For example, in the absence of deformation, the medium may flow over the outer layer smoothly, i.e., there may be a laminar flow of the medium over the outer layer. The change in form (e.g., structure and / or thickness) along the length of the outer layer resulting from the deformation caused by drag may introduce turbulence into the flow of the medium over the outer layer. For example, there may no longer be laminar flow of the medium over the outer layer, and instead there may be a turbulent flow of the medium over the outer layer. The turbulence at the medium-outer layer interface may be considered to be a source of noise, for example, the turbulence may cause local motions in the medium at the interface that may distort the signal and may introduce additional noise into the signal sensed by the sensors of the array internal to the outer layers. The additional noise may reduce the signal-to-noise ratio of the sensed signal, and may, for example, mask other forms of signal noise that may be of interest. Thus, the sensitivity of the sensors of the array may be adversely affected when the array is towed, and this may reduce the overall reliability of signal detection by the towed sensor array. Such a reduction in the sensitivity of the sensors caused by deformation of the outer layers of the array may increase with towing speed.

[0054] The performance of the sensors of the towed sensor array may also be affected if the sensors are damaged during deployment of the array. For example, the array may be stored prior to deployment and may be deployed into the water via a winch, which may exert stresses and / or strains on the towed sensor array. If the sensors internal to the towed sensor array, or any electronics coupled thereto, are not adequately protected, these internal components of the array may be crushed or pulled apart and damaged by the external forces applied during deployment.

[0055] If any of the sensors of the towed sensor array are damaged, they may need to be repaired or replaced, along with any protective layer(s) surrounding the sensors that may have also been damaged.

[0056] The present disclosure provides example towed sensor arrays that are more robust to stresses and strains. The example towed sensor arrays disclosed herein are more resistant to deformation as a result of applied stresses and strains, and thereby provide improved sensing reliability and sensitivity. The example towed sensor arrays disclosed herein are also more efficient to manufacture and enable damaged portions of the arrays to be more easily replaced.

[0057] Although the operation of a towed sensor array has been described above with respect to deployment of the array underwater it is to be understood that the example towed sensor arrays disclosed herein may be deployed, and towed, through any medium, such as air, or any other fluid and that in this case the same principles as outlined above apply to the detection of signals or other changes in environmental properties by the sensors of the array.

[0058] In the following description, for the purposes of explanation, numerous specific details of certain examples are set forth. Reference in the specification to "an example" or similar language means that a particular feature, structure, or characteristic described in connection with the example is included in at least that one example, but not necessarily in other examples. It should also be understood that examples may be combined in any combination where feasible.

[0059] The following description relates to a towed sensor array comprising first and second layers that are resistant to deformation, meaning that the first and second layers are resistant to changes in their original shape, such as compression, crushing or elongation (i.e., stretching) etc. As disclosed herein deformation in or along an axial direction of a towed sensor array may comprise e.g., elongation (i.e., stretching), and deformation in a radial direction of a towed sensor array may comprise e.g.compression or crushing etc.

[0060] It is also to be understood that the sensors of the towed sensor array disclosed herein may be configured to sense any changes in environment or to provide a measure of a property of the array itself, such as any one of, or any combination of location, depth, pitch, roll, and heading of the array. The sensors may be configured to provide absolute measurements of the surrounding environment or to detect changes in environment such as, but not limited to, changes in temperature or pressure, or may be configured to detect reception of, or changes in received waves such as acoustic waves, or electromagnetic waves, or to otherwise sense changes in a field such as an electric field or a magnetic field. The waves or fields sensed by the sensors of the array may or may not be encoded with data to form a signal for communication. For example, the sensors may be configured to sense changes in environment which may arise as a result of the transmission of communication or data signals, or may arise due to other activities which create detectable changes, such as the function or operation of electrical circuitry or any components that may emit noise, or changes to signals, such as echolocation signals, that may arise due to a change in the physical location of bodies within the environment of the array.

[0061] The sensors of the towed sensor array may comprise at least one of: a temperature sensor, a pressure sensor (which may provide a depth measurement for the array), an acoustic sensor, an electric charge or electric field sensor, a magnetic field (or magnetic charge) sensor (such as a compass, which may provide a heading of the array), a motion and / or orientation sensor (such as an accelerometer, for example a tri-axial accelerometer, and / or a gyroscope, which may also detect pitch and / or roll), a location sensor (such as GPRS), or a radiation sensor (such as a light sensor), where the radiation sensor may detect at least one of gamma ray, X-ray, ultraviolet, optical, infra-red, microwave and radio radiation.

[0062] Examples disclosed herein relate to towed sensor arrays that are configured to be robust to stresses and strains resulting from the application of external forces when the towed sensor arrays are deployed and / or towed during use. The examples enable the configuration of the towed sensor array to be more stable during sensing events by resisting deformation of the protective layer(s), and thereby preventing or limiting (i.e., reducing) deformations of protective layer(s) of the towed sensor array, which may otherwise result in an increase in noise caused by turbulent flows when the array is towed. The examples may also, or alternatively, prevent or limit damage to the sensors or other components internal to the array during towing or deployment of the array when external stress may be applied which may crush, break, or otherwise damage said components.

[0063] In the following description of the figures, the example towed sensor arrays of Figures 1 to 6 share several features in common. Corresponding features are referred to using similar reference numerals.

[0064] Figure 1 shows a schematic diagram of functional blocks of a towed sensor array 100. The towed sensor array 100 comprises a plurality of sensors including sensor 102a, sensor 102b, and sensor 102c. Although three sensors are depicted in Figure 1, it is noted that this is for illustration purposes only, and the plurality of sensors may comprise any number of sensors. For example, the plurality of sensors may comprise more, or less than three sensors.

[0065] The plurality of sensors (102a, 102b, 102c) are spatially separated along an axial direction 110 of the towed sensor array 100. The axial direction 110 may be the direction along which a longitudinal axis of the towed sensor array 100 extends. For example, the axial direction 110 may be aligned with the direction in which the array extends away from the vehicle which tows the array. In this case, the longitudinal axis of the towed sensor array may be aligned, i.e., parallel to, the direction in which the array extends away from the vehicle. The axial direction 110 may also be aligned parallel, or substantially parallel, to the direction of motion of the vehicle and / or array. However, it is to be understood that the alignment of the axial direction 110 of the array is not so limited. The towed sensor array 100 also has a radial direction 114, which extends across a cross-section of the towed sensor array 100.

[0066] It may be that each respective sensor of the plurality of sensors is spatially separated along the axial direction 110. Alternatively, it may be that more than one sensor is disposed at the same axial position along the axial direction 110. For example, a group of sensors comprising the same, or a combination of different sensors, or sensor types (i.e., sensors configured to detect different properties), may be disposed at the same axial position along the axial direction 110. Additionally, it may be that a same, or different grouping of sensors is spatially separated along the axial direction 110 of the towed sensor array 100.

[0067] The towed sensor array 100 further comprises a first layer 104, a second layer 106, and a third layer 108. The first layer 104 at least partially encloses the plurality of sensors (102a, 102b, 102c). For example, the first layer 204 may fully enclose the plurality of sensors or may partially enclose the plurality of sensors. Where the first layer 104 partially encloses the plurality of sensors, there may be gaps in the first layer 204 material extending around the plurality of sensors.

[0068] The second layer 106 at least partially encloses the first layer 104 and the third layer 108 encloses the second layer 106. Each of the first layer 104, second layer 106 and third layer 108 may be a protective layer of the towed sensor array 100.

[0069] The first layer 104 is formed of a structure resistant to deformation in the radial direction 114 of the array. As described above, the structure of the first layer 104 may be resistant to changes in the shape of the array in the radial direction 114 of the array. For example, the structure may be resistant to compression or crushing in the radial direction 114 of the towed sensor array 100. Such deformations may be induced by stresses and / or strains acting on the towed sensor array 100 as a result of drag, such as hydrodynamical or aerodynamical drag, from the array being towed through a medium. For example, it may be that the second layer 106 and / or the third layer 108 are subjected to drag during towing of the towed sensor array 100, and, as a result, the second layer 106 and / or third layer 108 may exert a force, or forces, on the first layer 104, which may stress or strain the first layer 104 in the radial direction 114.

