An optimized positioning method and system for sensing fiber optic perturbations

Abstract

The present invention discloses an optimized positioning method and system for sensing fiber perturbations. The method includes: obtaining the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix; equally dividing the sensing fiber into a number of sub-regions; based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, obtaining the true phase difference signal of each sub-region; sequentially performing autocorrelation calculation and cross-correlation calculation on the true phase difference signal to obtain a cross-correlation matrix; and determining the sub-region where the perturbation is located based on the cross-correlation matrix. By introducing the autocorrelation algorithm during the cross-correlation operation using the phase information of the original scattering signal, the improved method of the present invention can effectively eliminate the interference of false peaks and obtain the true positioning of the perturbation region.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber disturbance positioning, and particularly relates to an optimized positioning method and system for sensing optical fiber disturbances. Background Art

[0002] Distributed optical fiber sensing technology is a new type of sensing technology that uses long-distance optical fibers as sensing elements. It has the advantages of safety and reliability, high sensitivity, low cost, etc., and is widely used in various fields. Phase-sensitive optical time domain reflectometry (Φ-OTDR) is an important branch of distributed optical fiber sensing technology. It realizes quantitative measurement and positioning of external disturbances by analyzing the intensity, phase, and polarization state of the interference signal of the backward Rayleigh scattered light in the optical fiber. This technology has the characteristics of high positioning accuracy, strong multi-point disturbance positioning ability, large dynamic response range, etc., and has received extensive attention in recent years, and has shown great application potential in fields such as rail transit safety monitoring, smart grid status monitoring, and infrastructure perimeter security.

[0003] The Φ-OTDR system injects high-coherence optical pulses into the sensing optical fiber. Due to the coherent interference between the backward Rayleigh scattered lights generated by different scattering units on the optical fiber, the external disturbance can be located by receiving and analyzing the Rayleigh scattering trace. Since the phase signal is less affected by the light source power fluctuation and the optical fiber loss, and has strong anti-polarization noise and other interference capabilities. Therefore, compared with using the amplitude signal demodulation, using the phase signal for Φ-OTDR disturbance positioning can obtain higher system sensitivity. For example, patent CN114111860A discloses a distributed Φ-OTDR sensing method and system based on multi-frequency pulse coding, which relates to the technical field of distributed optical fiber sensing. It includes: the transmitting unit outputs an optical signal to the first coupler, and the first coupler divides the optical signal into a first optical signal and a second optical signal; the first optical signal is input into the modulation unit to obtain a modulated optical signal; the second optical signal is input into the receiving unit; the modulated optical signal is input into the sensing optical fiber after passing through the erbium-doped fiber amplifier; after being disturbed by the disturbance simulation unit, the sensing optical fiber returns the backward Rayleigh scattered optical signal carrying the disturbance information to the erbium-doped fiber amplifier and then inputs it into the receiving unit; the receiving unit mixes the received second optical signal and the backward Rayleigh scattered optical signal carrying the disturbance information and sends it to the processing unit to obtain the disturbance signal information. In actual sensing applications, when the sensing distance is long, the nonlinear effect will make the modulation effect of the disturbance signal at the end of the sensing optical fiber on the optical pulse smaller, the phase fluctuation caused by noise increases, and false positioning peaks as false alarm information are additionally generated. Therefore, eliminating false positioning peaks or highlighting true positioning peaks is a necessary measure to improve the system positioning accuracy. Summary of the Invention

[0004] In view of the defects existing in the above-mentioned prior art, the present invention provides an optimized positioning method and system for sensing fiber optic disturbances. By introducing an autocorrelation algorithm during cross-correlation operation using the phase information of the original scattered signal, this improved method can effectively eliminate false peak interference and obtain the true positioning of the disturbance area.

[0005] In a first aspect, the present invention provides an optimized positioning method for sensing fiber optic disturbances, including:

[0006] Obtain the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix;

[0007] Divide the sensing fiber into several sub-regions at equal intervals;

[0008] Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, obtain the true phase difference signal of each sub-region;

[0009] Perform autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix;

[0010] Based on the cross-correlation matrix, determine the sub-region where the disturbance is located.

