A method and system for locating a disturbed area of a sensing optical fiber based on a phase signal

Abstract

The present invention discloses a method and system for locating a disturbed area of a sensing optical fiber based on a phase signal. The method includes: collecting a backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix; equally dividing the sensing optical fiber to obtain a plurality of optical fiber regions; obtaining a winding phase difference signal of each optical fiber region according to the phase signal matrix; successively performing phase unwrapping, detrending, and cross-correlation processing on the winding phase difference signal to obtain a cross-correlation result; normalizing the cross-correlation result to determine the area where the disturbance occurs. The present invention reduces the amount of data processing by reducing the demodulation operation of the amplitude signal.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber disturbance positioning, and particularly relates to a method and system for positioning a disturbed area of a sensing optical fiber based on a phase signal. Background Art

[0002] As a new type of sensing technology, the distributed optical fiber sensing technology uses a long-distance optical fiber as a sensor device, and has many advantages such as safety and reliability, high sensitivity, and low cost, and has a very broad application prospect. The Phase-Sensitive Optical Time Domain Reflectometry (Φ-OTDR) is a kind of distributed optical fiber sensing technology, which mainly uses the backward Rayleigh scattering in the optical fiber to realize the quantitative measurement and positioning of the point to be measured. Because of its advantages such as high positioning accuracy, multi-point disturbance positioning, and large dynamic response range, it has attracted much attention in recent research and is widely used in scenarios such as structural health monitoring, railway track monitoring, security intrusion alarm, and power pipe gallery monitoring.

[0003] The Φ-OTDR system emits an optical pulse with high coherence into the sensing optical fiber, and the backward Rayleigh scattering lights generated by different scattering centers on the optical fiber interfere with each other. The external disturbance is located by analyzing the received Rayleigh scattering trace. At present, most of the research on Φ-OTDR disturbance positioning is based on the amplitude signal obtained by demodulating the original signal. For example, CN110806259A discloses a device for high-frequency disturbance positioning and detection of optical fiber sensing, including: a first laser, a first coupler, an acousto-optic modulator, an erbium-doped fiber amplifier, a first tunable attenuator, a first wavelength division multiplexer, a second wavelength division multiplexer, a second laser, a second coupler, a second tunable attenuator, a circulator, a sensing optical fiber, a Bragg fiber grating, a third coupler, an optical balanced detector, a data acquisition card, and a computer; the computer filters the electrical signal collected by the data acquisition card to separate the interference signals of two wavelengths, λ1 and λ2; the interference signal of the λ1 wavelength is quadrature demodulated to obtain the amplitude information of the signal, and then the variance processing is performed on the interference signal of the λ1 wavelength to obtain the position information of the external disturbance; the interference signal of the λ2 wavelength is phase demodulated to obtain the frequency information of the external disturbance. Although it can obtain the position and frequency information of the disturbance through the amplitude, in actual applications, the signal processing after obtaining the disturbance position sometimes only involves the phase signal. If the amplitude signal is used for positioning, the amplitude calculation with low subsequent utilization rate will be introduced in the demodulation preprocessing, resulting in data redundancy.

[0004] Therefore, how to provide a method for disturbing positioning through a phase signal is an urgent problem to be solved in this field. Summary of the Invention

[0005] In view of the defects existing in the above-mentioned prior art, the present invention provides a method and system for locating a disturbed area of a sensing optical fiber based on a phase signal. By collecting the backward Rayleigh scattering optical signal returned on the sensing optical fiber, when demodulating the backward Rayleigh scattering optical signal, only the phase signal needs to be obtained to locate the disturbed area, and the data processing amount is reduced by reducing the demodulation operation of the amplitude signal.

[0006] In a first aspect, the present invention provides a method for locating a disturbed area of a sensing optical fiber based on a phase signal, including:

[0007] Collecting the backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;

[0008] Dividing the sensing optical fiber at equal intervals to obtain a plurality of optical fiber regions;

[0009] Obtaining the winding phase difference signal of each optical fiber region according to the phase signal matrix;

[0010] Performing unwrapping, detrending, and cross-correlation processing on the winding phase difference signal in sequence to obtain a cross-correlation result;

[0011] Normalizing the cross-correlation result to determine the area where the disturbance occurs.

[0012] Further, dividing the sensing optical fiber at equal intervals specifically includes:

[0013] Dividing the sensing optical fiber at equal intervals with the acquisition points on the sensing optical fiber as the division nodes.

[0014] Further, collecting the backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix, including:

[0015] Injecting a plurality of optical pulses into the sensing optical fiber by using a Φ-OTDR distributed optical fiber sensing system;

[0016] Collecting the backward Rayleigh scattering signals of the plurality of optical pulses through the Φ-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix including time domain information and spatial domain information;

[0017] Performing phase demodulation on the two-dimensional signal matrix by using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size.