[0070] Additionally, or alternatively, such stresses or strains may result from handling as the towed sensor array 100 is deployed. For example, the towed sensor array 100 may be stored before use and deployed via mechanical means, such as a winch, which may pull or otherwise unwind the array from a stored configuration. It may be that the forces applied when unwinding or otherwise deploying the array stress and / or strain the array. It may also be that the array may be passed over, under or through deployment members, such as pulleys or fixed bends, which may also apply stresses and / or strains to the array. For example, the array may be deployed via at least one pulley member which may pinch or compress the array. It may be that the array is deployed via at least one fixed bend which may also pinch or compress the array. The resistance of the structure forming the first layer 104 to deformations in the radial direction 114 of the array may therefore prevent or limit the plurality of sensors from damage, such as crushing, or breaking of the sensor.

[0071] It may also be that the presence of the first layer 104 in the array prevents or limits (e.g., reduces) deformation along the radial direction 114 of the array of the other layers of the array, for example the second layer 106 and / or the third layer 108. For example, it may be that the first layer 104 providing a structure resistant to deformation in a radial direction of the array (which thereby provides a radial support layer, or a protective layer) also provides resistance to deformation in the radial direction 114 of the array of the second layer 106 and / or the third layer 108 by limiting, or preventing, compression of the first layer 104 by the second layer 106 and / or third layer 108, as will be explained in more detail below.

[0072] The second layer 106 comprises a structure resistant to deformation in, or along, the axial direction 110 of the array, wherein the structure resistant to deformation in, or along, the axial direction 110 of the array is formed of a plurality of fibres braided and / or twisted around the first layer 104. As described above, the structure of the second layer 106 may be resistant to changes in shape of the array in or along the axial direction 110 of the array. For example, the structure may be resistant to stretching or elongation along the axial direction 110 of the towed sensor array 100. Such deformations may be induced by stresses and / or strains acting on the towed sensor array 100 as a result of drag, such as hydrodynamical or aerodynamical drag, from the array being towed through a medium. It may be that, during towing, the array experiences a drag force which may increase as a function of the speed at which the array it towed through a medium. For example, when the array is deployed in water, it may experience hydrodynamic drag, which increases as a square function of the speed at which the array is moving (i.e., being towed). Additionally, or alternatively, such stresses may result from handling as the towed sensor array 100 is deployed.

[0073] It may be that the structure resistant to deformation along the axial direction of the array that is formed of the plurality of fibres braided and / or twisted around the first layer 104 may prevent or limit at least the second layer 106 from being stretched as a result of the drag exerted by the medium when the array is towed. This may prevent or limit a change in thickness (or form) of the at least second layer 106. For example, as the array is towed, the leading end of the array may experience a greater load from the drag force than the trailing end of the array due to the load from the drag force being cumulative along the length of the array. Without resistance to deformation, the cumulative load would lead to the second layer being stretched at the leading end of the array and compressed at the trailing end of the array as the second layer material is re-distributed under the load exerted from the drag. The structure resistant to deformation along the axial direction of the array may prevent or limit (i.e., reduce) the second layer 106 material being re-distributed from one location on the array (e.g., at a first axial position), to a different location on the array (e.g., at a second axial position). It may be that this robustness of the second layer to changes in thickness (or form) along the axial direction of the array when external forces are applied, maintains a smooth flow of the medium over the layers of the array, or reduces or prevents turbulent flow of the medium over the layers of the array, which reduces or prevents the introduction of additional noise into the signal sensed by the sensors when the array is towed. This may increase the reliability of the sensors.

[0074] Alternatively, it may be that the array can operate to within a given tolerance to changes in the thickness (or form) of the at least second layer 106. In this case, it may be that structure resistant to deformation along the axial directions of the array enables the array to be towed at greater speed, and thus subjected to greater drag, while still allowing operation within the given tolerance as the structure resistant to deformation along the axial directions of the array may reduce the deformation experienced by the second layer 106 as a result of the greater drag (and therefore load) exerted on the array at higher speeds.

[0075] It may also be that the presence of the second layer in the array prevents or limits deformation along the axial direction 110 of the array of the other layers of the array, for example the first layer 104 and / or the third layer 108. For example, it may be that the second layer 106 provides an axial support layer (i.e., a longitudinal axis support layer), or a protective layer to prevent or limit deformation in or along the axial direction 110 of the array. It may be that the structure resistant to deformation along the axial direction of the array of the second layer 106 also provides resistance to deformation along the axial direction of the array of the first layer 104 and / or the third layer 108. For example, it may be that the structure resistant to deformation along the axial direction of the array of the second layer 106, which is external to the first layer 104 and internal to the third layer 108 resists or limits the first layer 104 and / or third layer 108 from being deformed, e.g., elongated (or stretched) when forces are applied, for example, due to dissipation of the load within the second layer, or due to coupling of the layers, e.g., at layer interfaces. The dissipation of the load within the second layer 106 may prevent transfer of load to the inner first layer 104, which may prevent damage (e.g., by stretching) to the plurality of sensors. The coupling may prevent deformation of the third layer 108 provided external to the second layer 106, which may reduce or prevent turbulence and therefore noise caused by flows over the third layer 108 and provide improved sensing reliability and sensitivity. It may be that the coupling is provided by friction, for example friction between the inner surface of an outer layer and the outer surface of an inner layer.

[0076] The plurality of fibres may be twisted together around the first layer 104 to form the structure resistant to deformation along the axial direction of the array. The plurality of fibres may be braided together around the first layer 104 to form the structure resistant to deformation along the axial direction of the array. Alternatively, the plurality of fibres may be both twisted and braided together around the first layer 104 to form the structure resistant to deformation along the axial direction of the array. For example, it may be that along a first portion extending along the axial direction 110 of the towed sensor array 100 the plurality of fibres are twisted together around the first layer 104 and along a second portion extending along the axial direction 110 of the towed sensor array 100 the plurality of fibres are braided together around the first layer 104, or vice versa. The plurality of fibres may be alternately twisted and braided around the first layer 104 along the length of the towed sensor array 100 to form structure resistant to deformation along the axial direction of the array.

[0077] The braiding and / or twisting of the plurality of fibres around the first layer 104 may form a second layer 106 that extends radially around the first layer 104.

[0078] It may be that when external forces, such as drag, are exerted on the second layer 106, the plurality of fibres braided and / or twisted together around the first layer 104 co-operate to resist (i.e., prevent or limit) deformation, e.g., stretching, along the axial direction 110 of the array. For example, the braid and / or twist may comprise a plurality of co-operating members, i.e., subsets of the plurality of fibres that co-operate ( e.g., that act against each other) to balance out, or distribute the force applied to the surface or the body of the towed sensor array 100 and transferred to the braid and / or twist. For example, the structure resistant to deformation along the axial direction of the array formed of the plurality of fibres braided and / or twisted together may be a load distributing structure.

[0079] It may be that the co-operating members are configured to act against each other, i.e., to oppose each other, to resist deformation, e.g., stretching, along the axial direction of the array. For example, respective ones of the co-operating members may respond with an opposite reaction or a substantially opposite reaction, which may be an equal or a substantially equal opposite (or substantially opposite) reaction, to the application of the load from the external forces (such as drag etc.). In this way, the load may be distributed within the structure to prevent or limit (i.e., reduce) a net deformation (i.e., net elongation) of the second layer 106 along the axial direction 110 of the towed sensor array 100.

[0080] It may be that the presence of the first layer 104 beneath or under the second layer 106 in the array may further prevent or limit deformation of the second layer 106 along the axial direction 110 of the array. For example, it may be that when the external forces, such as drag, are exerted on the second layer, the braid and / or twist may be configured to elongate or stretch to a given extent. For example, the co-operating members of the braid and / or twist may cause the radial extent (e.g., radial cross-section) of the braid and / or twist to reduce when the braid and / or twist is elongated (or stretched). It may be that the resistance of the first layer 104 to radial deformation (e.g., compression) may limit or prevent the reduction in the radial extent of the braid and / or twist, thereby inhibiting elongation of the second layer and may therefore reduce or limit elongation of the braid and / or twist (i.e., preventing the braid and / or twist from elongating to the full given extent described above).