[0011] Further, obtaining the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix includes:

[0012] Use a Φ-OTDR distributed fiber optic sensing system to transmit N single-frequency optical pulses to the sensing fiber;

[0013] The receiving end of the Φ-OTDR distributed fiber optic sensing system collects the backward Rayleigh scattering signal generated by each optical pulse at M sampling points to obtain a two-dimensional signal matrix;

[0014] Multiply each row of the two-dimensional signal matrix by a pair of orthogonal carrier waves cos(2πft) and sin(2πft) respectively, and then pass through a low-pass filter for digital down-conversion to filter out high-frequency components to obtain two signals; where f is the frequency shift of the acousto-optic modulator;

[0015] After obtaining the phase of these two signals by taking the arctangent, combine them to obtain an N×M two-dimensional phase signal matrix.

[0016] Further, based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, obtaining the true phase difference signal of each sub-region includes:

[0017] Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, give the phase signals at both endpoints of each sub-region;

[0018] Perform differentiation on the phase signals at both endpoints of each sub-region to obtain a wrapped phase difference signal;

[0019] Restore the winding phase difference signal based on the unwrapping function to obtain the true phase difference signal;

[0020] Among them, the unwrapping function is specifically expressed as:

[0021]

[0022] Among them, represents the winding phase difference signal of the i-th sub-region, represents the true phase difference signal after unwrapping.

[0023] Furthermore, perform autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix, including:

[0024] Perform autocorrelation operation on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix;

[0025] Perform cross-correlation operation on the autocorrelation matrices corresponding to two consecutive single-frequency optical pulses emitted in sequence in the same sub-region to obtain a cross-correlation matrix.

[0026] Furthermore, perform autocorrelation operation on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix, including:

[0027] Multiply the true phase difference signal of each sub-region with the true phase difference signals of other sub-regions respectively to obtain multiple preliminary autocorrelation signals for each sub-region;

[0028] Superimpose the multiple preliminary autocorrelation signals of each sub-region to obtain the autocorrelation signal of each sub-region;

[0029] Integrate the autocorrelation signals of all sub-regions to give an autocorrelation matrix.

[0030] Furthermore, the autocorrelation matrix satisfies the following relationship:

[0031]

[0032] Among them, B represents the number of sub-regions into which the sensing optical fiber is divided, and the true phase difference signal within a single detection period is denoted as v, v = {v i , i ∈ [0, B - 1]}, v j represents the true phase difference signal corresponding to the j-th sub-region, v m+j represents the true phase difference signal separated by m sub-regions from v j , and R(v, v) m is the obtained autocorrelation matrix with the same size as the true phase difference signal.

[0033] Further, perform cross-correlation operation on the autocorrelation matrices corresponding to all consecutive two single-frequency optical pulses emitted in sequence within the same sub-region to obtain a cross-correlation matrix, including:

[0034] Based on the corresponding relationship between the sampling points in the sub-region and the time-domain phase signals of the two autocorrelation matrices, correspond the time-domain phase signals of the two autocorrelation matrices;

[0035] Based on the order of the sampling points in the sub-region, perform product processing on the time-domain phase signal of one autocorrelation matrix corresponding to each sampling point and the time-domain phase signal of the other autocorrelation matrix corresponding after increasing or decreasing a predetermined number of sampling points, and perform superposition processing on all the product processing results to obtain a cross-correlation function value;

[0036] Based on the number of sampling points in the sub-region, obtain all the numerical values from the minimum number of sampling points between two sampling points to the maximum number of sampling points between two sampling points;

[0037] Replace each numerical value with a predetermined number respectively, and perform product and superposition processing on the time-domain phase signals of the two autocorrelation matrices based on the predetermined number after each replacement to obtain multiple cross-correlation function values;

[0038] Integrate all the cross-correlation function values to obtain a cross-correlation matrix.

[0039] Further, based on the cross-correlation matrix, determine the sub-region where the perturbation is located, including:

[0040] Perform normalization processing on the cross-correlation matrix to obtain a normalized curve;

[0041] Screen the extreme points on the normalized curve according to a preset threshold;

[0042] Determine the sub-region where the perturbation occurs according to the screened extreme points.

[0043] Further, the normalized curve satisfies the following relationship:

[0044]

[0045] Where W is the number of divided sub-regions, C r ' is the normalization result of the r-th sub-region of the cross-correlation matrix, that is, the normalized curve, C r is the amplitude value of the r-th sub-region of the cross-correlation matrix, C max is the maximum value of the cross-correlation result over the entire W region, C min is the minimum value of the cross-correlation result over the entire W region.

[0046] Further, the determination of the preset threshold includes:

[0047] Obtain the historical disturbance signal strength range in the current environment;

[0048] Superimpose the minimum value of the historical disturbance signal strength range with the noise change amount to obtain a preset threshold; wherein, the noise change amount is -5 to -10 dB.

