CN113776566A - Distributed temperature strain sensing method based on sub-pulse extraction algorithm - Google Patents
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Abstract
The invention relates to the field of optical fiber sensing measurement, in particular to a distributed temperature strain sensing method based on a sub-pulse extraction algorithm, which comprises the following steps: firstly, acquiring Rayleigh scattering information and Brillouin scattering information in a large frequency range by using a detection signal in the large frequency range; secondly, obtaining Rayleigh scattering signals and Brillouin scattering signals with different frequencies by using a sub-pulse extraction algorithm; thirdly, forming a complete Rayleigh scattering pattern and a Brillouin gain spectrum, and acquiring the frequency shift conditions of a Rayleigh scattering pattern frequency axis and the Brillouin gain spectrum; and finally, according to different response coefficients of the temperature and the strain to the Rayleigh scattering signals and the Brillouin scattering signals, carrying out decoupling operation on the temperature and the strain to obtain temperature and strain sensing information along the optical fiber. The distributed optical fiber sensing system based on the Brillouin scattering solves the technical problem of cross-sensitivity of strain and temperature in the existing distributed optical fiber sensing system based on the Brillouin scattering or the distributed optical fiber sensing system based on the Rayleigh scattering.
Description
Technical Field
The invention relates to the field of optical fiber sensing measurement, in particular to a distributed temperature strain sensing method based on a sub-pulse extraction algorithm.
Background
Distributed optical fiber sensing systems are widely used in the fields of geological prospecting, structural health monitoring, temperature measurement and the like. Distributed optical fiber sensing based on Rayleigh scattering and Brillouin scattering is sensitive to temperature and strain, so that the two systems have the problem of cross sensitivity of temperature and strain, and the application of the distributed optical fiber sensing in engineering is limited.
Because the traditional distributed sensing based on Rayleigh scattering and the traditional distributed sensing based on Brillouin have larger difference in sensing mechanism, the two systems are difficult to organically fuse. In addition, because the distributed sensing based on the brillouin scattering needs to acquire a complete brillouin gain spectrum through frequency sweeping, the sensing process consumes very long time, and therefore the distributed sensing is commonly used for static or quasi-static sensing, and the fusion difficulty of two systems is further increased. Temperature and strain decoupling may be achieved using different responses of temperature and strain to the two polarization states of the polarization maintaining fiber. However, the response coefficients of temperature and strain to the two polarization states of the polarization-maintaining fiber are too close, so that the method has a large error in principle; and polarization maintaining fibers are too expensive, greatly increasing the cost of the system.
Disclosure of Invention
Based on the problems, the invention provides a distributed temperature strain sensing method based on a sub-pulse extraction algorithm, and solves the technical problem of cross sensitivity of strain and temperature in the conventional distributed optical fiber sensing system based on Brillouin scattering or the distributed optical fiber sensing system based on Rayleigh scattering.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a distributed temperature strain sensing method based on a sub-pulse extraction algorithm comprises the following steps:
step one, acquiring Rayleigh scattering information and Brillouin scattering information of a large frequency range by using a detection signal of the large frequency range;
step two, obtaining Rayleigh scattering signals and Brillouin scattering signals with different frequencies by using a sub-pulse extraction algorithm;
step three, forming a complete Rayleigh scattering pattern and a Brillouin gain spectrum, and acquiring the frequency shift conditions of a Rayleigh scattering pattern frequency axis and the Brillouin gain spectrum;
and step four, according to different response coefficients of the temperature and the strain to the Rayleigh scattering signals and the Brillouin scattering signals, decoupling operation is carried out on the temperature and the strain, and temperature and strain sensing information along the optical fiber is obtained.
Further, in the first step, the step of acquiring the rayleigh scattering information and brillouin scattering information in the large frequency range using the probe signal in the large frequency range includes:
injecting a detection signal with a large frequency range into a sensing optical fiber, separating the generated Rayleigh scattering signal from the Brillouin scattering signal, and then respectively acquiring the optical field information of the Rayleigh scattering signal and the Brillouin scattering signal by using a coherent detection module, wherein the acquired Rayleigh scattering signal and the Brillouin scattering signal are respectively regarded as the convolution of the detection signal and the Rayleigh scattering transfer function and the Brillouin scattering transfer function of the sensing optical fiber.
Further, the generated Rayleigh scattering signal and Brillouin scattering signal are separated through a dense wavelength division multiplexer, filters with different wavelengths and a wavelength selection switch.
Further, the coherent detection module is a 90 ° optical mixer, a 2 × 4 coupler, or a 2 × 2 coupler, where the local oscillator signal of the coherent detection module is an optical signal having coherence with the rayleigh scattering signal and the brillouin scattering.
