Distributed Measurement System for Abnormal Strain in Gas Pipeline Networks Based on Quantum Single Photon Detection

Abstract

This invention discloses a distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection, specifically relating to the field of fiber optic sensing and pipeline monitoring technology. It addresses the problem of existing technologies lacking effective means to extract extremely weak backscattered signal changes caused by early, minute strains in gas pipeline networks. The system uses an ultra-stable laser source to emit detection light pulses into sensing optical fibers laid along the gas pipeline network. A single-photon detector responds to the single-photon signal in the backscattered Rayleigh light and outputs a counting pulse sequence. A signal processing unit obtains the photon count rate based on adjacent single-photon events in the counting pulse sequence, divides the photon count rate into multiple continuous segments, constructs a recursive graph for the photon count rate sequences of each segment, extracts recursive quantization parameters, compares adjacent segments to obtain recursive feature differences, performs directional analysis to obtain bilateral attenuation asymmetry, and identifies segments with bilateral attenuation asymmetry exceeding the asymmetry threshold as abnormal locations.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing and pipeline monitoring technology, and more specifically, to a distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection. Background Technology

[0002] During operation, gas pipelines are subject to abnormal strain due to factors such as geological subsidence, third-party construction, and pipeline corrosion. This abnormal strain is a significant precursor to pipeline leaks and ruptures. Current technologies primarily employ distributed fiber optic sensing systems based on optical time-domain reflectometry (OTDR) for distributed measurement of abnormal strain in gas pipelines. These systems utilize narrow-pulse lasers to emit probe pulses into the sensing fiber. By measuring the intensity of backscattered Rayleigh light over time, loss information distributed along the fiber is obtained, allowing for the inference of micro-bending losses or rupture events caused by strain. However, conventional OTD employs linear photoelectric detection, whose noise floor is limited by the detector's thermal and shot noise, resulting in a limited dynamic range and insufficient ability to detect extremely weak backscattered signal changes caused by early, minute strains.

[0003] To address the distributed monitoring needs of early abnormal strain in gas pipeline networks, it is generally believed in the field that conventional optical time-domain reflectometry (OTDR) technology can be used to detect fiber loss events by performing time-domain analysis of the intensity of backscattered Rayleigh light. However, the change in local fiber microbending loss caused by early abnormal strain in gas pipelines is extremely small. The corresponding backscattered Rayleigh light power fluctuation is often submerged in the thermal noise and shot noise of the detection device. The field lacks effective direct extraction methods for such extremely weak signal changes submerged under the noise background. This makes it difficult to reliably perceive the distributed strain state before the abnormal strain in the gas pipeline network develops to the stage of significant damage to the pipe structure, thus restricting the improvement of the safety early warning capability of gas pipeline networks. Summary of the Invention

[0004] To overcome the aforementioned deficiencies of the prior art, the present invention provides a distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection includes: an ultra-steady laser source, sensing optical fibers laid along the gas pipeline network, a single-photon detector, and a signal processing unit.

[0007] Among them, the ultra-stable laser source emits probe light pulses toward the sensing fiber;

[0008] The single-photon detector collects the backscattered Rayleigh light generated by the probe light pulse in the sensing fiber, and responds to the single-photon signal in the backscattered Rayleigh light, outputting a counting pulse sequence corresponding to the single-photon event.

[0009] The signal processing unit obtains the photon count rate distributed along the sensing fiber based on the statistical characteristics of the time interval between adjacent single-photon events in the counting pulse sequence and the time relationship between the emission time of the probe light pulse;

[0010] The signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments, constructs a recursive graph for the photon count rate sequence of each segment and extracts the recursive quantization parameters, and compares the recursive quantization parameters of adjacent segments to obtain the recursive feature difference.

[0011] The signal processing unit performs directional analysis on the recursive feature difference to obtain the bilateral attenuation asymmetry of the recursive feature difference in each segment. The segment where the bilateral attenuation asymmetry exceeds the asymmetry threshold is identified as the abnormal location on the sensing fiber caused by abnormal strain of the gas pipeline network.

[0012] Furthermore, the output end of the ultra-stable laser source is connected to the incident end of the sensing fiber, the backscattered light return end of the sensing fiber is coupled to the photosensitive surface of the single-photon detector, and the electrical signal output end of the single-photon detector is connected to the signal input end of the signal processing unit.

[0013] Furthermore, the ultra-stable laser source emits probe light pulses toward the sensing fiber, including:

[0014] An ultra-stable laser source generates pulsed substrate light;

[0015] The pulsed substrate light is pulse-modulated to form a probe light pulse;

[0016] The probe light pulse enters the sensing fiber from the incident end after passing through the optical isolator.

[0017] Furthermore, the single-photon detector collects the backscattered Rayleigh light generated by the probe light pulse in the sensing fiber, and responds to the single-photon signal in the backscattered Rayleigh light, outputting a counting pulse sequence corresponding to the single-photon event, including:

[0018] When the probe light pulse propagates in the sensing optical fiber, it generates backscattered Rayleigh light.

[0019] Backscattered Rayleigh light returns from the backscattered light return end of the sensing fiber;

[0020] A single-photon detector collects the returned back Rayleigh scattered light;

[0021] A single-photon detector performs photoelectric conversion on the single-photon signal in the backscattered Rayleigh light to generate an electrical pulse;

[0022] Single-photon detectors shape electrical pulses into a sequence of counting pulses.

[0023] Furthermore, the signal processing unit obtains the photon count rate distributed along the sensing fiber based on the statistical characteristics of the time interval between adjacent single-photon events in the counting pulse sequence and the temporal relationship between the emission time of the probe light pulse, including:

[0024] Receive counting pulse sequence;

[0025] Extract the time interval between adjacent single-photon events in the counting pulse sequence;

[0026] Distribution characteristics of statistical time intervals;

[0027] Based on the distribution characteristics of the time interval and the temporal relationship between the emission time of the probe light pulse, the distribution characteristics of the time interval are mapped to the spatial location of the sensing fiber.

[0028] The photon count rate distributed along the sensing fiber is calculated based on the distribution characteristics of the time intervals mapped to the spatial location of the sensing fiber.

[0029] Furthermore, the distribution characteristics of the statistical time intervals include:

[0030] Generate a statistical histogram of the time interval between adjacent single-photon events in the counting pulse sequence;

[0031] Calculate the degree of deviation between the statistical histogram and the Poisson distribution, and use the degree of deviation as a distributional characteristic of the time interval.

[0032] Furthermore, the signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments, constructs a recursive graph for the photon count rate sequence of each segment, extracts recursive quantization parameters, and compares the recursive quantization parameters of adjacent segments to obtain the recursive feature difference, including:

[0033] The photon count rate distributed along the sensing fiber is divided into multiple continuous segments according to spatial location.