[0049] In a second aspect, the present invention also provides an optimized positioning system for sensing fiber optic disturbances, adopting the above-mentioned optimized positioning method for sensing fiber optic disturbances. The system includes:

[0050] A signal matrix acquisition module, which is used to acquire the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix;

[0051] A region division module, which is used to equally divide the sensing fiber into several sub-regions;

[0052] A signal analysis and processing module, which is used to obtain the true phase difference signal of each sub-region based on the correspondence between the two-dimensional phase signal matrix and all sub-regions;

[0053] A correlation processing module, which is used to perform autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix;

[0054] A disturbance determination module, which is used to determine the sub-region where the disturbance is located based on the cross-correlation matrix.

[0055] Furthermore, the signal analysis and processing module is also used for:

[0056] Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, give the phase signals at both endpoints of each sub-region;

[0057] Differentiate the phase signals at both endpoints of each sub-region to obtain a wrapped phase difference signal;

[0058] Restore the wrapped phase difference signal based on the unwrapping function to obtain the true phase difference signal.

[0059] Furthermore, the correlation processing module is also used for:

[0060] Perform autocorrelation operation on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix;

[0061] Based on the autocorrelation matrix, give the time-domain phase signals within all sub-regions;

[0062] Perform cross-correlation operation on the corresponding time-domain phase signals of all sequentially transmitted two single-frequency optical pulses in the same sub-region to obtain a cross-correlation matrix.

[0063] Furthermore, the correlation processing module is also used for:

[0064] Multiply the true phase difference signals of each sub-region with the true phase difference signals of other sub-regions respectively to obtain multiple preliminary autocorrelation signals for each sub-region;

[0065] Superimpose the multiple preliminary autocorrelation signals of each sub-region to obtain the autocorrelation signal of each sub-region;

[0066] Integrate the autocorrelation signals of all sub-regions to give the autocorrelation matrix.

[0067] An optimized positioning method and system for sensing fiber optic perturbations provided by the present invention has at least the following beneficial effects:

[0068] (1) Based on the linear relationship between the phase signal and the external perturbation, first through autocorrelation operation, the difference between the true positioning peak and the false positioning peak is enlarged, so that the relatively weak true positioning peak is enhanced; then through cross-correlation operation on the time-domain phase signals of the full fiber optic link in two consecutive detection periods, the positioning of the true perturbation is realized.

[0069] (2) The present invention effectively solves the problem of false peak interference generated during Φ-OTDR phase demodulation, can show obvious fluctuations at the perturbed location, and further improving the positioning reliability and reducing the influence of noise fluctuations can be achieved by performing global cross-correlation after autocorrelation. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 It is a flowchart of an optimized positioning method for sensing fiber optic perturbations provided by the present invention;

[0071] Figure 2 It is a flowchart of obtaining the true phase difference signal in a certain embodiment provided by the present invention;

[0072] Figure 3 It is a signal processing flowchart of the quadrature demodulation method in a certain embodiment provided by the present invention;

[0073] Figure 4 It is a distance-time graph of the autocorrelation result at the perturbed point in a certain embodiment provided by the present invention;

[0074] Figure 5 It is a distance-domain superimposed graph of the autocorrelation result at the perturbed point in a certain embodiment provided by the present invention;

[0075] Figure 6 It is a positioning schematic diagram of the autocorrelation algorithm in a certain embodiment provided by the present invention;

[0076] Figure 7 It is a schematic diagram of an optimized positioning system for sensing fiber optic perturbations provided by the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0077] To better understand the above technical solution, the following will describe the above technical solution in detail in conjunction with the accompanying drawings of the specification and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0078] 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.

[0079] 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 explicitly listed, or also includes elements inherent to such commodity or device. Without further limitation, the 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.

[0080] As Figure 1 shown, an optimized positioning method for sensing fiber perturbation may include:

[0081] Obtain the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix;

[0082] Divide the sensing fiber into a number of sub-regions at equal intervals;

[0083] Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, obtain the true phase difference signal of each sub-region;

[0084] Perform autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix;

[0085] Based on the cross-correlation matrix, determine the sub-region where the perturbation is located.