Further, in the second step, a sub-pulse extraction algorithm is used to obtain the rayleigh scattering signal and the brillouin scattering signal with different frequencies, and the specific process is as follows:
converting the collected Rayleigh scattering signal and Brillouin scattering signal into a frequency domain; then, multiplying the Rayleigh scattering signal and the Brillouin scattering signal by transfer functions of different frequencies respectively in a frequency domain; and finally, converting the calculation result into a time domain to obtain the Rayleigh scattering signal and the Brillouin scattering signal with different frequencies.
Further, the generating steps of the transfer functions of different frequencies are specifically as follows:
respectively generating sub-pulse signals and detection pulse signals with different frequencies in a digital domain, and converting the sub-pulse signals and the detection pulse signals into a frequency domain; and then dividing the sub-pulse signal by the detection pulse signal in the frequency domain to obtain the transfer functions of different frequencies.
Further, in the third step, a specific process of forming a complete rayleigh scattering pattern and brillouin gain spectrum, and acquiring the frequency shift conditions of the frequency axis of the rayleigh scattering pattern and brillouin gain spectrum includes:
respectively arranging the Rayleigh scattering signals and Brillouin scattering signals with different frequencies according to the sequence of different frequencies to obtain a complete Rayleigh scattering pattern and a Brillouin gain spectrum; then, carrying out delay estimation on the frequency axis of the Rayleigh scattering pattern to obtain the frequency shift condition of the frequency axis of the Rayleigh scattering pattern; lorentz fitting is carried out on the Brillouin gain spectrum, and the Brillouin frequency shift condition along the optical fiber can be obtained.
Further, in the fourth step, according to the different response coefficients of the temperature and the strain to the rayleigh scattering signal and the brillouin scattering signal, the temperature and the strain are decoupled, and the specific process of acquiring the temperature and strain sensing information along the optical fiber is as follows:
according to the frequency shift expression of the temperature and the strain on the Rayleigh scattering pattern and the Brillouin gain spectrum, a system of linear equations is established, the system of equations is solved, and the magnitude of the temperature and the magnitude of the strain can be obtained.
Compared with the prior art, the invention has the beneficial effects that: the distributed sensing based on Rayleigh scattering and the distributed sensing based on Brillouin scattering are integrated on the system; different Brillouin scattering information is obtained in a digital domain through a sub-pulse extraction algorithm, so that a time-consuming frequency sweeping process is avoided; according to different response coefficients of temperature and strain to Rayleigh scattering and Brillouin scattering, the decoupling of the temperature and the strain is realized.
Drawings
FIG. 1 is a schematic view of the structure of the apparatus of this embodiment 1;
FIG. 2 is a flowchart of the present embodiment 1;
fig. 3 is a schematic structural diagram of the apparatus of this embodiment 2.
The figure illustrates a laser module 1, a coupler 2, a modulator module 3, an arbitrary waveform generator 4, a circulator 5, a sensing optical fiber 6, a frequency shifter 7, a first coherent detection module 8, a second coherent detection module 9 and a dense wavelength division multiplexer 10.
Detailed Description
The invention will be further described with reference to the accompanying drawings. Embodiments of the present invention include, but are not limited to, the following examples.
Example 1
As shown in fig. 1, the present embodiment provides a distributed temperature strain sensing system based on optical time domain reflectometer, and the measurement system structure includes: the device comprises a laser module 1, a coupler 2, a modulator module 3, an arbitrary waveform generator 4, a circulator 5, a sensing fiber 6, a frequency shifter 7, a first coherent detection module 8, a second coherent detection module 9 and a Dense Wavelength Division Multiplexer (DWDM) 10.
Specifically, in embodiment 1, the continuous laser output by the laser module 1 is connected to the coupler 2 and divided into three parts, one part of the continuous laser is directly used as a local oscillator for rayleigh scattering coherent detection and is connected to the first coherent detection module 8, and the other part of the continuous laser is connected to the second coherent detection module 9 as a local oscillator after being subjected to a frequency shift close to the brillouin frequency shift; the other part generates a detection signal of a large frequency range through the modulator 3, wherein the driving signal of the modulator 3 is provided by the arbitrary waveform generator 4; the large frequency range detection signal generated by modulation is input from a port 1 of the circulator 5, and output from a port 2 of the circulator enters a sensing optical fiber 6; the Rayleigh scattering signal and the spontaneous Brillouin scattering signal generated by the sensing optical fiber 6 are input from the port 2 of the circulator 5, and the output from the port 3 enters the dense wavelength division multiplexer 10; two output ends of the dense wavelength division multiplexer 10 are respectively connected to signal ends of the first coherent detection module 8 and the second coherent detection module 9.
A distributed temperature strain sensing system based on an optical time domain reflectometer, which provides a distributed temperature strain sensing method based on a sub-pulse extraction algorithm, as shown in fig. 2, and includes the following steps:
step one, acquiring Rayleigh scattering information and spontaneous Brillouin scattering information in a large frequency range by using a detection signal in the large frequency range.
