CN117288424A - Sensing optical fiber disturbance area positioning method and system based on phase signals - Google Patents
Sensing optical fiber disturbance area positioning method and system based on phase signals Download PDFInfo
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Abstract
The invention discloses a method and a system for positioning a disturbance area of a sensing optical fiber based on a phase signal, wherein the method comprises the following steps: collecting a back Rayleigh scattering signal of a sensing optical fiber to obtain a phase signal matrix; equidistant dividing is carried out on the sensing optical fibers to obtain a plurality of optical fiber areas; obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix; sequentially carrying out unwrapping, trend removal item and cross-correlation treatment on the wrapped phase difference signals to obtain a cross-correlation result; and normalizing the cross-correlation result to determine the area where the disturbance occurs. The invention realizes the reduction of the data processing amount by reducing the demodulation operation of the amplitude signal.
Description
Technical Field
The invention relates to the technical field of optical fiber disturbance positioning, in particular to a method and a system for positioning a sensing optical fiber disturbance area based on a phase signal.
Background
The distributed optical fiber sensing technology is used as a novel sensing technology, long-distance optical fibers are used as sensing devices, and the distributed optical fiber sensing technology has the advantages of safety, reliability, high sensitivity, low cost and the like, and has a very wide application prospect. The Phase-sensitive optical time domain reflectometry (Phi-Sensitive Optical Time Domain Reflectometry, phi-OTDR) is a distributed optical fiber sensing technology, and mainly utilizes the back Rayleigh scattering in the optical fiber to realize quantitative measurement and positioning of a to-be-measured point, and has the advantages of high positioning precision, capability of realizing multi-point disturbance positioning, large dynamic response range and the like, thus attracting attention in the research of recent years, and being widely applied to the scenes such as structural health monitoring, railway track monitoring, security intrusion alarm, electric power piping lane monitoring and the like.
The phi-OTDR system transmits light pulses with high coherence into the sensing optical fiber, backward Rayleigh scattered light generated by different scattering centers on the optical fiber interfere with each other, and external disturbance positioning is realized by analyzing the received Rayleigh scattering trace. Current research on Φ -OTDR disturbance positioning is mostly based on an amplitude signal obtained by demodulating an original signal, for example, CN110806259a discloses an apparatus for optical fiber sensing high-frequency disturbance positioning and detection, which includes: the system comprises 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 laser, a second coupler, a second tunable attenuator, a circulator, a sensing fiber, a Bragg fiber grating, a third coupler, an optical balance detector, a data acquisition card and a computer; the computer filters the electric signals acquired by the data acquisition card to separate interference signals of two wavelengths of lambda 1 and lambda 2; carrying out quadrature demodulation on interference signals with the wavelength of lambda 1 to obtain amplitude information of the signals, and then carrying out variance processing on the interference signals with the wavelength of lambda 1 to obtain position information of external disturbance; and carrying out phase demodulation on interference signals with the wavelength of lambda 2 to obtain frequency information of external disturbance. Although the disturbance position and frequency information can be obtained through the amplitude, in practical application, signal processing after obtaining the disturbance position sometimes only involves a phase signal, and if the amplitude signal is used for positioning, subsequent amplitude calculation with low utilization rate is introduced during demodulation pretreatment, so that data redundancy is caused.
Therefore, how to provide a method for disturbance localization by phase signals is a problem to be solved in the art.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method and a system for positioning a disturbance area of a sensing optical fiber based on a phase signal. According to the invention, the backward Rayleigh scattering optical signal returned from the sensing optical fiber is collected, and the disturbance area can be positioned only by acquiring the phase signal when the backward Rayleigh scattering optical signal is demodulated, so that the data processing amount is reduced by reducing the demodulation operation of the amplitude signal.
In a first aspect, the present invention provides a method for positioning a disturbance area of a sensing optical fiber based on a phase signal, including:
collecting a back Rayleigh scattering signal of a sensing optical fiber to obtain a phase signal matrix;
equidistant dividing is carried out on the sensing optical fibers to obtain a plurality of optical fiber areas;
obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix;
sequentially carrying out unwrapping, trend removal item and cross-correlation treatment on the wrapped phase difference signals to obtain a cross-correlation result;
and normalizing the cross-correlation result to determine the area where the disturbance occurs.
Further, the method for equally dividing the transmission optical fibers specifically comprises the following steps:
and equally dividing the sensing optical fibers by taking the collecting points on the sensing optical fibers as dividing nodes.