[0086] Among them, obtaining the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix includes:

[0087] Use a Φ-OTDR distributed optical fiber sensing system to transmit N single-frequency optical pulses to the sensing fiber;

[0088] The receiving end of the Φ-OTDR distributed optical fiber sensing system collects the backward Rayleigh scattering signals generated by each optical pulse at M sampling points to obtain a two-dimensional signal matrix;

[0089] After multiplying each row of the two-dimensional signal matrix by a pair of orthogonal carriers cos(2πft) and sin(2πft) respectively, and then passing through a low-pass filter for digital down-conversion to filter out high-frequency components, two signals are obtained; where f is the frequency shift of the acousto-optic modulator;

[0090] After obtaining the phase of these two signals through the arctangent, they are combined to obtain an N×M two-dimensional phase signal matrix.

[0091] Among them, the determination of the sampling points is as follows: A predetermined number of sampling points are selected according to the length of the sensing optical fiber. In an actual application scenario, there are 10,000 sampling points for a 5-km sensing optical fiber, that is, sampling is performed every half meter. The larger the number of sampling points, the larger the data volume, the longer the calculation time, but the higher the data accuracy. The backward Rayleigh scattering signals at all sampling points are collected to obtain a two-dimensional signal matrix P, which can be expressed as:

[0092]

[0093] In the formula, a NM represents the backward Rayleigh scattering signal at the Nth row and Mth column.

[0094] As Figure 2 shown, after obtaining the two-dimensional phase signal matrix, the present invention can obtain the true phase difference signal of each sub-region based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, specifically including:

[0095] Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, the phase signals at both ends of each sub-region are given;

[0096] Differentiate the phase signals at both ends of each sub-region to obtain a wrapped phase difference signal containing the disturbance information within the sub-region;

[0097] Since there is a phase folding phenomenon in the wrapped phase difference signal curve, the original phase of the wrapped phase difference signal can be restored based on the unwrapping function to obtain the true phase difference signal;

[0098] Among them, the unwrapping function is specifically expressed as:

[0099]

[0100] Among them, represents the wrapped phase difference signal of the ith sub-region, represents the true phase difference signal after unwrapping.

[0101] Perform autocorrelation calculation and cross-correlation calculation on the true phase difference signals in sequence to obtain a cross-correlation matrix, including:

[0102] Perform autocorrelation operation on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix;

[0103] Perform cross-correlation operation on the autocorrelation matrices corresponding to two consecutive single-frequency optical pulses emitted in sequence in the same sub-region to obtain a cross-correlation matrix.

[0104] Among them, performing autocorrelation operation on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix, including:

[0105] Multiply the true phase difference signals of each sub-region with the true phase difference signals of other sub-regions respectively to obtain multiple preliminary autocorrelation signals for each sub-region;

[0106] Superimpose the multiple preliminary autocorrelation signals of each sub-region to obtain the autocorrelation signal of each sub-region;

[0107] Integrate the autocorrelation signals of all sub-regions to give an autocorrelation matrix.

[0108] Specifically, the autocorrelation matrix satisfies the following relationship:

[0109]

[0110] In the formula, B represents the number of sub-regions divided by the sensing optical fiber, and the true phase difference signal within a single detection period is denoted as v, v = {v i , i ∈ [0, B - 1]}, v j represents the true phase difference signal corresponding to the j-th sub-region, and v m+j represents the true phase difference signal separated by m sub-regions from v j , and R(v, v) m is the obtained autocorrelation matrix with the same size as the true phase difference signal.

[0111] Perform cross-correlation operation on the autocorrelation matrices corresponding to two consecutive single-frequency optical pulses emitted in sequence in the same sub-region to obtain a cross-correlation matrix, including:

[0112] Based on the corresponding relationship between the sampling points in the sub-region and the time-domain phase signals of the two autocorrelation matrices, correspond the time-domain phase signals of the two autocorrelation matrices;

[0113] Based on the order of the sampling points in the sub-region, the time-domain phase signals of an autocorrelation matrix corresponding to each sampling point are respectively multiplied with the time-domain phase signals of another autocorrelation matrix corresponding after increasing or decreasing a predetermined number of sampling points, and all the multiplication results are superimposed to obtain a cross-correlation function value;

[0114] Based on the number of sampling points in the sub-region, all the values from the minimum number of sampling points between two sampling points to the maximum number of sampling points are obtained;

[0115] Each value is respectively substituted for the predetermined number, and the multiplication and superposition processing of the time-domain phase signals of the two autocorrelation matrices are performed based on the predetermined number after each substitution to obtain multiple cross-correlation function values;

[0116] All the cross-correlation function values are integrated to obtain a cross-correlation matrix.