[0018] Further, performing phase demodulation on the two-dimensional signal matrix by using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size, including:

[0019] Multiplying the two-dimensional signal matrix by sin(2πΔf IF t) and cos(2πΔf IF t) respectively, filtering out the second harmonic components through a low-pass filter, and obtaining the in-phase component I and the quadrature component Q respectively;

[0020] The in-phase component and the quadrature component are subjected to arctangent processing to obtain a phase signal matrix

[0021] Among them, the phase signal matrix satisfies the following relationship:

[0022]

[0023]

[0024]

[0025] In the formula, I is the in-phase component, Q is the quadrature component, and P AC is the power of the backscattered Rayleigh signal, E is the amplitude information of the backscattered Rayleigh signal, represents the phase signal matrix, and Δf IF represents the frequency shift introduced by the acousto-optic modulator, and t is the time corresponding to the phase signal.

[0026] Furthermore, the winding phase difference signals of each optical fiber region are obtained according to the phase signal matrix, including:

[0027] All optical fiber regions are matched with the phase signal matrix to give the phase signals at both ends of each optical fiber region;

[0028] According to the phase signals at both ends of each optical fiber region, the corresponding winding phase difference signals are obtained, specifically including:

[0029]

[0030] In the formula, is the winding phase difference signal of the k-th optical fiber region, represents the phase time-domain signal corresponding to the k*ω-th acquisition point of the sensing optical fiber, and ω represents the number of acquisition points in the optical fiber region.

[0031] Furthermore, the winding phase difference signals are successively subjected to phase unwrapping, detrending, and cross-correlation processing to obtain cross-correlation results, including:

[0032] The winding phase difference signal is phase-unwrapped to obtain an unwrapped differential phase signal;

[0033] The unwrapped differential phase signal is detrended to obtain a detrended differential phase signal;

[0034] The detrended differential phase signals in two consecutive detection periods are overlapped and corresponded in both the time and space domains;

[0035] Perform cross-correlation operation on the differential phase signals after overlapping and corresponding to obtain the global cross-correlation result.

[0036] Furthermore, perform phase unwrapping on the wrapped phase difference signal to obtain the unwrapped differential phase signal, including:

[0037] Perform modulo 2π operation on the differential phase signal before unwrapping at the starting moment of each detection period to obtain the differential phase signal after unwrapping at the starting moment;

[0038] Based on the time sequence, perform modulo 2π operation on the difference between the differential phase signals before unwrapping at each moment of all detection periods and the differential phase signals before unwrapping at the previous moment to obtain the intermediate modulus value at each moment;

[0039] Superimpose the intermediate modulus value at each moment with the differential phase signal after unwrapping at the previous moment to obtain the differential phase signal after unwrapping at all moments of all detection periods;

[0040] The unwrapped differential phase signal satisfies the following relationship:

[0041]

[0042] In the formula, and respectively represent the differential phase signals before and after unwrapping at the nth moment of the kth detection period, and M[·] represents modulo 2π operation;

[0043] Perform cross-correlation operation on the differential phase signals after overlapping and corresponding to obtain the cross-correlation results of all fiber regions, including:

[0044] Perform convolution processing on the differential phase signals at each moment in two sets of consecutive detection periods in all the same fiber regions;

[0045] Superimpose the convolution processing results at all moments to obtain the cross-correlation results of the differential phase signals in two sets of consecutive detection periods in all fiber regions;

[0046] The cross-correlation result satisfies the following relationship:

[0047]

[0048] Among them, and are the differential phase signals of two sets of consecutive detection periods, W represents the number of fiber regions divided on the sensing fiber, that is and the number of columns, N is the number of acquisition points of the differential phase signal in the time domain, that is and the number of rows, represents and Perform cross - correlation operation on the k - th column of, C k The value of is the cross - correlation result of the differential phase signal in the k - th optical fiber region.

[0049] Furthermore, normalize the cross - correlation results of all optical fiber regions to obtain the normalization results of all optical fiber regions;

[0050] Based on the normalization results of all optical fiber regions, obtain the global cross - correlation localization curve;

[0051] Based on the global cross - correlation localization curve, select the position where the extreme value appears according to the preset threshold as the corresponding optical fiber region where the perturbation occurs.

[0052] Furthermore, normalize the cross - correlation results of all optical fiber regions to obtain the normalization results of all optical fiber regions, including:

[0053]

[0054] In the formula, C k ' is the normalization result in the k - th optical fiber region, is the maximum value of the cross - correlation results on the sensing optical fiber.

[0055] The global cross - correlation localization curve is:

[0056] C = {C k ', k ∈ [0, W - 1]}

[0057] In the formula, C is the global cross - correlation localization curve.