Further, collecting the back Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix, which comprises the following steps:
injecting a plurality of light pulses into the sensing optical fiber by adopting a phi-OTDR distributed optical fiber sensing system;
acquiring backward Rayleigh scattering signals of a plurality of light pulses through a phi-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and space domain information;
and carrying out phase demodulation on the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain phase signal matrixes with the same size.
Further, the phase demodulation is performed on the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain a phase signal matrix with the same size, which comprises the following steps:
the two-dimensional signal matrix is respectively combined with sin (2pi.DELTA.f IF t) and cos (2πΔf IF t) multiplying, filtering the frequency doubling component by a low-pass filter, and respectively obtaining an in-phase component I and a quadrature component Q;
performing arctangent processing on the in-phase component and the quadrature component to obtain a phase signal matrix
Wherein, the phase signal matrix satisfies the following relationship:
wherein I is an in-phase component, Q is a quadrature component, P AC For the power of the back Rayleigh scattering signal, E is the amplitude information of the back Rayleigh scattering signal,representing a matrix of phase signals, Δf IF The shift frequency introduced by the acousto-optic modulator is shown, and t is the time corresponding to the phase signal.
Further, obtaining a winding phase difference signal of each optical fiber area according to the phase signal matrix includes:
matching all the optical fiber areas with a phase signal matrix to give phase signals at two ends of each optical fiber area;
obtaining a corresponding winding phase difference signal according to the phase signals at two ends of each optical fiber area, wherein the winding phase difference signal comprises the following specific steps:
in the method, in the process of the invention,winding phase difference signal for kth fiber region, < >>And representing phase time domain signals of the k-th acquisition point of the sensing optical fiber at the corresponding position, wherein omega represents the number of the acquisition points in the optical fiber area.
Further, the unwrapping, trend removal and cross-correlation processing are sequentially performed on the wrapped phase difference signal to obtain a cross-correlation result, including:
phase unwrapping is carried out on the winding phase difference signal to obtain an unwrapped differential phase signal;
carrying out trend term removal treatment on the disentangled differential phase signals to obtain differential phase signals subjected to trend term removal;
performing overlapping correspondence on time and space double domains on the differential phase signals subjected to trend term removal in two groups of continuous detection periods;
and performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain a global cross-correlation result.
Further, the phase unwrapping is performed on the wrapped phase difference signal to obtain an unwrapped differential phase signal, including:
performing 2 pi modulo 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 time sequence, performing 2 pi modulo processing on the difference value of the differential phase signal before unwrapping at each moment in all detection periods and the differential phase signal before unwrapping at the previous moment to obtain an intermediate modulus value at each moment;
superposing the intermediate module value of each moment and the differential phase signal unwrapped at the previous moment to obtain differential phase signals unwrapped at all moments in all detection periods;
the unwrapped differential phase signal satisfies the following relationship:
in the method, in the process of the invention,and->Respectively representThe k detection period n is the differential phase signal before and after unwrapping, M [. Cndot.]Representing modulo 2 pi;
performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain cross-correlation results of all the optical fiber areas, wherein the cross-correlation results comprise:
carrying out convolution processing on differential phase signals of two groups of continuous detection periods in all the same optical fiber area at each moment;
overlapping convolution processing results at all moments to obtain cross-correlation results of differential phase signals of two groups of continuous detection periods in all optical fiber areas;
the cross-correlation results satisfy the following relationship:
wherein,and->For two sets of differential phase signals of consecutive detection periods, W represents the number of divided fiber areas on the sensing fiber, i.e.>And->N is the number of acquisition points of the differential phase signal in the time domain, i.e. +.>And->Line number of->Representation pair->And->Performs a cross-correlation operation on column k of (C) k The value of (2) is the cross-correlation result of the differential phase signal in the kth fiber region.
Further, normalizing the cross-correlation results of all the optical fiber areas to obtain normalized results of all the optical fiber areas;
obtaining a global cross-correlation positioning curve based on the normalization results of all the optical fiber areas;
and selecting the position where the extreme value appears as the corresponding optical fiber region where the disturbance occurs according to a preset threshold value based on the global cross-correlation positioning curve.
Further, normalizing the cross-correlation results of all the optical fiber areas to obtain normalized results of all the optical fiber areas, including:
wherein C is k ' is the normalized result in the kth fiber region,is the maximum value of the cross-correlation result on the sensing fiber.
The global cross-correlation positioning curve is:
C＝{C k ',k∈[0,W-1]}
wherein, C is a global cross-correlation positioning curve.
