CN116399379B - Distributed optical fiber acoustic wave sensing system and measuring method thereof - Google Patents
Distributed optical fiber acoustic wave sensing system and measuring method thereof Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 100
- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000012545 processing Methods 0.000 claims abstract description 24
- 230000009466 transformation Effects 0.000 claims abstract description 7
- 238000000354 decomposition reaction Methods 0.000 claims description 25
- 239000000835 fiber Substances 0.000 claims description 17
- 230000002159 abnormal effect Effects 0.000 claims description 9
- 239000011159 matrix material Substances 0.000 claims description 8
- 238000005259 measurement Methods 0.000 abstract description 6
- 238000001514 detection method Methods 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 17
- 230000008859 change Effects 0.000 description 12
- 239000000919 ceramic Substances 0.000 description 5
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- 230000009286 beneficial effect Effects 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000004973 liquid crystal related substance Substances 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 229910052691 Erbium Inorganic materials 0.000 description 1
- UYAHIZSMUZPPFV-UHFFFAOYSA-N erbium Chemical compound [Er] UYAHIZSMUZPPFV-UHFFFAOYSA-N 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/3537—Optical fibre sensor using a particular arrangement of the optical fibre itself
Abstract
The embodiment of the application provides a distributed optical fiber acoustic wave sensing system and a measuring method thereof, which relate to the technical field of distributed optical fiber sensing detection and comprise the steps of collecting backward Rayleigh scattering signals generated by vibration signals in a sensing optical fiber along a line in a preset time period; demodulating the collected backward Rayleigh scattering signal to obtain first demodulation information; constructing an original two-dimensional image through the first demodulation information, wherein the original two-dimensional image comprises an image of a time-distance domain formed by the first demodulation information corresponding to each position of the sensing optical fiber along the line in a preset time period; performing two-dimensional wavelet transformation image processing on the original two-dimensional image to eliminate noise information and obtain a noise-removed two-dimensional image; and reconstructing second demodulation information according to the denoising two-dimensional image, wherein the second demodulation information comprises demodulation information after the denoising information of each position along the sensing optical fiber, so that measurement errors are reduced, and the measurement accuracy of the distributed optical fiber acoustic wave sensing system is improved.
Description
Technical Field
The application relates to the technical field of distributed optical fiber sensing detection, in particular to a distributed optical fiber acoustic wave sensing system and a measuring method thereof.
Background
The principle of the distributed optical fiber acoustic wave sensing technology is that the change of physical quantity (such as sound, vibration and the like) required to be detected is obtained by detecting the phase change of Rayleigh scattered light along the sensing optical fiber. The distributed optical fiber acoustic wave sensing system has the advantages of light weight, small volume, high sensitivity, strong electromagnetic interference resistance and the like, and has extremely high application value in the fields of perimeter security, oil and gas exploration, pipeline monitoring and the like.
In the related art, in the measuring process of the distributed optical fiber acoustic wave sensing system, incident light can interfere with backward scattered light at a certain point along the sensing optical fiber, and the change of physical quantities such as acoustic wave or vibration at the point can cause the change of the phase of interference light, so that the change of acoustic wave or vibration at the point can be determined by demodulating the phase of interference light. Because the sensing optical fibers are continuously distributed in the space, the distributed optical fiber acoustic wave sensing system can quantitatively detect the change of the physical quantity of any point in the space, thereby realizing distributed sensing.
However, in the distributed optical fiber acoustic wave sensing system, when the information of each position along the transmission fiber is demodulated under the influence of random noise fluctuation such as laser phase noise, polarization noise, environmental noise, and the like, a plurality of abnormal information are contained in the obtained demodulation result. In addition, since the demodulation result is obtained from the noisy information, the time-domain waveform and amplitude fluctuation of the demodulation result are also large, thereby bringing about measurement errors.
Disclosure of Invention
The embodiment of the application provides a measuring method of a distributed optical fiber acoustic wave sensor system, which aims to solve the technical problem that a distributed optical fiber acoustic wave sensor in the prior art has larger measuring error.