[0034] Phase space reconstruction is performed on the photon count rate sequence of each segment to obtain the phase space trajectory of the photon count rate sequence of each segment;

[0035] A recursive graph for each segment is constructed based on the phase space trajectory of the photon count rate sequence for each segment;

[0036] Extract recursive quantization parameters from the recursive graph of each segment;

[0037] By comparing the recursive quantization parameters of adjacent segments, the recursive feature difference is obtained.

[0038] Furthermore, a recursive graph for each segment is constructed based on the phase space trajectory of the photon count rate sequence for each segment, including:

[0039] Calculate the distance between any two state points in the phase space trajectory;

[0040] Mark state point pairs whose distance is less than a preset distance threshold as recursive states;

[0041] Construct a recursion graph based on the distribution of recursive states.

[0042] Furthermore, the signal processing unit performs directional analysis on the recursive feature difference to obtain the two-sided attenuation asymmetry of the recursive feature difference in each segment. Segments where the two-sided attenuation asymmetry exceeds the asymmetry threshold are identified as abnormal locations on the sensing fiber where losses are caused by abnormal strain in the gas pipeline network, including:

[0043] Taking each segment as the center, the recursive feature difference is extracted segment by segment from both sides along the extension direction of the sensing fiber.

[0044] Calculate the decay rate of the left-side recursive feature difference and the decay rate of the right-side recursive feature difference for each segment.

[0045] By comparing the decay rate of the left-side recursive feature difference with the decay rate of the right-side recursive feature difference in each segment, the bilateral decay asymmetry of each segment is obtained.

[0046] The section where the attenuation asymmetry on both sides exceeds the asymmetry threshold is identified as the abnormal location on the sensing fiber caused by abnormal strain of the gas pipeline network.

[0047] Furthermore, the decay rate of the left-side recursive feature difference and the decay rate of the right-side recursive feature difference in each segment are calculated separately, including:

[0048] The spatial gradient of the left recursive feature difference along the extension direction of the sensing fiber is calculated as the left attenuation rate.

[0049] The spatial gradient of the right-side recursive feature difference along the direction of the sensing fiber extension is calculated as the right-side attenuation rate.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. A probe light pulse is emitted from an ultra-stable laser source to a sensing fiber optic cable laid along a gas pipeline network. A single-photon detector responds to the single-photon signal in the returned backscattered Rayleigh light. This releases the detection sensitivity of distributed fiber optic sensing from the background noise limitation of linear photoelectric detection. This allows the extremely weak backscattered light power changes caused by early abnormal strain in the gas pipeline network, which were originally submerged under thermal and shot noise, to be effectively captured in the form of the presence and time distribution of single-photon events. Based on this, the signal processing unit does not simply rely on the absolute value of the photon count rate for anomaly discrimination. Instead, it extracts the statistical characteristics of the time interval between adjacent single-photon events from the counting pulse sequence. It indirectly amplifies the weak signal changes by using the perturbation of the statistical law of photon arrival by abnormal strain. Thus, a reliable photon count rate distributed along the sensing fiber optic cable is obtained before the strain develops to the stage of significant damage to the pipeline structure, providing a perceptible physical basis for early warning.

[0052] 2. After obtaining the photon count rate distributed along the sensing fiber, the signal processing unit divides it into multiple continuous segments and constructs a recursive graph for the photon count rate sequence of each segment. Recursive quantization parameters are extracted from the recursive graph to quantitatively characterize the nonlinear dynamic characteristics of the photon count rate sequence of each segment. By comparing the recursive quantization parameters of adjacent segments, the recursive feature difference is obtained, extending the discrimination dimension of abnormal strain from a single signal amplitude to the dynamic structure level of the signal. The signal processing unit further performs directional analysis on the recursive feature difference to obtain the bilateral attenuation asymmetry of the recursive feature difference in each segment. Utilizing the physical characteristics of the asymmetric constraints on both sides when the stress caused by abnormal strain in the gas pipeline propagates along the pipe body, segments exceeding the asymmetry threshold are identified as abnormal locations. This multi-layered progressive analysis architecture effectively distinguishes between signal changes caused by real abnormal strain and symmetrical environmental noise interference, significantly reducing the false alarm probability while maintaining single-photon-level sensitivity, thus achieving highly reliable distributed measurement and precise positioning of abnormal strain in the gas pipeline. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection, as described in this invention.

[0054] Figure 2 This is a flowchart of the distributed measurement process for abnormal strain in gas pipeline networks according to the present invention. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0056] Example: Figure 1 A schematic diagram of the distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection is provided. The system includes: an ultra-stable laser source, a sensing optical fiber laid along the gas pipeline network, a single-photon detector, and a signal processing unit. The output end of the ultra-stable laser source is connected to the incident end of the sensing optical fiber. The backscattered light return end of the sensing optical fiber is coupled to the photosensitive surface of the single-photon detector. The electrical signal output end of the single-photon detector is connected to the signal input end of the signal processing unit.

[0057] Figure 2 A flowchart of the distributed measurement process for abnormal strain in gas pipeline networks according to this invention is provided. In this process, an ultra-steady laser source emits probe light pulses towards the sensing fiber.

[0058] The single-photon detector collects the backscattered Rayleigh light generated by the probe light pulse in the sensing fiber, and responds to the single-photon signal in the backscattered Rayleigh light, outputting a counting pulse sequence corresponding to the single-photon event.

[0059] The signal processing unit obtains the photon count rate distributed along the sensing fiber based on the statistical characteristics of the time interval between adjacent single-photon events in the counting pulse sequence and the time relationship between the emission time of the probe light pulse;

[0060] The signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments, constructs a recursive graph for the photon count rate sequence of each segment and extracts the recursive quantization parameters, and compares the recursive quantization parameters of adjacent segments to obtain the recursive feature difference.

[0061] The signal processing unit performs directional analysis on the recursive feature difference to obtain the bilateral attenuation asymmetry of the recursive feature difference in each segment. The segment where the bilateral attenuation asymmetry exceeds the asymmetry threshold is identified as the abnormal location on the sensing fiber caused by abnormal strain of the gas pipeline network.

[0062] The output end of the ultra-stable laser source is connected to the incident end of the sensing fiber via a fiber optic flange connector. The fiber optic flange connector couples the probe light pulse output from the ultra-stable laser source into the incident end of the sensing fiber. The fiber optic flange connector is a single-mode fiber optic flange connector. The ceramic ferrule inside the connector physically aligns the fiber end face of the ultra-stable laser source's output end with the fiber end face of the sensing fiber's incident end, ensuring that the insertion loss of the probe light pulse transmitted from the output end of the ultra-stable laser source to the incident end of the sensing fiber is controlled within a preset range.