Further, the trend term removing process is performed on the unwrapped differential phase signal to obtain a differential phase signal with the trend term removed, and the method further includes:
constructing a polynomial trend term model based on the disentangled differential phase signals;
solving various coefficients of a polynomial trend term model according to a least square method;
combining each coefficient with the polynomial trend term model to obtain a solved polynomial trend term model;
obtaining a differential phase signal with a trend term removed through the unwrapped differential phase signal with the trend term and the solved polynomial trend term model;
further, solving each coefficient of the polynomial trend term model according to the least square method comprises:
constructing an objective function by taking the minimum sum of squares of errors between the unwrapped differential phase signals and the polynomial trend term model as a target;
based on the solving function and the objective function, obtaining various coefficients of a polynomial trend term model;
wherein, the objective function satisfies the following relationship:
where SSE is the objective function,is a polynomial trend term model, S k A is a differential phase signal unwrapped for the kth fiber region j The j-th coefficient of the polynomial, k is the number of optical fiber areas, l is the length of the differential phase signal, and h is the order of the polynomial;
solving a function, satisfying the following relationship:
obtaining the differential phase signal after removing the trend term through the unwrapped differential phase signal containing the trend term and the solved polynomial trend term model, comprising:
in the formula, S is a differential phase signal after the trend term is removed.
In a second aspect, the present invention further provides a system for positioning a disturbance area of a sensing optical fiber based on a phase signal, where the method for positioning a disturbance area of a sensing optical fiber based on a phase signal is adopted, and the system includes:
the signal acquisition module is used for acquiring the back Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;
the light dividing module is used for equally dividing the sensing optical fibers to obtain a plurality of optical fiber areas;
the signal determining module is used for obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix;
the cross-correlation processing module is used for sequentially carrying out unwrapping, trend removal item and cross-correlation processing on the wrapped phase difference signals to obtain a cross-correlation result;
and the disturbance determining module is used for normalizing the cross-correlation result and determining the area where the disturbance occurs.
Further, the signal acquisition module is further configured to:
injecting a plurality of light pulses into the sensing optical fiber by adopting a phi-OTDR distributed optical fiber sensing system;
acquiring backward Rayleigh scattering signals of a plurality of light pulses through a phi-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and space domain information;
and carrying out phase demodulation on the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain phase signal matrixes with the same size.
Further, the cross-correlation processing module is further configured to:
phase unwrapping is carried out on the winding phase difference signal to obtain an unwrapped differential phase signal;
carrying out trend term removal treatment on the disentangled differential phase signals to obtain differential phase signals subjected to trend term removal;
performing overlapping correspondence on time and space double domains on the differential phase signals subjected to trend term removal in two groups of continuous detection periods;
and performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain cross-correlation results of all the optical fiber areas.
Further, the cross-correlation processing module is further configured to:
constructing a polynomial trend term model based on the disentangled differential phase signals;
solving various coefficients of a polynomial trend term model according to a least square method;
combining each coefficient with the polynomial trend term model to obtain a solved polynomial trend term model;
and obtaining the differential phase signal after removing the trend term through the disentangled differential phase signal and the solved polynomial trend term model.
Further, the disturbance determination module is further configured to:
normalizing the cross-correlation results of all the optical fiber areas to obtain normalized results of all the optical fiber areas;
obtaining a global cross-correlation positioning curve based on the normalization results of all the optical fiber areas;
and selecting the position where the extreme value appears as the corresponding optical fiber region where the disturbance occurs according to a preset threshold value based on the global cross-correlation positioning curve.
The invention provides a method and a system for positioning a disturbance area of a sensing optical fiber based on a phase signal, which at least comprise the following beneficial effects:
(1) Based on the linear relation between the phase signals and external disturbance, the disturbance location can be realized by only using the phase signals by performing cross-correlation operation on the time domain phase signals of all-fiber links in two detection periods.
(2) Because only the phase signal is utilized in the subsequent processing of disturbance positioning in the application of the phi-OTDR distributed optical fiber sensing system, the method for positioning by utilizing the phase signal can avoid the introduction of amplitude disturbance positioning calculation, thereby reducing the data processing amount, improving the instantaneity and the calculation effectiveness of the phi-OTDR distributed optical fiber sensing system and effectively solving the calculation redundancy problem introduced by the amplitude disturbance positioning under the condition of lower amplitude signal utilization rate in the application of the phi-OTDR distributed optical fiber sensing system.
(3) Distortion caused by frequency drift of a laser can be effectively eliminated through trending item removal processing, low-frequency and slow trending item influence is avoided, and finally cross-correlation processing is carried out, so that disturbance positioning can be completed only by using a phase signal, and a good disturbance positioning effect is achieved; especially for the disturbance detection of short distance, have outstanding positioning effect.