[0081] The towed sensor array 100 also comprises a fluid 112 disposed within the towed sensor array 100. The fluid may be a buoyancy providing fluid. For example, the fluid 112 may be selected to enable the towed sensor array 100 to be neutrally buoyant in the towing medium. For example, the fluid 112 may be a fluid, such as a liquid or gas, with a density lighter than the medium within which the towed sensor array is towed. For example, the fluid 112 may be a fluid, e.g., a liquid or gas, with a density lighter than water (e.g., salt or fresh water). The fluid 112 may also have a density that overcomes the weight of the components of the towed sensor array 100, including but not limited to the plurality of sensors, and the first, second and third layers. The fluid 112 may be a liquid hydrocarbon, such as a kerosene, or any other aviation fuel. However, it is to be understood that any suitable fluid, such as but not limited to e.g., transformer oil, silicon oil or sunflower oil may be used. The fluid 112 may be selected to be an environmentally friendly fluid. For example, the fluid 112 may be a fluid 112 with limited environmental impact, such as a biodegradable fluid. The selection of the fluid 112 may be based on the weight of the towed sensor array 100 and / or the fill fluid 112 volume available in the towed sensor array 100.

[0082] It may be that the fluid 112 may be selected to set the density of the towed sensor array. For example, it may be that the fluid 112 may be a fluid, e.g., a liquid or a gas, with a density heavier than the medium in which the array is towed, e.g., water.

[0083] The towed sensor array 100 also comprises a third layer 108, which is a fluid insulating layer. The third layer 108 is provided on top of the first layer 104 and the second layer 106 to insulate the plurality of sensors from the medium in which the array is towed. For example, to insulate the plurality of sensors from water.

[0084] It may be that the third layer 108 further prevents the fluid 112 disposed within the array from permeating outwards and e.g., escaping from the array. The third layer 108 may comprise a material that prevents fluid permeation therethrough. For example, the third layer 108 may be formed of a material that prevents permeation of the external medium therethrough and the fluid 112 therethrough. For example, the third layer 108 may be a liquid impermeable layer, such as a waterproof layer. The third layer 108 may be formed of a plastic, such as, for example polyurethane (PU). The third layer 108 may be formed of a thermoplastic, such as polyvinyl chloride (PVC), polyethylene (PE), thermoplastic polyurethane (PTU) or any other suitable fluid impermeable material.

[0085] The fluid 112 may be disposed within the at least the third layer 108 and may also be disposed within the second layer 106 and within the first layer 104 between each of the respective sensors and between the plurality of sensors and the first layer 104. For example, each element of the towed sensor array 100 disposed within the third layer 108 may be immersed in the fluid 112. For example, it may be that the fluid 112 immerses, or surrounds, each of the plurality of sensors, the first layer 104 and the second layer 106.

[0086] It may be that at least one of the first layer 104, second layer 106 and third layer 108 extend continuously, i.e., unbroken, along at the full length of the array, or at least along the active (i.e., sensing) length (or axial extent) of the towed sensor array 100. For example, it may be that at least one of the first layer 104, second layer 106 and third layer 108 may extend unbroken along the axial extent of the towed sensor array 100 within which the plurality of sensors 102 are disposed. For example, it may be that at least one of the first layer 104, second layer 106 and third layer 108 extend continuously, i.e., unbroken, along a length of the array of at least 50 metres, or more particularly along a length of at least 200 metres. It may be that an unbroken second layer 106 provides continuous, i.e., unbroken or smooth, load distribution along the length of the towed sensor array 100, which may improve the load distribution and thereby the resistance to deformation along the axial direction of the array.

[0087] Alternatively, it may be that, for example, the first layer 104 comprises a plurality of segments of resiliently compressible structures, or a plurality of rigid members spatially separated along the axial direction 110 of the towed sensor array 100. For example, it may be that providing the plurality of segments or rigid members with a spatial separation therebetween provides the resistance to deformation in the radial direction of the array and also increases the flexibility of the first layer to bending.

[0088] Some example structures of the first layer 104 that is resistant to deformation in the radial direction of the array are described below.

[0089] The structure resistant to deformation in the radial direction 114 of the array that forms the first layer 104 may be a resiliently compressible structure, and / or a structure comprising a plurality of rigid members, which may be spatially separated.

[0090] The first layer 104 may be formed of a resiliently compressible structure that may limit deformation in the axial direction 110 of the array by absorbing energy from the load exerted thereon and releasing the stored energy when the load is removed by way of returning the structure to its original shape. It may be that the resiliently compressible structure, and / or the structure comprising a plurality of rigid members forms a radial support structure.

[0091] The first layer 104 may further be flexible to off-axis deformation, for example deformations out of the plane of the longitudinal axis of the towed sensor array 100, such as bending of the array. It may be that the flexibility of the first layer 104 to off-axis deformations, such as bending, allows the towed sensor array 100 to be more easily deployed, such as via pulleys as described above.

[0092] Figure 2 illustrates a schematic diagram of an example towed sensor array 200.

[0093] The towed sensor array 200 comprises a plurality of sensors 202, which may comprise sensors (102a, 102b, 102c). The towed sensor array 200 further comprises the first layer 204, second layer 206 and third layer 208.

[0094] The schematic diagram of Figure 2 shows a cut-away view of the towed sensor array 200 along the axial direction 210. Although the layers illustrated in Figure 2 do not fully overlap, this representation is for illustrative purposes only, to allow easier distinction between the illustrated layers, and it may be that each of the first layer 204, second layer 206 and third layer 208 fully overlap, i.e., they do not have staggered start-points and or end-points. It may also be that each of said layers extends along the full axial length of the towed sensor array 200, or at least along the full axial length of the towed sensor array 200 along which the plurality of sensors are disposed.

[0095] As described above, it may be that at least one of the first layer 204, second layer 206 and third layer 208 extend continuously, i.e., unbroken, along at the full length of the array, or at least along the active (i.e., sensing) length (or axial extent) of the towed sensor array 200. For example, it may be that at least one of the first layer 204, second layer 206 and third layer 208 may extend unbroken along the axial extent of the towed sensor array 200 within which the plurality of sensors 202 are disposed. For example, it may be that at least one of the first layer 204, second layer 206 and third layer 208 extend continuously, i.e., unbroken, along a length of the array of at least 50 metres, or more particularly along a length of at least 200 metres.

[0096] Alternatively, it may be that, for example, the first layer 204 comprises a plurality of segments of resiliently compressible structures, or a plurality of rigid members spatially separated along the axial direction 210 of the towed sensor array 200. For example, it may be that providing the plurality of segments or rigid members with a spatial separation therebetween provides the resistance to deformation in the radial direction of the array and also increases the flexibility of the first layer to bending.

[0097] It may be that the towed sensor array 200 is coupled to a cable, such as a tow cable. For example, the tow cable may also be couplable to a vehicle and during deployment the vehicle may tow the towed sensor array 200 by way of the tow cable. It may be that, at least one of the layers, or, for example, each of the layers (e.g., the first layer 204, second layer 206 and third layer 208), may extend along the full axial length of the towed sensor array 200 and may also extend over a tow cable coupled to the towed sensor array 200. It may be that at least one, or each of the layers extends continuously or in a plurality of segments over the full length of the towed sensor array 200 and the tow cable. For example, it may be that the first layer 204, second layer 206 and third layer 208 extend along the full axial length of the towed sensor array 200 and the tow cable.

[0098] Where at least one of the layers, or each of the layers, extends over the full axial length of the array and over a tow cable, the fluid 212 may be disposed within at least the third layer 208 and may also be disposed within the second layer 206, within the first layer 204 and between the tow cable and the first layer 204. Each element of the towed sensor array 200 and the tow cable disposed within the third layer 208 may be immersed in the fluid 212. For example, it may be that the fluid 212 immerses, or surrounds, each of the plurality of sensors, the first layer 204, the second layer 206 and the tow cable.

[0099] It may be that the towed sensor array 200 is coupled to the tow cable via one or more vibration isolators, such as vibration isolation modules (VIMs). Alternatively, or additionally, it may be that one or more vibration isolators (e.g., VIMs) is fitted to an end of the towed sensor array 200 that is not coupled to the tow cable, for example, a trailing end of the towed sensor array 200. It may be that at least one of the layers, or each of the layers, extends over the full axial length of the towed sensor array 200, and over one or more vibration isolators (e.g., VIMs). It may be that at least one or each of the layers extend continuously over the full axial length of the towed sensor array 200, and over one or more vibration isolators. It may be that at least one or each of the layers extend in a plurality of segments over the full axial length of the towed sensor array 200, and over one or more vibration isolators. It may also be that the at least one of the layers, or the each of the layers, extends as described above (e.g., in a plurality of segments or continuously) over the full axial length of the towed sensor array 200, over one or more vibration isolators (e.g., VIMs) and optionally also over the tow cable.

