Apparatus and method for enhancing detection for events in fluid pipes

Abstract

An apparatus (100) for monitoring a fluid pipe (1), the apparatus comprising a cable (11) disposed within the pipe (1). The cable (11) comprises a plurality of sensing fibres (10, 502, 508, 510), wherein the plurality of sensing fibres (10, 502, 508, 510) are spliced together (504, 512, 506) at their respective ends to form a continuous looped configuration (500) within the cable (11). The apparatus further comprises a light emitter (101) for introducing light pulses into the continuous looped configuration (500), a light detector (110) for detecting backscattering of the light pulses from the continuous looped (configuration 500) and outputting a backscattering signal in response thereto as well as a processing unit (103) configured to process the backscattering signal to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe (1).

Description

[0001] Apparatus and Method for Enhancing Detection for Events in Fluid Pipes

[0002] Technical Field of the Invention

[0003] The present invention relates to monitoring of fluid pipes. In particular, the present invention is directed to monitoring of fluid pipe integrity, the monitoring of fluid flow within a fluid pipe and / or leak detection. The present invention further relates to an apparatus, a cable and a method for monitoring a fluid pipe as well as a network comprising one or more pipes monitored using the apparatus, the cable or the method of the present invention.

[0004] Background to the Invention

[0005] Many modem services rely upon a network of pipes to carry or distribute fluids. Examples include fresh water, waste water and sewage, and fuels such as oil or gas. It is common to monitor the operation of the network and the condition of pipes. In this manner, blockages, leaks or other issues can be identified and scheduled for repair.

[0006] Where pipes are provided above ground, monitoring may be achieved by visual inspection of the pipe exterior. In many cases, pipes are not accessible to visual inspection, being buried underground. Accordingly, pressure / audio sensors or the like may be utilised to detect vibrations of the pipe and thereby provide information on conditions within a pipe.

[0007] In particular implementations, distributed acoustic sensing (DAS) otherwise referred to as distributed vibration sensing (DVS) has been used for monitoring pipes. DAS involves the detection of backscattering of light pulses introduced into an optical fibre. The time of arrival and intensity of the backscattered light is measured for each pulse, the time at which the backscattered light is detected being related to the distance along the fibre the light has travelled before being scattered. Subsequent changes in the reflected intensity of successive pulses from a common region of the fibre correspond to variations in the strain applied to the fibre at that region, for instance due to vibrations experienced by the region of fibre. In this manner, the DAS fibre can act as a plurality of virtual microphones along the length of the fibre and can locate events causing acoustic signals down to an accuracy of around 1 meter. One example of this technique is our prior application WO2019 / 166809.

[0008] Whilst DAS is effective in many situations for monitoring flow within a pipe and detecting leaks, additional information on the condition of the pipe can be obtained by carrying out DSS and / or DTS using a sensing fibre. DTS may help identify adiabatic cooling in a gaseous fluid in the vicinity of a leak candidate and / or other temperature change indicative of a flow of heat between a pipe and surrounding ground of a different temperature. DSS may help identify changes in strain along the length of a pipe indicative of a potential for future failure of the pipe.

[0009] There are some factors that can limit the ability to monitor the condition of the pipe. In particular, small leaks may generate relatively small signals which cannot be easily detected using DSS, DTS or DAS sensing. Additionally, external noise and vibration can be transmitted through the pipe, masking any signals. This might be particularly common in urban areas where there are multiple other sources of mechanical vibration including traffic, industry and the like. Other examples may include flow noise, pump noise and similar. These high-noise or high-vibration environments can interfere with the accuracy of sensing fibres used in DAS, DTS and DSS.

[0010] In high- noise or high- vibration environments, the signal-to-noise ratio within the backscattering signal from one or more sensing fibres may be insufficient to successfully identify a detected event as a particular event, such as a leak. This challenge necessitates the development of methods to improve detection accuracy and confidence by enhancing the signal-to-noise ratio, enabling more effective noise cancellation and similar techniques. Moreover, utilizing a plurality of sensing fibres within the cable, each connected to a separate analyser at one end, can be costly and computationally inefficient. This inefficiency is particularly evident when noise levels that degrade the signal are periodic — occurring only intermittently — or are localized to specific sections of the pipe, rather than being uniformly distributed along its entire length. Therefore, there is a need for more efficient and cost-effective approaches to monitoring that can dynamically adapt to varying noise conditions while maintaining high detection accuracy and detection confidence levels. It is an object of the present invention to provide methods and apparatus which at least partially overcomes or alleviates at least some of the above problems.

[0011] Summary of the Invention

[0012] According to a first aspect of the present invention, there is provided an apparatus for monitoring a fluid pipe. The apparatus may comprise a cable disposed within the pipe. The cable may comprise a plurality of sensing fibres. The plurality of sensing fibres may be spliced together at their respective ends to form a continuous looped configuration within the cable. The apparatus may comprise a light emitter. The light emitter may be suitable for introducing light pulses into one end of the continuous looped configuration. The apparatus may comprise a light detector. The light detector may be suitable for detecting backscattering of the light pulses from the plurality of sensing fibres. The light detector may be suitable for outputting a backscattering signal in response to detecting backscattering of the light pulses from the plurality of sensing fibres. The apparatus may comprise a processing unit. The processing unit may be configured to process the backscattering signal to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe. The processing unit may be configured to analyse the backscattering signal from the plurality of sensing fibres. The processing unit may be configured to analyse the backscattering signal from the plurality of sensing fibres to improve detection of the particular events.

[0013] The processing unit may be configured to analyse the backscattering signal from some or all of the plurality of sensing fibres. Analysing the backscattering signal from the plurality of sensing fibres may comprise comparing and / or aggregating the backscattering signal from some or all of the plurality of sensing fibres. Comparing and / or aggregating data (e.g., the backscattering signal) from the plurality of sensing fibres may comprise integrating and / or overlaying channel specific data from some or all of the plurality of sensing fibres at predefined points along the respective fibres.

[0014] The configuration of the plurality of sensing fibres spliced together at their respective ends to form a continuous looped arrangement within the cable enables a comparative and / or aggregate analysis of the backscattering signals from some or all of the fibres in the looped configuration. Comparing and / or aggregating the backscattering signals from some or all of the fibres in the looped configuration significantly enhances the quality of the backscattering signal (e.g., by enhancing the signal-to-noise ratio within the signal), thereby facilitating a more precise and accurate identification of individual backscattering signal features characteristic of particular events within or in the vicinity of the fluid pipe. This enhancement leads to increased confidence in the detection and localization of the specific events.

[0015] Furthermore, the time-domain nature of the backscattering signal originating from each fibre in the looped configuration allows for the acquisition of backscattering signal features associated with a particular event at different times. This is because it takes the light pulses a predetermined amount of time to travel through each sensing fibre within the looped configuration. Accordingly, the backscattering of light pulses from the respective sensing fibres is detected at the processing unit at different times. This temporal variation provides the advantage of observing the evolution of backscattering signal features (caused by the particular event) over time, thereby enabling a more reliable identification and analysis of the particular event.

[0016] The particular event may comprise one or more of: a leak in the pipe, a change in external conditions or other events proximal to the pipe, the pipe bursting, a structural deformation of the pipe, a change in fluid flow within the pipe, a change in fluid pressure within the pipe, a blockage in the pipe, and / or valve operation. The skilled person will understand that other events may also be detected.

[0017] Processing the backscattering signal may comprise comparing the identified backscattering signal features within the backscattering signal against expected backscattering signal features of particular events to identify the particular event. By mapping the identified backscattering signal features to expected backscattering signal features of particular events, the processing unit can classify a detected event as the particular event (e.g., a leak) with varying levels of confidence. The levels of confidence associated with classifying a detected event as a particular event may depend on the specific external and / or internal pipe conditions, which will themselves affect background noise or signal-to-noise ratio.

[0018] The change in external conditions proximal to the pipe may comprise ground movement or soil displacement near the pipe. Such movements may be indicative of landslides, construction activity, or natural settling of the ground, all of which may impact the integrity of the pipe. The change in external conditions proximal to the pipe may comprise detection of temperature changes in the surrounding environment, which could indicate seasonal variations, underground fires, or proximity to other heatemitting infrastructure. The change in external conditions proximal to the pipe may comprise vibrations caused by nearby machinery or heavy vehicle traffic. Advantageously, detecting these changes in external conditions allows for proactive maintenance and risk mitigation, ensuring the continued safe operation of the fluid pipe.

[0019] A change in internal conditions to the pipe may cause increased background noise, which may cause the analyser to experience a dynamic range overload within a particular section or length of the sensing fibre. These may include increased local background noise due to pump operation, partial valve closure or increased flow velocity (this causing for instance increased fluid flow noise, increased noise from the flow acting on the surface of the sensing fibre, or increased flow causing the sensing fibre to move or otherwise vibrate within the pipe).

[0020] The valve operation may comprise opening of a valve to allow fluid to flow through a previously closed section of the pipe. The valve operation may comprise closing of a valve to stop fluid flow. The valve operation may comprise partial valve adjustments, such as throttling to control the flow rate. Monitoring these valve operations ensures efficient and safe management of fluid distribution within the pipe system. Pump parameters, such as pump speed and temporal pump operation also may be monitored to ensure efficient and safe management of fluid distribution within a pipe.

[0021] The structural deformation of the pipe may comprise bending of the pipe due to external pressure or ground movement. The structural deformation of the pipe may comprise corrosion or erosion over time that can thin the pipe walls. The structural deformation of the pipe may comprise buckling due to thermal expansion or contraction. Monitoring these structural deformations is crucial for early detection of potential failures, ensuring timely maintenance and prevention of more serious damage.

[0022] The continuous looped configuration may comprise a plurality of sensing fibres arranged substantially in parallel to each other along the longitudinal axis of the cable. Each sensing fibre may be spliced at one of its ends to an end of the adjacent sensing fibre to form the continuous loop-back configuration. Specifically, the end of one fibre may be spliced, or connected, to the beginning of the next fibre, creating a series of end-to-end connections that result in a continuous looped path.

[0023] The plurality of sensing fibres in the cable may be interconnected in this manner, ensuring that light pulses introduced into one end of the continuous looped configuration travel through the entire length of the looped configuration end exit through the other end of the continuous looped configuration. This looped configuration runs substantially parallel to the length of the cable and allows light pulses introduced at one end to travel through the entire length of the looped configuration and return through backscattering. The fibres are arranged in such a way that they cover the same segment of the pipe multiple times, enhancing the system's ability to detect and analyse events along the monitored section of the pipe. One or both ends of continuous looped configuration may be connected to the light emitter, the light detector and / or the processing unit. In some embodiments, the continuous looped configuration may be called a looped end-to-end concatenation.

[0024] By providing the sensing fibres within the pipe, good acoustic coupling between the sensing fibres and the pipe (and any fluid within the pipe) is assured and the sensing fibres can be used to detect pipe condition information including pressure waves, negative pressure waves, flow noise, temperature changes, strain changes within a body of the pipe, orifice noise, external noise proximal to the pipe or the like in a known manner.

[0025] The plurality of sensing fibres may comprise an odd number of sensing fibres. The plurality of sensing fibres may comprise an odd number of fibres due to the specific arrangement of the continuous looped configuration within the cable. In some embodiments, a sensing fibre runs from one end of the pipe to the other, with the looped configuration positioned somewhere along its length. When a loop is created (in the looped configuration), it may result in three sensing fibres running in parallel along at least a section of the cable: the original fibre and two additional fibres formed by the loop. If two loops are created, there may be five sensing fibres running in parallel along at least one section of the cable. This pattern may continue, with each additional loop adding two more fibres to the parallel configuration. The odd number of fibres may allow for efficient utilization of the sensing fibres and ensures comprehensive coverage and signal detection along the length of the pipe.