Drawings
FIG. 1 is a flow chart of a method for positioning disturbance areas of sensing optical fibers based on phase signals;
FIG. 2 is a flow chart of cross-correlation results obtained according to an embodiment of the present invention;
FIG. 3 is a flowchart of a method for positioning disturbance areas of a sensing fiber according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a phase time domain signal before and after unwrapping according to an embodiment of the present invention;
FIG. 5 is a graph showing the results before and after the detrending term according to one embodiment of the present invention;
FIG. 6 is a schematic diagram of three-dimensional phase difference distance versus time according to an embodiment of the present invention;
fig. 7 is a schematic diagram of cross-correlation positioning of phase time domain signals according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a sensing fiber disturbance zone positioning system based on phase signals.
Detailed Description
In order to better understand the above technical solutions, the following detailed description will be given with reference to the accompanying drawings and specific embodiments. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, the "plurality" generally includes at least two.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a product or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such product or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a commodity or device comprising such element.
As shown in fig. 1, the present invention provides a method for positioning a disturbance area of a sensing optical fiber based on a phase signal, which includes:
collecting a back Rayleigh scattering signal of a sensing optical fiber to obtain a phase signal matrix;
equidistant dividing is carried out on the sensing optical fibers to obtain a plurality of optical fiber areas;
obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix;
sequentially carrying out unwrapping, trend removal item and cross-correlation treatment on the wrapped phase difference signals to obtain a cross-correlation result;
and normalizing the cross-correlation result to determine the area where the disturbance occurs.
According to the invention, disturbance detection can be completed by connecting one end of the sensing optical fiber to be detected to the phi-OTDR distributed optical fiber sensing system, and the structure of the phi-OTDR distributed optical fiber sensing system is not damaged by replacing the sensing optical fiber to be detected. In addition, the disturbance positioning information can be obtained by directly utilizing a set of phi-OTDR distributed optical fiber sensing system to carry out cross correlation on two detection periods.
In an actual application scene, the method for acquiring the back Rayleigh scattering signal of the sensing optical fiber to obtain the phase signal matrix can comprise the following steps:
injecting a plurality of light pulses into the sensing optical fiber by adopting a phi-OTDR distributed optical fiber sensing system;
acquiring backward Rayleigh scattering signals of a plurality of light pulses through a phi-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and space domain information;
and carrying out phase demodulation on the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain phase signal matrixes with the same size.
Wherein, divide into to the sensing fiber equidistance: and equally dividing the sensing optical fibers by taking the collecting points on the sensing optical fibers as dividing nodes.
Specifically, the Φ -OTDR distributed optical fiber sensing system realizes sensing positioning by analyzing the back Rayleigh scattered light in the sensing optical fiber, and the time for the back Rayleigh scattered light at each point in the sensing optical fiber to reach the detection end is sequential, so that the time relation between the space position of the sensing optical fiber and the received signal can be given: l=ct/2 n, L is the distance position on the sensing fiber, c is the speed of light, n is the refractive index of the fiber, t is the time difference between the emission and reception of the light pulse;
the meaning represented by the collection points on the sensing fiber is: after each light pulse is injected into the sensing optical fiber, each receiving light is back to the sample position of the Rayleigh scattered light moment, and the sample position can obtain the distance position on the sensing optical fiber according to the time relation between the space position and the received signal.
Because the acquisition points are discrete, the spatial positions corresponding to the sensing optical fibers are also discrete, when the sensing optical fibers are equidistantly divided, the optical fibers are divided according to the acquisition points, and the spatial distances of the optical fibers corresponding to the acquisition points divided each time are equal.
After the back Rayleigh scattering signals of a plurality of light pulses are collected, a two-dimensional signal matrix can be subjected to phase demodulation by using a quadrature demodulation algorithm to obtain a phase signal matrix with the same size, which specifically comprises the following steps:
the two-dimensional signal matrix is respectively combined with sin (2pi.DELTA.f IF t) and cos (2πΔf IF t) filtering the double frequency component through a low-pass filter after multiplication to respectively obtain an in-phase component I and a quadrature component Q;
performing arctangent processing on the in-phase component and the quadrature component to obtain a phase signal matrix
Wherein the in-phase component I, the quadrature component Q and the phase signal matrixThe following relationships are respectively satisfied:
wherein I is an in-phase component, Q is a quadrature component, P AC For the power of the back Rayleigh scattering signal, E is the amplitude information of the back Rayleigh scattering signal,representing a matrix of phase signals, Δf IF The frequency shift introduced by the acousto-optic modulator is represented, t is the time corresponding to the phase signal, and m is an integer.