[0058] Furthermore, perform detrending processing on the unwrapped differential phase signal to obtain the detrended differential phase signal, and it also includes:

[0059] Construct a polynomial trend - term model based on the unwrapped differential phase signal;

[0060] Solve the coefficients of the polynomial trend - term model according to the least - squares method;

[0061] Combine the coefficients with the polynomial trend - term model to obtain the solved polynomial trend - term model;

[0062] Through the unwrapped differential phase signal with trend - term and the solved polynomial trend - term model, obtain the detrended differential phase signal;

[0063] Furthermore, solve the coefficients of the polynomial trend - term model according to the least - squares method, including:

[0064] Construct an objective function with the goal of minimizing the sum of squared errors between the unwrapped differential phase signal and the polynomial trend - term model;

[0065] Based on the solution function and the objective function, the coefficients of each term of the polynomial trend term model are obtained;

[0066] Among them, the objective function satisfies the following relationship:

[0067]

[0068]

[0069] In the formula, SSE is the objective function, is the polynomial trend term model, S k is the differential phase signal after unwrapping the k-th optical fiber region, a j is the j-th coefficient of the polynomial, k is the number of optical fiber regions, l is the length of the differential phase signal, and h is the order of the polynomial;

[0070] The solution function satisfies the following relationship:

[0071]

[0072] Through the unwrapped differential phase signal with trend terms and the solved polynomial trend term model, the differential phase signal after detrending is obtained, including:

[0073]

[0074] In the formula, S is the differential phase signal after detrending.

[0075] In a second aspect, the present invention also provides a sensing optical fiber disturbance region positioning system based on a phase signal, which adopts the above-mentioned sensing optical fiber disturbance region positioning method based on a phase signal. The system includes:

[0076] A signal acquisition module, which is used to collect the backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;

[0077] A light ray division module, which is used to equally divide the sensing optical fiber to obtain a plurality of optical fiber regions;

[0078] A signal determination module, which is used to obtain the wrapped phase difference signal of each optical fiber region according to the phase signal matrix;

[0079] A cross-correlation processing module, which is used to perform unwrapping, detrending, and cross-correlation processing on the wrapped phase difference signal in sequence to obtain a cross-correlation result;

[0080] A disturbance determination module, which is used to normalize the cross-correlation result to determine the region where the disturbance occurs.

[0081] Furthermore, the signal acquisition module is also used for:

[0082] A Φ-OTDR distributed optical fiber sensing system is used to inject multiple optical pulses into the sensing optical fiber;

[0083] The Φ-OTDR distributed optical fiber sensing system is used to collect the backward Rayleigh scattering signals of multiple optical pulses, and a two-dimensional signal matrix containing time domain information and spatial domain information is obtained;

[0084] The orthogonal demodulation algorithm is used to demodulate the phase of the two-dimensional signal matrix, and a phase signal matrix of the same size is obtained.

[0085] Furthermore, the cross-correlation processing module is also used for:

[0086] Unwrap the wrapped phase difference signal to obtain the unwrapped differential phase signal;

[0087] Perform detrending processing on the unwrapped differential phase signal to obtain the detrended differential phase signal;

[0088] Perform overlapping correspondence in both the time domain and the spatial domain on the detrended differential phase signals in two consecutive detection periods;

[0089] Perform cross-correlation operation on the overlapped and corresponding differential phase signals to obtain the cross-correlation results of all optical fiber regions.

[0090] Furthermore, the cross-correlation processing module is also used for:

[0091] Construct a polynomial trend term model based on the unwrapped differential phase signal;

[0092] Solve the coefficients of each term of the polynomial trend term model according to the least squares method;

[0093] Combine each coefficient with the polynomial trend term model to obtain the solved polynomial trend term model;

[0094] Through the unwrapped differential phase signal and the solved polynomial trend term model, obtain the detrended differential phase signal.

[0095] Furthermore, the perturbation determination module is also used for:

[0096] Normalize the cross-correlation results of all optical fiber regions to obtain the normalized results of all optical fiber regions;

[0097] Obtain the global cross-correlation positioning curve based on the normalized results of all optical fiber regions;

[0098] Based on the global cross-correlation positioning curve, select the position where the extreme value appears as the corresponding optical fiber region where the perturbation occurs according to the preset threshold.

[0099] The method and system for locating the disturbed area of a sensing optical fiber based on a phase signal provided by the present invention have at least the following beneficial effects:

[0100] (1) Based on the linear relationship between the phase signal and the external disturbance, by performing a cross-correlation operation on the time-domain phase signals of the entire optical fiber link within two detection periods, the disturbance can be located only by using the phase signal.

[0101] (2) Since in the application of the Φ-OTDR distributed optical fiber sensing system, only the phase signal is used in the subsequent processing of disturbance location. Therefore, by designing a method for locating using the phase signal, the present invention can avoid the introduction of amplitude disturbance location calculation, thereby reducing the amount of data processing, improving the real-time performance and computational effectiveness of the Φ-OTDR distributed optical fiber sensing system, and effectively solving the problem of computational redundancy introduced by amplitude disturbance location in the case of low utilization rate of amplitude signals in the application of the Φ-OTDR distributed optical fiber sensing system.