The embodiment of the application provides a measuring method of a distributed optical fiber acoustic wave sensing system, which comprises the steps of collecting backward Rayleigh scattering signals generated by vibration signals in a sensing optical fiber along a line in a preset time period;
demodulating the collected backward Rayleigh scattering signals to obtain first demodulation information, wherein the first demodulation information comprises demodulation information containing noise information at each position along the sensing optical fiber;
constructing an original two-dimensional image through the first demodulation information, wherein the original two-dimensional image comprises an image of a time-distance domain formed by the first demodulation information corresponding to each position of the sensing optical fiber along the line in a preset time period;
performing two-dimensional wavelet transformation image processing on the original two-dimensional image to eliminate noise information and obtain a noise-removed two-dimensional image;
reconstructing second demodulation information according to the denoising two-dimensional image, wherein the second demodulation information comprises demodulation information after the denoising information of each position along the sensing optical fiber.
In one possible implementation, the original two-dimensional image is subjected to two-dimensional wavelet transform image processing, including,
and carrying out wavelet decomposition on the original two-dimensional image through a discrete wavelet transform function to obtain a plurality of sub-images corresponding to the original two-dimensional image.
In one possible implementation, the two-dimensional wavelet transform image processing is performed on an original two-dimensional image, further comprising,
the level of wavelet decomposition is adjusted to obtain a corresponding number of sub-images, and the high-frequency component and the low-frequency component of the sub-images are acquired and processed to eliminate the abnormal value on the sub-images so as to obtain the denoising sub-images.
In one possible implementation, there is an adjustment threshold for the level of wavelet decomposition, within which the higher the level of wavelet decomposition, the less outliers the noise-removed sub-image is obtained.
In one possible implementation, the two-dimensional wavelet transform image processing is performed on the original two-dimensional image, and the method further comprises the step of performing wavelet reconstruction on the high-frequency component and the low-frequency component of the denoising sub-image by adopting an inverse discrete wavelet transform function to obtain a denoising two-dimensional image.
In one possible implementation, after reconstructing the second demodulation information from the denoised two-dimensional image, extracting time domain information of the vibration signal in the second demodulation information is included.
In one possible implementation, the original two-dimensional image and the noise-removed two-dimensional image each include two-dimensional graphical information of a time-distance domain or two-dimensional matrix information of a time-distance domain.
The embodiment of the application also provides a distributed optical fiber acoustic wave sensing system, which comprises a demodulation unit and a controller, wherein the demodulation unit is connected with the controller through signals;
the demodulation unit is configured to collect backward Rayleigh scattering signals within a preset time period, wherein the backward Rayleigh scattering signals comprise signals generated by a vibration signal in the distributed optical fiber acoustic wave sensing system;
the demodulation unit is further configured to demodulate the collected backward Rayleigh scattering signals to obtain first demodulation information, wherein the first demodulation information comprises demodulation information containing noise information at each position along the sensing optical fiber;
the controller is configured to construct an original two-dimensional image through the first demodulation information, wherein the two-dimensional image comprises a time-distance domain image formed by the first demodulation information corresponding to each position of the sensing optical fiber along the line in a preset time period;
the controller is further configured to perform two-dimensional wavelet transform image processing on the original two-dimensional image to eliminate noise information to obtain a noise-removed two-dimensional image;
the controller is further configured to reconstruct second demodulation information from the denoised two-dimensional image, the second demodulation information including the noise-cancelled demodulation information for each location along the sensing fiber.
The embodiment of the application provides a measuring method of a distributed optical fiber acoustic wave sensing system, which is characterized in that first demodulation information is obtained by demodulating a backward Rayleigh scattering signal, an original two-dimensional image is constructed by the first demodulation information, a two-dimensional wavelet transformation image processing is carried out on the original two-dimensional image to obtain a denoising two-dimensional image, a second demodulation information is obtained by reconstructing the denoising two-dimensional image, demodulation information after noise information is eliminated is obtained, abnormal information in the demodulation information is eliminated, time domain waveform and amplitude fluctuation of a demodulation result are reduced, measuring errors are reduced, and measuring precision of the distributed optical fiber acoustic wave sensing system is improved.