[0100] Where at least one of the layers, or each of the layers, extends over the full axial length of the array and over one or more vibration isolators, the fluid 212 may be disposed within the at least the third layer 208 and may also be disposed within the second layer 206, within the first layer 204, between the one or more vibration isolators and the first layer 204, and optionally also between each of more than one vibration isolators. Each element of the towed sensor array 200 and the one or more vibration isolators disposed within the third layer 208 may be immersed in the fluid 212. For example, it may be that the fluid 212 immerses, or surrounds, each of the plurality of sensors, the first layer 204, the second layer 206, and the one or more vibration isolators.

[0101] In the example towed sensor array 200 illustrated in Figure 2, the structure resistant to deformation along the axial direction of the array of the second layer 206 comprises a plurality of fibres braided together around the first layer. It may be that the plurality of fibres braided together around the first layer 204 is configured to internally balance torque, for example, as a result of the braiding. It may be that the internal torque balance provided by the plurality of fibres braided around the first layer 204 resists (e.g., limits or prevents) twisting of the second layer 206 when external forces, such as drag, are exerted on the towed sensor array 200. For example, the plurality of fibres may prevent twisting of the second layer, and thereby the array, around the longitudinal axis of the array.

[0102] The braid may comprise two or more fibres or yarns. For example, a yarn may comprise a plurality (or subset) of fibres grouped together. For example, the braid or twist may comprise between 2 to 50 fibres (i.e., individual fibres) or yarns, for example between 4 to 30 fibres or yarns, for example, 10, 20 or 30 fibres or yarns. However, the number of fibres (e.g., the total number of fibres) or yarns braided or twisted together is not so limited, and may, for example, comprise more than 50 fibres or yarns. It may also be that the number of fibres or yarns braided and / or twisted together may be selected to provide a required resistance to deformation along the axial direction of the array.

[0103] It may be that the braid comprises a plurality of fibres (or plurality of yarns) braided together around the first layer to form a layer extending at least radially around the first layer. For example, it may be that a plurality of radially adjacent fibres are added to the braid during the braiding process.

[0104] The braid may be formed of a single dimensional braid formed around the first layer 204, for example as a layer or shell.

[0105] The plurality of fibres forming the structure resistant to deformation along the axial direction of the array, such as the braid of Figure 2, comprise synthetic fibres (or strands). For example, synthetic fibres that have been chosen to have low elongation (or low extension) and / or high strength. Such synthetic fibres may include one or more synthetic polymers, such as an aromatic polyamide, or an aromatic polyester. For example, the aromatic polyamides may be aramids such as Kevlar® or Twaron®. It may be that the aromatic polyester is Vectran®. It may be that the synthetic polymers are melted or otherwise formed into the fibres (or strands) of the plurality of fibres. It may be that the plurality of fibres comprise a mixture of fibres. It may also be that the fibres are formed into yarns (or threads) which comprise more than one fibre, and may comprise more than one type of fibre, for example to form a composite yarn. It may be that the plurality of fibres braided and / or twisted around the first layer to form the structure resistant to deformation along the axial direction of the array comprises such yarns, including said composite yarns.

[0106] It may be that the second layer 206 formed of the plurality of fibres braided together around the first layer 204 disposed external to the first layer 204 and internal to the third layer 208 may enable the transfer of force exerted on the surface or body of the towed sensor array 200 through the third layer 208 to the second layer 206 at the respective position along the axial direction 210 of the array at which the external force was exerted. For example, it may be that the externally applied force is transferred directly to the second layer 206 of the array, and the braid thereof, as a result of the braiding of the fibres around the first layer due to the radial extent of the second layer, for example, due to the second layer radially surrounding the first layer 204. The direct transfer of force to the second layer 206 at the axial position at which the force is exerted on the towed sensor array 200 may enable improved transfer of load by the second layer 206.

[0107] As described above with respect to Figure 1, the plurality of fibres (or yarns) braided around the first layer 204 may be configured to resist, i.e., prevent or limit, deformation along the axial direction 210 of the towed sensor array 200. It may be that the angle between the respective plurality of fibres (or yarns) is selected to resist deformation, e.g., elongation or stretching, of the second layer 206 along the axial direction of the array. For example, it may be that decreasing the angle between the respective fibres of the braid may reduce the deformation, i.e., stretching, of the second layer when the external force is applied.

[0108] It may be that structure resistant to deformation along the axial direction of the array formed by the plurality of fibres braided together, (e.g., the load distributing structure) of the second layer 206 is continuous (i.e., unbroken) along the full axial length of the towed sensor array 200, or at least along the full axial length of the towed sensor array 200 along which the plurality of sensors 202 are disposed. For example, it may be that the structure is formed of a single axial element, and is not, for example formed of multiple axial elements connected together with e.g., interconnects.

[0109] For example, it may be that the second layer 106 extends continuously (i.e., unbroken or as a single axial element, not formed of multiple interconnected axial elements) over at least a length (e.g., an axial length of the array) of at least 50m, or at least 200m.

[0110] As a result of being a single or continuous axial element, as opposed to multiple interconnected axial elements, it may be that the structure resistant to deformation along the axial direction of the array of the second layer 206 is better able to distribute load along the axial direction 210 of the array, which may improve the protection of the sensors and / or the reliability of the sensor sensitivity during or after deployment of the towed sensor array.

[0111] For example, it may be that the second layer 206 distributes load continuously or smoothly (i.e., as a continuous or smooth function of axial direction 210, without points of discontinuity, deviation or reversal in the trend of load distribution function with axial direction 210) along at least the axial extent of the towed sensor array within which the plurality of sensors are at least partially enclosed. It may be that distributing the load continuously along at least the axial extent of the towed sensor array within which the plurality of sensors are at least partially enclosed improves the efficiency of the transfer of load along the array and may better limit deformation of the second layer. The continuous distribution of load may also improve the protection of the plurality of sensors and / or improve the sensitivity of the sensors.

[0112] It may also be that as a result of the structure resistant to deformation along the axial direction of the array of the second layer 206 being a single or continuous axial element at least along the extent of the array at which the plurality of sensors 202 are disposed, the plurality of sensors 202 may be more flexibly spaced along the axial direction 210 of the array.

[0113] For example, the plurality of sensors 202 may be regularly or irregularly spaced along the axial direction 210 of the array. As the second layer 206 may be a single or continuous axial element, the second layer 206 may form a single cavity within which the first layer 204 and the plurality of sensors 202 may be housed, for example, without internal dividers such as interconnects. As a result, the plurality of sensors 202 may be axially protected without the need for interconnects to be disposed between sensors, which may allow for improved precision in sensor spacing because overlap between the sensors and interconnects does not need to be avoided.

[0114] Each of the plurality of sensors may be spaced apart by a respective distance based on at least one characteristic of a signal to be detected. For example, the respective sensors may be spaced apart based on a frequency of a signal to be detected. The respective sensors may be spaced apart based on a sampling parameter of a signal to be detected, such as a Nyquist sampling frequency of a signal to be detected. Alternatively, the respective sensors may be spaced apart by an irregular distance or interval, for example to provide diversity in signal sampling, which may, for example, account for interference etc.

[0115] In the example towed sensor array 200 illustrated in Figure 2, the first layer 204 is formed of a resiliently compressible structure that is helical, i.e., is formed is formed of a helix, or a coil. The first layer 204 of the example towed sensor array 200 is wrapped (or wound) around the plurality of sensors 202. The helix of the first layer 204 may comprise any number of turns. It may be that the number of turns of the helix is selected based on a required resistance to deformation of the first layer 204 and / or the required flexibility to bending. The first layer 204 at least partially encloses the plurality of sensors 202 due to the structure of the helix. The first layer 204 is illustrated as a helix of given direction (or handed-ness), however the helical structure of the first layer 204 may be of any direction (or handed-ness). The helix may be a resiliently compressible structure. For example, when a load, such as a stress is exerted on to the helical structure of the first layer 204, the structure is resiliently compressed. However, further compression is limited by the storing of energy of the helix to prevent further radial compression. When the load e.g., stress, is removed, the helical structure returns to its original (un-compressed), or substantially original shape.