[0063] Optical coupling is achieved between the backscattered light return end of the sensing fiber and the photosensitive surface of the single-photon detector via a fiber optic patch cord. The backscattered Rayleigh light output from the backscattered light return end of the sensing fiber is transmitted through the fiber optic patch cord and then illuminates the photosensitive surface of the single-photon detector. The photosensitive surface of the single-photon detector is the light-receiving surface of the single-photon avalanche diode or superconducting nanowire single-photon detection device inside the single-photon detector. The distance between the output end face of the fiber optic patch cord and the photosensitive surface of the single-photon detector is set according to the size and numerical aperture of the photosensitive surface of the single-photon detector, so that the spot of backscattered Rayleigh light emitted from the fiber optic patch cord completely covers the photosensitive surface of the single-photon detector.

[0064] The electrical signal output terminal of the single-photon detector is connected to the signal input terminal of the signal processing unit via a coaxial cable. The counting pulse sequence output by the single-photon detector is transmitted to the signal processing unit via the coaxial cable. The signal input terminal of the signal processing unit is an analog or digital signal input interface with a defined characteristic impedance. The characteristic impedance of the coaxial cable is matched with the output impedance of the electrical signal output terminal of the single-photon detector and the input impedance of the signal input terminal of the signal processing unit.

[0065] The output end of the ultrastable laser source refers to the fiber optic output port on the ultrastable laser source equipment used to output probe light pulses. The incident end of the sensing fiber refers to the end face of the sensing fiber closer to the ultrastable laser source. After the probe light pulse enters the sensing fiber from the incident end, it propagates forward within the fiber. During propagation, the probe light pulse undergoes Rayleigh scattering with the fiber core material. Some of the Rayleigh scattered light returns in the opposite direction to the propagation direction of the probe light pulse, forming backscattered Rayleigh light. This backscattered Rayleigh light propagates in the opposite direction along the sensing fiber to the backscattered light return end. The backscattered light return end and the incident end of the sensing fiber share the same end face. The backscattered Rayleigh light is output from the backscattered light return end of the sensing fiber. The electrical signal output end of the single-photon detector refers to the interface through which the single-photon detector outputs electrical signals.

[0066] The sensing fiber is laid along the gas pipeline network, either on the outer wall of the pipeline or in the soil adjacent to it. The incident end and the backscattered light return end of the sensing fiber are located on the same side of the fiber. The ultra-stable laser source and the single-photon detector are located within the same monitoring station of the gas pipeline network. The signal processing unit is located within the same monitoring station or connected to the monitoring station via a communication link. Single-mode fiber optic patch cords are used, and SMA interface coaxial cables with a specified characteristic impedance are selected.

[0067] An ultrastable laser source generates pulsed substrate light. The ultrastable laser source is a narrow-linewidth laser employing frequency stabilization technology. An internal laser resonant cavity generates continuous laser output. This continuous laser output is then intensity-modulated by an internal intensity modulator to form pulsed substrate light. The intensity modulator can be an acousto-optic modulator or an electro-optic modulator. Based on an externally input modulation signal, the intensity modulator periodically modulates the continuous laser output, converting it into pulsed substrate light with a preset repetition frequency and a preset initial pulse width. The center wavelength of the pulsed substrate light lies within the transmission window of the sensing fiber; for example, the center wavelength is 1550 nanometers. The frequency stabilization technology of the ultrastable laser source refers to locking the laser frequency to a reference frequency of the absorption spectral lines of atoms or molecules, or to the resonant frequency of a high-precision optical reference cavity, thereby controlling the frequency drift of the pulsed substrate light output by the ultrastable laser source within a preset frequency drift range. The preset frequency drift range is set based on the requirement that the photon count rate measurement error caused by frequency drift does not exceed the upper limit when a single-photon detector counts photons in backscattered Rayleigh light. The preset frequency drift range is set as follows: based on the relationship between the Rayleigh scattering cross-section of the sensing fiber and the change in the intensity of the backscattered Rayleigh light, the correspondence between the frequency drift and the change in the intensity of the backscattered Rayleigh light is determined. Based on the lower resolvable limit of the single-photon detector for the change in the intensity of the backscattered Rayleigh light, the maximum allowable frequency drift is calculated, and this maximum allowable frequency drift is used as the upper limit of the preset frequency drift range.

[0068] The pulsed substrate light is pulse-modulated to form a probe light pulse. After being output from the ultrastable laser source, the pulsed substrate light enters the pulse modulator, which performs secondary pulse shaping on the substrate light, adjusting its pulse width and peak power to form the probe light pulse. The pulse modulator sets the pulse width of the probe light pulse according to the length of the sensing fiber and the spatial resolution. The relationship between the pulse width and spatial resolution is: spatial resolution equals the pulse width of the probe light pulse multiplied by the speed of light in the sensing fiber, then divided by 2. The pulse modulator sets the peak power of the probe light pulse according to the saturation count rate of the single-photon detector or the maximum incident photon flux allowed when the single-photon detector is in the linear response region. This ensures that when the backscattered Rayleigh light generated by the probe light pulse in the sensing fiber reaches the single-photon detector, the single-photon detector's response to the single-photon event within a single detection cycle is within the linear response region. The linear response region of a single-photon detector refers to the range of incident photon flux within which the count rate of the output counting pulse sequence of the single-photon detector is linearly related to the photon flux incident on the photosensitive surface of the single-photon detector. The upper limit of the linear response region of a single-photon detector is determined by the dead time and the probability of the following pulse. The repetition period of the probe pulse is set according to the length of the sensing fiber. The repetition period of the probe pulse satisfies the following condition: the repetition period is greater than twice the length of the sensing fiber divided by the speed of light in the sensing fiber. This ensures that the backscattered Rayleigh light generated by the previous probe pulse in the sensing fiber is completely received by the single-photon detector before the next probe pulse enters the sensing fiber from the incident end.

[0069] The probe light pulse enters the sensing fiber from the input end after passing through an optical isolator. The optical isolator is a fiber-coupled type, positioned in the optical path between the pulse modulator and the input end of the sensing fiber. The probe light pulse enters the optical isolator from its input port and exits from its output port, then enters the sensing fiber from its input end via a fiber optic flange connector. The optical isolator utilizes the Faraday rotation effect of magneto-optical crystals to allow the forward-propagating probe light pulse to pass through with low insertion loss. The reverse-propagating optical signal is blocked by the polarizer and analyzer inside the optical isolator, preventing backscattered Rayleigh light and Fresnel reflection light generated in the sensing fiber from returning to the pulse modulator and the ultra-stable laser source, thus avoiding disturbances to the frequency stability of the ultra-stable laser source caused by the returning light. The isolation level of the optical isolator is set according to the sensitivity of the ultra-stable laser source to the returning light, ensuring that the optical power of the returning light is attenuated below the upper limit of the allowable returning light power of the ultra-stable laser source.