The embodiment of the application also provides a distributed optical fiber acoustic wave sensing system, which adopts the measuring method in any one of the technical schemes, so that the distributed optical fiber acoustic wave sensing system has all the beneficial effects of the measuring method in any one of the technical schemes, and is not repeated here.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application. In the drawings:
FIG. 1 is a schematic diagram of a distributed optical fiber acoustic wave sensor system according to an embodiment of the present application;
FIG. 2 is a diagram showing steps of a method for measuring a distributed optical fiber acoustic wave sensor system according to an embodiment of the present application;
FIG. 3 is a diagram of an implementation step of S400 in FIG. 2;
FIG. 4 is a two-dimensional image corresponding to demodulation information of vibration signals measured by a measuring method of a distributed optical fiber acoustic wave sensing system according to the related art;
FIG. 5 is a two-dimensional image corresponding to demodulation information of a vibration signal measured by a measuring method of a distributed optical fiber acoustic wave sensing system according to an embodiment of the present application;
FIG. 6 is a time domain diagram of vibration positions corresponding to the two-dimensional image of FIG. 4;
fig. 7 is a time domain diagram of vibration positions corresponding to the two-dimensional image in fig. 5.
Reference numerals illustrate:
1-a laser emitting unit; 2-a circulator; a 3-sensing unit; a 4-demodulation unit;
a 101-laser; 102-an isolator; 103-an acousto-optic modulator; 1031-a function generator; 104-a first erbium-doped fiber amplifier; 105-a first filter;
301-sensing optical fibers; 302-a first piezoelectric ceramic;
401-a second erbium-doped fiber amplifier; 402-a second filter; 403-couplers; 404-a first faraday rotator mirror; 405-a second faraday rotator mirror; 406-a second piezoelectric ceramic; 407-detector; 408-acquisition card.
Detailed Description
The principle of the distributed optical fiber acoustic wave sensing technology is to obtain the change of the physical quantity (such as sound, vibration, etc.) to be detected by detecting the phase change of the rayleigh scattered light along the sensing optical fiber 301. The distributed optical fiber acoustic wave sensing system has the advantages of light weight, small volume, high sensitivity, strong electromagnetic interference resistance and the like, and has extremely high application value in the fields of perimeter security, oil and gas exploration, pipeline monitoring and the like.
In the related art, in the measurement process of the distributed optical fiber acoustic wave sensing system, incident light interferes with back scattered light at a point along the sensing optical fiber 301, and the change of physical quantity such as acoustic wave or vibration at the point causes the change of the phase of interference light, so that the change of acoustic wave or vibration at the point can be determined by demodulating the phase of interference light. Since the sensing optical fibers 301 are continuously distributed in space, the distributed optical fiber acoustic wave sensing system can quantitatively detect the change of the physical quantity at any point in space, thereby realizing distributed sensing.
However, in the distributed optical fiber acoustic wave sensing system, when the information of each position along the transmission fiber is demodulated under the influence of random noise fluctuation such as laser phase noise, polarization noise, environmental noise, and the like, a plurality of abnormal information are contained in the obtained demodulation result. In addition, since the demodulation result is obtained from the noisy information, the time-domain waveform and amplitude fluctuation of the demodulation result are also large, thereby bringing about measurement errors.
Therefore, the embodiment of the application provides a distributed optical fiber acoustic wave sensing system and a measuring method thereof, which are used for solving the technical problem that the measuring error is caused by the fact that the obtained demodulation result contains a plurality of abnormal information when the distributed optical fiber acoustic wave sensing system demodulates the information of all positions along the transmission optical fiber in the prior art.
Fig. 1 is a schematic structural diagram of a distributed optical fiber acoustic wave sensor system according to an embodiment of the present application.
In some examples, referring to fig. 1, the distributed optical fiber acoustic wave sensing system generally includes a laser emitting unit 1, a circulator 2, a sensing unit 3, a demodulation unit 4, and a controller, where an output terminal of the laser emitting unit 1 is connected to a first input terminal of the circulator 2, a first output terminal of the circulator 2 is connected to an output terminal of the sensing unit 3, a second output terminal of the circulator 2 is connected to the demodulation unit 4, and an output terminal of the demodulation unit 4 is connected to the controller.