[0102] (3) Through detrending processing, the distortion caused by the laser frequency drift can be effectively eliminated, and the influence of low-frequency and slow trend terms can be avoided. Finally, by performing cross-correlation processing, the disturbance can be located only by using the phase signal, and it has a good disturbance location effect; especially for short-distance disturbance detection, it has an outstanding location effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] Figure 1 It is a flowchart of a method for locating the disturbed area of a sensing optical fiber based on a phase signal provided by the present invention;

[0104] Figure 2 It is a flowchart of obtaining the cross-correlation result in a certain embodiment provided by the present invention;

[0105] Figure 3 It is a flowchart of a method for locating the disturbed area of a sensing optical fiber in a certain embodiment provided by the present invention;

[0106] Figure 4 It is a schematic diagram of the phase time-domain signals before and after unwrapping in a certain embodiment provided by the present invention;

[0107] Figure 5 It is a schematic diagram of the results before and after detrending in a certain embodiment provided by the present invention;

[0108] Figure 6 It is a three-dimensional schematic diagram of phase difference distance - time in a certain embodiment provided by the present invention;

[0109] Figure 7 It is a schematic diagram of cross-correlation location of the phase time-domain signal in a certain embodiment provided by the present invention;

[0110] Figure 8Schematic diagram of a sensing optical fiber disturbance area positioning system provided by the present invention. Detailed implementation manners

[0111] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the specification drawings and specific implementation manners. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0112] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "the" and "said" used in the embodiments of the present invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. "Plural" generally includes at least two.

[0113] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a commodity or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such commodity or device. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the commodity or device including the said element.

[0114] As Figure 1 shown, the present invention provides a method for positioning a disturbance area of a sensing optical fiber based on a phase signal, including:

[0115] Collect the backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;

[0116] Divide the sensing optical fiber at equal distances to obtain a number of optical fiber regions;

[0117] Obtain the winding phase difference signal of each optical fiber region according to the phase signal matrix;

[0118] Perform unwrapping, detrending and cross-correlation processing on the winding phase difference signal in sequence to obtain a cross-correlation result;

[0119] Normalize the cross-correlation result to determine the area where the disturbance occurs.

[0120] In the present invention, disturbance detection can be completed by simply connecting one end of the sensing optical fiber to be measured to a Φ-OTDR distributed optical fiber sensing system, and replacing the sensing optical fiber to be measured does not require damaging the structure of the Φ-OTDR distributed optical fiber sensing system. In addition, the present invention directly uses a set of Φ-OTDR distributed optical fiber sensing systems to perform cross-correlation on two detection cycles to obtain disturbance location information.

[0121] In an actual application scenario, the present invention collects the backward Rayleigh scattering signals of the sensing optical fiber to obtain a phase signal matrix, which may include:

[0122] Injecting multiple optical pulses into the sensing optical fiber by using a Φ-OTDR distributed optical fiber sensing system;

[0123] Collecting the backward Rayleigh scattering signals of multiple optical pulses through a Φ-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time-domain information and spatial-domain information;

[0124] Performing phase demodulation on the two-dimensional signal matrix by using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size.

[0125] Among them, the equal-distance division of the sensing optical fiber is: dividing the sensing optical fiber at equal distances with the acquisition points on the sensing optical fiber as the division nodes.

[0126] Specifically, the Φ-OTDR distributed optical fiber sensing system realizes sensing and positioning by analyzing the backward Rayleigh scattered light in the sensing optical fiber. The backward Rayleigh scattered light at each point in the sensing optical fiber arrives at the detection end at different times. Therefore, the time relationship between the spatial position of the sensing optical fiber and the received signal can be given: L = ct / 2n, where L is the distance position on the sensing optical fiber, c is the speed of light, n is the refractive index of the optical fiber, and t is the time difference between the emission and reception of the optical pulse;

[0127] The meaning represented by the acquisition points on the sensing optical fiber is: after each optical pulse is injected into the sensing optical fiber, the sampling positions at the moments of receiving the backward Rayleigh scattered light. The distance position on the sensing optical fiber can be obtained from the time relationship between the spatial position and the received signal for this sampling position.

[0128] Since the acquisition points are discrete, the corresponding spatial positions on the sensing optical fiber are also discrete. When dividing the sensing optical fiber at equal distances, dividing according to the acquisition points, the optical fiber spatial distances corresponding to the number of acquisition points for each division are equal.

[0129] After collecting the backward Rayleigh scattering signals of multiple optical pulses, phase demodulation can be performed on the two-dimensional signal matrix by using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size. Specifically, it may include:

[0130] Multiplying the two-dimensional signal matrix by sin(2πΔf IFt) and cos(2πΔf IF After multiplying with t), the second - harmonic components are filtered out by a low - pass filter to obtain the in - phase component I and the quadrature component Q respectively;

[0131] The in - phase component and the quadrature component are subjected to arctangent processing to obtain the phase signal matrix

[0132] Among them, the in - phase component I, the quadrature component Q, and the phase signal matrix respectively satisfy the following relationships:

[0133]

[0134]

[0135]

[0136] In the formula, I is the in - phase component, Q is the quadrature component, P AC is the power of the backward Rayleigh scattering signal, E is the amplitude information of the backward Rayleigh scattering signal, represents the phase signal matrix, Δf IF represents the frequency shift introduced by the acousto - optic modulator, t is the time corresponding to the phase signal, and m is an integer.