The method comprises the steps of injecting a detection signal with a large frequency range into a sensing optical fiber, separating a generated Rayleigh scattering signal from a Brillouin scattering signal, and then respectively collecting light field information of the Rayleigh scattering signal and spontaneous Brillouin scattering signal by using a coherent detection module, wherein the collected Rayleigh scattering signal and spontaneous Brillouin scattering signal are respectively regarded as convolution of the detection signal and a Rayleigh scattering transfer function and a spontaneous Brillouin scattering transfer function of the sensing optical fiber.
In addition, the generated Rayleigh scattering signals and the spontaneous Brillouin scattering signals are separated through a dense wavelength division multiplexer, filters with different wavelengths and a wavelength selection switch.
In addition, the coherent detection module is a 90 ° optical mixer, a 2 × 4 coupler, or a 2 × 2 coupler, wherein the local oscillator signal of the coherent detection module is an optical signal having coherence with the rayleigh scattering signal and the spontaneous brillouin scattering.
Step two, obtaining Rayleigh scattering signals and spontaneous Brillouin scattering signals with different frequencies by using a sub-pulse extraction algorithm, thereby realizing one-time obtaining of Rayleigh scattering patterns and Brillouin gain spectrums;
converting the collected Rayleigh scattering signal and spontaneous Brillouin scattering signal into a frequency domain; then, multiplying the Rayleigh scattering signal and the spontaneous Brillouin scattering signal by transfer functions of different frequencies respectively in a frequency domain; and finally, converting the calculation result into a time domain to obtain Rayleigh scattering signals and spontaneous Brillouin scattering signals with different frequencies.
In addition, generating sub-pulse signals and detection pulse signals with different frequencies on a digital domain respectively and converting the sub-pulse signals and the detection pulse signals into a frequency domain; and then dividing the sub-pulse signal by the detection pulse signal in the frequency domain to obtain the transfer functions of different frequencies.
And step three, forming a complete Rayleigh scattering pattern and a Brillouin gain spectrum, and acquiring the frequency shift conditions of a Rayleigh scattering pattern frequency axis and the Brillouin gain spectrum.
The Rayleigh scattering signals and the spontaneous Brillouin scattering signals with different frequencies are respectively arranged according to the sequence of different frequencies, so that a complete Rayleigh scattering pattern and a complete Brillouin gain spectrum can be obtained; then, carrying out delay estimation on the frequency axis of the Rayleigh scattering pattern to obtain the frequency shift condition of the frequency axis of the Rayleigh scattering pattern; lorentz fitting is carried out on the Brillouin gain spectrum, and the Brillouin frequency shift condition along the optical fiber can be obtained.
And step four, according to different response coefficients of the temperature and the strain to the Rayleigh scattering signals and the Brillouin scattering signals, decoupling operation is carried out on the temperature and the strain, and temperature and strain sensing information along the optical fiber is obtained.
According to the frequency shift expression of the temperature, the strain, the Rayleigh scattering pattern and the Brillouin gain spectrum, a linear equation set is established, the equation set is solved, and the temperature and the strain can be obtained.
Example 2
The embodiment provides a distributed temperature strain sensing system based on an optical time domain reflectometer, which specifically comprises the following steps:
as shown in fig. 3, a distributed temperature strain sensing system based on an optical time domain analyzer includes: the device comprises a laser module 1, a coupler 2, a modulator module 3, an arbitrary waveform generator 4, a circulator 5, a sensing optical fiber 6, a frequency shifter 7, a first coherent detection module 8, a second coherent detection module 9 and a dense wavelength division multiplexer 10.
Specifically, in embodiment 2, the continuous laser output by the laser module 1 is connected to the coupler 2 and divided into three parts, one part of the continuous laser is directly used as a local oscillator for rayleigh scattering coherent detection and is connected to the coherent detection module 8, and the other part of the continuous laser is connected from the tail end of the sensing fiber 6 after frequency shift close to brillouin frequency shift and is used as a measurement signal; the other part generates a detection signal of a large frequency range through the modulator 3, wherein the driving signal of the modulator 3 is provided by the arbitrary waveform generator 4; the large frequency range detection signal generated by modulation is input from a port 1 of the circulator 5, and output from a port 2 of the circulator enters a sensing optical fiber 6; a Rayleigh scattering signal generated by the sensing optical fiber 6 and a measurement signal amplified by stimulated Brillouin scattering are input from a port 2 of the circulator 5, and an output from a port 3 enters the dense wavelength division multiplexer 10; two output ends of the dense wavelength division multiplexer 10 are respectively connected to signal ends of the first coherent detection module 8 and the second coherent detection module 9.