Illustratively, the laser emitting unit 1 emits a laser signal, the laser signal is output to the sensing unit 3 via the first input end and the first output end of the circulator 2, the laser signal propagates along the sensing optical fiber 301 of the sensing unit 3 to detect a vibration signal in an environment to be detected, and generates backward rayleigh scattered light, the backward rayleigh scattered light is output to the demodulating unit 4 via the second output end of the circulator 2, the demodulating unit 4 demodulates the backward rayleigh scattered light, and the demodulated information is output to the controller.
Fig. 2 is a diagram of implementation steps of a measurement method of a distributed optical fiber acoustic wave sensor system according to an embodiment of the present application. Fig. 3 is a diagram of an implementation step of S400 in fig. 2.
The embodiment of the application provides a measuring method of a distributed optical fiber acoustic wave sensing system, referring to fig. 2 and 3, comprising the following steps:
collecting backward Rayleigh scattering signals generated by vibration signals in the line of the sensing optical fiber 301 in a preset time period;
demodulating the collected backward Rayleigh scattering signals to obtain first demodulation information, wherein the first demodulation information comprises demodulation information containing noise information at each position along the sensing optical fiber 301;
constructing an original two-dimensional image by the first demodulation information, wherein the original two-dimensional image comprises an image of a time-distance domain formed by the first demodulation information corresponding to each position of the sensing optical fiber 301 along the line in a preset time period;
performing two-dimensional wavelet transformation image processing on the original two-dimensional image to eliminate noise information and obtain a noise-removed two-dimensional image;
the second demodulation information is reconstructed from the denoised two-dimensional image, and includes the demodulation information after the noise information is removed at each position along the sensing fiber 301.
The embodiment of the application provides a measuring method of a distributed optical fiber acoustic wave sensing system, which is characterized in that first demodulation information is obtained by demodulating a backward Rayleigh scattering signal, an original two-dimensional image is constructed by the first demodulation information, a two-dimensional wavelet transformation image processing is carried out on the original two-dimensional image to obtain a denoising two-dimensional image, a second demodulation information is obtained by reconstructing the denoising two-dimensional image, demodulation information after noise information is eliminated is obtained, abnormal information in the demodulation information is eliminated, time domain waveform and amplitude fluctuation of a demodulation result are reduced, measuring errors are reduced, and measuring precision of the distributed optical fiber acoustic wave sensing system is improved.
In some examples, performing two-dimensional wavelet transform image processing on the original two-dimensional image includes performing wavelet decomposition on the original two-dimensional image by a discrete wavelet transform function to obtain a plurality of sub-images corresponding to the original two-dimensional image.
For example, the wavelet decomposition may be calculated by referring to the following formula:
；
wherein, the liquid crystal display device comprises a liquid crystal display device,represents a scaling factor->Represents a translation factor->Representing vibration signal +.>The function of the mother wavelet is represented,is->Complex conjugate of->Representing a wavelet decomposition function.
The first sub-image is obtained after the primary wavelet decomposition of the original two-dimensional image, wherein the first sub-image is averagely divided into a low-frequency component and three high-frequency components, the three high-frequency components comprise three parts of horizontal high frequency, vertical high frequency and diagonal high frequency, the secondary decomposition is carried out on the original two-dimensional image, namely, the area of the low-frequency component of the first sub-image is continuously averagely divided into the low-frequency component and the three high-frequency components, and the multi-stage decomposition is carried out on the original two-dimensional image, so that the method is just like.
The low frequency component after wavelet decomposition represents contour information of an image and can be regarded as effective information.
According to the embodiment of the application, the original two-dimensional image is subjected to wavelet decomposition through the discrete wavelet transform function, so that a plurality of sub-images corresponding to the original two-dimensional image can be obtained, and further, the high-frequency component and the low-frequency component of each sub-image are obtained, so that the sub-images can be subjected to noise removal.
The method includes the steps of performing two-dimensional wavelet transform image processing on an original two-dimensional image, and adjusting the level of wavelet decomposition to obtain a corresponding number of sub-images, and acquiring and processing high-frequency components and low-frequency components of the sub-images to eliminate abnormal values on the sub-images and remove noise of the sub-images.