[0116] The example towed sensor array 200 may optionally further comprise a sensor positioning member 216, which may be a positioning tape. The sensor positioning member 216 may extend along the length of the array and may indicate the position that the sensors, and optionally other internal components of the array, such as wiring etc, are to be located. The indicated position may be the position at which the components are to be located when the array is tensioned, for example with a stress of strain arising from, or equivalent to, the forces exerted by drag on the towed sensor array when deployed. It may be that the sensor positioning member 216 is used during assembly of the towed sensor array 200.

[0117] In the alternative example towed sensor array 300 illustrated in Figure 3, the first layer comprises a resiliently compressible structure that is a lattice. It is to be understood that while the first layer 304 is illustrated as a lattice, the resiliently compressible structure of the first layer 304 may alternatively be an irregular resiliently compressible structure, such as a sleeve with irregularly shaped and / or spaced cut-outs.

[0118] The first layer 204, first layer 304, or any other alternative resiliently compressible structure may be a single axial element, and may extend continuously, e.g., unbroken, along at least the axial extent of the towed sensor array within which the pluralities of sensors are disposed.

[0119] Alternatively, not illustrated, the first layer may comprise a plurality of rigid members, such as rings. The rings of the first layer may be disposed around the plurality of sensors and may be spatially separated along the axial direction of the array. Alternatively, the rings may be directly adjacent each other, or may be a combination of adjacent and spatially separated. The first layer may at least partially enclose the plurality of sensors by way of each of the plurality of rings enclosing a portion of the plurality of sensors. It may be that when a load, such as a stress is exerted on to rigid rings of the first layer 204, the rigid rings do not deform. It may be that at least one of the number of rigid rings and the distance or spatial separation between members may be varied to alter the resistance to deformation of the first layer and / or the flexibility of the first layer to bending of the array. For example, the number of rings may be increased to provide greater resistance to deformation in the radial direction of the array.

[0120] Although the plurality of members (e.g., the plurality of rigid members) of the first layer has been described as rings, the members (e.g., the plurality of rigid members) may be of any shape.

[0121] It may be that the structure of the first layer (104, 204, 304) that is resistant to deformation in a radial direction of the array comprises a material suitable for additive manufacturing, injection molding, casting or forming from solid. It may also be that the first layer (104, 204, 304) comprises a flexible (e.g., elastic) or rigid material of high strength. For example, it may be that the first layer (104, 204, 304) comprises a carbon-fibre or composite thereof. Alternatively, it may be that the first layer (104, 204, 304) comprises a polyamide, such as Nylon.

[0122] Figure 3 also illustrates an alternative example second layer 306 that comprises a plurality of fibres twisted together around the first layer 304. Similarly to the second layer 206 illustrated in Figure 2 comprising the plurality of fibres braided together around the first layer 204, the plurality of fibres twisted together around the first layer 304 illustrated in Figure 3 may be a load distributing structure. The plurality of fibres twisted together around the first layer 304 may also extend unbroken along the axial direction 310 of the towed sensor array 300 and may additionally distribute load continuously along the axial extent of the array within which the plurality of sensors 302 are disposed. The plurality of fibres twisted together around the first layer 304 may also be configured to transfer load exerted externally directly to the second layer at the axial position of the array at which the load is exerted by way of the radial extension of the twisted fibres around the first layer 304.

[0123] The plurality of fibres twisted together around the first layer 304 may comprise the same type, number and grouping of fibres as described above with respect to Figure 2. For example, the second layer 306 comprising a plurality of fibres twisted around the first layer 304may comprise synthetic fibres, and may comprise a plurality of subsets of fibres (or yarns) twisted together. It may be that the number of subsets of fibres, and / or the number of fibres in each subset of fibres may be selected to balance the flexibility of the second layer 306 to bending with the resistance of the second layer 306 to deformation (e.g., stretching) along the axial direction 310 of the array.

[0124] Also similarly to the pluralities of fibres braided together around the first layer 204, the plurality of fibres twisted together around the first layer 304 may comprise co-operating members, and may be additionally configured to internally balance torque. For example, the plurality of fibres of the second layer 306 may comprise an equal number of fibres (or yarns) twisted together in opposing (i.e., opposite) directions. For example, the second layer 306 may comprise a first plurality of fibres formed (e.g., twisted) into a helix of a first direction (e.g., clockwise or counter-clockwise, or right-handed or left-handed) around the first layer 304, and a second plurality of fibres formed (e.g., twisted) into a helix of a second direction, opposite to the first direction, around the first layer 304. The first and second plurality of fibres may form the co-operating members described above. It may be that each of the plurality of fibres formed into a helix of a given direction may be a yarn. Alternatively, it may be that each respective helix comprises a plurality of yarns.

[0125] It may be that the first and second plurality of fibres twisted together may act under the load exerted by the external forces (such as drag) to cancel out, or limit, net torque within the braid, which may limit the twisting of the second layer 306 under the applied load. For example, it may prevent twisting of the second layer, and thereby the array, around the longitudinal axis of the array. As a result, a second layer 306 comprising an equal number of fibres twisted together around the first layer 304 in opposing directions is further resistant to deformation (e.g., twisting and elongation) along the axial direction 310 of the array.

[0126] Figures 2 and 3 also illustrate a fluid damper 212. Fluid damper 212 surrounds the plurality of sensors, and is disposed between each sensor and beneath the first layer. Fluid damper 212 attenuates flow of the fluid 112 within the towed sensor array. For example, it may be that fluid damper 212 prevents or limits displacement of the fluid 112 within the towed sensor array. Flow or displacement of the fluid 112 within the towed sensor array may otherwise occur as a result of the movement of the towed sensor array or as a result of forces exerted on the towed sensor array.

[0127] The fluid damper 212 may comprise a foam, such as an open cell foam. It may be that the structure of the foam of the fluid damper 212 attenuates flow of the fluid 112 within the towed sensor array while also allowing the fluid 112 to be disposed throughout the towed sensor array, internal to the third layer. For example, it may be that respective cells of the open cell structure of the fluid damper 212 confine the displacement of fluid 112 disposed therewithin.

[0128] The fluid damper 212 may also provide mechanical support to the plurality of sensors. For example, it may also be that fluid damper 212 provides a physical barrier between the plurality of sensors and the other elements of the towed sensor array, e.g., the first layer, for example to provide further protection to the plurality of sensors.

[0129] It is to be understood that although the braided second layer 206 of Figure 2 is illustrated in combination with the helical first layer 204 and the twisted second layer 306 of Figure 3 is illustrated in combination with the first layer 304 formed of a lattice, any of the example first layers, second layers and third layers disclosed herein may be combined. For example, the structure of the second layer that is resistant to deformation along the axial direction of the array may be formed of one of: a plurality of fibres braided together around a first layer formed of one of: a resiliently compressible structure, for example comprising a helix or lattice; or a plurality of rigid members, for example comprising rings; a plurality of fibres twisted together around a first layer formed of one of: a resiliently compressible structure, for example comprising a helix or lattice; or a plurality of rigid members, for example comprising rings; or a plurality of fibres braided and twisted together around a first layer formed of one of: a resiliently compressible structure, for example comprising a helix or lattice; or a plurality of rigid members, for example comprising rings.

[0130] Figure 4 illustrates a schematic diagram of an example towed sensor array 400. The schematic diagram of Figure 4 shows a radial cross-section of the towed sensor array 400, which may be the same as example towed sensor array 200. In the radial cross-section view of the towed sensor array 400, the first layer 404 at least partially encloses (i.e., partially surrounds) the plurality of sensors 402. The second layer 406 at least partially encloses (or surrounds) the first layer 404. The third layer 408 encloses (or surrounds) the second layer 406 to insulate the elements of the towed sensor array 400 internal to the third layer 408 (e.g., at least the plurality of sensors 402) from at least fluid ingress from the surrounding medium in which the towed sensor array 400 is towed, and optionally fluid egress of the fill fluid disposed within the array. It is to be understood that while the radial cross-section of the towed sensor array 400 is illustrated in Figure 4 as circular, it may be differently shaped. For example, the radial cross-section may be substantially circular, elongated (i.e., elliptical or substantially elliptical), rectangular or squared-off etc.

[0131] Figure 5 illustrates a magnified view of a portion of the radial cross-section of an example towed sensor array, which may be similar to towed sensor array 400, or any of the example towed sensor arrays disclosed herein. In Figure 5, an inner surface 516 of the third layer 508 is illustrated, as is an outer surface 518 of the second layer 506. The first layer 504, second layer 506, third layer 508 and plurality of sensors 502 may be the same as described above with respect to any of the example towed sensor arrays described herein.