[0026] A skilled person would recognise that the cable may comprise any suitable number of sensing fibres. Additionally, the continuous looped configuration may comprise any number of sensing fibres. In some embodiments, the cable and / or the continuous looped configuration may comprise at least 3 sensing fibres, at least 5 sensing fibres, at least 7 sensing fibres, at least 9 sensing fibres, at least 11 sensing fibres, at least 13 sensing fibres or any number of fibres suitable in any given circumstance. In some embodiments, the plurality of sensing fibres in the looped configuration may comprise an even number of sensing fibres.

[0027] The cable may comprise a fibre optic cable. The cable may comprise an external protective sheath. The external sheath may be opaque. The plurality of sensing fibres may be located within (or encased within) the external sheath.

[0028] Each sensing fibre may be a single mode optical fibre, some sensing fibres within a cable may additionally be of multi-mode format. In some embodiments, each sensing fibre may be provided with an individual sheath. Each individual sensing fibre sheath may additionally be opaque.

[0029] In some embodiments, the light emitter, light detector module and processing unit may be integrated into an analyser or an analyser system. Such an analyser or an analyser system may be provided with a user interface. The user interface may enable a user to control operation of the apparatus and / or review indications relating to the condition of the monitored pipe.

[0030] In the context of the present application, the term ‘fluid’ may refer to any material, liquid or gaseous, including and fuels such as oil or gas or associated distillates, additionally in industrial uses which may include mining and similar, the invention may more specifically refer to a primarily water-based fluid, such as potable water, pre-treatment water, wastewater or water-based slurries.

[0031] Similarly, in the context of the present application, the term ‘pipe’ may refer to any fluid conduit used to convey a fluid (gas, liquid or a mixture including a slurry) between two points, spaced apart at or below local ground level. In particular, the ‘pipe’ may traverse at a relatively regular displacement from local ground level, without requiring the ‘pipe’ to be horizontal.

[0032] The light emitter may be a laser. The emitted light may any suitable wavelength for transmission along and backscattering within the sensing fibres. The light emitter and light detector may be integrated into a light transceiver unit. Suitable wavelengths are most typically in the infra-red spectrum.

[0033] In some embodiments, all of the sensing fibres of the plurality of sensing fibres (within the continuous looped configuration) may be identical. For example, all of the sensing fibres of the plurality of sensing fibres may have substantially the same sensitivity and / or response in a predetermined frequency range.

[0034] In some embodiments, this uniformity offers distinct advantages. With identical fibres, the backscattering signals originating from the sensing fibres in the continuous looped configuration can be directly compared to enhance the signal-to-noise ratio.

[0035] At least one sensing fibre of the plurality of sensing fibres (within the continuous looped configuration) may have a different sensitivity than the other sensing fibres of the plurality of sensing fibres. At least one sensing fibre of the plurality of sensing fibres may have a different response in a predetermined frequency range than the other sensing fibres of the plurality of sensing fibres.

[0036] The sensitivity may comprise an acoustic sensitivity, a sensitivity to strain induced vibrations and / or sensitivity to temperature variations.

[0037] Having at least one sensing fibre within the continuous looped configuration that has a different sensitivity than the other sensing fibres offers significant technical advantages. Aggregating and / or comparing data from fibres with different sensitivities can enhance the detection capabilities of the system in various scenarios. For instance, certain events may produce weak acoustic signals that can only be detected by a fibre with higher acoustic sensitivity. Conversely, in high-noise environments, such as when a pipe is situated close to a busy road, a backscattering signal from a fibre with high sensitivity may oversaturate the analyser. In such cases, a backscattering signal from a fibre with a lower sensitivity may allow the analyser to successfully identify signal characteristics of a particular event.

[0038] Additionally, having fibres with different frequency responses can be particularly beneficial. One sensing fibre may be especially sensitive in a specific frequency range associated with a particular event, such as a small leak, while another fibre may be especially sensitive in a different frequency range associated with another type of event, such as a larger leak. This variation in frequency response allows the analyser to accurately identify and characterize a wide range of events by leveraging the distinct sensitivity and frequency response profiles of the fibres. By comparing and aggregating the data from these fibres, the system can more reliably detect and analyse events, leading a more comprehensive understanding of the pipe's condition.

[0039] Advantageously, it is desirable to provide multiple sensing fibres for redundancy, such fibres may additionally be optimised for differing sensitivity. The sensing fibres may be distributed within the cable in such a manner to ensure good quality sensing in multiple directions relative to the cable. For example, the sensing fibres may be packed in a regular array across the cable in a direction transverse to the cable axis.

[0040] In some embodiments, the sensing fibres of the plurality of sensing fibres may be provided in a linear formation within the cable. In such embodiments, each sensing fibre may lie substantially parallel to the cable axis. In other embodiments, the sensing fibres may be provided in a helical formation centred on the cable axis. A helical formation can improve the structural stability of the cable. Furthermore, a helical formation beneficially ensures that individual sensing fibres have exposure to detectable events in all directions around the cable over the length of the cable.

[0041] In some embodiments, the plurality of sensing fibres of the continuous looped configuration may each have a different sensitivity. In some embodiments, the plurality of sensing fibres of the continuous looped configuration may each have a different response in a predetermined frequency range.

[0042] The one or more sensing fibres of the plurality of sensing fibres within the looped configuration may have a lower sensitivity than the other sensing fibres due to being positioned further away from an exterior of the cable than the other sensing fibres. The one or more fibres with a lower sensitivity may be positioned closer to a central axis of the cable.

[0043] Positioning one or more of the sensing fibres closer to the exterior of the cable may increase that fibre's sensitivity as it places the sensing fibre in closer proximity to the external forces within the fluid pipe. The shorter distance between the exterior of the cable and the one or more sensing fibres may effectively improve the sensitivity of the one or more sensing fibres. This positioning may allow the sensing fibre to more directly and accurately detect physical changes such as acoustic vibrations, temperature fluctuations, and mechanical stresses. When a sensing fibre is located near an external surface of the cable, it experiences greater and more immediate interactions with external stimuli, leading to stronger backscattering signal features within a backscattering signal. This enhanced sensitivity may be crucial for detecting subtle events and changes in conditions around the pipe, ensuring more precise and reliable monitoring. By strategically placing one or more fibres (for use in the looped configuration) closer to the cable's exterior, the apparatus can improve its responsiveness and effectiveness in capturing critical data necessary for pipeline monitoring.

[0044] The one or more sensing fibres of the plurality of sensing fibres may have a different sensitivity due to their inherent structural properties. These inherent properties may include variations in material composition, chemical composition and / or the sensing fibre structure.

[0045] The plurality of sensing fibres may each comprise an optical fibre. The optical fibre may comprise a core and an external layer surrounding the core. The optical fibre may optionally comprise an opaque sheath encasing the external layer.

[0046] The one or more sensing fibres of the plurality of sensing fibres may comprise scoring or etching on an outer surface of the external layer. The scoring or etching may cause the one or more sensing fibres to have a different sensitivity.

[0047] In some embodiments, an outer surface of the external layer surrounding the core may comprise micro-etching patterns to increase the fibre’s sensitivity to strain, acoustic and pressure changes. Scoring with specific patterns may also create localized points that enhance the fibre’s response to vibrations or acoustic signals.

[0048] The one or more sensing fibres of the plurality of sensing fibres may comprise different thicknesses of the external layer. The different thicknesses of the external layer may cause the one or more sensing fibres to have different sensitivities. In some embodiments, one or more sensing fibres of the plurality of sensing fibres may comprise external layers manufactured from different materials.

[0049] The variations in the thickness of the external layers may affect the fibres' interactions with external stimuli. A thicker external layer may provide a greater mechanical protection and reduce sensitivity to external perturbations, making it suitable for environments with high levels of noise or vibration. Conversely, a thinner external layer allows the sensing fibre to be more responsive to subtle changes in temperature, pressure, or strain, enhancing its ability to detect fine backscattering signal features in quieter environments.

[0050] The one or more sensing fibres of the plurality of sensing fibres may comprise layers having different chemical compositions. The different chemical compositions of the layers may cause the one or more sensing fibres to have different sensitivities.

[0051] The distinct chemical compositions of the layers within the plurality of sensing fibre may influence the fibres' interactions with external environmental factors such as temperature, pressure, and mechanical stress. In one embodiment, the layers may be made out of a doped silica material. Varying the levels of impurity within the silica material may enhance or reduce the fibre’s sensitivity. Advantageously, by employing layers with different chemical compositions, the apparatus may tailor the sensitivity of each sensing fibre within the looped configuration to specific types of events or environmental conditions, thereby improving the overall accuracy and reliability of pipeline monitoring.

[0052] The processing unit may be configured to switch to analysing the backscattering signal from one or more different sensing fibres of the plurality of sensing fibres in response to detecting that one or more sensing fibres of the plurality of sensing fibres are oversaturated. In one example, the processing unit may be configured to analyse the backscattering signal from an initial set of sensing fibres of the plurality of sensing fibres. The initial set of sensing fibres may comprise all of the sensing fibres of the plurality of sensing fibres. The processing unit may subsequently detect that one or more of the sensing fibres of the plurality of sensing fibres have become oversaturated (i.e., the backscattering signal from one or more of the sensing fibres is oversaturating the analyser). In response to detecting that one or more of the sensing fibres of the plurality of sensing fibres has become oversaturated, the processing unit may be configured to switch to analysing the backscattering signal from a different set of sensing fibres of the plurality of sensing fibres. The different set of sensing fibres may be different to the initial set of sensing fibres of the plurality of sensing fibres. For example, the processing unit may stop analysing the backscattering signal from any of the sensing fibres which have been overs aturated.

[0053] In some embodiments, the processing unit may be configured to switch to analysing the backscattering signal from only one of the sensing fibres of the plurality of sensing fibres.

[0054] Adaptively selecting just one of the sensing fibres of the plurality of sensing fibres for analysis may allow events to be better resolved. For instance where a more sensitive fibre of the plurality of sensing fibres is oversaturated, then a less sensitive fibre from the looped configuration may provide useful results, and conversely where a signal is indeterminate or low in comparison with background noise then a more sensitive fibre within the looped configuration may be adaptively selected.

[0055] The cable may comprise at least two sections along its longitudinal axis. More specifically, the cable may comprise a first section comprising at least one individual sensing fibre. The cable may comprise a second section comprising the continuous looped configuration. An end of the individual sensing fibre may be connected to a first end of the continuous looped configuration.

[0056] The at least one individual sensing fibre may comprise a single standalone sensing fibre. The at least one individual sensing fibre may not form a part of (i.e., may be separate from) the continuous looped configuration. The first section may comprise multiple individual sensing fibres, but only one of these individual sensing fibres may be connected to (or spliced to) the continuous looped configuration. In this manner, the individual sensing fibre and the continuous looped configuration may effectively form one continuous sensing fibre structure. The light emitter may be configured to introduce light pulses into one end of the individual sensing fibre. The light pulses may be subsequently configured to travel through the individual sensing fibre and the continuous looped configuration. The light detector may be configured to detect backscattering of the light pulses from both the individual sensing fibre and the continuous looped configuration and output a backscattering signal in response thereto. The processing unit may be configured to process this backscattering signal (from both the individual sensing fibre and the continuous looped configuration) to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe. The processing unit may also be configured to compare and / or aggregate data from the plurality of sensing fibres of the continuous looped configuration to improve detection of the particular events. In another embodiment the processing unit may select a single fibre from the looped configuration for analysis.

[0057] Having the cable configured with at least two distinct sections — one with at least one individual sensing fibre and another with a continuous looped configuration — offers significant advantages. The looped configuration may be strategically positioned in locations along the pipe that experience high noise levels, thereby benefiting from an improved signal-to-noise ratio within the backscattering signal. This placement ensures that areas with substantial external interference, such as sections near busy roads or industrial machinery, are provided with enhanced monitoring capabilities. Enhanced monitoring capabilities may also be required for sections with low fluid pressure (e.g., sections which always experience low fluid pressure or sections which sporadically experience low fluid pressure). Conversely, the relatively quiet sections of the pipe, which do not require the same level of noise mitigation, can be effectively monitored using a single sensing fibre. Adaptive selection of analysis of a single fibre from the looped section may also be advantageously used. This approach not only optimizes the use of resources by deploying the more complex and resource-intensive looped configuration only where necessary but also enhances the overall quality of the backscattering signal in problematic pipe sections. The cable may comprise three sections along its longitudinal axis. A first section and a third section may each comprise an individual sensing fibre. A second section may comprise the continuous looped configuration. An end of the single sensing fibre of the first section may be connected to the first end of the continuous looped configuration. A second end of the continuous looped configuration may be connected to an end of the single sensing fibre of the third section.