[0070] The output of the ultra-stable laser source is connected to the input of the pulse modulator via fiber optic patch cords. The output of the pulse modulator is connected to the input port of the optical isolator via fiber optic patch cords. The output port of the optical isolator is connected to the incident end of the sensing fiber via a fiber optic flange connector. All of the above fiber optic patch cords are single-mode fiber optic patch cords, and the length of the fiber optic patch cords is selected such that the total additional insertion loss introduced by each fiber optic patch cord does not exceed a preset loss threshold. The preset loss threshold is set based on the optical power budget of the pulsed substrate light output from the ultra-stable laser source and the minimum incident photon flux required by the single-photon detector. The preset loss threshold is set as follows: subtract the optical power of the probe light pulse after pulse modulation and optical isolator from the optical power of the pulsed substrate light output from the ultra-stable laser source, then subtract the transmission loss of the probe light pulse in unidirectional transmission in the sensing fiber, and then subtract the transmission loss of the backscattered Rayleigh light in reverse transmission in the sensing fiber. The estimated optical power of the backscattered Rayleigh light reaching the photosensitive surface of the single-photon detector is obtained. The additional insertion loss value that makes the estimated optical power of the backscattered Rayleigh light lower than the minimum detectable photon flux of the single-photon detector is used as the preset loss threshold.

[0071] When a probe light pulse propagates in a sensing fiber, it generates backscattered Rayleigh light. After entering the sensing fiber from its incident end, the probe light pulse propagates forward along the fiber. During propagation, the probe light pulse interacts with the molecules of the fiber's core material. Photons of the probe light pulse are scattered by these molecules, with a portion of these scattered photons scattering in the opposite direction to the propagation direction of the probe light pulse; these scattered photons constitute the backscattered Rayleigh light. The locations of the backscattered Rayleigh light are continuously distributed along the sensing fiber, and the location of each photon in the backscattered light corresponds to the spatial coordinates of the location where the probe light pulse reaches that location. The intensity of the backscattered Rayleigh light is proportional to the instantaneous power of the probe light pulse at the corresponding location and the Rayleigh scattering coefficient of the sensing fiber at that location. The Rayleigh scattering coefficient of the sensing fiber at any spatial location is determined by the density and refractive index distribution of the fiber's core material at that location. When abnormal strain occurs in the gas pipeline network, the local stress applied by the abnormal strain to the sensing fiber changes the density and refractive index distribution of the fiber core material at the abnormal strain location, thereby changing the Rayleigh scattering coefficient of the sensing fiber at the abnormal strain location. This causes the intensity of the back Rayleigh scattered light to change at the abnormal strain location. The change in the intensity of the back Rayleigh scattered light is ultimately reflected in the change of the photon count rate distributed along the sensing fiber at the abnormal strain location obtained by the signal processing unit.

[0072] Backscattered Rayleigh light returns from the backscattered light return end of the sensing fiber. This backscattered light propagates in the sensing fiber in the opposite direction to the probe light pulse propagation direction. During this reverse propagation, the backscattered light attenuates due to transmission loss in the sensing fiber, and finally exits from the backscattered light return end. The backscattered light return end and the incident end of the sensing fiber share the same end face. After exiting from the backscattered light return end, the backscattered light is transmitted via fiber optic patch cord to the photosensitive surface of the single-photon detector.

[0073] A single-photon detector collects the returned backscattered Rayleigh light. This backscattered light enters the single-photon detector from its photosensitive surface via an optical fiber jumper. The single-photon detector is either a single-photon avalanche photodiode or a superconducting nanowire single-photon detector. Operating in Geiger mode, the bias voltage of the single-photon detector is set above its avalanche breakdown voltage, allowing a single photon incident on the photosensitive surface to trigger an avalanche effect, generating a macroscopically measurable electrical pulse signal. The detection efficiency of the single-photon detector in Geiger mode is defined as the probability that a single photon incident on the photosensitive surface is successfully detected and an electrical pulse is output. The detection efficiency is determined by the detector's material, structure, and bias voltage. The intensity of the backscattered Rayleigh light is extremely weak, and photons in this light arrive at the photosensitive surface of the single-photon detector as discrete single photons. The single-photon detector detects each arriving single photon independently.

[0074] A single-photon detector (SPD) converts a single-photon signal in backscattered Rayleigh light into an electrical pulse through photoelectric conversion. When a photon is absorbed by the SPD, an electron-hole pair is generated inside. Under the influence of the high electric field inside the SPD, this electron-hole pair undergoes avalanche multiplication, forming a macroscopic current pulse. This macroscopic current pulse is converted into a voltage pulse by a transimpedance amplifier inside the SPD; the voltage pulse is the electrical pulse. The amplitude of the electrical pulse is related to the operating bias voltage and gain of the SPD. The rise time of the electrical pulse is determined by the avalanche setup time of the SPD, and the width of the electrical pulse is determined by the time constant of the quenching circuit inside the SPD. After generating the electrical pulse, the SPD enters a dead time, during which it does not respond to the incident photon. The duration of the dead time is determined by the design parameters of the quenching and reset circuits of the SPD. The maximum count rate of the SPD is the reciprocal of the dead time. In distributed measurement of abnormal strain in gas pipeline networks, the dead time of the single-photon detector is set based on the length of the sensing fiber and the repetition period of the probe light pulse. The setting method is as follows: based on the length of the sensing fiber and the propagation speed of light in the sensing fiber, the length of the time window for the backscattered Rayleigh light to return from the backscattered light return end of the sensing fiber is calculated. The dead time of the single-photon detector is set to be less than or equal to the round-trip time corresponding to the spatial resolution of the sensing fiber. This ensures that within the time window for the backscattered Rayleigh light to return, the single-photon detector can effectively count the single-photon events in the continuously arriving backscattered Rayleigh light, avoiding photon count loss due to the dead time.

[0075] A single-photon detector shapes electrical pulses into a counting pulse sequence. The electrical pulses are input to a comparator circuit inside the single-photon detector. The comparator circuit compares the amplitude of the electrical pulse with a preset discrimination level. When the amplitude of the electrical pulse exceeds the preset discrimination level, the comparator circuit outputs a standard digital pulse signal, which is one of the counting pulses in the counting pulse sequence. The preset discrimination level is set based on the noise characteristics of the single-photon detector. The setting method is as follows: under conditions of no backscattered Rayleigh light incident, the amplitude distribution of the dark counting electrical pulses output by the single-photon detector is measured. The upper limit of the amplitude distribution of the dark counting electrical pulses is taken as the lower limit of the preset discrimination level. Simultaneously, the lower limit of the amplitude distribution of the single-photon response electrical pulses output by the single-photon detector in response to weak light signals is taken as the upper limit of the preset discrimination level. An amplitude value between the lower and upper limits of the preset discrimination level is selected as the preset discrimination level, ensuring that the preset discrimination level can distinguish between single-photon response events and dark counting events. Each counting pulse in the counting pulse sequence output by the comparator circuit inside the single-photon detector corresponds to a successfully detected single-photon event in the backscattered Rayleigh light. The time interval between adjacent counting pulses in the counting pulse sequence records the time interval between adjacent single-photon events. The counting pulse sequence output by the single-photon detector is transmitted to the signal processing unit via a coaxial cable.