The above is an embodiment of the present invention. The specific parameters in the above embodiments and examples are only for the purpose of clearly illustrating the invention verification process of the inventor and are not intended to limit the scope of the invention, which is defined by the claims, and all equivalent structural changes made by using the contents of the specification and the drawings of the present invention should be covered by the scope of the present invention.
Claims (8)
1. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm is characterized by comprising the following steps of:
step one, acquiring Rayleigh scattering information and Brillouin scattering information of a large frequency range by using a detection signal of the large frequency range;
step two, obtaining Rayleigh scattering signals and Brillouin scattering signals with different frequencies by using a sub-pulse extraction algorithm;
step three, forming a complete Rayleigh scattering pattern and a Brillouin gain spectrum, and acquiring the frequency shift conditions of a Rayleigh scattering pattern frequency axis and the Brillouin gain spectrum;
and step four, according to different response coefficients of the temperature and the strain to the Rayleigh scattering signals and the Brillouin scattering signals, decoupling operation is carried out on the temperature and the strain, and temperature and strain sensing information along the optical fiber is obtained.
2. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 1, wherein in the first step, the process of acquiring the rayleigh scattering information and the brillouin scattering information of the large frequency range by using the detection signal of the large frequency range includes:
injecting a detection signal with a large frequency range into a sensing optical fiber, separating the generated Rayleigh scattering signal from the Brillouin scattering signal, and then respectively acquiring the optical field information of the Rayleigh scattering signal and the Brillouin scattering signal by using a coherent detection module, wherein the acquired Rayleigh scattering signal and the Brillouin scattering signal are respectively regarded as the convolution of the detection signal and the Rayleigh scattering transfer function and the Brillouin scattering transfer function of the sensing optical fiber.
3. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 2, wherein the separation of the generated rayleigh scattering signal from the brillouin scattering signal is achieved by a dense wavelength division multiplexer, filters of different wavelengths and a wavelength selection switch.
4. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 2, wherein the coherent detection module is a 90 ° optical mixer, a 2 × 4 coupler or a 2 × 2 coupler, and the local oscillator signal of the coherent detection module is an optical signal having coherence with rayleigh scattering signals and brillouin scattering.
5. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 1, wherein in the second step, the sub-pulse extraction algorithm is used to obtain the rayleigh scattering signal and the brillouin scattering signal with different frequencies, and the specific process is as follows:
converting the collected Rayleigh scattering signal and Brillouin scattering signal into a frequency domain; then, multiplying the Rayleigh scattering signal and the Brillouin scattering signal by transfer functions of different frequencies respectively in a frequency domain; and finally, converting the calculation result into a time domain to obtain the Rayleigh scattering signal and the Brillouin scattering signal with different frequencies.
6. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 5, wherein the generation steps of the transfer functions of different frequencies are specifically as follows:
respectively generating sub-pulse signals and detection pulse signals with different frequencies in a digital domain, and converting the sub-pulse signals and the detection pulse signals into a frequency domain; and then dividing the sub-pulse signal by the detection pulse signal in the frequency domain to obtain the transfer functions of different frequencies.
7. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 1, wherein in the third step, a complete rayleigh scattering pattern and brillouin gain spectrum are formed, and a specific process of obtaining the frequency shift conditions of the rayleigh scattering pattern frequency axis and the brillouin gain spectrum is as follows:
respectively arranging the Rayleigh scattering signals and Brillouin scattering signals with different frequencies according to the sequence of different frequencies to obtain a complete Rayleigh scattering pattern and a Brillouin gain spectrum; then, carrying out delay estimation on the frequency axis of the Rayleigh scattering pattern to obtain the frequency shift condition of the frequency axis of the Rayleigh scattering pattern; lorentz fitting is carried out on the Brillouin gain spectrum, and the Brillouin frequency shift condition along the optical fiber can be obtained.
8. The distributed temperature strain sensing method based on the sub-pulse extraction algorithm according to claim 1, wherein in the fourth step, according to response coefficients of temperature and strain for different rayleigh scattering signals and brillouin scattering signals, decoupling operation is performed on temperature and strain, and a specific process for acquiring temperature and strain sensing information along an optical fiber is as follows:
according to the frequency shift expression of the temperature and the strain on the Rayleigh scattering pattern and the Brillouin gain spectrum, a system of linear equations is established, the system of equations is solved, and the magnitude of the temperature and the magnitude of the strain can be obtained.
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| CN115371716A (en) * | 2022-10-25 | 2022-11-22 | 杭州水务数智科技股份有限公司 | Distributed optical fiber sensor multi-signal detection method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115371716A (en) * | 2022-10-25 | 2022-11-22 | 杭州水务数智科技股份有限公司 | Distributed optical fiber sensor multi-signal detection method |
| CN115371716B (en) * | 2022-10-25 | 2023-02-14 | 杭州水务数智科技股份有限公司 | Distributed optical fiber sensor multi-signal detection method |
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