[0117] In an actual application scenario, performing cross-correlation operation on the autocorrelation matrices corresponding to all consecutive two single-frequency optical pulses emitted in sequence in the same sub-region to obtain a cross-correlation matrix may include:

[0118] 1) First, the time-domain phase signals in the sub-region where the two autocorrelation matrices are located are respectively denoted as x(n) and y(n), where n is the sequence number of the time-domain sampling points.

[0119] 2) Then, keeping x(n) unchanged, y(n) is shifted to the right by m sampling points to obtain y(n - m), where m is the amount of sliding and can take positive or negative values.

[0120] 3) Next, the signal values at the corresponding positions of x(n) and y(n - m) are multiplied, and the sum of all the multiplications is obtained to get the value of the cross-correlation function Rxy(m) at the moment of m, which reflects the similarity degree of the two waveforms of x(n) and y(n - m).

[0121] 4) Finally, repeating the above steps, changing the value of m, obtaining the cross-correlation function values Rxy(m) at different moments of m, and forming these values into a vector or matrix, the cross-correlation matrix C is obtained.

[0122] Based on the cross-correlation matrix, determining the sub-region where the perturbation is located includes:

[0123] Performing normalization processing on the cross-correlation matrix to obtain a normalized curve; satisfying the following relationship:

[0124]

[0125] where W is the number of sub-regions divided, C r ' is the normalization result of the r-th sub-region of the cross-correlation matrix, that is, the normalized curve, C ris the amplitude value of the r-th sub-region of the cross-correlation matrix, C max is the maximum value of the cross-correlation result over the entire W region, C min is the minimum value of the cross-correlation result over the entire W region;

[0126] Screen the extreme points on the normalized curve according to a preset threshold;

[0127] Determine the sub-region where the perturbation occurs according to the screened extreme points.

[0128] When the present invention screens extreme points, the determination of the preset threshold may include:

[0129] Obtain the historical perturbation signal intensity range in the current environment;

[0130] Superimpose the noise variation amount on the minimum value of the historical perturbation signal intensity range to obtain the preset threshold; where the noise variation amount is -5 to -10 dB.

[0131] Among them, for a Φ-OTDR distributed optical fiber sensing system for a certain or specific multiple perturbation events, the perturbation signal intensity will be within a certain range. Therefore, a value lower than its typical value by -5 to -10 dB is recognized as the preset threshold noise. In addition, since the present invention adopts the autocorrelation operation step, the multi-extremum problem can be effectively solved. The fluctuation amplitude of the autocorrelation result of the signal in the non-perturbation region is much smaller than that of the autocorrelation result in the perturbation region (as Figure 5 and Figure 6 shown). After autocorrelation processing, the amplitude caused by false perturbations (noise) will be greatly reduced, and a smaller preset threshold can be set to filter the noise.

[0132] Due to the problem of multiple extreme values in the global cross-correlation result, the present invention improves the reliability of the overlapping phase cross-correlation positioning algorithm by introducing autocorrelation. The reason why the true positioning peak obtained by cross-correlation is not obvious is mainly that it is weaker compared with the false positioning peak, that is, the difference between the extreme value and the randomly fluctuating noise is not obvious. Through the autocorrelation operation, the difference between the true positioning peak and the false positioning peak can be enlarged, so that the relatively weak true positioning peak can be enhanced, which is convenient for subsequent analysis and identification.

[0133] In an actual application scenario, the present invention provides an optimized positioning method for sensing fiber perturbations, including the following steps:

[0134] Step 1: Collect sensing data. Specifically, use a Φ-OTDR distributed optical fiber sensing system to transmit N single-frequency optical pulses to the sensing fiber, and the receiving end samples the backward Rayleigh scattering signal generated by each optical pulse with a length of M to form an original signal containing time-domain information and spatial-domain information, in the form of a two-dimensional signal matrix A N×M ;

[0135] In this example, the length of the sensing optical fiber is 14 km, and each spatial sampling point corresponds to an optical fiber length of 50 cm. Therefore, there are a total of 28,000 spatial sampling points on the sensing optical fiber. The optical pulse emission frequency of the Φ-OTDR distributed optical fiber sensing system is 2 kHz, that is, 2000 optical pulses are emitted per second. The single detection period is 250 ms, that is, within each detection period, the Φ-OTDR distributed optical fiber sensing system emits 500 optical pulses to the sensing optical fiber and receives 500 backscattered Rayleigh scattering signals. Therefore, the size of the two-dimensional signal matrix D is 500×28000.