[0058] The first and third sections may comprise multiple individual sensing fibres, but only one of these individual sensing fibres may be connected to (or spliced to) the continuous looped configuration. In this manner, the individual sensing fibres and the continuous looped configuration may effectively form one continuous sensing fibre structure. The light emitter may be configured to introduce light pulses into one end of the individual sensing fibre of the first section. The light pulses may be subsequently configured to travel through the individual sensing fibre of the first section and the continuous looped configuration and the individual sensing fibre of the third section. The light detector may be configured to detect backscattering of the light pulses from the individual sensing fibre of the first section, the continuous looped configuration and the individual sensing fibre of the third section and output a backscattering signal in response thereto. The processing unit may be configured to process this backscattering signal (from the individual sensing fibres of the first section and the third section as well as the continuous looped configuration) to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe. The processing unit may also be configured to compare and / or aggregate data from the plurality of sensing fibres of the continuous looped configuration to improve detection of the particular events.

[0059] In some embodiments, the first section may be located at the start of the cable run, the second section may be located centrally along the cable run, and the third section may be located at the end of the cable run. The exact location of the looped configuration may be determined on a case-by-case basis, according to the noise levels and other environmental factors along the cable run. A skilled person will recognize that the cable may comprise any number of sections and any number of looped configurations and individual sensing fibres, arranged in any order as needed to suit the specific requirements of the pipe and its surroundings. For example, the cable may comprise more than three sections, each comprising either the looped configuration or the individual sensing fibre.

[0060] The ends of the individual sensing fibres and the first end and the second end of the continuous looped configuration may be spliced together using optical splicing techniques. The optical splicing techniques may comprise a fusion splice, a mechanical splice, and / or a connector splice.

[0061] The splicing of the plurality of sensing fibres which form the continuous looped configuration may comprise a fusion splice, a mechanical splice, or a connector splice.

[0062] Fusion splicing may involve melting the fibre ends together to form a single, continuous fibre. Advantageously, fusion splicing may provide the lowest insertion loss, typically around 0.1 to 0.05 dB. Additionally, fusion splicing may provide the most reliable joint, ensuring minimal signal attenuation and high-quality backscattering signals. Mechanical splicing may comprise aligning and holding the fibres together using a mechanical fixture and / or an optical gel. Mechanical splicing may offer a faster and easier process than fusion splicing, with an insertion loss typically around 0.2 to 0.75 dB, without the need for specialized equipment, mechanical splicing may include the technique of an angled cleave to each fibre in order to minimise reflections form the junction. Connector splicing may comprise connecting the fibre ends using optical connectors such as E2000 APC connectors. Advantageously, connector splicing allows for easy and quick connection and disconnection, providing flexibility and modularity for fibres to be easily replaced or reconfigured as needed. Connector splices may typically have an insertion loss around 0.2 to 0.5 dB. By employing these splicing techniques, the apparatus can ensure optimal performance, flexibility, and ease of maintenance, tailored to the specific requirements and conditions of the monitoring environment.

[0063] A section of the cable may comprise both a separate individual sensing fibre and the continuous looped configuration. The individual sensing fibre may be configured to run independently alongside the looped configuration within the section of the cable. The separate individual sensing fibre and the continuous looped configuration may be positioned in parallel to each other along the longitudinal axis of the cable.

[0064] In this embodiment, the individual sensing fibre may run alongside the looped configuration, allowing both types of fibre arrangements to coexist within the same section of the cable. The individual sensing fibre may not be directly connected to the looped configuration. Advantageously, this arrangement allows both types of fibre arrangements to operate independently within the same cable section.

[0065] The apparatus may further comprise a switch. The switch may be operable to select use of either the individual sensing fibre or the continuous looped configuration. An end of the individual sensing fibre and an end of the continuous looped configuration may each be connected to the switch. The switch may be controlled by the processing unit. The processing unit may be configured to control an operation of the switch. More specifically, the processing unit may instruct the switch to cause the light emitter to switch between introducing the light pulses into the individual sensing fibre and the continuous looped configuration. The processing unit may instruct the switch to cause the light detector to switch between detecting backscattering of the light pulses from individual sensing fibre and the continuous looped configuration.

[0066] If the individual fibre is selected, the light emitter may be configured to introduce light pulses into one end of the individual fibre. If the individual fibre is selected, the light detector may be configured to detect backscattering of the light pulses from the individual sensing fibre and output a second backscattering signal in response thereto. If the individual fibre is selected, the processing unit may be configured to processes the second backscattering signal from the individual sensing fibre.

[0067] If the continuous looped configuration is selected, the light emitter may be configured to introduce light pulses into one end of the continuous looped configuration. If the continuous looped configuration is selected, the light detector may be configured to detect backscattering of the light pulses from the continuous looped configuration and output a first backscattering signal in response thereto. If the continuous looped configuration is selected, the processing unit may be configured to processes the first backscattering signal from the continuous looped configuration, which may then process adaptively all, several of just one for the sensing fibres of the plurality of sensing fibres for analysis based on internal and external pipe conditions.

[0068] The switch may be controlled adaptively based on detected backscattering signal characteristics, conditions within or in a vicinity of the fluid pipe, predefined sensing requirements, or pipe hydraulic operating parameters which may change over time.

[0069] More specifically, the processing unit may be configured to control the operation of the switch based on detecting that a signal-to noise ratio is below a predetermined threshold, detecting that the individual sensing fibre and / or one or more of the sensing fibres within the continuous looped configuration are oversaturated, or detecting an inconclusive event.

[0070] In one embodiment, the processing unit may be configured to switch between the looped configuration and the individual sensing fibre based on conditions within or in the vicinity of the fluid pipe. For example, at night, when there is little to no traffic, the signal-to-noise ratio may be acceptable for the apparatus to operate effectively using the single sensing fibre. During these quieter periods, the apparatus may efficiently utilize the single fibre, conserving computational resources and maintaining effective monitoring. However, during the day, when noise levels increase due to traffic or other environmental factors, the signal-to-noise ratio may degrade. In such scenarios, the processing unit may switch to the continuous looped configuration, which offers enhanced backscattering data quality by improving the signal-to-noise ratio. In one example, the processing unit may be configured to switch between the looped configuration and the individual sensing fibre in response to detecting low fluid flow within the fluid pipe and / or detecting a high operating fluid pressure within the pipe. Advantageously, this adaptive switching ensures optimal performance of the apparatus under varying environmental conditions.

[0071] In one embodiment, the processing unit may be configured to switch between the looped configuration and the individual sensing fibre based on backscattering signal characteristics. The processing unit may be configured to switch to the looped configuration upon determining that the signal-to-noise ratio has fallen below a predetermined threshold. The processing unit may be configured to switch to the use of the continuous looped configuration based on determining that a backscattering signal feature is indicative of an inconclusive event, or in the event of determination of oversaturation

[0072] The processing unit may employ machine learning algorithms to determine when to switch between the looped configuration and the individual sensing fibre. By analysing backscattering data collected over time, the machine learning algorithms may be configured to learn to predict noise patterns and other environmental factors that affect signal quality. These algorithms can then inform the processing unit's decisions, allowing it to proactively switch between the individual sensing fibre and the continuous looped configuration as needed. This intelligent control mechanism improves the system's efficiency and effectiveness, ensuring continuous and reliable monitoring of the fluid pipe.

[0073] In some embodiments, a section of the cable comprising both a separate individual sensing fibre and the continuous looped configuration may be connected to the first section and / or the third section (which comprise the individual sensing fibre) and / or the second section (which comprises the continuous looped configuration).

[0074] The light detector module may be configured to detect backscattering of the light pulses in multiple different sensing modes. The processing unit may be configured to control the light detector module to switch between the multiple different sensing modes.

[0075] The multiple different sensing modes may comprise a distributed acoustic sensing (DAS) mode. The multiple different sensing modes may comprise a distributed strain sensing (DSS) mode. The multiple different sensing modes may comprise a distributed temperature sensing (DTS) mode.

[0076] The sensing fibres (i.e., the plurality of sensing fibres within the continuous looped configuration and / or the individual sensing fibre) may comprise any sensing fibres suitable for use in DAS, DTS and / or DSS sensing. The sensing fibres may comprise any optical fibres that are suitable for transmitting light.

[0077] Switching the detection modes in the apparatus for monitoring the fluid pipe offers significant advantages in increasing the confidence level of detecting and classifying particular events, such as leaks. By switching between multiple sensing modes, the system can gather diverse types of data, each providing unique insights into the physical state of the pipe. This multimodal approach allows for cross-verification of detected inconclusive events, enhancing the accuracy and reliability of event identification.

[0078] The DAS mode may comprise a sensing technique utilized within the monitoring apparatus to detect acoustic signals and vibrations along the length of the sensing fibres (e.g., the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration). In the DAS mode, Rayleigh scattering within the sensing fibre may be leveraged for sensing purposes.

[0079] In the DAS mode, the processing unit may be configured to process the backscattering signal (from the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration) to determine an acoustic vibration experienced by particular points on individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration, and hence particular locations along the pipe. The processing unit may be configured to compare the determined acoustic vibration against expected acoustic profiles of particular events to identify the particular event. The processing unit may be configured to identify the particular event using various other algorithmic processes.

[0080] The DSS mode may comprise a sensing technique employed within the apparatus to detect static and quasi-static strain variations along the sensing fibres (and thus the fluid pipe). DSS may utilise Brillouin scattering for sensing purposes. In DSS, light pulses injected into the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration may undergo Brillouin scattering, and the resulting frequency shift may be measured to determine strain variations along the respective fibres. By analysing these shifts in the backscattered light, DSS can accurately detect and localize strain-induced events, such as structural deformations, pressure changes, or mechanical stresses, along the entire length of the respective fibres (and thus the associated length of the pipe comprising the fibre).

[0081] The DTS mode may comprise a sensing technique utilized by the apparatus to measure temperature variations along the respective sensing fibres. In DTS, Brillouin scattering and / or Raman scattering may be used for sensing purposes. When light pulses are injected into the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration, these pulses may interact with the respective fibre’s molecular structure, undergoing Brillouin and Raman scattering. The resulting frequency shifts and intensity changes may be measured to determine temperature variations along the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration. By analysing these changes in the backscattered light, temperature fluctuations, such as hotspots, thermal gradients, or ambient temperature changes, may be detected and localized along the entire length of the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration (and thus along the entire length of the fluid pipe).

[0082] The processing unit may be configured to compare the determined temperature variations against expected temperature profiles of particular events to identify the particular event. In one example, this could involve matching a temperature change profile to an adiabatic cooling signature, so as to identify a leak in a pipe where the fluid is gaseous. In other examples, this could involve excluding processing of signals with a profile characteristic of a known external heat source / sink such as an industrial site overlying or close to a buried pipe.

[0083] The light emitter may be configured to introduce light pulses with particular characteristics into the individual sensing fibre and / or the plurality of the sensing fibres within the looped configuration. The processing unit may be configured to control the light emitter to vary the characteristics of the emitted light pulses.

[0084] Varying the characteristics of the emitted light pulses may comprise reducing or increasing a pulse width. Varying the characteristics of the emitted light pulses may comprise reducing or increasing a pulse repetition frequency. Varying the processing characteristics of the emitted light pulses may comprise reducing or increasing a gauge length.