Illustratively, the level of wavelet decomposition is adjusted to obtain a low-frequency component and a high-frequency component of the sub-image, the pixel value of the low-frequency component is increased according to a nonlinear stretching rule, and noise reduction processing is performed on the high-frequency component to obtain a noise-removed sub-image.
Illustratively, there is an adjustment threshold for the level of wavelet decomposition, within which the higher the level of wavelet decomposition, the less outliers the noise-removed sub-image is obtained.
When the level of wavelet decomposition increases, the number of low-frequency components and the number of high-frequency components increase, and noise of the sub-image increases due to the increase of the high-frequency components, so that noise reduction processing is required for more high-frequency components, and there is a residual outlier in the high-frequency components after the noise reduction processing, and therefore, when the high-frequency components increase to a certain value, the residual outlier increases accordingly, and therefore, within the adjustment threshold, the higher the level of wavelet decomposition, the less the outlier of the noise-removed sub-image is obtained.
According to the embodiment of the application, the sub-image in the adjustment threshold is obtained by adjusting the wavelet decomposition level, and the low-frequency component and the high-frequency component of the sub-image are processed, so that the noise interference in the sub-image is eliminated, and the noise-removed sub-image is obtained.
The method for processing the two-dimensional wavelet transform image of the original two-dimensional image further comprises the step of carrying out wavelet reconstruction on high-frequency components and low-frequency components of the denoising sub-image by adopting an inverse discrete wavelet transform function to obtain the denoising two-dimensional image.
The wavelet reconstruction is, for example, image reconstruction by using the low-frequency component with increased pixel value and the high-frequency component with noise reduction, so as to obtain a contrast enhanced image, i.e. an undenoised two-dimensional image.
According to the embodiment of the application, through wavelet reconstruction, the high-frequency component and the low-frequency component of the denoising sub-image are subjected to wavelet reconstruction by adopting an inverse discrete wavelet transform function, so that a denoising two-dimensional image with the noises eliminated is obtained, and the subsequent reconstruction of second demodulation information is facilitated.
In some examples, reconstructing the second demodulation information from the denoised two-dimensional image includes extracting time domain information of the vibration signal in the second demodulation information.
In some examples, the original two-dimensional image and the denoised two-dimensional image each include two-dimensional graphical information of a time-distance domain or two-dimensional matrix information of a time-distance domain.
It should be noted that, the time in the time-distance domain corresponds to a preset time period, and the distance corresponds to each position along the sensing optical fiber 301.
In some examples, referring to fig. 1, the laser emitting unit 1 includes a laser 101, an isolator 102, an acousto-optic modulator 103, a first erbium-doped amplifier, and a first filter 105, an output of the laser 101 is connected to an input of the isolator 102, an output of the isolator 102 is connected to an input of the acousto-optic modulator 103, an output of the acousto-optic modulator 103 is connected to an input of the erbium-doped amplifier, and an output of the erbium-doped amplifier is connected to an input of the first filter 105. The laser 101 is configured to emit a laser signal to an input of the isolator 102; the isolator 102 is configured such that the laser beam is output unidirectionally by the isolator 102 to the acousto-optic modulator 103. The acousto-optic modulator 103 is connected to a function generator 1031, the function generator 1031 being configured to drive the acousto-optic modulator 103 to modulate the pulse width between pulses of the laser signal and the number of frequencies between pulses. The first erbium-doped fiber amplifier 104 is configured to amplify the laser signal output by the output terminal of the acousto-optic modulator 103. The first filter 105 is configured to filter the disturbance light of the laser signal.
The sensing unit 3 comprises a sensing optical fiber 301, the first output end of the circulator 2 is connected with the sensing optical fiber 301, and the sensing optical fiber 301 is configured to transmit laser signals and interfere with vibration signals along the sensing optical fiber 301 to generate backward Rayleigh scattering signals.