[0137] After dividing the sensing optical fiber into several optical fiber regions, the winding phase difference signals of each optical fiber region can be obtained according to the phase signal matrix, including:

[0138] Matching all the optical fiber regions with the phase signal matrix to give the phase signals at both ends of each optical fiber region;

[0139] According to the phase signals at both ends of each optical fiber region, the corresponding winding phase difference signals are obtained. Among them, the winding phase difference signals can specifically include:

[0140]

[0141] In the formula, is the winding phase difference signal, represents the time - domain information (phase time - domain signal) of the phase signal corresponding to the i - th acquisition point of the sensing optical fiber, ω represents the number of acquisition points in the optical fiber region. The phase signal matrix includes the phase time - domain signal and the phase spatial - domain signal. Each column of the phase signal matrix represents the phase time - domain signal at a spatial position, and the number of columns of the phase signal matrix represents the number of spatial positions; through the spatial positions at both ends of all optical fiber regions, the corresponding phase time - domain signals at both ends of the optical fiber region can be matched, that is, the phase signals at both ends of the optical fiber region are obtained.

[0142] Such as Figure 2As shown, after obtaining the wrapped phase difference signal, the present invention can successively perform phase unwrapping, detrending, and cross-correlation processing on the wrapped phase difference signal to obtain the cross-correlation result, specifically including:

[0143] Perform phase unwrapping on the wrapped phase difference signal to obtain the unwrapped differential phase signal; including:

[0144] Perform modulo 2π operation on the differential phase signal before unwrapping at the start time of each detection period to obtain the differential phase signal after unwrapping at the start time;

[0145] Based on the time sequence, perform modulo 2π operation on the difference between the differential phase signal before unwrapping at each moment of all detection periods and the differential phase signal before unwrapping at the previous moment to obtain the intermediate modulus value at each moment;

[0146] Superimpose the intermediate modulus value at each moment on the differential phase signal after unwrapping at the previous moment to obtain the differential phase signal after unwrapping at all moments of all detection periods;

[0147] The differential phase signal after unwrapping satisfies the following relationship:

[0148]

[0149] In the formula, and respectively represent the differential phase signals before and after unwrapping at the nth moment of the kth detection period, and M[·] represents modulo 2π operation;

[0150] Perform detrending processing on the differential phase signal after unwrapping to obtain the differential phase signal after detrending; including:

[0151] Construct a polynomial trend term model based on the differential phase signal after unwrapping;

[0152] Solve the coefficients of the polynomial trend term model according to the least squares method;

[0153] Combine the coefficients with the polynomial trend term model to obtain the solved polynomial trend term model;

[0154] Through the differential phase signal after unwrapping and the solved polynomial trend term model, obtain the differential phase signal after detrending; where the differential phase signal after unwrapping is the differential phase signal containing the trend term;

[0155] Perform overlapping correspondence in both the time and space domains on the differential phase signals after detrending in two consecutive detection periods;

[0156] Perform cross-correlation operation on the differential phase signals after overlapping correspondence to obtain the cross-correlation results of all optical fiber regions, including:

[0157] Perform convolution processing on the differential phase signals at all the same optical fiber regions at each moment of two sets of consecutive detection periods;

[0158] Superimpose the convolution processing results at all moments to obtain the cross-correlation result of the differential phase signals of two sets of consecutive detection periods in all optical fiber regions;

[0159] The cross-correlation result satisfies the following relationship:

[0160]

[0161] Wherein, and are the differential phase signals of two sets of consecutive detection periods, W represents the number of optical fiber regions divided on the sensing optical fiber, that is, and are the number of columns of, N is the number of acquisition points of the differential phase signal in the time domain, that is, and are the number of rows of, represents performing cross-correlation operation on the k-th column of and , represents is the b-th row and k-th column of, C k The value of is the cross-correlation result of the differential phase signal in the k-th optical fiber region.

[0162] Wherein, one set of detection periods corresponds to one set of optical pulses. For example, injecting 200 optical pulses into the sensing optical fiber is one set of detection periods. The meanings of the differential phase signals after detrending in two sets of consecutive detection periods are: two sets of continuously injected optical pulses respectively correspond to two sets of differential phase signals after detrending; in addition, the moment of the detection period corresponds to the injection of one optical pulse, that is, the time sequence of one set of detection periods corresponds to the injection order of the optical pulses. For example, the 0 moment corresponds to the first injected optical pulse, and the 1 moment corresponds to the second injected optical pulse.

[0163] Since the narrow linewidth laser used in the Φ-OTDR distributed optical fiber sensing system has a slow frequency drift, there is an offset trend term in the obtained unwrapped differential phase signal. Therefore, the present invention uses the least squares method to fit and eliminate the trend term carried by the differential phase signal. Specifically, according to the least squares method to solve the coefficients of the polynomial trend term model, it may include:

[0164] Construct an objective function with the minimum sum of the squares of the errors between the unwrapped differential phase signal and the polynomial trend term model as the target;

[0165] Based on the solution function and the objective function, obtain the coefficients of the polynomial trend term model;

[0166] Among them, the construction of the objective function can satisfy the following relationship:

[0167]

[0168]

[0169] In the formula, SSE is the objective function, is the polynomial trend term model, S k is the differential phase signal after unwrapping the k-th optical fiber region, a j is the j-th coefficient of the polynomial, k is the number of optical fiber regions, l is the length of the differential phase signal, and h is the order of the polynomial;

[0170] The solution function satisfies the following relationship:

[0171]

[0172] Through the unwrapped differential phase signal and the solved polynomial trend term model, the differential phase signal after detrending is obtained, including:

[0173]

[0174] In the formula, S is the differential phase signal after detrending.