[0085] Increasing the pulse width enhances sensitivity by allowing more photons to interact with the sensing fibre, thus improving the signal-to-noise ratio and detecting more subtle changes in the backscattered light. However, this comes at the expense of spatial resolution, as longer pulse widths reduce the ability to pinpoint event locations. Increasing the pulse repetition frequency improves the signal-to-noise ratio by increasing the rate of measurements and the acoustic frequencies that can be correctly classified due to Nyquist sampling criteria but may reduce overall length of run. The pulse repetition frequency and pulse width must be chosen initially at least, based on the sensing fibre length, typical audio bandwidth of events, and required signal-to-noise ratio. Adjusting the gauge length, which averages measurements over a specific fibre length, enhances the signal-to-noise ratio through averaging but reduces spatial resolution, making it harder to pinpoint exact event locations.

[0086] The processing unit may be configured to process the backscattering signal using a further processing algorithm. This processing algorithm may be configured to extend a dynamic range of the backscattering signal and reduce saturation.

[0087] The activation of the additional processing algorithm may be selected on case- by-case basis. For example the processing algorithm may only be employed for specific sections of fibre, where confidence levels associated with detecting and / or classifying the particular events need to be improved. The processing algorithm may improve the confidence level of each of the identified backscattering signal features within the backscattering signal. By improving the confidence level of each of the identified backscattering signal features within the backscattering signal, the processing algorithm may be configured to classify the inconclusive event as a particular event.

[0088] This selective use of the processing algorithm offers several advantages. Primarily, it conserves processing computing resources by avoiding the immediate deployment of a highly processor-intensive algorithm, thereby optimizing the apparatus’s overall efficiency. By first attempting to classify the event through simpler, less resource-demanding methods — such as switching sensing modes, switching between the individual sensing fibre and / or the plurality of the sensing fibres, or adjusting light pulse characteristics — the apparatus prioritizes more efficient pathways to event classification and confidence levels.

[0089] According to a second aspect of the invention, there is provided a method for monitoring a fluid pipe. The method may comprise introducing light pulses into one end of a continuous looped configuration within a cable disposed in the fluid pipe. The continuous looped configuration may be formed from a plurality of sensing fibres that are spliced together at their respective ends. The method may comprise detecting backscattering of the light pulses from the plurality of sensing fibres of the continuous looped configuration. The method may comprise outputting a backscattering signal in response to the detected backscattering of the light pulses. The method may comprise processing the backscattering signal to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe. The method may comprise analysing the backscattering signal from the plurality of sensing fibres to improve detection of the particular events.

[0090] At least one sensing fibre of the plurality of sensing fibres may have a different sensitivity and / or a different response in a predetermined frequency range than the other sensing fibres of the plurality of sensing fibres.

[0091] The method may comprise detecting that one or more sensing fibres of the plurality of sensing fibres are oversaturated. The method may comprise switching to analysing the backscattering signal from one or more different sensing fibres of the plurality of sensing fibres.

[0092] A section of the cable may comprise both a separate individual sensing fibre and the continuous looped configuration. The separate individual sensing fibre may be configured to run independently alongside the continuous looped configuration.

[0093] The method may further comprise switching between monitoring the fluid pipe using the individual fibre and the continuous looped configuration based on detecting that a signal-to noise ratio is below a predetermined threshold. The method may further comprise switching between monitoring the fluid pipe using the individual fibre and the continuous looped configuration based on detecting that the individual sensing fibre and / or one or more of the sensing fibres within the continuous looped configuration are oversaturated. The method may further comprise switching between monitoring the fluid pipe using the individual fibre and the continuous looped configuration based on detecting an inconclusive event.

[0094] The processing unit may be configured to switch between the use of the individual fibre, or the continuous looped configuration based on detected backscattering signal characteristics, environmental conditions within or in a vicinity of the fluid pipe, or predefined sensing requirements.

[0095] Detecting the inconclusive event may comprise assigning a confidence level to each of the identified backscattering signal features within the backscattering signal. Detecting the inconclusive event may comprise determining that the confidence level of a first backscattering signal feature or a first group of backscattering signal features lies in an intermediate confidence range. Detecting the inconclusive event may comprise determining that the first backscattering signal feature or the first group of backscattering signal features are indicative of an inconclusive event.

[0096] The inconclusive confidence range may serve as a crucial threshold within the monitoring apparatus, delineating levels of certainty regarding the presence or absence of particular events. Positioned between a low and a high confidence level, this range may represent a zone of ambiguity where the interpretation of backscattering signal features is neither definitively affirmative nor outright negative.

[0097] More specifically, the inconclusive confidence range may lie between a low confidence level and a high confidence level. Below the low confidence level, the processing unit may be configured to recognise that no particular event has taken place. For example, below the low confidence level, the processing unit may be configured to recognise that there is no leak within the pipe. Above the high confidence level, the processing unit may be configured to immediately recognise that the particular event has taken place. For example, above the high confidence level, the processing unit may be configured to recognise that there is indeed a leak within the pipe.

[0098] Additionally or alternatively, the processing unit may be configured to switch to the use of the continuous looped configuration based on determining that the signal- to-noise ratio of the backscattering signal has fallen below a predetermined threshold, or that an overs aturation threshold has been exceeded.

[0099] Equally, the processing unit may be configured to switch to the use of the individual sensing fibre based on determining that the signal-to-noise ratio of the backscattering signal is above the predetermined threshold. The predetermined threshold may be selected adaptively on case-by-case basis depending on the type of the processing unit and / or the confidence requirements associated with detecting the particular event set by the user. The predetermined threshold may be modified and refined by machine learning over time.

[0100] According to a third aspect of the present invention, there is provided a pipe network comprising one or more pipes monitored using the apparatus of the first aspect of the present invention and / or the method of the second aspect of the present invention.

[0101] According to a fourth aspect of the invention, there is provided a cable suitable for use in monitoring a fluid pipe. The cable may comprise a plurality of sensing fibres, wherein the plurality of sensing fibres are spliced together at their respective ends to form a continuous looped configuration within the cable.

[0102] The cable may comprise at least two sections along its longitudinal axis. A first section may comprise at least one individual sensing fibre and a second section may comprise the continuous looped configuration. An end of the individual sensing fibre may be connected to (or spliced to) a first end of the continuous looped configuration.

[0103] A section of the cable may comprise a separate individual sensing fibre and the continuous looped configuration. The separate individual sensing fibre may be configured to run independently alongside the continuous looped configuration.

[0104] The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the aspects, methods, examples or embodiments described herein may be applied to any other method, aspect, example, embodiment or feature. Further, the description of any aspect, method, example or feature may form part of or the entirety of an embodiment of the invention as defined by the claims. Any of the examples described herein may be an example which embodies the invention defined by the claims and thus an embodiment of the invention.

[0105] Detailed Description of the Invention In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

[0106] Figure 1 is a schematic block diagram of an apparatus for monitoring a fluid pipe, the apparatus including a cable comprising a separate individual sensing fibre and a continuous looped configuration;

[0107] Figure 2 is (a) a schematic illustration of fluid pipe monitored using a cable according to the present invention and (b) a schematic illustration of temperature variation along the pipe of figure 2a;

[0108] Figure 3a is a schematic cross-section of an example of a cable according to the present invention.

[0109] Figure 3b is a schematic diagram showing an operation of a switch for use in the sensing apparatus of figure 1 ;

[0110] Figure 4 is (a) a schematic diagram of an example of a structure of one of the sensing fibres within the continuous looped configuration and (b) a schematic diagram of an example of the separate individual sensing fibre.

[0111] Figure 5 is (a) a schematic illustration of a single section of the cable comprising the continuous looped configuration and (b) a schematic illustration of a single section of the cable comprising both the continuous looped configuration and the separate individual sensing fibre.

[0112] Figure 6 is (a) a schematic illustration of a cable comprising a first section, a second section and a third section and (b) is a zoomed-in view of the second section of the cable shown in Figure 6a.

[0113] Figure 7 is a flow diagram of a method for monitoring a fluid pipe using the continuous looped configuration.

[0114] Figure 8 is (a) a first part and (b) a second part of a flow diagram of a method for monitoring a fluid pipe using both the continuous looped configuration and the separate individual sensing fibre. Figure 9 is a flow diagram of a method for detecting an inconclusive event.

[0115] Figure 1 is a schematic block diagram of an apparatus 100 for monitoring a fluid pipe 1 (shown in Figure 2a). The apparatus 100 includes a cable 11 comprising a separate individual sensing fibre 22 and a continuous looped configuration 500 (best seen in Figure 5 a). The continuous looped configuration comprises a plurality of sensing fibres, including a first sensing fibre 10. The structure of the continuous looped configuration will be described in more detail with reference to Figures 5a-6b. A first end of the first sensing fibre 10 and a first end of the individual sensing fibre 22 are schematically shown in Figure 1.

[0116] The apparatus 100 is operable to carry out distributed acoustic sensing (DAS), distributed strain sensing (DSS) and distributed temperature sensing (DTS) within the pipe 1 using the individual sensing fibre 22 and / or the continuous looped configuration 500.

[0117] The individual sensing fibre 22 and the plurality of fibres (including the first fibre 10) which form the continuous looped configuration 500 comprise optical fibres. In some embodiments, the individual sensing fibre 22 and each of the plurality of fibres within the continuous looped configuration 500 have different sensitivities. In other embodiments, the individual sensing fibre 22 and some or all of the plurality of fibres within the continuous looped configuration 500 have the same sensitivity. The reasons for the varying sensitivities of the respective sensing fibres will be described in more detail with reference to Figures 3a, 4a and 4b.

[0118] The skilled person will recognise that the cable 11 may comprise one or more additional sensing fibres in addition to the plurality of sensing fibres which form the continuous looped configuration 500 and the individual sensing fibre 22.

[0119] An example of an internal structure of the cable 11 will be described in more detail with reference to Figure 3 a.

[0120] The cable 11 is provided within a fluid pipe 1. The fluid pipe 1 is monitored using at least the continuous looped configuration 500 and in some embodiments using the individual sensing fibre 22. In the description below, the invention is primarily described in terms of monitoring of a pipe 1 carrying water. Nevertheless, the skilled person will appreciate that the invention may be applied to pipes carrying other fluids including, but not limited to, waste water, sewage or fuels such as oil, gas, distillates or the like and chemical or mining and industrial products.

[0121] The apparatus 100 comprises a switch 200, a light emitter 101, a light detector module 110 and a processing unit 103. The light emitter 101, the light detector module 110 and the processing unit 103 together form an analyser 203.

[0122] A first end of the first sensing fibre 10 and a first end of the individual sensing fibre 22 are both coupled to the switch 200. The switch 200 is also connected to the analyser 203. More specifically, the switch 200 is connected to both the light emitter 101 and the light detector module 110. The light emitter 101 and the light detector module 110 are connected to the processing unit 103.

[0123] The light emitter 101 is configured to emit light pulses into the first end of the first sensing fibre 10 and / or the first end of the individual sensing fibre 22. These light pulses have particular characteristics. More specifically, the light pulses may comprise a specific pulse width, pulse repetition frequency and / or the processed gauge length.

[0124] In this embodiment, the light emitter 101 comprises a laser. The emitted light pulses may comprise any suitable wavelength for transmission along and backscattering within the sensing fibres 10, 22.

[0125] The light detector module 110 detects backscattered light from at least the continuous looped configuration 500 and / or the individual sensing fibre 22. The time of arrival of the backscattered light from the continuous looped configuration 500 and / or the individual sensing fibre 22 following the emission of the light pulse relates to the location of the backscattering site along the continuous looped configuration 500 and / or the individual sensing fibre 22. The skilled person will understand that the light detector module 110 may be configured to detect backscattered light from some or all of the sensing fibres within the cable 11 , as needed.

[0126] The light detector module 110 is configured to detect backscattering of the light pulses from the continuous looped configuration 500 and / or the individual sensing fibre 22 in multiple different sensing modes and output a backscattering signal in response thereto. The skilled person will understand that the light detector module 110 may be configured to output a specific backscattering signal in response to any detected backscattering of the light pulses from some or all of the sensing fibres within the cable 11.

[0127] More specifically, the light detector module 110 is configured to detect backscattering of the light pulses from the sensing fibres in the distributed acoustic sensing (DAS) mode, the distributed strain sensing (DSS) mode and the distributed temperature sensing (DTS) mode.