The demodulation unit 4 comprises a second erbium doped fiber amplifier 401, a second filter 402, a detector 407, an acquisition card 408, a coupler 403, a first faraday rotator mirror 404 and a second faraday rotator mirror 405. The input end of the second erbium-doped fiber amplifier 401 is connected with the second output end of the circulator 2, the output end of the second erbium-doped fiber amplifier 401 is connected with the input end of the filter, the output end of the filter is connected with the first end of the coupler 403, the second end of the coupler 403 is connected with the input end of the detector 407, the output end of the detector 407 is connected with the input end of the acquisition card 408, the third end of the coupler 403 is connected with the first faraday rotator mirror 404, and the fourth end of the coupler 403 is connected with the second faraday rotator mirror 405.
The laser signal is input by the laser 101, sequentially passes through the isolator 102, the acousto-optic modulator 103, the erbium-doped fiber amplifier and the filter, and then is output to the sensing fiber 301 through the first output end of the circulator 2, the vibration signal along the sensing fiber 301 generates a backward rayleigh scattering signal within a preset time, and the backward rayleigh scattering signal is output to the demodulation unit 4 through the first input end and the second output end of the circulator 2 in sequence.
The backward Rayleigh scattering signal after entering the demodulation unit 4 enters the first Faraday rotator mirror 404 through the erbium-doped fiber amplifier and the filter, a part of the first end of the coupler 403 and the third end of the coupler 403 are reflected to the third end of the coupler 403 by the first Faraday rotator mirror 404, the other part of the backward Rayleigh scattering signal is output to the second Faraday rotator mirror 405 through the fourth end of the coupler 403, a second piezoelectric ceramic 406 is arranged at the second Faraday rotator mirror 405, a carrier signal is loaded through the second piezoelectric ceramic 406 to modulate the other part of the backward Rayleigh scattering signal, the modulated backward Rayleigh scattering signal is reflected to the fourth end of the coupler 403 by the second Faraday rotator mirror 405, the backward Rayleigh scattering signal of the fourth end of the coupler 403 and the backward Rayleigh scattering signal of the third end of the coupler 403 are all output to the second end of the coupler 403 and are mutually interfered and collected by the collecting card 408, the collecting card 408 is connected with the controller, the collecting card 408 outputs the collected signal to the controller, and the interference generated demodulation information is processed in the controller.
In some examples, referring to fig. 2 and 3, a method of measuring a distributed fiber optic acoustic wave sensing system includes the steps of:
s100: the backward Rayleigh scattering signal generated by the vibration signal along the line of the sensing optical fiber 301 in a preset time period is collected.
For example, in testing the distributed optical fiber acoustic wave sensing system, the distributed optical fiber acoustic wave sensing system may be set up, a vibration signal is applied to the first piezoelectric ceramic 302 on the sensing optical fiber 301 on the function generator 1031, and the distributed optical fiber acoustic wave sensing system is used to collect backward rayleigh scattering signals generated by the sensing optical fiber 301 along the line in a preset time period.
And S200, demodulating the collected backward Rayleigh scattering signals to obtain first demodulation information, wherein the first demodulation information comprises demodulation information containing noise information at each position along the sensing optical fiber 301.
The collected backward Rayleigh scattering signal is subjected to phase demodulation to obtain first demodulation information.
S300, constructing an original two-dimensional image through the first demodulation information, wherein the original two-dimensional image comprises an image of a time-distance domain formed by the first demodulation information corresponding to each position of the sensing optical fiber 301 along the line in a preset time period.
Illustratively, the original two-dimensional image includes two-dimensional graphic information of a time-distance domain or two-dimensional matrix information of a time-distance domain.
S400, performing two-dimensional wavelet transformation image processing on the original two-dimensional image to eliminate noise information and obtain a noise-removed two-dimensional image.
Illustratively, the noise-removed two-dimensional image includes two-dimensional graphic information of a time-distance domain or two-dimensional matrix information of a time-distance domain.
S410, carrying out wavelet decomposition on the original two-dimensional image through a discrete wavelet transform function to obtain a plurality of sub-images corresponding to the original two-dimensional image.
S420: the level of wavelet decomposition is adjusted to obtain a corresponding number of sub-images, and the high-frequency component and the low-frequency component of the sub-images are acquired and processed to eliminate the abnormal value on the sub-images so as to obtain the denoising sub-images.