[0076] The signal processing unit receives the counting pulse sequence. The counting pulse sequence output by the single-photon detector arrives at the signal input terminal of the signal processing unit via a coaxial cable, and the signal processing unit receives the counting pulse sequence through the signal input terminal. Each counting pulse in the counting pulse sequence corresponds to a successfully detected single-photon event in the backscattered Rayleigh light. The arrival time of each counting pulse in the counting pulse sequence is recorded by the signal processing unit, and the timing reference for the arrival time of each counting pulse shares the same internal clock reference as the emission time of the probe light pulse.

[0077] The signal processing unit extracts the time interval between adjacent single-photon events in the counting pulse sequence. The unit sequentially reads the arrival times of two adjacent counting pulses from the sequence and calculates the difference between them. This difference is the time interval between adjacent single-photon events. The time interval reflects the time difference between the arrival of two adjacent single-photon events in the backscattered Rayleigh light at the single-photon detector.

[0078] The signal processing unit statistically analyzes the distribution characteristics of time intervals. The process of analyzing the distribution characteristics of time intervals in the signal processing unit includes: the signal processing unit generating a statistical histogram of the time intervals between adjacent single-photon events in the counting pulse sequence based on the time intervals between adjacent single-photon events; the signal processing unit calculating the degree of deviation between the statistical histogram and the Poisson distribution, and using this deviation as a distribution characteristic of the time intervals.

[0079] The process of generating a statistical histogram of the time intervals between adjacent single-photon events in a counting pulse sequence is as follows: The signal processing unit divides the extracted time intervals between adjacent single-photon events into multiple time interval intervals according to a preset time interval interval width. It then counts the number of time intervals between adjacent single-photon events falling within each time interval. A statistical histogram is generated by plotting the time interval intervals on the horizontal axis and the number of time intervals between adjacent single-photon events falling within each time interval on the vertical axis. The preset time interval interval width is set based on the time resolution of the single-photon detector and the length of the sensing fiber. The setting method is to set the time interval interval width to an integer multiple of the time resolution of the single-photon detector, ensuring that the interval width can distinguish the statistical changes in the time intervals of photons arriving in the backscattered Rayleigh light, while also ensuring that the number of time intervals between adjacent single-photon events within each time interval is statistically significant.

[0080] The process of calculating the deviation between the statistical histogram and the Poisson distribution is as follows: The signal processing unit constructs a Poisson distribution with the same average time interval as the statistical histogram, based on the average time interval between adjacent single-photon events in the statistical histogram. The signal processing unit calculates the difference between the count value of each time interval in the statistical histogram and the expected count value of the reference Poisson distribution in the corresponding time interval. The square of the difference for each time interval is divided by the expected count value of the reference Poisson distribution in the corresponding time interval. The summation is then applied to all time intervals to obtain the deviation. The deviation is calculated as: D = ∑[(Oi - Ei)] 2 / Ei]; where D represents the degree of deviation, Oi represents the count value of the i-th time interval in the statistical histogram, Ei represents the expected count value of the reference Poisson distribution in the corresponding i-th time interval, and i represents the index of the time interval, with i ranging from 1 to the total number of time intervals.

[0081] In distributed measurement of abnormal strain in gas pipeline networks, under strain-free conditions in the sensing fiber, the arrival time of photons in backscattered Rayleigh light follows a Poisson distribution, while the time interval between adjacent single-photon events follows an exponential distribution. When abnormal strain occurs in the gas pipeline network, the local stress caused by the abnormal strain alters the scattering characteristics of the sensing fiber at the location of the abnormal strain, causing the photon statistical law of the backscattered Rayleigh light to deviate from the Poisson distribution. The degree of deviation precedes the change in the absolute value of the photon count rate. Therefore, using the degree of deviation as a distribution feature of the time interval allows for earlier detection of abnormal strain. Compared to conventional methods that directly calculate the photon count rate, this method extracts information from the statistical law of photon arrival by utilizing the distribution feature of the time interval. It leverages the ability of a single-photon detector to record the precise arrival time of each single-photon event, indirectly amplifying weak signal changes submerged under noise by perturbing the photon statistical law, resulting in higher detection sensitivity.

[0082] The signal processing unit maps the distribution characteristics of the time intervals to the spatial location of the sensing fiber based on the temporal relationship between the time interval distribution and the emission time of the probe light pulse. The mapping process is as follows: the signal processing unit records the arrival time of each single-photon event. For each single-photon event, the unit calculates the time difference between the arrival time and the emission time of the probe light pulse, multiplies this time difference by the speed of light in the sensing fiber, and then divides by 2 to obtain the spatial location of the sensing fiber corresponding to each single-photon event. Each time interval between adjacent single-photon events corresponds to two single-photon events. The signal processing unit maps the deviation between the time intervals of adjacent single-photon events to the spatial location of the sensing fiber corresponding to the midpoint of the two single-photon events between the time intervals of adjacent single-photon events.

[0083] The signal processing unit calculates the photon count rate distributed along the sensing fiber based on the distribution characteristics of the time intervals mapped to the spatial positions of the sensing fiber. The signal processing unit converts these time interval distribution characteristics into photon count rates distributed along the sensing fiber. The conversion method involves: the signal processing unit pre-establishing a calibration relationship between the time interval distribution characteristics and the photon count rate. This calibration relationship is established by measuring the corresponding deviation under different photon count rate conditions. Based on the calibration relationship, the signal processing unit converts the deviation of the spatial positions mapped to the sensing fiber into the photon count rate at the corresponding spatial positions, thereby obtaining the photon count rate distributed along the sensing fiber. The process of establishing the calibration relationship is as follows: under strain-free conditions, the signal processing unit changes the peak power of the probe light pulse to change the intensity of the backscattered Rayleigh light at different spatial positions in the sensing fiber, thereby obtaining different photon count rates. The signal processing unit calculates the deviation under different photon count rates, obtaining a calibration curve showing the deviation as a function of the photon count rate. This calibration curve is stored in the signal processing unit as the calibration relationship.

[0084] The photon count rate distributed along the sensing fiber reflects the intensity distribution of back Rayleigh scattered light at each spatial location along the sensing fiber. When the gas pipeline experiences abnormal strain at a certain location, the intensity of back Rayleigh scattered light at the abnormal strain location changes due to the change in the Rayleigh scattering coefficient of the sensing fiber. This change in the intensity of back Rayleigh scattered light is reflected in the photon count rate distributed along the sensing fiber as a deviation between the photon count rate at the corresponding spatial location and the photon count rate at adjacent spatial locations.