[0136] Step 2: Perform orthogonal demodulation on the two-dimensional signal matrix A N×M to obtain the phase signal matrix P N×M ;

[0137] In this example, in order to extract the phase signal from the beat frequency signal output by the Φ-OTDR distributed optical fiber sensing, the Hilbert orthogonal transform is used, that is, the beat frequency signal is multiplied by sin(2πΔft) and cos(2πΔft) respectively, and the double-frequency component is removed through a low-pass filter (LPF) to obtain the in-phase component I and the quadrature component Q, and then the arctangent value of the two is calculated, which is the phase information;

[0138] In this example, the process of orthogonal demodulation is as Figure 3 shown. Among them, the low-pass filter can use a 100-order Hamming window FIR (Finite Impulse Response) filter with a bandwidth of 2 MHz.

[0139] Step 3: Divide the phase signal matrix P N×M equidistantly into several sub-regions according to the sensing optical fiber, and calculate the difference between the phase signals at both ends of each sub-region to obtain the wrapped phase difference signal. The wrapped phase difference signal in the i-th sub-region is expressed as represents the original phase time-domain information at the position corresponding to the i-th sampling point of the optical fiber, and ω represents the number of sampling points in the sub-region;

[0140] In this example, 100 points are sampled in a single sub-region. Therefore, the sensing optical fiber can be divided into 280 sub-regions. 100 points correspond to the set differential window length, and its value directly affects the minimum value of the actual spatial resolution. In the actual application process, the window length should be adjusted according to the requirements. If it is too large, it is difficult to achieve the ideal spatial resolution. If it is too small, the operation time cost of the system algorithm will increase;

[0141] Step 4: Perform phase unwrapping on the wrapped phase difference signal to restore the disturbed phase and obtain the true phase difference signal;

[0142] In this example, the values of the originally continuous phases are limited to [-π, +π] after demodulation. To restore the original phases, the wrapped phases need to be compensated and the phases extended to (-∞, +∞) to eliminate the jumps and fades in the phase signals.

[0143] Step 5: The values of random noise at any moment are random and have weak correlation with each other. Therefore, its autocorrelation result reaches the maximum at zero and rapidly decays to near 0 at other moments. Perform autocorrelation operation on the true phase difference signal matrix in each detection period. The autocorrelation operation can be expressed as:

[0144]

[0145] wherein, the phase difference signal matrix in a single detection period is denoted as v, v = {v i , i ∈ [0, B - 1]}, B represents the number of sub-regions divided on the optical fiber link, and R(v, v) m is the obtained autocorrelation matrix of the same size as the original signal;

[0146] In this example, the two groups of true phase difference signals for autocorrelation need to be acquired within the same detection period. Due to the random fluctuations of the noise, its autocorrelation result shows flat small spikes or low peaks, while the perturbation acts on the optical fiber all the time within a very short time, so its autocorrelation result shows abrupt peaks. Although there is a phase difference in the perturbation time-domain waveforms obtained after processing different signals, the similarity between their autocorrelation results is relatively high, and the fluctuation amplitude of the autocorrelation result of the signal in the non-perturbation region is much smaller than that in the perturbation region, as shown in Figure 4 and Figure 5 . Introducing the autocorrelation algorithm further enlarges the difference between the perturbation region and the non-perturbation region, which is beneficial to improving the positioning efficiency. Among them, Figure 4 a, Figure 5 a is the difference between the perturbation region and the non-perturbation region before introducing the autocorrelation algorithm, Figure 4 b, Figure 5 b is the difference between the perturbation region and the non-perturbation region after introducing the autocorrelation algorithm.

[0147] Step 6: Select the autocorrelation matrices P 1 and P 2 in two consecutive detection periods, perform overlapping matching in the time and space double domains, and perform cross-correlation operation on the autocorrelation signals of P 1 and P 2 in each sub-region;

[0148] Step 7: For the cross-correlation matrix C rPerform normalization processing, and screen the extreme points on the curve according to a preset threshold to determine the regional location where the disturbance occurs. The normalization formula can be expressed as:

[0149]

[0150] where W is the number of divided sub-regions, and C r ' is the normalization result of the r-th sub-region of the cross-correlation matrix, that is, the normalized curve, and C r is the amplitude value of the r-th sub-region of the cross-correlation matrix, and C max is the maximum value of the cross-correlation result over the entire W region, and C min is the minimum value of the cross-correlation result over the entire W region.