[0175] In the non-disturbed region of the sensing optical fiber, due to the influence of only random noise, the fluctuations in two consecutive detection periods are small and irregular. However, due to external disturbances, the fluctuations in two consecutive detection periods on both sides have a periodic pattern, and the cross-correlation value of the optical fiber region affected by external disturbances will be much larger than that of the non-disturbed region. Based on this, the present invention normalizes the cross-correlation result to determine the region where the disturbance occurs, which may include:

[0176] Normalize the cross-correlation results of all optical fiber regions to obtain the normalization results of all optical fiber regions; including:

[0177]

[0178] In the formula, C k ' is the normalization result within the k-th optical fiber region, is the maximum value of the cross-correlation result on the sensing optical fiber;

[0179] Based on the normalization results of all optical fiber regions, the global cross-correlation positioning curve is obtained; including:

[0180] C = {C k ', k ∈ [0, W - 1]}

[0181] In the formula, C is the global cross-correlation positioning curve;

[0182] Based on the global cross - correlation localization curve, select the position where the extreme value appears according to a preset threshold as the corresponding optical fiber area where the disturbance occurs.

[0183] Among them, the selection of the preset threshold can be determined using a priori disturbance data sets. Specifically: use the normalization results within the optical fiber area to process the signal data at multiple known disturbance occurrence positions, statistically analyze the normalization results in the area where the disturbance occurs, and set the preset threshold as the lowest value among them. When actually determining the optical fiber area where the disturbance occurs, divide the global cross - correlation localization curve by this preset threshold. If there is an intersection between the global cross - correlation localization curve and the preset threshold, it indicates that there is a disturbance in the sensing optical fiber, and the optical fiber area corresponding to the part of the global cross - correlation localization curve greater than the preset threshold is determined as the disturbance occurrence area.

[0184] Such as Figure 3 shown, in an actual application scenario, the method for locating the disturbance area of the sensing optical fiber of the present invention may include:

[0185] Step 1: Use a Φ - OTDR distributed optical fiber sensing system to collect sensing data. Each time the system emits an optical pulse into the sensing optical fiber, the receiving end will obtain a back - scattered Rayleigh signal with a sampling length of M. When N optical pulses are injected into the sensing optical fiber, a two - dimensional signal matrix D containing time - domain information and spatial - domain information can be obtained. N×M ;

[0186] In this example, the sensing optical fiber is 14 km long, corresponding to a total of 35000 spatial sampling points. The optical pulse emission frequency set by the system is 1 kHz, and one detection period is 200 ms, corresponding to the sensing signals returned after 200 consecutive optical pulses are injected into the optical cable, that is, the size of D is 200×35000.

[0187] Step 2: Use the orthogonal demodulation algorithm to demodulate the phase of the original signal matrix to obtain a phase signal matrix P of the same size. N×M ;

[0188] In this example, the orthogonal demodulation method multiplies the beat frequency signal output by the Φ - OTDR system by sin(2πΔf IF t) and cos(2πΔf IF t) respectively, filters out the second - harmonic components through a low - pass filter, and obtains the in - phase component I and the quadrature component Q respectively. The phase signal is the arctangent of the two.

[0189] Step 3: Divide the spatial acquisition points corresponding to the entire - link optical fiber at equal distances, and perform a difference on the phase signals at both ends of each sub - region to obtain a wrapped phase - difference signal containing the disturbance information within the region.

[0190] In this example, the number of spatial acquisition points corresponding to the entire optical fiber link is 35,000, and the regional division length is set to 200 points, resulting in a total of 175 sub-sensing regions.

[0191] Step 4: There are multiple jumps in the wrapped phase difference signal. To restore the true phase value, phase unwrapping is required.

[0192] In this example, the phase unwrapping includes two parts: the distance domain and the time domain. The unwrapping in the distance domain is used to avoid drastic jumps caused by phase fading, and the unwrapping in the time domain is used to restore the true phase value. The phase time-domain signals obtained before and after unwrapping are respectively as Figure 4 shown in (a) and Figure 4 shown in (b).

[0193] Step 5: The detrending process is performed on the differential phase signal obtained after unwrapping to obtain the differential phase signal after detrending. The differential phase signal is a two-dimensional matrix with time-domain information and spatial-domain information For each positioning calculation, the phase signal matrices and in two consecutive detection periods are overlapped and corresponding in both the time and space domains;

[0194] In this example, the results before and after detrending of the present invention are as Figure 5 shown. Before detrending, the phase signal deviates from the baseline and there is an obvious trend term. After detrending, the distortion caused by laser frequency drift is effectively eliminated, avoiding the influence of low-frequency and slow trend terms.