[0085] The signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments according to spatial location. Starting from the spatial position corresponding to the incident end of the sensing fiber, the signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments according to a preset segment length. Each continuous segment corresponds to a continuous spatial range on the sensing fiber. The preset segment length is set according to the spatial resolution of the sensing fiber and the positioning accuracy requirements of abnormal strain detection in the gas pipeline network. The setting method is as follows: the preset segment length is set to an integer multiple of the spatial resolution of the sensing fiber, so that the number of photon count rate data points contained in each continuous segment meets the data length requirements of phase space reconstruction, and at the same time, the spatial interval between adjacent segments can distinguish the spatial range of abnormal strain in the gas pipeline network extending along the pipe body. For example, the preset segment length is 5 to 10 times the spatial resolution of the sensing fiber.

[0086] The signal processing unit performs phase space reconstruction on the photon count rate sequence for each segment, obtaining the phase space trajectory of the photon count rate sequence for each segment. The phase space reconstruction process is as follows: for each segment of the photon count rate sequence, the signal processing unit reconstructs the photon count rate sequence from a one-dimensional time series into a phase space trajectory in a multi-dimensional phase space based on the embedding dimension and delay time. The embedding dimension is determined based on the estimated nonlinear degrees of freedom of the photon count rate sequence. The estimation method is as follows: the signal processing unit performs spurious nearest neighbor analysis on the photon count rate sequence, calculating the proportion of adjacent state points moving further apart in the phase space as the embedding dimension increases, under different embedding dimensions. The embedding dimension when the proportion of spurious nearest neighbors is lower than a preset threshold is taken as the embedding dimension of the photon count rate sequence. The preset threshold is set based on the photon counting noise level of the single-photon detector for backscattered Rayleigh light. The setting method is as follows: the preset threshold is set as the estimated proportion of spurious nearest neighbors caused by the state point fluctuations caused by the dark counting of the single-photon detector in the phase space. The delay time is determined based on the autocorrelation function of the photon count rate sequence. The determination method is as follows: the signal processing unit calculates the autocorrelation function of the photon count rate sequence and takes the delay time at which the autocorrelation function first drops to a preset proportion of its maximum value as the phase space reconstruction delay time. The preset proportion is set according to the relationship between the coherence time of the backscattered Rayleigh light in the sensing fiber and the sampling interval of the photon count rate sequence; for example, the preset proportion is 1 / e. The signal processing unit performs time-delayed embedding of the photon count rate sequence using the embedding dimension and the delay time. It extracts consecutive data points of each embedding dimension from the photon count rate sequence according to the delay time interval, forming a state point in the phase space. All state points are arranged in chronological order to form the phase space trajectory of each segment of the photon count rate sequence.

[0087] A recursive graph for each segment is constructed based on the phase space trajectory of the photon count rate sequence for each segment. The process of constructing the recursive graph for each segment is as follows: the signal processing unit calculates the distance between any two state points in the phase space trajectory, marks state point pairs whose distances are less than a preset distance threshold as recursive states, and constructs the recursive graph based on the distribution of the recursive states. When calculating the distance between any two state points in the phase space trajectory, the signal processing unit calculates the Euclidean distance between each state point and all other state points in the phase space trajectory. To calculate the Euclidean distance, the signal processing unit squares the differences between the coordinate components of each state point in phase space, sums them, and then takes the square root to obtain the Euclidean distance between the two state points. The preset distance threshold is set based on the average distance between state points in the phase space trajectory and the signal-to-noise ratio (SNR) of the photon count rate sequence. The setting method is as follows: the signal processing unit calculates the average distance between all pairs of state points in the phase space trajectory, and sets the preset distance threshold as the average distance multiplied by a preset distance scaling factor. The preset distance scaling factor is determined based on the SNR of the counting pulse sequence output by the single-photon detector. The higher the SNR, the smaller the preset distance scaling factor, enabling the preset distance threshold to distinguish between state point proximity caused by nonlinear dynamic similarity and state point proximity caused by noise. The signal processing unit marks state point pairs with a distance less than the preset distance threshold as recursive states. Each state point in the phase space trajectory corresponds to a photon count rate data point at a spatial location on the sensing fiber. The signal processing unit constructs a recursion graph based on the distribution of recursive states. The recursion graph is a binary matrix, with both the number of rows and columns equal to the total number of state points in the phase space trajectory. When the distance between the *a*th and *b*th state points is less than a preset distance threshold, the element in the *a*th row and *b*th column of the binary matrix is ​​set to 1; when the distance between the *a*th and *b*th state points is greater than or equal to the preset distance threshold, the element in the *a*th row and *b*th column of the binary matrix is ​​set to 0. Elements with a value of 1 in the recursion graph indicate that the corresponding state point pair is in a recursive state, while elements with a value of 0 indicate that the corresponding state point pair is not in a recursive state. The texture structure of the recursion graph reflects the nonlinear dynamic characteristics of the photon count rate sequence.

[0088] In distributed measurement of abnormal strain in gas pipeline networks, the photon count rate sequence of the sensing fiber exhibits stable nonlinear dynamic characteristics in the strain-free region, and its recurrence graph displays a uniformly distributed recurrence state. When abnormal strain occurs in the gas pipeline network, the local stress exerted by the abnormal strain on the sensing fiber causes changes in the scattering characteristics of the sensing fiber in the abnormal strain region, thereby altering the nonlinear dynamic characteristics of the photon count rate sequence and changing the distribution pattern of the recurrence state in the recurrence graph. Recurrence graph analysis can capture the changes in the nonlinear dynamic characteristics of the photon count rate sequence caused by abnormal strain. The changes in nonlinear dynamic characteristics caused by abnormal strain occur significantly before the changes in the photon count rate amplitude. Therefore, recurrence graph analysis has higher sensitivity for detecting early abnormal strain than methods that only analyze changes in the photon count rate amplitude.

[0089] The signal processing unit extracts recursive quantization parameters from the recursive graph of each segment. These parameters include recursion rate, determination rate, average diagonal length, recursion entropy, and laminar flow rate. The recursion rate is the proportion of elements with a value of 1 in the recursive graph to the total number of elements in the recursive graph; it reflects the degree of clustering of state points in the phase space trajectory. The determination rate is the proportion of elements with a value of 1 constituting the diagonal structure in the recursive graph to the total number of elements with a value of 1; it reflects the degree of deterministic regularity in the photon count rate sequence. The average diagonal length is the average length of all diagonal structures in the recursive graph; it reflects the persistence of dynamic states in the photon count rate sequence. The recursion entropy is the Shannon entropy of the diagonal structure length distribution in the recursive graph; it reflects the complexity of the texture structure of the recursive graph. The laminar flow rate is the proportion of elements with a value of 1 constituting the vertical line structure in the recursive graph to the total number of elements with a value of 1; it reflects the degree of state invariance in the photon count rate sequence.