[0128] The switch 200 is operable to cause the light emitter 101 to switch between introducing the light pulses into the continuous looped configuration 500 (more specifically into the first end of the first sensing fibre 10 which forms a part of the continuous looped configuration 500) and the individual sensing fibre 22. In one embodiment, switch 200 comprises a switchable light guiding device configured to guide the light pulses from the light emitter 101 into the first end of the first sensing fibre 10 of the continuous looped configuration 500 or the individual sensing fibre 22.

[0129] Additionally, the switch 200 may be operable to cause the light detector module 110 to switch between detecting backscattering of the light pulses from the continuous looped configuration 500 and detecting backscattering of the light pulses from the individual sensing fibre 22. In one embodiment, the switch 200 comprises a switchable light guiding device configured to guide the backscattering of the light pulses from the continuous looped configuration 500 or the individual sensing fibre 22 into the light detector module 110.

[0130] The processing unit 103 is configured to control the operation of the switch 200. More specifically, the processing unit 103 is configured to instruct the switch 200 to cause the light emitter 101 to switch between introducing the light pulses into the continuous looped configuration 500 and introducing the light pulses into the individual sensing fibre 22. Similarly, the processing unit 103 is configured to instruct the switch 200 to cause the light detector 110 to switch between detecting backscattering of the light pulses from the continuous looped configuration 500 and detecting backscattering of the light pulses from the individual sensing fibre 22. DAS mode comprises a sensing technique utilized within the monitoring apparatus 100 to detect acoustic signals and vibrations along the length of the continuous looped configuration 500 and the individual sensing fibre 22. In the DAS mode, Rayleigh scattering within the continuous looped configuration 500 and / or the individual sensing fibre 22 is leveraged for sensing purposes.

[0131] DSS mode comprises a sensing technique employed within the monitoring apparatus 100 to detect static and quasi-static strain variations along the continuous looped configuration 500 and / or the individual sensing fibre 22 (and consequently the static and quasi-static strain variations along the pipe 1). DSS utilises Brillouin scattering for sensing purposes. In DSS, light pulses injected into the continuous looped configuration 500 and / or the individual sensing fibre 22 by the light emitter 101 undergo Brillouin scattering, and the resulting frequency shift is measured to determine strain variations along the respective fibres.

[0132] DTS mode comprises an integral sensing technique utilized by the monitoring apparatus 100 to measure temperature variations along the continuous looped configuration 500 and / or the individual sensing fibre 22 (and consequently temperature variations along the pipe 1). In DTS, Brillouin scattering and / or Raman scattering are used for sensing purposes.

[0133] The backscattering signals from the continuous looped configuration 500 and / or the individual sensing fibre 22 are passed to a processing unit 103 for processing. The processing unit 103 is configured to process the backscattering signals from the continuous looped configuration 500 and / or the backscattering signals from individual sensing fibre 22 to identify backscattering signal features characteristic of a particular event. A skilled person will recognise how to carry out DAS, DSS and DTS sensing using the backscattering signals originating from the continuous looped configuration 500 and / or the individual sensing fibre 22.

[0134] The particular event may comprise one or more of: a leak in the pipe 1 , a change in external conditions proximal to the pipe 1, the pipe 1 bursting, a structural deformation of the pipe 1, a change in fluid flow within the pipe 1, a change in fluid pressure within the pipe 1, a blockage in the pipe 1, and / or pump or valve operation or other events. The processing unit 103 may be configured to compare the identified backscattering signal features within the backscattering signal from the continuous looped configuration 500 and / or the backscattering signal from individual sensing fibre 22 against expected backscattering signal features of particular events to identify the particular event. By mapping the identified backscattering signal features to expected backscattering signal features of particular events, the processing unit 103 can classify a detected event as the particular event (e.g., a leak) with varying levels of confidence. The levels of confidence associated with classifying a detected event as a particular event may depend on the specific external and / or internal pipe conditions.

[0135] The processing unit 103 will typically be local to the light emitter 101 and light detector 110 but may be alternatively provided at a remote location. In the latter case, a communication unit (not shown) would be operable to communicate remotely with the processing unit 103.

[0136] The light detector module 110 may be a combined Rayleigh spectrometer and Brillouin spectrometer and / or Raman spectrometer as illustrated in Figure 1. In this embodiment, the light detector module 110 may comprise a multimode spectrometer. The skilled person would understand that in other embodiments the light detector module 110 may comprise separate Rayleigh spectrometer, Brillouin spectrometer and a Raman spectrometer.

[0137] The processing unit 103 may be configured to switch between processing the backscattering signal originating from the continuous looped configuration 500 and the backscattering signal originating from the individual sensing fibre 22 as will be described in more detail with reference to Figures 8a and 8b. Additionally, in some embodiments the light detector module 110 may be configured to switch between the DAS, DTS and DSS modes. In another example, the processing unit 103 may be configured to cause the light emitter 101 to vary the characteristics of the emitted light pulses.

[0138] Turning now to figure 2a, there is shown a schematic illustration of fluid pipe 1 monitoring using the cable 11 according to the present invention. The cable 11 comprises a plurality of sensing fibres which form the continuous looped configuration 500 (best seen in Figure 5a, including the first sensing fibre 10) and the individual sensing fibre 22.

[0139] In the event that the pipe 1 has a leak 2, vibrations 3 characteristic of orifice noise will travel through the fluid until they impinge on the sensing fibres 10, 22 within the cable 11. Such vibration cause Rayleigh scattering and thus provide the DAS backscattering signal which is detected by the light detection module 110. Subsequent operation of the processing unit 103 will determine the occurrence of vibrations 10, 22 and the position along the sensing fibres 10, 22 at which these vibrations occur. Accordingly, the processing unit 103 can identify a leak 2 and the position of the leak 2 along the length of pipe 1.

[0140] As shown in figure 2a, the pipe 1 runs under a road 20. By way of example, vehicles 21 travelling along the road 20 generate vibrations 22 which can travel though the ground to the pipe 1. The vibrations 22 generate additional DAS backscattering signals that are also present in the backscattering signals originating from the continuous looped configuration 500 and the individual sensing fibre 22. If the leak 2 is small (for example, if the leak 2 comprises a relatively small pinhole leak), the DAS backscattering signal due to the leak 2 may be difficult to detect using a sensing fibre which has a low sensitivity.

[0141] In some embodiments, the DAS backscattering signal due to the leak 2 may be partially masked by the DAS backscattering signals generated by the vibrations 22. In environments with high levels of vibrations, sensitive sensing fibres may become oversaturated (i.e., the backscattering signal may oversaturate the analyser). It may be difficult to identify a DAS backscattering signal feature due to the leak 2 if the backscattering signal is oversaturated.

[0142] In some embodiments, the processing unit 103 may determine that a backscattering signal feature or a group of backscattering signal features within the backscattering signal detected by the light detector module 110 are indicative of an inclusive event. Upon identifying an inconclusive event, the processing unit 103 employs various techniques to try and classify the inconclusive event as the particular event (e.g., a leak 2 in the pipe 1). These techniques will be described in more detail with reference to Figures 8 a, 8b and 9. Turning now to figure 2b, the temperature profile of the pipe fluid generated from analysis of the DTS detection signal is also illustrated. As illustrated, the temperature profile has a dip 15, which is characteristic of adiabatic cooling associated with a leak from a pressurised fluid pipe. Processing of the DTS signal (originating from the continuous looped configuration 500 and / or the individual sensing fibre 22) by the processing unit 103 can therefore confirm that an inconclusive event detected using the DAS mode indeed comprises a leak 2. The DTS detection signal can also help the processing unit 103 to more accurately identify a position of the leak 2 along the length of pipe 1.

[0143] Although not shown in the Figures, there may exist a strain profile of the pipe 1 generated from analysis of the DSS detection signal. The strain profile of the pipe 1 may also indicate a presence of the leak 1. Processing of the DSS signal (originating from the continuous looped configuration 500 and the individual sensing fibre 22) by the processing unit 103 can therefore confirm that an inconclusive event detected using the DAS mode indeed comprises a leak 2. The DSS detection signal can also help the processing unit 103 to identify a position of the leak 2 along the length of pipe 1.

[0144] The cable 11 may be mounted to an inside surface of the pipe 1. The cable 11 may preferentially be laid in the pipe invert, in a minimised flow region and optimally distant from appurtenances such as air valves and spur connections. Furthermore, in this particular example, the cable 11 is shown provided within a microduct 12. The microduct 12 forms a barrier between the cable 11 and the fluid within pipe 1. The microduct 12 may be filled with acoustic gel or fluid (not shown). This can improve acoustic coupling between the microduct 12 and the sensing fibres 10, 22.

[0145] Turning now to Figure 3a, there is shown a schematic cross-section of an example of the cable 11 according to the present invention.

[0146] The cable 11 comprises an internal strength member 210, six inner sensing fibres 272, six data fibre bundles 208, six middle sensing fibres 204 (for the sake of clarity only one of the middle sensing fibres is labelled) and a wire armour 270. The wire armour 270 comprises 18 armour wires 206 (only one of which is labelled in the figure for the sake of clarity) and six outer sensing fibres 274. The cable 11 further comprises an outer sheath 262 having an external surface 260. The inner sensing fibres 272 comprise the first sensing fibre 10 (which forms a part of the continuous looped configuration 500 within the cable). The outer sensing fibres 274 comprise the individual sensing fibre 22. In addition to the first sensing fibre 10, the continuous looped configuration 500 may additionally comprise one or more of inner sensing fibres 272, outer sensing fibres 274 and / or middle sensing fibres 204 as will be described with reference to Figure 5 a. Additionally, although in this embodiment the first sensing fibre 10 are a part of the inner sensing fibres 272 and the individual sensing fibre 22 are a part of the outer sensing fibres 274, the skilled person will understand that the first sensing fibre 10 and the individual sensing fibre 22 may comprise any one of the inner sensing fibres 272, outer sensing fibres 274 or middle sensing fibres 204 as required.

[0147] The sensing fibres 272, 204, 274 are adapted to be used for carrying out DAS, DTS and / or DSS sensing.

[0148] The internal strength member 210 is positioned in a centre of the cable 11, extending along a central axis of the cable 11. The internal strength member 210 comprises an elongate rod made out of a suitable metal or a suitable polymer. The strength member provides additional strength and stability for the cable 11 in the axial direction. This can help ensure the cable 11 is not damaged by axial forces, for instance if the cable 11 is pulled along a pipe during installation.

[0149] The data fibre bundles 208 each comprise multiple optical fibres configured for data transmission. Each data fibre bundle 208 is of substantially the same size. This provides for convenient packing within the cable 101. As shown in the figure, the bundles 208 are regularly packed in a hexagonal close packed (HCP) array or a quasi- HCP array.

[0150] The inner sensing fibres 272 are regularly packed around the internal strength member 210. The inner sensing fibres 272 are positioned in a circular arrangement around the internal strength member 210. The inner sensing fibres 272 are positioned in the internal interstitial spaces of the hexagonal close packed (HCP) array or a quasi- HCP array formed by the data fibre bundles 208. The inner sensing fibres 272 are positioned between the internal strength member 210 and the data fibre bundles, as viewed in a direction perpendicular to the axis of the cable 11. The middle sensing fibres 204 are provided in edge interstitial spaces between data fibre bundles 208 at the outer edge of the regular packing of data fibre bundles 208. The middle sensing fibres 204 are regularly spaced out around the axis of the cable 11. The middle sensing fibres 204 are positioned between the data fibre bundles 208 and the wire armour 270, as viewed in a direction perpendicular to the axis of the cable 11.

[0151] The wire armour 270 comprises a layer of parallel wires 206 and outer sensing fibres 274 wrapped around the data fibre bundles 208 and the middle sensing fibres 204. The outer sensing fibres 274 are regularly arranged within the wire armour 270.