[0195] The phase difference distance-time three-dimensional diagram of two consecutive detection periods is as Figure 6 shown. The phase fluctuation in the perturbed area is more obvious than that in the non-perturbed area, and the random fluctuations caused by noise cannot be guaranteed to appear in both detection periods.

[0196] Step 6: Perform cross-correlation operation on the and full-link time-domain signals.

[0197] Step 7: Normalize the cross-correlation results of the time-domain phase signals of each sensing region.

[0198] Step 8: Obtain the global cross-correlation positioning curve, and select the position where the extreme value appears according to the required threshold as the corresponding area where the perturbation occurs.

[0199] In this example, a PZT is placed at 14 km on a 14.3 km sensing optical fiber to apply a 10 Hz sinusoidal perturbation. The cross-correlation positioning map of the phase time-domain signal of the entire optical fiber link calculated is as Figure 7As shown, a relatively large positioning peak appears at 14 km, which is consistent with the actual position where the disturbance is applied.

[0200] As Figure 8 shown, the present invention also provides a positioning system for the disturbed area of a sensing optical fiber based on a phase signal, which adopts the above-mentioned positioning method for the disturbed area of a sensing optical fiber based on a phase signal. The system includes:

[0201] A signal acquisition module, which is used to acquire the backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;

[0202] A light ray division module, which is used to equally divide the sensing optical fiber to obtain a number of optical fiber regions;

[0203] A signal determination module, which is used to obtain the wrapped phase difference signal of each optical fiber region according to the phase signal matrix;

[0204] A cross-correlation processing module, which is used to perform unwrapping, detrending, and cross-correlation processing on the wrapped phase difference signal in sequence to obtain a cross-correlation result;

[0205] A disturbance determination module, which is used to normalize the cross-correlation result to determine the area where the disturbance occurs.

[0206] The signal acquisition module is also used for:

[0207] Injecting a plurality of optical pulses into the sensing optical fiber by using a Φ-OTDR distributed optical fiber sensing system;

[0208] Collecting the backward Rayleigh scattering signals of the plurality of optical pulses through the Φ-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and spatial domain information;

[0209] Performing phase demodulation on the two-dimensional signal matrix by using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size.

[0210] The cross-correlation processing module is also used for:

[0211] Performing phase unwrapping on the wrapped phase difference signal to obtain an unwrapped differential phase signal;

[0212] Performing detrending processing on the unwrapped differential phase signal to obtain a detrended differential phase signal;

[0213] Performing overlapping correspondence in both the time domain and the spatial domain on the detrended differential phase signals in two consecutive detection periods;

[0214] Performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain the cross-correlation results of all optical fiber regions.

[0215] The cross-correlation processing module is also used for:

[0216] Construct a polynomial trend term model based on the unwrapped differential phase signal;

[0217] Solve the coefficients of each term of the polynomial trend term model according to the least squares method;

[0218] Combine the coefficients with the polynomial trend term model to obtain the solved polynomial trend term model;

[0219] Obtain the detrended differential phase signal through the unwrapped differential phase signal and the solved polynomial trend term model.

[0220] The perturbation determination module is further configured to:

[0221] Normalize the cross-correlation results of all fiber regions to obtain the normalized results of all fiber regions;

[0222] Obtain the global cross-correlation positioning curve based on the normalized results of all fiber regions;

[0223] Based on the global cross-correlation positioning curve, select the position where the extreme value appears as the corresponding fiber region where the perturbation occurs according to the preset threshold.

[0224] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

Claims

1. A method for locating the disturbance region of a sensing optical fiber based on phase signals, characterized in that, it includes: Collect the backward Rayleigh scattering signals of the sensing optical fiber to obtain a phase signal matrix; Divide the sensing optical fiber at equal distances to obtain several optical fiber regions; Obtain the winding phase difference signals of each optical fiber region according to the phase signal matrix; Perform unwrapping, detrending, and cross-correlation processing on the winding phase difference signals in sequence to obtain a cross-correlation result; Normalize the cross-correlation result to determine the region where the disturbance occurs; Among them, performing unwrapping, detrending, and cross-correlation processing on the winding phase difference signals in sequence to obtain a cross-correlation result includes: Perform phase unwrapping on the winding phase difference signals to obtain the unwrapped differential phase signals, including: performing modulo 2π processing on the differential phase signals before unwrapping at the starting moment of each detection period to obtain the differential phase signals after unwrapping at the starting moment; based on the time sequence, perform modulo 2π processing on the difference between the differential phase signals before unwrapping at each moment of all detection periods and the differential phase signals before unwrapping at the previous moment to obtain the intermediate modulus values at each moment; superimpose the intermediate modulus values at each moment on the differential phase signals after unwrapping at the previous moment to obtain the differential phase signals after unwrapping at all moments of all detection periods; Perform detrending processing on the unwrapped differential phase signals to obtain the detrended differential phase signals; Perform overlapping correspondence in both the time and space domains on the detrended differential phase signals within two consecutive detection periods; Perform cross-correlation operation on the differentially phase signals after overlapping correspondence to obtain the cross-correlation results of all optical fiber regions.