After dividing the sensing optical fiber into a plurality of optical fiber areas, winding phase difference signals of the optical fiber areas can be obtained according to a phase signal matrix, and the method comprises the following steps:
matching all the optical fiber areas with a phase signal matrix to give phase signals at two ends of each optical fiber area;
obtaining a corresponding winding phase difference signal according to the phase signals at two ends of each optical fiber area, wherein the winding phase difference signal specifically comprises:
in the method, in the process of the invention,for winding phase difference signal>Time domain information (phase time domain signal) representing the phase signal at the position corresponding to the ith acquisition point of the sensing fiber, and ω represents the number of acquisition points in the fiber region. The phase signal matrix comprises a phase time domain signal and a phase space domain signal, each column of the phase signal matrix represents the phase time domain signal at one space position, and the column number of the phase signal matrix represents the number of the space positions; through the space positions of the two ends of the optical fiber area, the phase time domain signals corresponding to the two ends of the optical fiber area can be obtained by matching, and the phase signals of the two ends of the optical fiber area can be obtained.
As shown in fig. 2, after obtaining a winding phase difference signal, the present invention may sequentially perform disentangling, trending term removal and cross-correlation processing on the winding phase difference signal to obtain a cross-correlation result, which specifically includes:
phase unwrapping is carried out on the winding phase difference signal to obtain an unwrapped differential phase signal; comprising the following steps:
performing 2 pi modulo 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 time sequence, performing 2 pi modulo processing on the difference value of the differential phase signal before unwrapping at each moment in all detection periods and the differential phase signal before unwrapping at the previous moment to obtain an intermediate modulus value at each moment;
superposing the intermediate module value of each moment and the differential phase signal unwrapped at the previous moment to obtain differential phase signals unwrapped at all moments in all detection periods;
the unwrapped differential phase signal satisfies the following relationship:
in the method, in the process of the invention,and->Representing the differential phase signals before and after unwrapping, M [. Cndot.]Representing modulo 2 pi;
carrying out trend term removal treatment on the disentangled differential phase signals to obtain differential phase signals subjected to trend term removal; comprising the following steps:
constructing a polynomial trend term model based on the disentangled differential phase signals;
solving various coefficients of a polynomial trend term model according to a least square method;
combining each coefficient with the polynomial trend term model to obtain a solved polynomial trend term model;
obtaining a differential phase signal after removing trend terms through the disentangled differential phase signal and the solved polynomial trend term model; the disentangled differential phase signal is a differential phase signal containing trend terms;
performing overlapping correspondence on time and space double domains on the differential phase signals subjected to trend term removal in two groups of continuous detection periods;
performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain cross-correlation results of all the optical fiber areas, wherein the cross-correlation results comprise:
carrying out convolution processing on differential phase signals of two groups of continuous detection periods in all the same optical fiber area at each moment;
overlapping convolution processing results at all moments to obtain cross-correlation results of differential phase signals of two groups of continuous detection periods in all optical fiber areas;
the cross-correlation results satisfy the following relationship:
wherein,and->For two sets of differential phase signals of consecutive detection periods, W represents the number of divided fiber areas on the sensing fiber, i.e.>And->N is the number of acquisition points of the differential phase signal in the time domain, i.e. +.>And->Line number of->Representation pair->And->Performs a cross-correlation operation on column k of +.>Representation->Row b, column k, C k The value of (2) is the cross-correlation result of the differential phase signal in the kth fiber region.
Wherein, a group of detection periods corresponds to a group of light pulses, for example, 200 light pulses are injected into the sensing optical fiber to form a group of detection periods, and the meaning of the differential phase signals after trend term removal in two groups of continuous detection periods is as follows: the two groups of continuously injected light pulses respectively correspond to the two groups of differential phase signals after trend removal; in addition, the timing of the detection period corresponds to the injection sequence of one light pulse, i.e., the timing of a group of detection periods corresponds to the injection sequence of the light pulses, for example, the timing 0 corresponds to the first injected light pulse and the timing 1 corresponds to the second injected light pulse.