[0090] The signal processing unit compares the recursive quantization parameters of adjacent segments to obtain the recursive feature difference. The recursive feature difference reflects the degree of difference in nonlinear dynamic characteristics between two adjacent segments. The recursive feature difference is calculated as follows: For each pair of adjacent segments, the signal processing unit calculates the difference in recursion rate, the difference in determination rate, the difference in average diagonal length, the difference in recursion entropy, and the difference in laminar flow rate between the adjacent segments. The absolute values ​​of the differences in recursion rate, determination rate, average diagonal length, recursion entropy, and laminar flow rate are then summed to obtain the recursive feature difference. The recursive feature difference is calculated as follows: Δ = |RR1 - RR2| + |DET1 - DET2| + |L1 - L2| + |ENTR1 - ENTR2| + |LAM1 - LAM2|; where Δ represents the recursive feature difference, RR1 represents the recursion rate of the first segment in the adjacent segments, RR2 represents the recursion rate of the second segment in the adjacent segments, DET1 represents the determination rate of the first segment in the adjacent segments, DET2 represents the determination rate of the second segment in the adjacent segments, L1 represents the average diagonal length of the first segment in the adjacent segments, L2 represents the average diagonal length of the second segment in the adjacent segments, ENTR1 represents the recursion entropy of the first segment in the adjacent segments, ENTR2 represents the recursion entropy of the second segment in the adjacent segments, LAM1 represents the laminar flow rate of the first segment in the adjacent segments, and LAM2 represents the laminar flow rate of the second segment in the adjacent segments.

[0091] The recursive characteristic difference exhibits a non-zero but small value in the unstrained section of the sensing fiber due to noise, while it exhibits a larger value between the anomalous strain section and the adjacent unstrained section due to the significant difference in nonlinear dynamic characteristics. The signal processing unit outputs the recursive characteristic difference for subsequent directionality analysis and anomaly location determination.

[0092] The signal processing unit extracts recursive feature differences segment by segment along the extension direction of the sensing fiber, centering on each segment. The unit selects a segment as the current segment and, starting from its spatial location, extracts the recursive feature differences between each segment to the left of the current segment and its adjacent segments, segment by segment, along the extension direction of the sensing fiber towards the incident end. Simultaneously, it extracts the recursive feature differences between each segment to the right of the current segment and its adjacent segments, segment by segment, along the extension direction of the sensing fiber towards the incident end away from the sensing fiber. The signal processing unit performs this extraction operation on each segment, obtaining the spatial distribution sequence of the recursive feature differences on the left and right sides of each segment.

[0093] Calculate the attenuation rate of the left-side recursive feature difference and the attenuation rate of the right-side recursive feature difference for each segment. Calculate the spatial gradient of the left-side recursive feature difference along the direction of the sensing fiber extension as the left-side attenuation rate, and calculate the spatial gradient of the right-side recursive feature difference along the direction of the sensing fiber extension as the right-side attenuation rate.

[0094] The spatial gradient of the left-side recursive feature difference along the direction of the sensing fiber is calculated as follows: The signal processing unit linearly fits the recursive feature difference values ​​in the spatial distribution sequence of the left-side recursive feature difference to the spatial distance between the corresponding segment and the current segment, and takes the absolute value of the slope of the linear fit as the left-side attenuation rate. The spatial gradient of the right-side recursive feature difference along the direction of the sensing fiber is calculated as follows: The signal processing unit linearly fits the recursive feature difference values ​​in the spatial distribution sequence of the right-side recursive feature difference to the spatial distance between the corresponding segment and the current segment, and takes the absolute value of the slope of the linear fit as the right-side attenuation rate. The spatial gradient of the left-side recursive feature difference along the direction of the sensing fiber is calculated as follows: Where GL represents the spatial gradient of the left-side recursive feature difference along the direction of the sensing fiber extension, and dj represents the spatial distance between the j-th segment on the left and the current segment. This represents the average spatial distance between all left segments and the current segment, where Δj represents the recursive feature difference corresponding to the j-th left segment. This represents the average of the differences in all left-hand recursive features.

[0095] The spatial gradient of the right-hand recursive feature difference along the direction of the sensing fiber extension is calculated as follows: Where GR represents the spatial gradient of the recursive feature difference on the right along the direction of the sensing fiber extension, and dk represents the spatial distance between the k-th segment on the right and the current segment. Δk represents the average spatial distance between all right-hand segments and the current segment, and Δk represents the recursive feature difference corresponding to the k-th right-hand segment. This represents the average of the differences in all right-hand recursive features.

[0096] In distributed measurement of abnormal strain in gas pipeline networks, when abnormal strain occurs at a certain location in the gas pipeline network, the local stress exerted by the abnormal strain on the sensing fiber propagates outwards along the extension direction of the sensing fiber, centered on the location of the abnormal strain, and gradually attenuates. During the propagation of local stress, the scattering characteristics of the sensing fiber change most significantly at the location of the abnormal strain, gradually returning to a strain-free state towards both sides. The recursive characteristic difference exhibits its maximum value between the segment where the abnormal strain is located and adjacent segments, gradually decreasing with increasing spatial distance from the location of the abnormal strain. Since the constraints on the pipe structure of the gas pipeline network are usually asymmetrical on both sides of the abnormal strain location—for example, one side may be constrained by a fixed pipe support while the other side is free—the attenuation rate of the local stress differs between the two sides. This difference manifests as unequal attenuation rates on the left and right sides. Compared to methods that rely solely on the maximum value of the recursive characteristic difference for anomaly localization, utilizing the asymmetry between the attenuation rates on the left and right sides can distinguish between changes in the recursive characteristic difference caused by genuine abnormal strain and fluctuations in the symmetrical recursive characteristic difference caused by environmental noise, thus reducing the probability of false alarms.

[0097] The signal processing unit compares the attenuation rate of the recursive feature difference on the left side with the attenuation rate on the right side of each segment to obtain the bilateral attenuation asymmetry for each segment. The bilateral attenuation asymmetry is calculated as the absolute value of the difference between the left and right attenuation rates divided by the sum of the left and right attenuation rates. The bilateral attenuation asymmetry is calculated as: Φ = |GL - GR| / (GL + GR); where Φ represents the bilateral attenuation asymmetry, GL represents the spatial gradient of the left recursive feature difference along the direction of the sensing fiber, and GR represents the spatial gradient of the right recursive feature difference along the direction of the sensing fiber. The value of the bilateral attenuation asymmetry ranges from 0 to 1. When the attenuation rate on the left side is equal to the attenuation rate on the right side, the bilateral attenuation asymmetry is 0, indicating that the attenuation trend of the recursive feature difference is completely symmetrical on both sides, corresponding to a strain-free segment or symmetrical environmental noise interference. When the difference between the decay rate on the left and the decay rate on the right increases, the asymmetry of the decay on both sides approaches 1, indicating that the decay trend of the recursive characteristic difference is significantly asymmetrical on the left and right sides, corresponding to the asymmetric stress distribution caused by abnormal strain in the gas pipeline network.