2. The method for locating the disturbance region of a sensing optical fiber according to claim 1, characterized in that, Collecting the backward Rayleigh scattering signals of the sensing optical fiber to obtain a phase signal matrix includes: Using a Φ-OTDR distributed optical fiber sensing system to inject multiple optical pulses into the sensing optical fiber; Collecting the backward Rayleigh scattering signals of the multiple optical pulses through the Φ-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and spatial domain information; Performing phase demodulation on the two-dimensional signal matrix using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size.

3. The method for locating the disturbance region of a sensing optical fiber according to claim 2, characterized in that, Performing phase demodulation on the two-dimensional signal matrix using an orthogonal demodulation algorithm to obtain a phase signal matrix of the same size includes: Multiply the two-dimensional signal matrix by sin(2πΔf IF t) and cos(2πΔf IF t) respectively, filter out the double-frequency components through a low-pass filter, and obtain the in-phase component and the quadrature component respectively; Performing arctangent processing on the in-phase component and the quadrature component to obtain a phase signal matrix.

4. The method for locating the disturbance region of a sensing optical fiber according to claim 1, characterized in that, Normalizing the cross-correlation result to determine the region where the disturbance occurs includes: Normalizing the cross-correlation results of all optical fiber regions to obtain the normalization results of all optical fiber regions; Obtaining a global cross-correlation positioning curve based on the normalization results of all optical fiber regions; Based on the global cross-correlation positioning curve, selecting the position where the extreme value appears as the corresponding optical fiber region where the disturbance occurs according to a preset threshold.

5. The method for locating the disturbance region of a sensing optical fiber according to claim 1, characterized in that, Perform cross - correlation operation on the differential phase signals after overlapping correspondence to obtain the cross - correlation results of all fiber regions, including: Perform convolution processing on the differential phase signals at each moment in all the same fiber regions of two consecutive detection periods; Superimpose the convolution processing results at all moments to obtain the cross - correlation results of the differential phase signals of two consecutive detection periods in all fiber regions.

6. The method for locating the disturbed region of a sensing optical fiber according to claim 1 or 5, characterized in that, Perform detrending processing on the unwrapped differential phase signal to obtain the differential phase signal after detrending, and further include: Construct a polynomial trend - term model based on the unwrapped differential phase signal; Solve the coefficients of each term of the polynomial trend - term model according to the least - squares method; Combine each coefficient with the polynomial trend - term model to obtain the solved polynomial trend - term model; Obtain the differential phase signal after detrending through the unwrapped differential phase signal and the solved polynomial trend - term model.

7. The method for locating the disturbed region of a sensing optical fiber according to claim 6, characterized in that, Solving the coefficients of each term of the polynomial trend - term model according to the least - squares method includes: Construct an objective function with the goal of minimizing the sum of the squares of the errors between the unwrapped differential phase signal and the polynomial trend - term model; Based on the solution function and the objective function, obtain the coefficients of each term of the polynomial trend - term model.

8. A system for locating the disturbed region of a sensing optical fiber based on phase signals, adopting the method for locating the disturbed region of a sensing optical fiber based on phase signals according to any one of claims 1 - 7, characterized in that, The system includes: A signal acquisition module, which is used to acquire the backward Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix; An optical fiber division module, which is used to equally divide the sensing optical fiber to obtain several fiber regions; A signal determination module, which is used to obtain the wrapped phase difference signal of each fiber region according to the phase signal matrix; A cross - correlation processing module, which is used to perform unwrapping, detrending and cross - correlation processing on the wrapped phase difference signal in sequence to obtain cross - correlation results; A disturbance determination module, which is used to normalize the cross - correlation results to determine the region where the disturbance occurs; Among them, performing unwrapping, detrending and cross - correlation processing on the wrapped phase difference signal in sequence to obtain cross - correlation results includes: Perform phase unwrapping on the wrapped phase difference signal to obtain the unwrapped differential phase signal, including: perform modulo 2π processing on the differential phase signal before unwrapping at the starting moment of each detection period to obtain the differential phase signal after unwrapping at the starting moment; based on the time sequence, perform modulo 2π processing on the difference between the differential phase signal before unwrapping at each moment of all detection periods and the differential phase signal before unwrapping at the previous moment to obtain the intermediate modulus value at each moment; superimpose the intermediate modulus value at each moment on the differential phase signal after unwrapping at the previous moment to obtain the differential phase signal after unwrapping at all moments of all detection periods; Perform detrending processing on the unwrapped differential phase signal to obtain the differential phase signal after detrending; Perform time and space double-domain overlapping correspondence on the detrended differential phase signals within two sets of consecutive detection periods; Perform cross-correlation operation on the differential phase signals after overlapping correspondence to obtain the cross-correlation results of all fiber optic regions.

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