[0152] In some embodiments, the wires 206 and the outer sensing fibres 274 within the wire armour 270 may be arranged in a helical formation around the axis of the cable 11. The pitch of the helical formation may match the pitch of the data fibre bundles 208. The pitch of the helical wire formation may be in the opposite direction to the pitch of the data fibre bundles. This can reduce coil memory compared to armour 270 formed from wires 206 and outer sensing fibres 274 with a helical formation in the same direction as the data fibre bundles 208.

[0153] The wire armour 270 is provided within the outer sheath 262. The outer sheath maybe formed from a polymer. Selection of polymer is based on the fluid in which the cable is deployed, and for instance in a water pipe will be of material with suitable approval for use within a potable water network.

[0154] The inner sensing fibres 272 are positioned furthest away from the external surface 260 of the cable 11 and thus comprise a lowest sensitivity. This is because the longer distance between the inner sensing fibres 272 and the external surface 260 of the cable 11 reduces the acoustic coupling and / or temperature conduction between the exterior of the cable 11 and the inner sensing fibres.

[0155] The outer sensing fibres 274 are positioned closest to the external surface 260 of the cable 11 and thus comprise a highest sensitivity. This is because the shorter distance between the outer sensing fibres 274 and the external surface 260 of the cable 11 increases the acoustic coupling and / or temperature conduction between the exterior of the cable 11 and the outer sensing fibres. The middle sensing fibres 204 are positioned between the inner sensing fibres 272 and the outer sensing fibres 274 as viewed in a direction perpendicular to the axis of the cable 11. The sensitivity of the middle sensing fibres 204 is between the lower sensitivity of the inner sensing fibres 272 and the higher sensitivity of the outer sensing fibres 274.

[0156] The inner sensing fibres 272 may all have an equal sensitivity, the middle sensing fibres 204 may all have an equal sensitivity and the outer sensing fibre 274 may all have an equal sensitivity. The inner sensing fibres 272, the middle sensing fibres 204 and the outer sensing fibres 274 all have a different sensitivity due to their relative position within the cable 11.

[0157] The structure of the cable 11 outlined in Figure 3a is just one example of a cable that may be used for monitoring the fluid pipe 1 in accordance with the present invention. A skilled person in the field could propose alternative packing arrangements, alternative numbers of data fibre bundles, sensing fibres, and similar components to suit specific applications and environmental conditions in the pipe 1.

[0158] Turning now to Figure 3b, there is provided a schematic diagram 202 showing an operation of the switch 200 for use in the sensing apparatus of figure 1.

[0159] As shown in Figure 3b, the optical switch 200 is coupled to the inner sensing fibres 272, the outer sensing fibres 274 and the middle sensing fibres 204. The optical switch 200 is also coupled to the light detector module 110 operating in a particular sensing mode 250.

[0160] As previously mentioned, the switch may also be coupled to the light emitter 101 (shown in Figure 1). The switch 200 may be operable to cause the light emitter 101 to switch between introducing the light pulses into the inner sensing fibres 272 (which include the first sensing fibre 10 of the continuous looped configuration 500) and the outer sensing fibres 274 (which include the individual sensing fibre 22). In this embodiment, the switch 200 is also operable to cause the light emitter 101 to switch to introducing the light pulses into the middle sensing fibres 204.

[0161] Additionally, the switch 200 is operable to cause the light detector module 110 to switch between detecting backscattering of the light pulses from the inner sensing fibres 272 (which include the first sensing fibre 10 of the continuous looped configuration 500), the outer sensing fibres 274 (which include the individual sensing fibre 22). The processing unit 103 is configured to control the operation of the switch 200.

[0162] The skilled person will recognise that in some embodiments, the first sensing fibre 10 and the individual sensing fibre 22 may have the same relative position within the cable 11 (for example, both the first sensing fibre 10 and the individual sensing fibre 22 may be positioned in the wire armour 270). The difference in sensitivity between the first sensing fibre 10 and the individual sensing fibre 22 may be only due a difference in their inherent structural properties.

[0163] Figure 3 a shows a schematic diagram of an example of a structure of the first sensing fibre 10 and Figure 3b shows a schematic diagram of an example of a structure of the individual sensing fibre 22.

[0164] The skilled person will recognise that any one of the pluralities of sensing fibres forming the continuous looped configuration 500 and / or the individual sensing fibre 22 may comprise the structure shown in Figure 3a, or a structure shown in Figure 3b, as required.

[0165] Both the first sensing fibre 10 and the individual sensing fibre 22 comprise a core 700. The core 700 serves as a central conduit for light transmission. More specifically, the light pulses originating from the light emitter 101 are introduced into the core 700. The core 700 may be made of silica glass.

[0166] The first sensing fibre 10 comprises a first external layer 702 surrounding the core 700. The individual sensing fibre 22 comprises a second external layer 708 surrounding the core 700.

[0167] The layers 702, 708 are made of silica glass but with a differing refractive index than the core 700. The layer 704 may vary in thickness or material to adjust sensitivity and / or frequency response of the sensing fibre.

[0168] The individual sensing fibre 22 further comprises scoring 710 on an outer surface of the layer 708. The scoring 700 causes the individual sensing fibre 22 to have an increased sensitivity and a different frequency response than the first sensing fibre 10.

[0169] The skilled person would recognise that the external surface of the second layer 708 may comprise scoring 710 having different micro-etching patterns as needed. The scoring 710 may comprise one or more grooves, notches, channels or indentations as needed.

[0170] The first 702 and the second 708 layers may have different chemical compositions. The different chemical compositions of the respective layers 702, 708 may cause the first 10 sensing fibre and the individual sensing fibre 22 to have different sensitivities.

[0171] Both the first sensing fibre 10 and the individual sensing fibre 22 comprise an opaque sheath 704 surrounding the respective first 702 and the second 708 external layers. Advantageously, the sheath is configured to protect the external layers 702, 708 and core 700 from environmental and mechanical damage. The sheath may additionally be opaque and may be made out of a polymer material. The polymer material may comprise acrylic, polyethylene, PVC or similar.

[0172] The skilled person will understand that the structure of the one or more of the sensing fibres (e.g., any one of the plurality of sensing fibres which form the continuous looped configuration 500 and / or the individual sensing fibre 22) may be modified to adjust their sensitivity as needed.

[0173] Turning now to Figure 5a, there is shown a schematic illustration of a single section of the cable 11 which comprises the continuous looped configuration 500.

[0174] In this embodiment, the continuous looped configuration 500 comprises the first sensing fibre 10, a second sensing fibre 502, a third sensing fibre 508 and a fourth sensing fibre 510. In this embodiment, the continuous looped configuration 500 comprises 3 loop backs.

[0175] The first end of the first sensing fibre 10 is connected to the analyser 203. The second end of the first sensing fibre 10 is spliced to a first end of the second sensing fibre 502 at point 504. A second end of the second sensing fibre 502 is spliced to a first end of the third sensing fibre 508 at point 512. A second end of the third sensing fibre 508 is spliced to a first end of the fourth sensing fibre 510 at point 506. In this manner, a series of end-to-end connections that result in a continuous looped path is formed.

[0176] The plurality of sensing fibres 10, 502, 508, 510 in the cable 11 are interconnected in to ensure that light pulses introduced into the first end of the first sensing fibre 10 travel through the entire length of the looped configuration 500 (i.e., through the first fibre 10, the second fibre 502, the third fibre 508 and the fourth fibre 510) end exit through the second end of the fourth fibre 510. This looped configuration 500 runs substantially parallel to the length of the cable and allows light pulses introduced at one end to travel through the entire length of the looped configuration 500 and return through backscattering to analyzer 203. The fibres 10, 502, 508, 510 are arranged in such a way that they cover the same segment of the pipe 11 multiple times, enhancing the system's ability to detect and analyze events along the monitored section of the pipe.

[0177] The skilled person will recognise that the continuous looped configuration 500 may comprise any number of sensing fibres and loops. For example, the continuous looped configuration 500 may comprise 5 sensing fibres (as shown in Figure 6b). In some embodiments, the looped configuration 500 may comprise an odd number of sensing fibres (as shown in Figures 6a and 6b).

[0178] In this embodiment, the plurality of sensing fibres 10, 502, 508, 510 are arranged substantially in parallel to each other along the longitudinal axis of the cable 11.

[0179] In some embodiments, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres within the continuous looped configuration 500 may be identical. For example, all of the sensing fibres of the plurality of sensing fibres may have substantially the same sensitivity and / or response in a predetermined frequency range.

[0180] In one embodiment, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise the inner sensing fibres 272. In other embodiments, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise the outer sensing fibres 274 or middle sensing fibres 204. In one embodiment, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres do not have scoring on the first external layer 702 (as shown in Figure 4a). In one embodiment, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres have scoring on the first external layer 702 (as shown in Figure 4b). In one embodiment, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise the same thicknesses of the external layer 702, 704. In one embodiment, all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise external layers 702, 704 having the same chemical composition.

[0181] In some embodiments, this uniformity offers distinct advantages. With identical fibres 10, 502, 508, 510, the backscattering signals originating from the sensing fibres 10, 502, 508, 510 in the continuous looped configuration 500 can be directly compared or aggregated by the processing unit 103 to enhance the signal-to-noise ratio within the backscattering signal.

[0182] At least one sensing fibre of the plurality of sensing fibres 10, 502, 508, 510 (within the continuous looped configuration 500) may have a different sensitivity than the other sensing fibres of the plurality of sensing fibres 10, 502, 508, 510. At least one sensing fibre of the plurality of sensing fibres 10, 502, 508, 510 may have a different response in a predetermined frequency range than the other sensing fibres of the plurality of sensing fibres 10, 502, 508, 510.

[0183] The sensitivity may comprise an acoustic sensitivity, a sensitivity to strain induced vibrations and / or sensitivity to temperature variations.

[0184] In one embodiment, one or more of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise the inner sensing fibres 272, the outer sensing fibres 274 or middle sensing fibres 204. In one embodiment, one or more of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres do not have scoring on the first external layer 702 (as shown in Figure 4a). In one embodiment, one or more of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres have scoring on the first external layer 702 (as shown in Figure 4b). In one embodiment, some or all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise the different thicknesses of the external layer 702, 704. In one embodiment, some or all of the sensing fibres 10, 502, 508, 510 of the plurality of sensing fibres comprise external layers 702, 704 having the different chemical compositions. Having at least one sensing fibre within the continuous looped configuration 500 that has a different sensitivity than the other sensing fibres may offer significant technical advantages. Aggregating and / or comparing data from fibres 10, 502, 508, 510 with different sensitivities can enhance the detection capabilities of the apparatus 100 in various scenarios. For instance, certain events may produce weak acoustic signals that can only be detected by a fibre with higher acoustic sensitivity (e.g., the outer sensing fibre 274 and / or a fibre with scoring on the external layer). Conversely, in high- noise environments, such as when a pipe is situated close to a busy road 20, a backscattering signal from a fibre with high sensitivity (e.g., the outer sensing fibre 274 and / or a fibre with scoring on the external layer) may oversaturate the analyser 203. In such cases, a backscattering signal from a fibre with a lower sensitivity (e.g., middle sensing fibre 204 or the inner sensing fibre 272 or a fibre with no scoring on the external layer) may allow the analyser 203 to successfully identify signal characteristics of a particular event.

[0185] Additionally, having fibres with different frequency responses can be particularly beneficial. This variation in frequency response allows the analyser 203 to accurately identify and characterize a wide range of events by leveraging the distinct sensitivity and frequency response profiles of the fibres 10, 502, 508, 510. By comparing and aggregating the data from these fibres 10, 502, 508, 510, the analyser 203 can more reliably detect and analyse events, leading a more comprehensive understanding of the pipe's 1 condition.

[0186] The splicing 504, 512, 506 of the plurality of sensing fibres 10, 502, 508, 510 which form the continuous looped configuration 500 may comprise a fusion splice, a mechanical splice, and / or a connector splice.

[0187] Turning now to Figure 5b there is shown a schematic illustration of a single section 520 of the cable 11 comprising both the continuous looped configuration 500 and the separate individual sensing fibre 22.