Because the narrow linewidth laser adopted by the phi-OTDR distributed optical fiber sensing system has slow frequency drift, the obtained unwrapped differential phase signal has an offset trend term, and therefore, the trend term carried by the differential phase signal is eliminated by adopting least square fitting. Specifically, solving each coefficient of the polynomial trend term model according to the least square method may include:
constructing an objective function by taking the minimum sum of squares of errors between the unwrapped differential phase signals and the polynomial trend term model as a target;
based on the solving function and the objective function, obtaining various coefficients of a polynomial trend term model;
wherein, the construction of the objective function can satisfy the following relation:
where SSE is the objective function,is a polynomial trend term model, S k A is a differential phase signal unwrapped for the kth fiber region j The j-th coefficient of the polynomial, k is the number of optical fiber areas, l is the length of the differential phase signal, and h is the order of the polynomial;
solving a function, satisfying the following relationship:
obtaining the differential phase signal after removing the trend term through the disentangled differential phase signal and the solved polynomial trend term model, wherein the method comprises the following steps:
in the formula, S is a differential phase signal after the trend term is removed.
In the non-disturbance area of the sensing optical fiber, the fluctuation in the continuous two detection periods is small and irregular due to the influence of random noise only, the fluctuation in the continuous two detection periods is regular due to external disturbance, and the cross-correlation value of the optical fiber area subjected to external disturbance is far greater than that of the non-disturbance area. Based on the above, the method normalizes the cross-correlation result, and determines the area where the disturbance occurs, which may include:
normalizing the cross-correlation results of all the optical fiber areas to obtain normalized results of all the optical fiber areas; comprising the following steps:
wherein C is k ' is the normalized result in the kth fiber region,is the maximum value of the cross-correlation result on the sensing optical fiber;
obtaining a global cross-correlation positioning curve based on the normalization results of all the optical fiber areas; comprising the following steps:
C＝{C k ',k∈[0,W-1]}
wherein, C is a global cross-correlation positioning curve;
and selecting the position where the extreme value appears as the corresponding optical fiber region where the disturbance occurs according to a preset threshold value based on the global cross-correlation positioning curve.
The selection of the preset threshold value can be determined by using a priori disturbance data set, specifically: and processing the signal data of a plurality of known disturbance occurrence positions by using the normalization result in the optical fiber region, counting the normalization result of the disturbance occurrence position region, and setting a preset threshold value as the lowest value. When the optical fiber region where disturbance occurs is actually determined, the global cross-correlation positioning curve is divided through the preset threshold value, if the global cross-correlation positioning curve intersects with the preset threshold value, the sensing optical fiber has disturbance, and the optical fiber region corresponding to the optical fiber region which is larger than the preset threshold value in the global cross-correlation positioning curve is determined as the disturbance occurrence region.
As shown in fig. 3, in an actual application scenario, the method for positioning a disturbance zone of a sensing optical fiber of the present invention may include:
step 1: the sensing data is acquired by using a phi-OTDR distributed optical fiber sensing system, each time the system transmits an optical pulse to a sensing optical fiber, a receiving end can obtain a backward Rayleigh scattering signal with the sampling length of M, and when N optical pulses are injected into the sensing optical fiber, a two-dimensional signal matrix D containing time domain information and space domain information can be obtained N×M ；
In the example, the sensing optical fiber is 14km long, the total space sampling point is 35000 points, the light pulse transmitting frequency set by the system is 1kHz, the primary detection period is 200ms, and the sensing signal returned after 200 continuous light pulses are injected into the optical cable, namely the size of D is 200 multiplied by 35000.
Step 2: the original signal matrix is subjected to phase demodulation by using a quadrature demodulation algorithm to obtain a phase signal matrix P with the same size N×M ；
In this example, the orthogonal demodulation method combines the beat signal output by the phi-OTDR system with sin (2pi.DELTA.f IF t) and cos (2πΔf IF t) multiplying, filtering the frequency doubling component by a low-pass filter, and respectively obtaining an in-phase component I and a quadrature component Q, wherein the phase signal is the arctangent of the two components.
Step 3: equidistant division is carried out on the space acquisition points corresponding to the all-link optical fibers, and phase signals at two end points of each subarea are differentiated to obtain winding phase difference signals containing disturbance information in the subarea;
in the example, the number of space acquisition points corresponding to the optical fiber full link is 35000, the area division length is set to 200 points, and 175 sub-sensing areas can be obtained in total.
Step 4: the winding phase difference signal has a plurality of jumps, and phase unwrapping is needed to restore the real phase value;
in this example, the unwrapping of the phase includes two parts, namely a distance domain and a time domain, where the unwrapping of the distance domain is used to avoid a severe jump caused by phase fading, and the unwrapping of the time domain is used to restore a true phase value, and the phase time domain signals obtained before and after unwrapping are shown in fig. 4 (a) and fig. 4 (b), respectively.