S430: and carrying out wavelet reconstruction on the high-frequency component and the low-frequency component of the denoising sub-image by adopting an inverse discrete wavelet transform function to obtain a denoising two-dimensional image.
S500, reconstructing second demodulation information according to the denoising two-dimensional image, wherein the second demodulation information comprises demodulation information after the denoising information of each position along the sensing optical fiber 301.
And S510, extracting time domain information of the vibration signal in the second demodulation information.
Fig. 4 is a two-dimensional image corresponding to demodulation information of a vibration signal measured by a measuring method of a distributed optical fiber acoustic wave sensing system in the related art. Fig. 5 is a two-dimensional image corresponding to demodulation information of a vibration signal measured by a measuring method of a distributed optical fiber acoustic wave sensing system according to an embodiment of the present application. Fig. 6 is a time domain diagram of vibration positions corresponding to the two-dimensional image in fig. 4. Fig. 7 is a time domain diagram of vibration positions corresponding to the two-dimensional image in fig. 5.
For example, referring to fig. 4, the schematic diagram in fig. 4 is that the vibration signal applied to the sensing optical fiber 301 is measured by using the distributed optical fiber acoustic wave sensing system in the related art, and as can be seen from viewing fig. 3, there are multiple highlight interferences a in the area a and multiple interferences at the vibration signal analog diagram in the area B in fig. 3, so that the resolution of the vibration signal analog diagram in the area B is lower.
Referring to fig. 5, the schematic diagram in fig. 5 is that the vibration signal along the sensing optical fiber 301 is measured by using the measuring method of the distributed optical fiber acoustic wave sensing system in the embodiment of the present application, and it can be seen from observing fig. 5 that, compared with fig. 4, the highlight interference in the area A1 corresponding to the area a in fig. 5 is reduced and darkened, and similarly, the highlight interference in the area B1 corresponding to the area B in fig. 3 is also reduced in fig. 4, and the resolution of the vibration signal diagram in the area B1 is higher.
Similarly, referring to fig. 6, a vibration position time domain diagram corresponding to the two-dimensional image in fig. 4, a curve C is a vibration position time domain curve of the vibration signal, and referring to fig. 7, a vibration position time domain diagram corresponding to the two-dimensional image in fig. 5, a curve D is a vibration position time domain curve of the vibration signal. As can be seen from a comparison between fig. 6 and fig. 7, the vibration position time domain curve in fig. 7 has smaller fluctuation amplitude than the vibration position time domain curve in fig. 6.
As can be seen from comparison of fig. 4 and fig. 5, and comparison of fig. 6 and fig. 7, a measurement method of the distributed optical fiber acoustic wave sensing system is adopted to measure a certain vibration signal applied to the sensing optical fiber 301, so that interference of noise on the vibration signal is removed, and measurement accuracy is improved.
A distributed optical fiber acoustic wave sensing system comprises a demodulation unit 4 and a controller, wherein the demodulation unit 4 is connected with the controller through signals;
the demodulation unit 4 is configured to collect backward Rayleigh scattering signals within a preset time period, wherein the backward Rayleigh scattering signals comprise signals generated by a distributed optical fiber acoustic wave sensing system by vibration signals;
the demodulation unit 4 is further configured to demodulate the collected backward rayleigh scattering signals to obtain first demodulation information, where the first demodulation information includes demodulation information including noise information at each position along the sensing optical fiber 301;
the controller is configured to construct an original two-dimensional image by the first demodulation information, wherein the two-dimensional image comprises a time-distance domain image formed by the first demodulation information corresponding to each position of the sensing optical fiber 301 along the line in a preset time period;
the controller is further configured to perform two-dimensional wavelet transform image processing on the original two-dimensional image to eliminate noise information to obtain a noise-removed two-dimensional image;
the controller is further configured to reconstruct second demodulation information from the denoised two-dimensional image, the second demodulation information including the noise-cancelled demodulation information for each location along the sensing fiber 301.
The embodiment of the application also provides a distributed optical fiber acoustic wave sensing system, which adopts the measuring method in any one of the technical schemes, so that the distributed optical fiber acoustic wave sensing system has all the beneficial effects of the measuring method in any one of the technical schemes, and is not repeated here.