[0188] Features of the continuous looped configuration 500 have been described with reference to Figure 5 a. The individual sensing fibre 22 is configured to run independently alongside the looped configuration 500 within the section of the cable 520. The separate individual sensing fibre 22 and the continuous looped configuration 500 are positioned in parallel to each other along the longitudinal axis of the cable 11.

[0189] In this embodiment, the individual sensing fibre 22 runs alongside the looped configuration 500, allowing both types of fibre arrangements to coexist within the same section 520 of the cable 11. The individual sensing fibre 22 is not directly connected to the looped configuration 500. Advantageously, this arrangement allows both types of fibre arrangements 500, 22 to operate independently within the same cable section.

[0190] The individual sensing fibre 22 may comprise any one of the inner sensing fibres 272, outer sensing fibres 274 or middle sensing fibres 204 as required. Additionally or alternatively, the individual sensing fibre 22 may or may not comprise scoring 710 on an outer surface of the external layer 708.

[0191] The first end of the individual sensing fibre 22 is connected to the switch 200 and the first end of the first sensing fibre of the continuous looped configuration 500 is connected to the switch 200. The switch is operable to select use of either the individual sensing fibre 22 or the continuous looped configuration 500 as described with reference to Figure 1. Method of switching between the individual sensing fibre 22 and the continuous looped configuration 500 will be described with reference to Figure 8a and 8b.

[0192] Turning to Figures 6a and 6b. In Figure 6a there is shown a schematic illustration of an example 600 of a cable 11 in accordance with the present invention. The cable 600 comprises a first section 602, a second section 604 and a third section 606. Figure 6b shows a zoomed-in view of the second section 604 of the cable 11 shown in Figure 6a.

[0193] The first section 602 comprises a first individual sensing fibre 608 and the third section 606 comprises a second individual sensing fibre 610. The second section 604 comprises the continuous looped configuration 500.

[0194] In this embodiment, the continuous looped configuration 500 comprises five sensing fibres. More specifically, the continuous looped configuration 500 comprises a fifth sensing fibre 612, a sixth sensing fibre 614, a seventh sensing fibre 616, an eighth sensing fibre 618 and a ninth sensing fibre 620. In this embodiment, the continuous looped configuration 500 comprises 4 loop-backs.

[0195] A first end 608a of the fifth sensing fibre 612 is spliced to an end of the first individual sensing fibre. A second end of the fifth sensing fibre 612 is spliced to a first end of the sixth sensing fibre 614 at point 626. A second end of the sixth sensing fibre is spliced to a first end of the seventh sensing fibre 616 at point 622. A second end of the seventh sensing fibre 616 is spliced to a first end of the eighth sensing fibre 618 at point 628. A second end of the eighth sensing fibre 618 is spliced to a first end of the ninth sensing fibre 620 at point 624. A second end of the ninth sensing fibre 620 is spliced to a first end of the second individual sensing fibre 610. A second end 610a of the second individual sensing fibre 610 is connected to the analyser 203. In this manner a continuous optical path within the cable 11 is formed.

[0196] The light emitter 101 is configured to introduce light pulses into the second end of the second individual sensing fibre 610. The light pulses are subsequently configured to travel through the second individual sensing fibre 610, the continuous looped configuration 500 and the first individual sensing fibre 608. The light detector 110 is configured to detect backscattering of the light pulses from the second individual sensing fibre 610, the continuous looped configuration 500 and the first individual sensing fibre 608 and output a backscattering signal in response thereto. The processing unit 103 is configured to process this backscattering signal to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe 1. The processing unit 103 is also be configured to compare and / or aggregate data from the plurality of sensing fibres 612, 614, 616, 618, 620 of the continuous looped configuration 500 to improve detection of the particular events.

[0197] The skilled person will understand that the first 602 and third 606 sections may comprise multiple individual sensing fibres, but only one of these individual sensing fibres may be connected to (or spliced to) the continuous looped configuration 500.

[0198] In some embodiments, the first section 602 may be located at the start of the cable 11 run, the second section 604 may be located centrally along the cable 11 run, and the third section 606 may be located at the end of the cable 11 run. The exact location of the looped configuration 500 may be determined on a case-by-case basis, according to the noise levels and other environmental factors along the cable 11 run. A skilled person will recognize that the cable may comprise any number of sections and any number of looped configurations 55 and individual sensing fibres 608, 610, arranged in any order as needed to suit the specific requirements of the pipe 1 and its surroundings.

[0199] Turning now to Figure 7, there is shown a flow diagram of a method 1000 for monitoring a fluid pipe 1 using the continuous looped configuration 500.

[0200] At block 1002, a cable 11 comprising the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 forming the continuous looped configuration 500 are provided within the pipe 1. For example, the cable 11 be inserted into the fluid pipe 1 and subsequently mounted to an inside surface of the fluid pipe 1.

[0201] At block 1004, the light emitter 101 introduces light pulses with particular characteristics into the continuous looped configuration 500. For example, the light emitter 101 may introduce light pulses into the first end of the first sensing fibre 10 or the second end 610a of the ninth 620 sensing fibre. The particular characteristics of the light pulses include an initial: pulse width, pulse repetition frequency and gauge length.

[0202] At block 1006, the light detector module 110 detects backscattering of the light pulses from the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 forming the continuous looped configuration 500. In this embodiment the light detector module 110 may comprise a multi-mode spectrometer capable of operating in each of DAS, DTS and DSS modes.

[0203] At block 1008, the light detector module 110, is configured to output a backscattering signal in response to the detected backscattering of the light pulses from the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 forming the continuous looped configuration 500.

[0204] At block 1010, the processing unit 103, processes the backscattering signal to identify backscattering signal features characteristic of a particular event within or in a vicinity of the fluid pipe (e.g., a leak). In one example, the processing unit 103 can be configured to compare the determined vibration frequencies and amplitudes of the DAS detection signal against expected vibration profiles of particular events. This can enable detection or exclusion of particular sources of vibration. In one example, this could involve matching the backscattering signal features to preset orifice noise profiles, flow noise profiles and / or monitoring negative pressure waves indicative of leak commencement.

[0205] At block 1012, the processing unit 103, analyses the backscattering signal from some or all of the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 to improve detection of the particular events. More specifically, the processing unit 103 may be configured to compare and / or aggregate data (i.e. backscattering signals) from some or all of the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 to improve detection of the particular events.

[0206] Advantageously, by comparing and aggregating data from the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 forming the continuous looped configuration 500, the processing unit 103 significantly enhances event detection compared to using a single sensing fibre. This method allows for cross-validation of backscattering signals, improving the accuracy and reliability of event detection, as subtle changes that might be missed by a single fibre can be captured more effectively. The aggregation of data from multiple fibres also enhances the signal-to-noise ratio, filtering out noise and ensuring clearer signal detection, particularly in environments with high external interference. Additionally, the apparatus 100 allows for comparing signals from multiple fibres over time and allows the user to detect backscattering from a plurality of sensing fibres which may have different sensitivities and frequency responses.

[0207] At block 1014, the processing unit may determine whether that one or more sensing fibres of the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 has become oversaturated. More specifically, the processing unit may determine whether the backscattering signal from one or more of the sensing fibres of the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 is causing the analyser to become oversaturated (i.e., the dynamic range of the analyser is exceeded).

[0208] If the one or more sensing fibres of the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 has become oversaturated the method proceeds to block 1016. If the sensing fibres have not become oversaturated the method reverts to block

[0209] 1012.

[0210] At block 1016, the processing unit may switch to analysing the backscattering signal from one or more different sensing fibres of the plurality of sensing fibres in response to determining that one or more sensing fibres of the plurality of sensing fibres 10, 502, 508, 510, 612, 614, 616, 618, 620 has become oversaturated. For example, the processing unit may stop analysing the backscattering signal from any sensing fibres which have been oversaturated. In this manner, then the processing unit may adaptively choose to run an analysis on only one (or several) of the plurality of sensing fibres within the continuous looped configuration based on the determined oversaturation of any of the fibres individually within the looped configuration.

[0211] Advantageously, since the timing of a reflected pulse of light may be used to determine the exact location of a detection event (e.g., acoustic vibration, strain or temperature variation) along a sensing fibre, then a specific fibre or fibres within the continuous looped configuration may be readily isolated for analysis.

[0212] Turning now to Figures 8a and 8b, there are shown flow diagrams of a method 800a, 800b for monitoring a fluid pipe 1 using both the continuous looped configuration 500 and the separate individual sensing fibre 22. This method may be carried out in a pipe comprising a section 520 of the cable 11 shown in Figure 5b.

[0213] At block 802, a cable 11 comprising both the continuous looped configuration 500 and the separate individual sensing fibre 22 are provided within the pipe 1. In this embodiment, the individual sensing fibre 22 is configured to run independently alongside the looped configuration 500 and both the individual sensing fibre 22 and the looped configuration 500 are connected to the switch 200 and the analyser 203.

[0214] At block 804, the light emitter 101 introduces light pulses with particular characteristics into the individual sensing fibre 22. For example, the light emitter 101 introduces light pulses with particular characteristics into one end of the individual sensing fibre 22.

[0215] At block 806, the light detector module the light detector module 110 detects backscattering of the light pulses from the individual sensing fibre 22. At block 808, the light detector module 110, is configured to output a second backscattering signal in response to the detected backscattering of the light pulses from the individual sensing fibre 22.

[0216] At block 810, the processing unit 103 processes the second backscattering signal to identify backscattering signal features characteristic of a particular event within or in a vicinity of the fluid pipe (e.g., a leak). In one example, this could involve matching the backscattering signal features to preset orifice noise profiles, flow noise profiles and / or monitoring negative pressure waves indicative of leak commencement.

[0217] At block 812, the processing unit 103 determines whether the signal-to-noise ratio of the second backscattering signal has fallen below a predetermined threshold. The predetermined threshold may be set by a user on case-by-case basis according to predefined sensing requirements. If the signal-to-noise ratio of the second backscattering signal has fallen below a predetermined threshold the method proceeds to block 816. Otherwise, the method proceeds back to block 810.

[0218] At block 814, the processing unit 103 determines whether an inconclusive event has been detected. The method for detecting an inconclusive event will be described in more detail with reference to Figure 9.

[0219] If the inconclusive event has been detected the method proceeds to block 816. If the inconclusive event has not been detected the method proceeds back to block 810.

[0220] At block 815, the processing unit 103 determines whether the individual sensing fibre 22 has become oversaturated. The individual sensing fibre 22 may be oversaturated when the backscattering signal from the individual sensing fibre 22 causes the analyser 203 to become oversaturated. In this example, the analyser 203 may become oversaturated if the backscattering signal from the individual sensing fibre 22 exceeds the dynamic range of the analyser 203.

[0221] If the individual sensing fibre 22 has become oversaturated the method proceeds to block 816. If the individual sensing fibre 22 has not become oversaturated the method proceeds back to block 810. At block 816, the processing unit switches to monitoring the pipe 1 using the continuous looped configuration 500 as described in blocks 1004, 1006, 1008, 1010 and 1012, 1014 and 1016 of method 1000 in Figure 7.

[0222] The skilled person will recognise that the processing unit 103 may be configured to switch to monitoring the pipe 1 using the continuous looped configuration 500 for any number of reasons including: detecting predetermined backscattering signal characteristics, detecting predetermined environmental conditions within or in a vicinity of the fluid pipe, or other predefined sensing requirements.

[0223] The processing unit 103 may employ machine learning algorithms to determine when to switch between the looped configuration 500 and the individual sensing fibre 22. By analysing backscattering data collected over time, the machine learning algorithms may be configured to learn to predict noise patterns and other environmental factors that affect signal quality. These algorithms can then inform the processing unit's 103 decisions, allowing it to proactively switch between the individual sensing fibre 22 and the continuous looped configuration 500 as needed.