[0132] The inner surface 516 of the third layer 508 may comprise an interference structure. The interference structure may be configured to increase grip between the inner surface 516 of the third layer 508 and the outer surface 518 of the second layer 506. For example, the interference structure may be configured to increase friction between the inner surface 516 of the third layer 508 and the outer surface 518 of the second layer 506.

[0133] The interference structure may be any structure that acts to increase friction therebetween. The interference structure may be a structure (e.g., a surface structure or texture etc) that co-operates with a structure (e.g., a surface structure or texture etc) of the outer surface 518 of the second layer 506. For example, it may be that interference structure of the third layer 508 and the outer surface 518 of the second layer 506 form an interlocking structure. For example, the interference structure and the outer surface 518 of the second layer 506 may comprise corresponding (respective) features, such as recesses and protrusions, at coincident (or overlapping) positions on the respective layers. For example, at a particular radial position, the interference structure may comprise a recess, and the outer surface 518 of the second layer 506 may comprise a corresponding (i.e., co-operating) protrusion, or vice versa. It may be that the corresponding features of the interference structure and the outer surface 518 of the second layer 506 may co-operate to couple the third layer 508 to the second layer 506, for example by providing abutments or structures to resist axial movement of the third layer 508 with respect to the second layer 506. It may be that the corresponding features of the interference structure of the third layer 508 and the outer surface 518 of the second layer 506 may also co-operate to transfer load between the third layer 508 and the second layer 506, for example by way of the increase in friction between the respective surfaces of the layers and / or coupling etc. As a result, the interference structure may improve the transfer of load (e.g., may improve the efficiency of the transfer of load) exerted by external forces (such as drag) from the third layer 508 to the second layer 506 formed of the structure resistant to deformation along the axial direction of the array. As a result, the interference structure may further limit deformation of the towed sensor array.

[0134] It may be that the co-operating outer surface 518 of the second layer 506 may comprise the surface of the braid and / or twist of any of the second layers disclosed herein.

[0135] It may be that the interference structure is formed around the outer surface 518 of the second layer 506 to provide the corresponding (co-operating) features, as will be discussed further below. However, the interference structure may be formed in any way that provides the corresponding (co-operating) features.

[0136] Figure 6 illustrates a schematic diagram of functional blocks of an example towing configuration for a towed sensor array, such as any of the towed sensor arrays disclosed herein. The example towing configuration comprises a vehicle 602, a towed sensor array 604, and a connector 608. The vehicle 602 tows the towed sensor array 604 in a direction of travel 606. The direction of travel 606 may be parallel, or substantially parallel to the axial direction 610 of the towed sensor array 604. The connector 608 couples or otherwise connects the vehicle 602 to the towed sensor array 604. The connector 608 may be a tow cable.

[0137] The direction of travel 606 may be determined by the direction in which the vehicle 602 travels, i.e., the direction of travel 606 may be the direction of travel of the vehicle 602. Alternatively, it may be the direction of travel of the towed sensor array 604, which may be the same or substantially the same as the direction of travel of the vehicle 602. For example, the direction of travel 606 may be the primary component of the direction in which the towed sensor array 604 is travelling as a result of being towed. For example, it may be the towing direction, as opposed to a direction, or component thereof, that the towed sensor array 604 moves in as a result of currents etc. in the medium through which the array is towed.

[0138] The towed sensor array 604 has a leading end 612. The leading end 612 is the front end of the towed sensor array 604, as defined with respect to the direction of travel 606. For example, the leading end 612 is the end of the array closest to the vehicle 602 towing the towed sensor array 604. The towed sensor array 604 also has a trailing end 614. The trailing end 614 is the back end of the towed sensor array 604, as defined with respect to the direction of travel 606.

[0139] It may be that the plurality of fibres braided and / or twisted together around the first layer to form the second layer, comprises a number of fibres that is variable along the axial direction 610 of the towed sensor array 604. For example, the structure resistant to deformation along the axial direction of the array may comprise a variable number of fibres braided and / or twisted together. It may be that a portion of the second layer closer to, proximate to, or at, the leading end 612 of the towed sensor array 604 comprises a larger number of fibres than a portion of the second layer closer to, proximate to, or at, the trailing end 614 of the towed sensor array 604. It may be that a portion of the second layer closer to, proximate to, or at, the leading end 612 of the towed sensor array 604 may experience a higher load than a portion of the second layer closer to, proximate to, or at, the trailing end 614 of the towed sensor array 604 as a result of external forces, such as drag, acting on the towed sensor array 604. For example, as a result of hydrodynamical drag or aerodynamical drag from the towed sensor array 604 being towed through a liquid or gas, the load experienced by the towed sensor array 604 may be cumulative along the length, or axial extent, of the array. For example, the load exerted on the array at a given axial position may increase as a function of the length of the array extending beyond said axial position. As a result, at an axial position of the array closer to, proximate to, or at the leading end 612 of the towed sensor array 604, the array and layers thereof may experience more load than at an axial position closer to, proximate to, or at the trailing end 614 of the towed sensor array 604. It may be that by increasing the number of fibres in the plurality of fibres forming the second layer at an axial position closer to etc., the leading end 612 of the towed sensor array 604, the deformation along the axial direction 610 of the towed sensor array 604 may be better resisted, or limited. Alternatively, by decreasing the number of fibres in the plurality of fibres forming the second layer at an axial position closer to etc., the trailing end 614 of the towed sensor array 604, it may be that the resistance to deformation of the second layer along the axial direction 610 of the towed sensor array 604 can be provided, or maintained, more efficiently, e.g., with less material. It may also be that a variable number of fibres along the axial direction 610 of the towed sensor array 604 decreases the weight of the towed sensor array 604. A decrease in the weight of the towed sensor array may increase the flexibility in choice of the fluid 112, which provides buoyancy.

[0140] Several example methods of manufacturing the example towed sensor arrays disclosed herein are described below.

[0141] Figure 7 is a flow chart illustrating an example method of making or manufacturing a towed sensor array. In block 702, the method comprises providing a plurality of sensors spatially separated along an axial direction of the towed sensor array. In block 704 a first layer at least partially enclosing the plurality of sensors is provided. The provided first layer is formed of a structure resistant to deformation in a radial direction of the array. In block 706, a second layer at least partially enclosing the first layer is provided. The provided second layer comprises a structure resistant to deformation along the axial direction of the array formed of a plurality of fibres braided and / or twisted together around the first layer. In block 708, a third layer enclosing the second layer is provided. The provided third layer is a fluid insulating layer. In block 710, a fluid disposed therewithin is provided.

[0142] The respective plurality of sensors, first layer, second layer, third layer and fluid may be the same as, or similar to, any of the example sensors and respective layers described above with respect to Figures 1 to 6.

[0143] The fluid may be provided internal to the third layer. The fluid may be provided to surround, or immerse, the plurality of sensors, first layer and second layer of the towed sensor array. It may also be that the fluid is provided to surround, or immerse, a fluid damper disposed between the plurality of sensors and the first layer.

[0144] The first layer may be provided around the plurality of sensors. The second layer may be provided around the first layer. The third layer may be provided around the second layer.

[0145] The second layer may be provided directly around the first layer. The third layer may be provided directly around the second layer.

[0146] The second layer may be provided over the first layer as a continuous layer over the length of the towed sensor array, or at least along an axial extent of the array within which the plurality of sensors are disposed.

[0147] The third layer may be provided over the second as a continuous layer over the length of the towed sensor array, or at least along an axial extent of the array within which the plurality of sensors are disposed.

[0148] The first, second and third layers are provided along at least an axial length of the towed sensor array comprising the plurality of sensors, along the full axial length of the towed sensor array, along the full axial axial length of the towed sensor array and a tow cable coupled to the array, along the full axial axial length of the towed sensor array and over one or more vibration isolators, or along the full axial axial length of the towed sensor array, a tow cable coupled to the array and one or more vibration isolators, as described above.

[0149] Figure 8 is a flow chart illustrating an example method where providing the first layer comprises in block 806 winding a first layer around the plurality of sensors. The other blocks are similar to the correspondingly numbered blocks illustrated in Figure 7.

[0150] It may be that the first layer is helical or coiled, as described in some of the examples above, and the helical first layer may be wound around the plurality of sensors. The helical or coiled nature of the first layer may allow the first layer to be wound around the plurality of sensors instead of requiring that the first layer be provided over the full axial extent of the plurality of sensors, for example by pulling, sliding or stretching the first layer over the length of the plurality of sensors.