Claims (7)
1. A method for measuring a distributed optical fiber acoustic wave sensing system, comprising:
collecting backward Rayleigh scattering signals generated by vibration signals along the sensing optical fiber within a preset time period;
demodulating the collected backward Rayleigh scattering signals to obtain first demodulation information, wherein the first demodulation information comprises demodulation information of time-distance domains containing noise information of all positions along the sensing optical fiber;
constructing an original two-dimensional image of a time-distance domain through the first demodulation information, wherein the original two-dimensional image comprises an image of the time-distance domain formed by the first demodulation information corresponding to each position of the sensing optical fiber along the line in the preset time period, and the original two-dimensional image comprises two-dimensional graphic information of the time-distance domain or two-dimensional matrix information of the time-distance domain;
performing two-dimensional wavelet transformation image processing on the original two-dimensional image to eliminate noise information to obtain a noise-removed two-dimensional image, wherein the noise-removed two-dimensional image comprises two-dimensional graphic information of a time-distance domain or two-dimensional matrix information of a time-distance domain;
reconstructing second demodulation information according to the denoising two-dimensional image, wherein the second demodulation information comprises demodulation information after the denoising information of each position along the sensing optical fiber.
2. The method for measuring a distributed optical fiber acoustic wave sensor system according to claim 1, wherein said performing two-dimensional wavelet transform image processing on said original two-dimensional image comprises,
and carrying out wavelet decomposition on the original two-dimensional image through a discrete wavelet transform function to obtain a plurality of sub-images corresponding to the original two-dimensional image.
3. The method for measuring a distributed optical fiber acoustic wave sensor system according to claim 2, wherein said performing two-dimensional wavelet transform image processing on said original two-dimensional image further comprises,
and adjusting the wavelet decomposition level to obtain a corresponding number of sub-images, and acquiring and processing the high-frequency components and the low-frequency components of the sub-images to eliminate abnormal values on the sub-images and remove noise of the sub-images.
4. A method of measuring a distributed optical fiber acoustic wave sensing system according to claim 3 wherein the level of wavelet decomposition has an adjustment threshold within which the higher the level of wavelet decomposition, the less outliers the noise-canceling sub-image.
5. The method for measuring a distributed optical fiber acoustic wave sensor system according to claim 3, wherein the processing of the two-dimensional wavelet transform image on the original two-dimensional image further comprises performing wavelet reconstruction on the high-frequency component and the low-frequency component of the denoising sub-image by using an inverse discrete wavelet transform function to obtain the denoising two-dimensional image.
6. The method according to any one of claims 1 to 5, wherein after reconstructing the second demodulation information from the noise-removed two-dimensional image, extracting time domain information of the vibration signal in the second demodulation information.
7. The distributed optical fiber acoustic wave sensing system is characterized by comprising a demodulation unit and a controller, wherein the demodulation unit is connected with the controller through signals;
the demodulation unit is configured to collect backward Rayleigh scattering signals within a preset time period, wherein the backward Rayleigh scattering signals comprise signals generated by vibration signals in the distributed optical fiber acoustic wave sensing system;
the demodulation unit is further configured to demodulate the collected backward Rayleigh scattering signals to obtain first demodulation information, wherein the first demodulation information comprises demodulation information of time-distance domains containing noise information of all positions along the sensing optical fiber;
the controller is configured to construct an original two-dimensional image of a time-distance domain through the first demodulation information, wherein the original two-dimensional image comprises a time-distance domain image formed by the first demodulation information corresponding to each position of the sensing optical fiber along the line in the preset time period, and the original two-dimensional image comprises two-dimensional graphic information of the time-distance domain or two-dimensional matrix information of the time-distance domain;
the controller is further configured to perform two-dimensional wavelet transform image processing on the original two-dimensional image to eliminate noise information to obtain a noise-removed two-dimensional image, wherein the noise-removed two-dimensional image comprises two-dimensional graphic information of a time-distance domain or two-dimensional matrix information of a time-distance domain;
the controller is further configured to reconstruct second demodulation information from the denoised two-dimensional image, the second demodulation information including noise information removed demodulation information for each location along the sensing fiber.
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