[0224] Switching between monitoring the pipe 1 using the individual sensing fibre 22 and the continuous looped configuration 500 based on detecting an inconclusive event or when the signal-to-noise ratio of the backscattering signal falls below a threshold, or when oversaturation of the analyser is determined, offers significant advantages. When an inconclusive event is detected, or when the signal quality degrades, the system can adaptively switch to the continuous looped configuration 500, which typically provides a better signal-to-noise ratio due to the aggregation of data from multiple fibres. This switch enhances the ability to accurately identify and analyse the event. Conversely, when the signal-to-noise ratio is within acceptable limits, monitoring with individual sensing fibre 22 is more resource-efficient, reducing computational load and power consumption.

[0225] If a detected event cannot be successfully identified as a particular event after switching to monitoring the pipe 1 using the continuous looped configuration 500 the method proceeds to step 818. At block 818, the processing unit 103 causes the light emitter 101 to vary the characteristics of the emitted light pulses. Varying the characteristics of the emitted light pulse may comprise reducing or increasing: the pulse width, the pulse repetition frequency and / or the gauge length.

[0226] After varying the characteristics of the emitted light pulses, the processing unit 103 is configured to process the backscattering signal detected by light detector module 110 at a later point in time to try and classify the inconclusive event as the particular event.

[0227] Adjusting the characteristics of the light pulses can refine the resolution and sensitivity of the measurements. This may allow the processing unit 103 to correctly identify an inconclusive event as a particular event.

[0228] Upon not being able to classify the inconclusive event after varying the characteristics of the emitted light pulse, the method may proceed to block 820.

[0229] At block 820, the processing unit 103 causes the light detector module 110 to switch to a different sensing mode. In one embodiment, the processing unit 103 causes the light detector module 110 to switch to the DTS or DSS sensing mode from DAS mode.

[0230] Switching the detection modes offers significant advantages in increasing the confidence level of detecting and classifying particular events, such as leaks. By switching between multiple sensing modes, the system can gather diverse types of data, each providing unique insights into the physical state of the pipe. This multimodal approach allows for cross-verification of detected inconclusive events, enhancing the accuracy and reliability of event identification

[0231] After switching the sensing modes, the processing unit 103 is configured to process the backscattering signal detected by light detector module 110 at a later point in time to classify the inconclusive event as the particular event.

[0232] Upon not being able to classify the inconclusive event after switching the sensing modes, the method may proceed to block 822. At block 822, the processing unit 103 is configured to employ a processing algorithm. The processing algorithm may be configured to extend the dynamic range of the backscattering signal.

[0233] The processing unit may use various Al techniques and machine learning models for the selection for any or all of sensing fibre structures (e.g., the individual sensing fibre 22 or the continuous looped configuration 500), system parameters (e.g., light pulse parameters), sensing modes (e.g., DAS, DSS and DTS modes) and data postprocessing techniques (i.e., employing the processing algorithm). These Al techniques and machine learning models will determine which, when and in what combination and / or sequence these changes / selections are enacted. Al techniques and machine learning techniques will enable the apparatus 100 to determine and update adaptively, on a continuous basis, how the use of the options of parameters, analysis modes and fibre selections. These selections will be applied case-by-case to either an entire sensor cable 11 run or selected differentially for individual sections of the cable 11 run.

[0234] Turning now to Figure 9 there is shown a flow diagram of a method 900 for detecting an inconclusive event.

[0235] At block 910, the processing unit 103 assigns a confidence level to each of the identified backscattering signal features within the backscattering signal.

[0236] At block 912, the processing unit 103, determines that the confidence level of a first backscattering signal feature or a first group of backscattering signal lie in an intermediate confidence range. The backscattering signal features may be lie below the high confidence level (above which the events are conclusively identified or classified) due to background noise in the signal (e.g., vibrations 22) or because the leak 2 is small.

[0237] At block 914, the processing unit 103, determines that the first backscattering signal feature or the first group of backscattering signal features are indicative of an inconclusive event.

[0238] It will be understood that the invention is not limited to the examples and embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and subcombinations of one or more features described herein. In particular, the sequence of operations shown in Figures 7, 8a, 8b and 9 are merely exemplary. Any of the operations shown in the methods 700, 800a, 800b and 900 may be performed in a different order that achieves substantially the same result.

Claims

CLAIMS1. An apparatus for monitoring a fluid pipe, the apparatus comprising: a cable disposed within the fluid pipe, the cable comprising a plurality of sensing fibres, wherein the plurality of sensing fibres are spliced together at their respective ends to form a continuous looped configuration within the cable; a light emitter for introducing light pulses into one end of the continuous looped configuration; a light detector for detecting backscattering of the light pulses from the plurality of sensing fibres and outputting a backscattering signal in response thereto; a processing unit configured to process the backscattering signal to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe, and to analyse the backscattering signal from some or all of the plurality of sensing fibres to improve detection of the particular events.

2. An apparatus according to claim 1 , wherein analysing the backscattering signal comprises comparing and / or aggregating the backscattering signal from the plurality of sensing fibres.

3. An apparatus according to claim 1 or claim 2, wherein the plurality of sensing fibres comprise an odd number of sensing fibres.

4. An apparatus according to any one of the preceding claims, wherein at least one sensing fibre of the plurality of sensing fibres has a different sensitivity and / or a different response in a predetermined frequency range than the other sensing fibres of the plurality of sensing fibres.

5. An apparatus according to any one of the preceding claims, wherein the plurality of sensing fibres each have a different sensitivity and / or a different response in a predetermined frequency range.

6. An apparatus according to claim 4 or claim 5, wherein the one or more sensing fibres of the plurality of sensing fibres have a lower sensitivity than the othersensing fibres due to being positioned further away from an exterior of the cable than the other sensing fibres.

7. An apparatus according to any one of claims 4 to 6, wherein the one or more sensing fibres of the plurality of sensing fibres have a different sensitivity due to their inherent structural properties.

8. An apparatus according to any one of the preceding claims, wherein the plurality of sensing fibres each comprise an optical fibre, the optical fibre having a core, an external layer surrounding the core and optionally an opaque sheath encasing the external layer.

9. An apparatus according to claim 8 when dependent on claim 4, wherein the one or more sensing fibres of the plurality of sensing fibres comprise scoring or etching on an outer surface of the external layer, the scoring or etching causing the one or more sensing fibres to have different sensitivities.

10. An apparatus according to claim 8 or claim 9, wherein the one or more sensing fibres of the plurality of sensing fibres comprise different thicknesses of the external layer, the different thicknesses of the external layer causing the one or more sensing fibres to have different sensitivities.

11. An apparatus according to any one of claims 8 to 10, wherein the one or more sensing fibres of the plurality of sensing fibres comprise external layers having different chemical compositions, the different chemical compositions of the external layers causing the one or more sensing fibres to have different sensitivities.

12. An apparatus according to any one of the preceding claims, wherein the processing unit is configured to switch to analysing the backscattering signal from one or more different sensing fibres of the plurality of sensing fibres in response to detecting that one or more sensing fibres of the plurality of sensing fibres are oversaturated.

13. An apparatus according to any one of the preceding claims, wherein the cable comprises at least two sections along its longitudinal axis, a first section comprising at least one individual sensing fibre and a second section comprisingthe continuous looped configuration, wherein an end of the individual sensing fibre is connected to a first end of the continuous looped configuration.

14. An apparatus according to claim 13, wherein the cable comprises three sections along its longitudinal axis, a first section and a third section each comprising an individual sensing fibre, and a second section comprising the continuous looped configuration, wherein an end of the individual sensing fibre of the first section is connected to the first end of the continuous looped configuration, and a second end of the continuous looped configuration is connected to an end of the individual sensing fibre of the third section.

15. An apparatus according to claim 13 or claim 14, wherein the ends of the individual sensing fibres and the first end and the second end of the continuous looped configuration are spliced together using optical splicing techniques, wherein the optical splicing techniques comprise a fusion splice, a mechanical splice, and / or a connector splice.

16. An apparatus according to any one of the preceding claims, wherein the splicing in the continuous looped configuration comprises a fusion splice, a mechanical splice, and / or a connector splice.

17. An apparatus according to any one of the preceding claims, wherein a section of the cable comprises both a separate individual sensing fibre and the continuous looped configuration, wherein the separate individual sensing fibre is configured to run independently alongside the continuous looped configuration.

18. An apparatus according to claim 17, the apparatus further comprising a switch operable to select use of either the individual sensing fibre or the continuous looped configuration.

19. An apparatus according to claim 18, wherein if the individual fibre is selected, the light emitter is configured to introduce light pulses into one end of the individual fibre, the light detector is configured to detect backscattering of the light pulses from the individual sensing fibre and output a second backscatteringsignal in response thereto, and the processing unit is configured to processes the second backscattering signal from the individual sensing fibre.

20. An apparatus according to claim 18, wherein if the continuous looped configuration is selected, the light emitter is configured to introduce light pulses into one end of the continuous looped configuration, the light detector is configured to detect backscattering of the light pulses from the continuous looped configuration and output a first backscattering signal in response thereto, and the processing unit is configured to processes the first backscattering signal from the continuous looped configuration21. An apparatus according to any one of claims 18 to 20, wherein the processing unit is configured to control the operation of the switch based on: detecting that a signal-to noise ratio is below a predetermined threshold; detecting that the individual sensing fibre and / or one or more of the sensing fibres within the continuous looped configuration are oversaturated; or detecting an inconclusive event.

22. An apparatus according to any one of the preceding claims, wherein the light detector module is configured to detect backscattering of the light pulses in multiple different sensing modes and the processing unit is configured to control the light detector module to switch between the sensing modes.

23. An apparatus according to claim 22, wherein the multiple different sensing modes comprise at least: a distributed acoustic sensing (DAS) mode, a distributed strain sensing (DSS) mode and a distributed temperature sensing (DTS) mode.

24. An apparatus according to any one of the preceding claims, wherein the light emitter is configured to introduce light pulses with particular characteristics and the processing unit is configured to control the light emitter to vary the characteristics of the emitted light pulses.

25. An apparatus according to any one of the preceding claims, wherein the processing unit is configured to process the backscattering signal using aprocessing algorithm, wherein the processing algorithm is configured to extend a dynamic range of the backscattering signal.

26. A method for monitoring a fluid pipe, the method comprising: introducing light pulses into one end of a continuous looped configuration within a cable disposed in the fluid pipe, wherein the continuous looped configuration is formed from a plurality of sensing fibres that are spliced together at their respective ends; detecting backscattering of the light pulses from the plurality of sensing fibres of the continuous looped configuration; outputting a backscattering signal in response to the detected backscattering of the light pulses; processing the backscattering signal to identify backscattering signal features characteristic of particular events within or in a vicinity of the fluid pipe; analysing the backscattering signal from some or all of the plurality of sensing fibres to improve detection of the particular events.

27. A method according to claim 26, wherein at least one sensing fibre of the plurality of sensing fibres has a different sensitivity and / or a different response in a predetermined frequency range than the other sensing fibres of the plurality of sensing fibres.

28. A method according to claim 26 or claim 27, wherein the method further comprises: detecting that one or more sensing fibres of the plurality of sensing fibres are oversaturated; and switching to analysing the backscattering signal from one or more different sensing fibres of the plurality of sensing fibres.

29. A method according to any one of claims 26 to 28, wherein a section of the cable comprises both a separate individual sensing fibre and the continuouslooped configuration, wherein the separate individual sensing fibre is configured to run independently alongside the continuous looped configuration.

30. A method according to claim 29, the method further comprising switching between monitoring the fluid pipe using the individual fibre and the continuous looped configuration based on: detecting that a signal-to noise ratio is below a predetermined threshold; detecting that the individual sensing fibre and / or one or more of the sensing fibres within the continuous looped configuration are oversaturated; or detecting an inconclusive event.

31. A pipe network comprising one or more pipes monitored using the apparatus of any one of claims 1 to 25 and / or the method of any one of claims 26 to 30.

32. A cable suitable for use in monitoring a fluid pipe, the cable comprising a plurality of sensing fibres, wherein the plurality of sensing fibres are spliced together at their respective ends to form a continuous looped configuration within the cable.

33. A cable according to claim 32, wherein a section of the cable comprises a separate individual sensing fibre and the continuous looped configuration, wherein the separate individual sensing fibre is configured to run independently alongside the continuous looped configuration.

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