[0151] It may be that during manufacture (or assembly) the plurality of sensors are held at tension after they are provided. For example, it may be that the plurality of sensors, which may be provided with respect to a sensor positioning member, are wrapped around at least one drum to hold the array under tension during assembly. It may be that at least a length of the plurality of sensors provided to the array is exposed, to allow the first layer to be provided (e.g., wound around the sensors). The exposed length may be relatively short compared to the overall length of the assembled array. For example, the exposed length may be e.g., 10 metres, or less. The exposed length may be 3 metres. The first layer may be wound around the exposed length.

[0152] The first layer may be wound round the pluralities of sensors in individual segments. For example, the assembled first layer may comprise a plurality of first layer segments. It may be that individual segments are wound around the exposed length individually. For example, after a first segment of the first layer has been wound around a first exposed length, the length of the array with the first layer provided may be wound around a drum, for example a drum adjacent to a workbench, to hold the array at tension and expose a second length of the plurality of sensors for providing with a second segment of the first layer. It may be that the process of exposing a length of sensors, winding a first layer segment on to the exposed length of sensors, winding the length of the provided first layer around a drum and exposing a subsequent length of sensors may be repeated until segments of the first layer are provided to the full length of the array.

[0153] The method illustrated in Figure 8 may further comprise an optional block 807 between blocks 806 and 808, which comprises coupling(i.e., coupling together) respective segments of the provided first layer. For example, after a (second) segment of the first layer has been provided to a length of the array, it may be coupled to a previously provided (first) segment of the first layer. For example, the second segment may be heat sealed, glued or otherwise affixed to the first segment of the first layer. It may be that coupling the first layer segments provides a first layer that is continuous (or substantially), or unbroken (or substantially unbroken), along an axial extent of the assembled array within which the plurality of sensors are disposed.

[0154] Alternatively, it may be that the first layer that is provided to (e.g., wound around) the plurality of sensors is one continuous, e.g., unbroken, element, i.e., is already one continuous element.

[0155] It may be that as a result of the helical structure of the first layer, the winding of the first layer around the plurality of sensors allows the first layer to be provided to the array in a smaller work space (such as on a smaller workbench), which may allow the towed sensor array to be manufactured more efficiently. For example, it may be that the method of manufacturing described herein does not limit an assembled length of the array to, or approximately to, a length of a workspace (e.g., a workbench). For example, it may be that the method of manufacturing described herein enables a towed sensor array of length at least 200 metres to be manufactured on a 10 metre workbench.

[0156] Additionally, the helical structure of the first layer may allow the first layer to be provided to a damaged portion of an array more easily (i.e., with less complexity) in order to repair a damaged towed sensor array. It may also be that the providing of the first layer to the plurality of sensors by providing segments of the first layer to the plurality of sensors further increases the efficiency of the array manufacture or array repair.

[0157] Alternatively, the first layer may be provided to the plurality of sensors by fitting the resiliently compressible structure (e.g., lattice) or rigid members (e.g., rings), described above with respect to Figure 3, to the plurality of sensors. For example, by sliding the members over the length of the plurality of sensors, or by providing a resiliently compressible structure with an opening therein over the plurality of sensors, e.g., laterally, and further by sealing the resiliently compressible structure. Similarly to the helical first layer described above, it may be that the alternative methods comprise providing a plurality of segments of the first layer to the plurality of sensors, and may further optionally comprise coupling the respective first layer segments.

[0158] In optional block 804, the example method may further comprise forming the first layer (e.g, prior to providing it to, or around, the plurality of sensors). For example, in optional block 804 the method may comprise forming a helical first layer, or a plurality of segments of a helical first layer, for example 3 metre length segments (e.g., prior to winding the first layer, or first layer segments, around the plurality of sensors).

[0159] The first layer (e.g., the resiliently compressible structure, and / or the structure comprising a plurality of rigid members) may be formed by injection molding. Alternatively, the first layer may be formed by an additive manufacture process, such as 3D printing etc. However, it is to be understood that the first layer may be formed from any suitable process, for example including, but not limited to, casting or forming from solid.

[0160] Figure 9 is a flow chart illustrating an example method comprising in block 906 forming (and thereby providing) a second layer at least partially enclosing the first layer by braiding and / or twisting together a plurality of fibres around the first layer (and the plurality of sensors). The remaining blocks of Figure 9 are similar to the correspondingly numbered blocks illustrated in Figure 7 or Figure 8.

[0161] It may be that the number of braids and / or twists of which the second layer is formed may be selected to provide resistance to deformation of the second layer along the axial direction of the towed sensor array. It may be that the number of twists and / or number of braid interlaces per unit length of the second layer may be based on at least one of: a required resistance to deformation, the length of the total array, the speed of towing and a required flexibility of the array to bending.

[0162] It may be that the braid or twist is formed by twisting or braiding together two or more fibres, or subsets of fibres (yarns). For example, the plurality of fibres of the second layer may be grouped into subset of fibres to form yarns, and two or more yarns may be twisted or braided together. For example, the braid or twist may be formed by braiding or twisting together between 2 to 50 fibres (i.e., individual fibres) or yarns, for example between 4 to 30 fibres or yarns, for example, 10, 20 or 30 fibres or yarns. However, the number of fibres or yarns braided or twisted together is not so limited, and may, for example, comprise more than 50 fibres or yarns. It may also be that the number of fibres (e.g., the total number of fibres) or yarns, braided and / or twisted together may be selected to provide a required resistance to deformation along the axial direction of the array.

[0163] It may be that the twist is formed by twisting together an even number of fibres or yarns. For example, it may be that the twist is formed by twisting together an equal number of fibres or yarns in opposite directions. It may be that the twist is formed by twisting together fibres or yarns comprising a given number of fibres or yarns formed (e.g., twisted) into a helix of a first direction with fibres or yarns comprising the same number of fibres or yarns formed (e.g., twisted) into a helix of a second (e.g., opposite) direction.

[0164] It may be that braiding together the plurality of fibres (or yarns) comprises selecting the angle between the respective plurality of fibres (or yarns) based on a required resistance to deformation, e.g., elongation or stretching, of the second layer 206 along the axial direction of the array. For example, it may be that decreasing the angle between the respective fibres (or yarns) of the braid may reduce the deformation, i.e., stretching, of the second layer. The angle between respective fibres (or yarns) formed by braiding the fibres may be, approximately, 30 degrees.

[0165] It may be that the braid is formed by braiding together a plurality of fibres (or yarns) around the first layer 204 , for example to form a layer or shell around the first layer 204. The plurality of fibres are braided together in a given (e.g., single) dimension around the first layer 204.

[0166] It may be that the second layer is formed by twisting and / or braiding together, synthetic fibres, such as any of the synthetics fibres disclosed herein with respect to Figure 2.

[0167] Braiding or twisting the plurality of fibres (or yarns) may further comprise increasing or decreasing the number of fibres (or the number of yarns) in the braid or twist. For example, adding or removing fibres (or yarns) from the braid or twist as the braid is braided, or the twist is twisted.

[0168] In block 906 of Figure 9, the plurality of fibres (or yarns) are braided and / or twisted together in situ around the first layer, as opposed to, for example, being braised and / or twisted and then provided to, or around the first layer. In this way, the plurality of fibres (or yarns) may be braided and / or twisted directly to, or around, the first layer.

[0169] Once the first layer has been provided to the plurality of sensors, the plurality of sensors provided with the first layer may be fed from the drum (i.e., an assembly drum), around which it is wound, through a braiding and / or twisting apparatus. The plurality of fibres may be braided and / or twisted together around the first layer to form the second layer. The array with the second layer provided may then be wound on to a second drum (e.g., a storage drum).

[0170] It may be that as a result of the braiding and / or twisting of the second layer around the first layer, e.g., in situ around the first layer, the second layer may be provided to the array in a smaller work space (such as on a smaller workbench), for example because the plurality of fibres may be braided and / or twisted around an exposed length of the first layer fed off the assembly drum, e.g., without requiring the full length of the array to be presented for forming the second layer around the first layer. This may allow the towed sensor array to be manufactured more efficiently.

[0171] Braiding or twisting the plurality of fibres around the first layer may further comprise increasing or decreasing the number of fibres or the number of yarns in the braid or twist as the braid is braided or the twist is twisted. For example, adding or removing fibres or yarns from the braid or twist as the braid is braided, or the twist is twisted.