[0098] The signal processing unit identifies sections where the bilateral attenuation asymmetry exceeds the asymmetry threshold as abnormal locations on the sensing fiber optic cable where losses are caused by abnormal strain in the gas pipeline network. The asymmetry threshold is set based on the statistical distribution of bilateral attenuation asymmetry caused by noise in the unstrained section of the sensing fiber optic cable. The setting method is as follows: under unstrained conditions, the signal processing unit calculates the bilateral attenuation asymmetry of each section, calculates the mean and standard deviation of the bilateral attenuation asymmetry, and sets the asymmetry threshold to the mean of the bilateral attenuation asymmetry plus, for example, three times the standard deviation. When the bilateral attenuation asymmetry of a certain section exceeds the asymmetry threshold, the signal processing unit marks that section as a candidate abnormal strain section and determines the spatial location of the candidate abnormal strain section as the abnormal location on the sensing fiber optic cable where losses are caused by abnormal strain in the gas pipeline network. The signal processing unit outputs the abnormal location.

[0099] All calculations involved in the embodiments are dimensionless numerical calculations, and the preset parameters and thresholds in the calculations are set by those skilled in the art according to the actual situation.

[0100] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0101] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection, characterized in that, include: Ultra-stable laser source, sensing optical fiber laid along the gas pipeline network, single-photon detector and signal processing unit; Among them, the ultra-stable laser source emits probe light pulses toward the sensing fiber; The single-photon detector collects the backscattered Rayleigh light generated by the probe light pulse in the sensing fiber, and responds to the single-photon signal in the backscattered Rayleigh light, outputting a counting pulse sequence corresponding to the single-photon event. The signal processing unit obtains the photon count rate distributed along the sensing fiber based on the statistical characteristics of the time interval between adjacent single-photon events in the counting pulse sequence and the time relationship between the emission time of the probe light pulse; The signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments, constructs a recursive graph for the photon count rate sequence of each segment and extracts the recursive quantization parameters, and compares the recursive quantization parameters of adjacent segments to obtain the recursive feature difference. The signal processing unit performs directional analysis on the recursive feature difference to obtain the bilateral attenuation asymmetry of the recursive feature difference in each segment. The segment where the bilateral attenuation asymmetry exceeds the asymmetry threshold is identified as the abnormal location on the sensing fiber caused by abnormal strain of the gas pipeline network.

2. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 1, characterized in that, The output end of the ultra-stable laser source is connected to the incident end of the sensing fiber, the backscattered light return end of the sensing fiber is coupled to the photosensitive surface of the single-photon detector, and the electrical signal output end of the single-photon detector is connected to the signal input end of the signal processing unit.

3. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 1, characterized in that, An ultra-steady laser source emits probe light pulses into the sensing fiber, including: An ultra-stable laser source generates pulsed substrate light; The pulsed substrate light is pulse-modulated to form a probe light pulse; The probe light pulse enters the sensing fiber from the incident end after passing through the optical isolator.

4. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 1, characterized in that, A single-photon detector collects the backscattered Rayleigh light generated by the probe light pulse in the sensing fiber, and responds to the single-photon signal in the backscattered Rayleigh light, outputting a counting pulse sequence corresponding to the single-photon event, including: When the probe light pulse propagates in the sensing optical fiber, it generates backscattered Rayleigh light. Backscattered Rayleigh light returns from the backscattered light return end of the sensing fiber; A single-photon detector collects the returned back Rayleigh scattered light; A single-photon detector performs photoelectric conversion on the single-photon signal in the backscattered Rayleigh light to generate an electrical pulse; Single-photon detectors shape electrical pulses into a sequence of counting pulses.

5. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 1, characterized in that, The signal processing unit obtains the photon count rate distributed along the sensing fiber based on the statistical characteristics of the time interval between adjacent single-photon events in the counting pulse sequence and the temporal relationship between the emission time of the probe light pulse, including: Receive counting pulse sequence; Extract the time interval between adjacent single-photon events in the counting pulse sequence; Distribution characteristics of statistical time intervals; Based on the distribution characteristics of the time interval and the temporal relationship between the emission time of the probe light pulse, the distribution characteristics of the time interval are mapped to the spatial location of the sensing fiber. The photon count rate distributed along the sensing fiber is calculated based on the distribution characteristics of the time intervals mapped to the spatial location of the sensing fiber.

6. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 5, characterized in that, The distribution characteristics of statistical time intervals include: Generate a statistical histogram of the time interval between adjacent single-photon events in the counting pulse sequence; Calculate the degree of deviation between the statistical histogram and the Poisson distribution, and use the degree of deviation as a distributional characteristic of the time interval.

7. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 1, characterized in that, The signal processing unit divides the photon count rate distributed along the sensing fiber into multiple continuous segments, constructs a recursive graph for the photon count rate sequence of each segment, extracts recursive quantization parameters, and compares the recursive quantization parameters of adjacent segments to obtain the recursive feature difference, including: The photon count rate distributed along the sensing fiber is divided into multiple continuous segments according to spatial location. Phase space reconstruction is performed on the photon count rate sequence of each segment to obtain the phase space trajectory of the photon count rate sequence of each segment; A recursive graph for each segment is constructed based on the phase space trajectory of the photon count rate sequence for each segment; Extract recursive quantization parameters from the recursive graph of each segment; By comparing the recursive quantization parameters of adjacent segments, the recursive feature difference is obtained.

8. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 7, characterized in that, A recursive graph for each segment is constructed based on the phase space trajectory of the photon count rate sequence for each segment, including: Calculate the distance between any two state points in the phase space trajectory; Mark state point pairs whose distance is less than a preset distance threshold as recursive states; Construct a recursion graph based on the distribution of recursive states.

9. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 1, characterized in that, The signal processing unit performs directional analysis on the recursive feature differences to obtain the bilateral attenuation asymmetry of the recursive feature differences in each segment. Segments where the bilateral attenuation asymmetry exceeds the asymmetry threshold are identified as abnormal locations on the sensing fiber caused by abnormal strain in the gas pipeline network, including: Taking each segment as the center, the recursive feature difference is extracted segment by segment from both sides along the extension direction of the sensing fiber. Calculate the decay rate of the left-side recursive feature difference and the decay rate of the right-side recursive feature difference for each segment. By comparing the decay rate of the left-side recursive feature difference with the decay rate of the right-side recursive feature difference in each segment, the bilateral decay asymmetry of each segment is obtained. The section where the attenuation asymmetry on both sides exceeds the asymmetry threshold is identified as the abnormal location on the sensing fiber caused by abnormal strain of the gas pipeline network.

10. The distributed measurement system for abnormal strain in gas pipeline networks based on quantum single-photon detection according to claim 9, characterized in that, Calculate the decay rate of the left-side recursive feature difference and the decay rate of the right-side recursive feature difference for each segment, including: The spatial gradient of the left recursive feature difference along the extension direction of the sensing fiber is calculated as the left attenuation rate. The spatial gradient of the right-side recursive feature difference along the direction of the sensing fiber extension is calculated as the right-side attenuation rate.

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