[0151] In this example, by introducing the autocorrelation algorithm, the problem of false alarms with multiple extreme values introduced by the cross-correlation algorithm can be effectively solved. On a 14.3 km long sensing optical fiber, a PZT is set at 14 km from the starting point to generate a 50 Hz sinusoidal disturbance, and the cross-correlation localization curve of the time-domain phase signal on the sensing optical fiber is calculated. The localization results before and after the improvement are as Figure 5 shown ([[]] Figure 5 a is before improvement, Figure 5 b is after improvement). Among them, Figure 6 the localization curve of a has extreme values at 10 km, 13 km, and 14 km. After the autocorrelation improvement algorithm, Figure 6 the localization curve of b only has a significant localization peak at 14 km, which is consistent with the disturbance position. This result verifies that the improved algorithm can effectively eliminate the false alarm problem of false peaks.

[0152] As Figure 7 shown, the present invention also provides an optimized localization system for sensing optical fiber disturbances. Using the above-mentioned optimized localization method for sensing optical fiber disturbances, the system includes:

[0153] A signal matrix acquisition module, which is used to acquire the backward Rayleigh scattering signal of the sensing optical fiber to obtain a two-dimensional phase signal matrix;

[0154] A region division module, which is used to equally divide the sensing optical fiber into several sub-regions;

[0155] A signal analysis and processing module, which is used to obtain the true phase difference signal of each sub-region based on the correspondence between the two-dimensional phase signal matrix and all sub-regions;

[0156] A correlation processing module, which is used to perform autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix;

[0157] A disturbance determination module, which is used to determine the sub-region where the disturbance is located based on the cross-correlation matrix.

[0158] The signal matrix acquisition module is further configured to:

[0159] Use a Φ-OTDR distributed optical fiber sensing system to transmit N single-frequency optical pulses to the sensing optical fiber;

[0160] The receiving end of the Φ-OTDR distributed optical fiber sensing system collects the backward Rayleigh scattering signals generated by each optical pulse at M sampling points to obtain a two-dimensional signal matrix;

[0161] After multiplying each row of the two-dimensional signal matrix by a pair of orthogonal carriers cos(2πft) and sin(2πft) respectively, digital down-conversion is performed through a low-pass filter to filter out high-frequency components to obtain two signals;

[0162] After obtaining the phase of these two signals through the arctangent, they are combined to obtain a two-dimensional phase signal matrix of N×M.

[0163] The signal analysis and processing module is further configured to:

[0164] Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, the phase signals at both endpoints of each sub-region are given;

[0165] Differentiate the phase signals at both endpoints of each sub-region to obtain a wrapped phase difference signal;

[0166] Based on the unwrapping function, the wrapped phase difference signal is restored to obtain a true phase difference signal.

[0167] The correlation processing module is further configured to:

[0168] Perform autocorrelation operations on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix;

[0169] Based on the autocorrelation matrix, the time-domain phase signals within all sub-regions are given;

[0170] Perform cross-correlation operations on the time-domain phase signals corresponding to two sequentially transmitted single-frequency optical pulses in the same sub-region to obtain a cross-correlation matrix.

[0171] The correlation processing module is further configured to:

[0172] Multiply the true phase difference signal of each sub-region by the true phase difference signals of other sub-regions respectively to obtain multiple preliminary autocorrelation signals for each sub-region;

[0173] Superimpose the multiple preliminary autocorrelation signals of each sub-region to obtain the autocorrelation signal of each sub-region;

[0174] Integrate the autocorrelation signals of all sub-regions to give an autocorrelation matrix.

[0175] The perturbation determination module is further configured to:

[0176] normalize the cross-correlation matrix to obtain a normalized curve;

[0177] screen the extreme points on the normalized curve according to a preset threshold;

[0178] determine the sub-region where the perturbation occurs according to the screened extreme points.

[0179] 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 concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as 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 is also intended to include these modifications and variations.