Step 5: the obtained differential phase signal after unwrapping is subjected to trending term processing to obtain a differential phase signal after trending term processing, wherein the differential phase signal is a two-dimensional matrix with time domain information and space domain informationEach time the positioning calculation is performed on the phase signal matrix in two groups of continuous detection periods>And->Performing overlapping correspondence on the time and space double domains;
in this example, the results before and after the trend removal term are shown in fig. 5, before the trend removal, the phase signal deviates from the baseline, and there is an obvious trend term, and the phase signal effectively eliminates the distortion caused by the frequency drift of the laser after passing through the trend term, so as to avoid the influence of the low-frequency and slow trend term.
As shown in fig. 6, the phase difference distance-time three-dimensional graph in two consecutive detection periods shows that the phase fluctuation of the disturbed area is more pronounced than that of the non-disturbed area, and the random fluctuation caused by noise cannot be guaranteed to occur in both detection periods.
Step 6: for a pair ofAnd->And cross-correlation is performed on the full-link time domain signals of the (c).
Step 7: the cross-correlation results of the time domain phase signals for each sensing region are normalized.
Step 8: and obtaining a global cross-correlation positioning curve, and selecting the position where the extreme value appears as the corresponding area where the disturbance occurs according to the set threshold value of the requirement.
In this example, a 14km position on the 14.3km sensing optical fiber is placed with a PZT to apply a 10Hz sinusoidal disturbance, and the calculated optical fiber full-link phase time domain signal cross correlation positioning chart shows a larger positioning peak at the 14km position, as shown in fig. 7, and is consistent with the actual disturbance application position.
As shown in fig. 8, the present invention further provides a sensing optical fiber disturbance zone positioning system based on a phase signal, and the sensing optical fiber disturbance zone positioning method based on the phase signal is adopted, where the system includes:
the signal acquisition module is used for acquiring the back Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;
the light dividing module is used for equally dividing the sensing optical fibers to obtain a plurality of optical fiber areas;
the signal determining module is used for obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix;
the cross-correlation processing module is used for sequentially carrying out unwrapping, trend removal item and cross-correlation processing on the wrapped phase difference signals to obtain a cross-correlation result;
and the disturbance determining module is used for normalizing the cross-correlation result and determining the area where the disturbance occurs.
The signal acquisition module is also used for:
injecting a plurality of light pulses into the sensing optical fiber by adopting a phi-OTDR distributed optical fiber sensing system;
acquiring backward Rayleigh scattering signals of a plurality of light pulses through a phi-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and space domain information;
and carrying out phase demodulation on the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain phase signal matrixes with the same size.
The cross-correlation processing module is further configured to:
phase unwrapping is carried out on the winding phase difference signal to obtain an unwrapped differential phase signal;
carrying out trend term removal treatment on the disentangled differential phase signals to obtain differential phase signals subjected to trend term removal;
performing overlapping correspondence on time and space double domains on the differential phase signals subjected to trend term removal in two groups of continuous detection periods;
and performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain cross-correlation results of all the optical fiber areas.
The cross-correlation processing module is further configured to:
constructing a polynomial trend term model based on the disentangled differential phase signals;
solving various coefficients of a polynomial trend term model according to a least square method;
combining each coefficient with the polynomial trend term model to obtain a solved polynomial trend term model;
and obtaining the differential phase signal after removing the trend term through the disentangled differential phase signal and the solved polynomial trend term model.
The disturbance determination module is further configured to:
normalizing the cross-correlation results of all the optical fiber areas to obtain normalized results of all the optical fiber areas;
obtaining a global cross-correlation positioning curve based on the normalization results of all the optical fiber areas;
and selecting the position where the extreme value appears as the corresponding optical fiber region where the disturbance occurs according to a preset threshold value based on the global cross-correlation positioning curve.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (10)
1. The method for positioning the disturbance area of the sensing optical fiber based on the phase signal is characterized by comprising the following steps of:
collecting a back Rayleigh scattering signal of a sensing optical fiber to obtain a phase signal matrix;
equidistant dividing is carried out on the sensing optical fibers to obtain a plurality of optical fiber areas;
obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix;
sequentially carrying out unwrapping, trend removal item and cross-correlation treatment on the wrapped phase difference signals to obtain a cross-correlation result;
and normalizing the cross-correlation result to determine the area where the disturbance occurs.
2. The method for locating a disturbance zone of a sensing fiber according to claim 1, wherein collecting the backward rayleigh scattering signal of the sensing fiber to obtain a phase signal matrix comprises:
injecting a plurality of light pulses into the sensing optical fiber by adopting a phi-OTDR distributed optical fiber sensing system;
acquiring backward Rayleigh scattering signals of a plurality of light pulses through a phi-OTDR distributed optical fiber sensing system to obtain a two-dimensional signal matrix containing time domain information and space domain information;
and carrying out phase demodulation on the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain phase signal matrixes with the same size.