[0172] A given number of fibres or yarns may be braided and / or twisted around the first layer of the array proximate to, or at, the leading end of the array, and the number of fibres or yarns may be decreased as the braid is braided, or the twist it twisted, around the first layer (i.e., as the second layer is progressively provided along the axial direction of the array, for example starting at the leading end and finishing at the trailing end of the array), or vice versa, where the number of fibres or yarns is increased as the second layer is provided from the trailing end to the leading end.

[0173] Figure 10 is a flow chart illustrating an example method comprising in block 1008 providing the third layer by extruding the third layer on to the second layer. The remaining blocks of Figure 10 are similar to the correspondingly numbered blocks illustrated in any of Figures 7 to 9.

[0174] Extruding the third layer on to the second layer comprises extruding a third layer material, such as the plastic or thermoplastic materials disclosed herein, on to the second layer , e.g., on to an outer surface of the second layer. In this way, the third layer may be provided directly to, or around, the second layer. It may be that extruding the third layer material comprises heating a third layer material or providing a heated (or otherwise flexible) third layer material to an extruding apparatus and forcing the heated (or flexible) third layer material through the extruding element on to the surface of the second layer. For example, the heated (or flexible) third layer material may be forced between two dies that may comprise an inner die that guides the third layer material on top of the second layer and an outer die that shapes an outer layer of the third layer, and for example may control the thickness of the third layer.

[0175] It may also be that extruding the third layer optionally also comprises actively cooling, or otherwise setting, the third layer material.

[0176] It may be that extruding the third layer on to the second layer is a particularly efficient method of providing the third layer. For example, it may reduce the amount of third layer material required to provide the third layer to the array, e.g., by reducing waste, which may reduce the environmental impact of making the array.

[0177] Providing the third layer, for example by extruding the third layer on to the second layer, may further comprise providing the interference structure of the third layer.

[0178] It may be that extruding the third layer on to the second layer may form the interference structure of the inner surface of the third layer. For example, it may be that co-operating (e.g., surface) structures (e.g., corresponding recesses and protrusions) of the inner surface of the third layer (the interference structure) and the outer surface of the second layer are formed by extruding the third layer material on to the second layer. For example, the interference structure may be formed around the braid and / or twist of the second layer. The interference structure may comprise a negative-space structure formed with respect to the outer surface (e.g., braid and / or twist) of the second layer. For example, the interference structure may be formed of an imprint of the outer surface of the second layer on the inner surface of the third layer. Extruding the third layer on to the second layer to form the interference structure may further comprise causing the third layer material to flow over the outer surface of the second layer and / or in to the structures (or texture) of the outer surface of the second layer.

[0179] The interference structure may be provided by other means, for example stamping or other patterning techniques.

[0180] It may be that any of the example methods described herein further comprise providing a plurality of sensors spatially separated along the axial direction of a towed sensor array by spatially separating the sensors based on at least one characteristic of a signal to be detected. For example, spacing the respective sensors apart based on a frequency of a signal to be detected or for sample, spacing the respective sensors apart based on a sampling parameter of a signal to be detected, such as a Nyquist sampling frequency of a signal to be detected. The at least one characteristic of a signal to be detected may optionally be determined or received.

[0181] The respective sensors may be spaced apart by an irregular distance or interval, for example to provide diversity in signal sampling that may account for interference etc.

[0182] Within the scope of this application it is expressly intended that the various examples and alternatives set out in the preceding paragraphs, in the claims and / or in the description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all examples and / or features of any example can be combined in any way and / or combination, for example it may be that apparatus features correspond to method features or vice versa, unless such features are incompatible.

[0183] The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner.

[0184] In this specification, the phrase “at least one of A or B” and the phrase “at least one of A and B” should be interpreted to mean any one or more of the plurality of listed items A, B, etc., taken jointly and severally in any and all permutations.

[0185] Where functional units are described as separate hardware, any of the functionality may be integrated or combined into fewer hardware components.

Claims

1. Towed sensor array comprising:a plurality of sensors spatially separated along an axial direction of the towed sensor array;a first layer at least partially enclosing the plurality of sensors, wherein the first layer is formed of a structure resistant to deformation in a radial direction of the array;a second layer at least partially enclosing the first layer, wherein the second layer comprises a structure resistant to deformation along the axial direction of the array formed of a plurality of fibres braided and / or twisted together around the first layer;a third layer enclosing the second layer, wherein the third layer is a fluid insulating layer; anda fluid disposed therewithin.

2. The towed sensor array of claim 1, wherein at least one of the first layer, second layer and third layer extends unbroken along an axial extent of the towed sensor array within which the plurality of sensors of the array are disposed.

3. The towed sensor array of claim 1 or claim 2, wherein the structure resistant to deformation along the axial direction of the array of the second layer formed of the plurality of fibres braided and / or twisted together is a load distributing structure.

4. The towed sensor array of any one of claims 1 to 3, wherein the structure resistant to deformation along the axial direction of the array of the second layer formed of the plurality of fibres braided and / or twisted together is configured to internally balance torque.

5. The towed sensor array of claim 4, wherein the plurality of fibres twisted together around the first layer comprises an equal number of fibres twisted in opposite directions around the first layer.

6. The towed sensor array of any one of claims 1 to 5, wherein the plurality of fibres comprise synthetic polymers.

7. The towed sensor array of any one of claims 1 to 6 wherein the plurality of fibres of the second layer comprises a number of fibres that is variable along the axial direction of the towed sensor array.

8. The towed sensor array of claim 7, wherein a portion of the second layer proximate to a leading end of the towed sensor array comprises a larger number of fibres than a portion of the second layer proximate to a trailing end of the towed sensor array.

9. The towed sensor array of any one of claims 1 to 8, wherein the first layer is flexible to off-axis deformation of the towed sensor array.

10. The towed sensor array of any one of claims 1 to 9, wherein the first layer is formed of a resiliently compressible structure, and / or a structure comprising a plurality of rigid members.

11. The towed sensor array of any one of claims 1 to 10, wherein the structure of the first layer is helical.

12. The towed sensor array of any one of claims 1 to 11, wherein the first layer comprises a material suitable for additive manufacturing or injection molding.

13. The towed sensor array of any one of claims 1 to 12, wherein the third layer comprises a material that prevents fluid permeation therethrough.

14. The towed sensor array of any one of claims 1 to 13, wherein the fluid disposed therewithin is a liquid with a density less than water.

15. The towed sensor array of any one of claims 1 to 14, wherein an inner surface of the third layer comprises an interference structure.

16. The towed sensor array of claim 15, wherein the interference structure interlocks with the outer surface of the second layer.

17. The towed sensor array of any one of claims 1 to 16, wherein the each of the plurality of sensors are configured to detect changes in, or provide measurements of, one or more of: acoustic waves, magnetic fields, electric fields, pressure, temperature, motion, location, orientation and incident light.

18. The towed sensor array of any one of claims 1 to 17, wherein each of the plurality of sensors are regularly or irregularly spaced along the axial direction of the towed sensor array.

19. The towed sensor array of any one of claims 1 to 18, wherein each of the plurality of sensors are spaced apart by a respective distance based on at least one characteristic of a signal to be detected.

20. A method of manufacturing a towed sensor array comprising:providing a plurality of sensors spatially separated along an axial direction of the towed sensor array;providing a first layer at least partially enclosing the plurality of sensors, wherein the first layer is formed of a structure resistant to deformation in a radial direction of the array ;providing a second layer at least partially enclosing the first layer, wherein the second layer comprises a structure resistant to deformation along the axial direction of the array formed of a plurality of fibres braided and / or twisted together around the first layer;providing a third layer enclosing the second layer, wherein the third layer is a fluid insulating layer; andproviding a fluid disposed therewithin.

21. The method of claim 20, wherein providing the first layer comprises winding the first layer around the plurality of sensors.

22. The method of claim 20 or claim 21, wherein providing the first layer comprises providing segments of the first layer to the plurality of sensors.

23. The method of any one of claims 20 to 22, wherein providing the first layer comprises forming the first layer by an additive manufacturing process, or by an injection molding process.

24. The method of any one of claims 20 to 23, wherein the plurality of fibres are braided and / or twisted directly around the first layer provided to the plurality of sensors.

25. The method of any one of claims 20 to 24, wherein providing the third layer comprises extruding a third layer material on to the second layer.

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