Claims

1. An optimized positioning method for sensing fiber optic perturbations, characterized in that, it includes: Obtain the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix; Divide the sensing fiber into a number of sub-regions at equal distances; Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, obtain the true phase difference signal of each sub-region; Perform autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix; Based on the cross-correlation matrix, determine the sub-region where the perturbation is located; Among them, performing autocorrelation calculation and cross-correlation calculation on the true phase difference signal in sequence to obtain a cross-correlation matrix includes: Perform autocorrelation operation on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix; Perform cross-correlation operation on the autocorrelation matrices corresponding to two consecutive single-frequency optical pulses emitted in sequence in the same sub-region to obtain a cross-correlation matrix, including: Based on the correspondence between the sampling points in the sub-region and the time-domain phase signals of the two autocorrelation matrices, correspond the time-domain phase signals of the two autocorrelation matrices; Based on the order of the sampling points in the sub-region, multiply the time-domain phase signal of one autocorrelation matrix corresponding to each sampling point by the time-domain phase signal of the other autocorrelation matrix corresponding to after increasing or decreasing a predetermined number of sampling points, and superimpose all the multiplication results to obtain a cross-correlation function value; Based on the number of sampling points in the sub-region, obtain all the values from the minimum number of sampling points between two sampling points to the maximum number of sampling points between two sampling points; Replace each value with a predetermined number respectively, and perform multiplication and superposition processing on the time-domain phase signals of the two autocorrelation matrices based on the predetermined number after each replacement to obtain multiple cross-correlation function values; Integrate all the cross-correlation function values to obtain a cross-correlation matrix.

2. The optimized positioning method according to claim 1, characterized in that, Obtaining the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix includes: Use a Φ-OTDR distributed fiber optic sensing system to emit N single-frequency optical pulses to the sensing fiber; The receiving end of the Φ-OTDR distributed fiber optic sensing system collects the backward Rayleigh scattering signal generated by each optical pulse at M sampling points to obtain a two-dimensional signal matrix; Multiply each row of the two-dimensional signal matrix by a pair of orthogonal carriers cos(2πft) and sin(2πft) respectively, and then pass through a low-pass filter for digital down-conversion to filter out high-frequency components to obtain two signals; where f is the frequency shift of the acousto-optic modulator; After obtaining the phase of these two signals by arctangent, combine them to obtain an N×M two-dimensional phase signal matrix.

3. The optimized positioning method according to claim 1, characterized in that, Based on the cross-correlation matrix, determining the sub-region where the perturbation is located includes: Perform normalization processing on the cross-correlation matrix to obtain a normalized curve; Screen the extreme points on the normalized curve according to a preset threshold; Based on the screened extreme points, determine the sub-region where the perturbation occurs.

4. The optimized positioning method according to claim 3, characterized in that, The determination of the preset threshold includes: Obtain the historical disturbance signal strength range in the current environment; Superimpose the noise variation amount on the minimum value of the historical disturbance signal strength range to obtain a preset threshold.

5. The optimized positioning method according to claim 1, characterized in that Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, obtain the true phase difference signal of each sub-region, including: Based on the correspondence between the two-dimensional phase signal matrix and all sub-regions, give the phase signals at both ends of each sub-region; Differentiate the phase signals at both ends of each sub-region to obtain a wrapped phase difference signal; Based on the unwrapping function, restore the wrapped phase difference signal to obtain the true phase difference signal.

6. The optimized positioning method according to claim 1, characterized in that Perform autocorrelation operations on the true phase difference signals of each single-frequency optical pulse in different sub-regions to obtain an autocorrelation matrix, including: Multiply the true phase difference signal of each sub-region with the true phase difference signals of other sub-regions respectively to obtain multiple preliminary autocorrelation signals for each sub-region; Superimpose the multiple preliminary autocorrelation signals of each sub-region to obtain the autocorrelation signal of each sub-region; Integrate the autocorrelation signals of all sub-regions to give an autocorrelation matrix.

7. The optimized positioning method according to claim 6, characterized in that The autocorrelation matrix satisfies the following relationship: Among them, B represents the number of sub-regions into which the sensing optical fiber is divided, and the true phase difference signal within a single detection period is denoted as v, v = {v i , i ∈ [0, B - 1]}, where v j represents the true phase difference signal corresponding to the j-th sub-region, and v m+j represents the true phase difference signal separated from v j by m sub-regions. R(v, v) m is the obtained autocorrelation matrix with the same size as the true phase difference signal.

8. An optimized positioning system for sensing fiber perturbations, using the optimized positioning method for sensing fiber perturbations according to any one of claims 1-7, characterized in that The system includes: A signal matrix acquisition module, which is used to acquire the backward Rayleigh scattering signal of the sensing fiber to obtain a two-dimensional phase signal matrix; A region division module, which is used to equally divide the sensing fiber into several sub-regions; A signal analysis and processing module, which is used to obtain the true phase difference signal of each sub-region based on the correspondence between the two-dimensional phase signal matrix and all sub-regions; A correlation processing module, which is used to perform autocorrelation calculations and cross-correlation calculations on the true phase difference signal in sequence to obtain a cross-correlation matrix; A perturbation determination module, which is used to determine the sub-region where the perturbation is located based on the cross-correlation matrix.

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