3. The method for locating a disturbance zone of a sensing fiber according to claim 2, wherein the phase demodulation of the two-dimensional signal matrix by using a quadrature demodulation algorithm to obtain the phase signal matrix with the same size comprises the following steps:
the two-dimensional signal matrix is respectively combined with sin (2pi.DELTA.f IF t) and cos (2πΔf IF t) multiplying, filtering the frequency doubling component by a low-pass filter, and respectively obtaining an in-phase component and a quadrature component;
and performing arctangent processing on the in-phase component and the quadrature component to obtain a phase signal matrix.
4. The method for locating disturbance areas of a sensing fiber according to claim 1, wherein normalizing the cross-correlation results to determine the area where the disturbance occurs comprises:
normalizing the cross-correlation results of all the optical fiber areas to obtain normalized results of all the optical fiber areas;
obtaining a global cross-correlation positioning curve based on the normalization results of all the optical fiber areas;
and selecting the position where the extreme value appears as the corresponding optical fiber region where the disturbance occurs according to a preset threshold value based on the global cross-correlation positioning curve.
5. The method for locating a disturbance zone of a sensing fiber according to claim 1, wherein the sequentially performing unwrapping, trending and cross-correlation processing on the wrapped phase difference signal to obtain a cross-correlation result comprises:
phase unwrapping is carried out on the winding phase difference signal to obtain an unwrapped differential phase signal;
carrying out trend term removal treatment on the disentangled differential phase signals to obtain differential phase signals subjected to trend term removal;
performing overlapping correspondence on time and space double domains on the differential phase signals subjected to trend term removal in two groups of continuous detection periods;
and performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain cross-correlation results of all the optical fiber areas.
6. The method for locating a disturbance zone of a sensing fiber according to claim 5, wherein phase unwrapping the wrapped phase difference signal to obtain an unwrapped differential phase signal comprises:
performing 2 pi modulo 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 time sequence, performing 2 pi modulo processing on the difference value of the differential phase signal before unwrapping at each moment in all detection periods and the differential phase signal before unwrapping at the previous moment to obtain an intermediate modulus value at each moment;
and superposing the intermediate module value at each moment and the differential phase signal unwrapped at the previous moment to obtain the differential phase signal unwrapped at all moments in all detection periods.
7. The method for locating disturbance areas of sensing optical fibers according to claim 6, wherein performing cross-correlation operation on the overlapped and corresponding differential phase signals to obtain cross-correlation results of all the optical fiber areas comprises:
carrying out convolution processing on differential phase signals of two groups of continuous detection periods in all the same optical fiber area at each moment;
and superposing convolution processing results at all moments to obtain cross-correlation results of differential phase signals of two groups of continuous detection periods in all optical fiber areas.
8. The method for locating a disturbance zone of a sensing fiber according to claim 6 or 7, wherein the step of performing a detrack process on the unwrapped differential phase signal to obtain a detrack differential phase signal, further comprises:
constructing a polynomial trend term model based on the disentangled differential phase signals;
solving various coefficients of a polynomial trend term model according to a least square method;
combining each coefficient with the polynomial trend term model to obtain a solved polynomial trend term model;
and obtaining the differential phase signal after removing the trend term through the disentangled differential phase signal and the solved polynomial trend term model.
9. The method for locating a disturbance zone of a sensing fiber according to claim 8, wherein solving coefficients of a polynomial trend term model according to a least square method comprises:
constructing an objective function by taking the minimum sum of squares of errors between the unwrapped differential phase signals and the polynomial trend term model as a target;
and obtaining each coefficient of the polynomial trend term model based on the solving function and the objective function.
10. A sensing optical fiber disturbance zone positioning system based on a phase signal, which adopts the sensing optical fiber disturbance zone positioning method based on the phase signal as claimed in any one of claims 1 to 9, and is characterized in that the system comprises:
the signal acquisition module is used for acquiring the back Rayleigh scattering signal of the sensing optical fiber to obtain a phase signal matrix;
the light dividing module is used for equally dividing the sensing optical fibers to obtain a plurality of optical fiber areas;
the signal determining module is used for obtaining winding phase difference signals of all the optical fiber areas according to the phase signal matrix;
the cross-correlation processing module is used for sequentially carrying out unwrapping, trend removal item and cross-correlation processing on the wrapped phase difference signals to obtain a cross-correlation result;
and the disturbance determining module is used for normalizing the cross-correlation result and determining the area where the disturbance occurs.
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