High-precision raman temperature demodulation method and device for dam and pipeline monitoring

Abstract

The present application relates to the field of temperature safety detection in distributed optical fiber sensing technology, and particularly relates to a high-precision Raman temperature demodulation method and device for dam and pipeline monitoring, the demodulation method comprising the following steps: S1, differentially reconstructing the collected chaotic Raman backscattering light signal to obtain a reconstructed Raman scattering signal; S2, performing twice cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain twice cross-correlation signals, and deriving the twice cross-correlation signals to determine the start point and end point positions of the temperature change region; and S3, calculating the temperature of the optical fiber along the line according to the correlation peak-to-peak value of the twice cross-correlation signals. The present application can realize high spatial resolution of centimeter level on a long distance by differential reconstruction, and can amplify the effective chaotic Raman scattering signal and improve the signal-to-noise ratio of the system by twice cross-correlation operation and the autocorrelation characteristics of the chaotic pulse laser.

Description

Technical Field

[0001] This invention relates to the field of temperature safety detection in distributed optical fiber sensing technology, specifically a high-precision Raman optical fiber temperature demodulation method and device for monitoring leaks in dams and pipelines. It improves the signal-to-noise ratio of the chaotic Raman distributed optical fiber sensing system based on the multi-order differential reconstruction chaotic correlation method. Background Technology

[0002] Pipeline transportation is the lifeline of a nation's modern industry and economic development. Pipeline leakage is the most significant threat to pipeline safety, often caused by the gradual expansion of micro-leaks. When a pipeline is in a micro-leak state (leakage diameter less than 20mm), especially a pinhole leak, the affected fiber optic length is often less than the system's spatial resolution. This causes the subtle temperature changes in the leak area to be submerged in the ambient temperature noise within the corresponding spatial resolution length, making it difficult to identify the temperature change characteristics caused by the micro-leak. Ultimately, this leads to a loss of the opportunity for early detection and intervention, potentially triggering major disasters such as pipeline explosions or hazardous media leaks. Furthermore, water conservancy and transportation engineering is a public service system used to ensure the efficient and normal operation of national or regional socio-economic activities. Therefore, achieving dam safety monitoring and ensuring the safe operation of transportation have become major strategic needs for both national and local governments.

[0003] Traditional Raman distributed fiber optic sensing technology is a distributed sensing method that uses the Raman backscattering effect in optical fibers to obtain temperature information, and it has important applications in pipeline leakage and dam safety monitoring. However, due to its limitation by the pulsed light time-domain reflectometry principle, it can only achieve a spatial resolution on the order of meters, making it difficult to accurately detect temperature changes caused by micro-leakage, thus posing a significant hazard. Summary of the Invention

[0004] To address these shortcomings, this invention overcomes the deficiencies of existing technologies and proposes a high-precision Raman temperature demodulation method and device for dam and pipeline monitoring. Based on the multi-order differential reconstruction chaotic correlation method, chaotic light is used instead of traditional pulsed laser light to enter the sensing fiber. After performing multi-order differential reconstruction operations on the Raman backscattered signal, the reconstructed signal is cross-correlated with the chaotic pulse reference signal to achieve centimeter-level high spatial resolution over long sensing distances, while simultaneously improving the system's signal-to-noise ratio.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by this invention is as follows: a high-precision Raman temperature demodulation method for dam and pipeline monitoring, based on a chaotic Raman distributed fiber optic sensing device. The chaotic Raman distributed fiber optic sensing device includes: a pulsed chaotic light source, a beam splitter, a wavelength division multiplexer, a sensing fiber, a photodetector, and a data acquisition card. The pulsed chaotic laser emitted by the pulsed chaotic light source is split into two beams by the beam splitter. One beam is used as a reference beam and detected by the photodetector. The other beam, used as a probe beam, enters the sensing fiber after passing through the wavelength division multiplexer. In the sensing fiber, the generated chaotic Raman backscattered anti-Stokes light is output by the wavelength division multiplexer and detected by the photodetector. The photodetector sends the detected reference light signal and the Raman backscattered anti-Stokes light signal to the data acquisition card. The demodulation method includes the following steps:

[0006] S1. Perform differential reconstruction on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal;

[0007] S2. Perform two cross-correlation operations on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals. Calculate the derivatives of the two cross-correlation signals and determine the starting and ending positions of the temperature change region based on the derivatives.

[0008] S3. Calculate the temperature along the optical fiber based on the correlation peak-to-peak values ​​of the two cross-correlation signals. The calculation formula is as follows:

[0009]

[0010] Where T represents the temperature of the temperature-varying region, h is Planck's constant, Δν is the Raman frequency shift, k is the Boltzmann constant, P is the input power, and R... a (T0) represents the value of the temperature modulation function of the anti-Stokes light at ambient temperature T0, C peak1 C represents the peak-to-peak value of a single correlation. peak2 The peak value of the second correlation peak is represented by s, which represents the intensity ratio of the probe light to the reference light, and P is the peak value of the second correlation peak. r (j) and P r (j+1) represents the power of the j-th and (j+1)-th data points of the reference signal, I a (n) is the anti-Stokes intensity.

[0011] In step S2, the point where the first derivative of the two cross-correlation signals is zero is taken as the starting point of the temperature change region, and the point where the second derivative is zero and the third derivative is not zero is taken as the ending point of the temperature change region.

[0012] In step S1, the calculation formula for differential reconstruction is:

[0013] I c (n)=I a((n+1)·L f )-I a (n·L f );

[0014] Among them, I c (n) represents the nth sampled data after reconstruction, I a ((n+1)·L f ) and I a (n·L f ) represent the light intensity information of the (n+1)th and nth sampled data of the chaotic Raman backscattering signal, respectively.

[0015] In step S2, the specific method for performing two cross-correlation operations on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals is as follows:

[0016] S201. Perform cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain a first cross-correlation signal;

[0017] S202. Perform cross-correlation operation again on the chaotic pulse reference signal and the first cross-correlation signal to obtain the second cross-correlation signal.

[0018] Furthermore, this invention also provides a high-precision Raman temperature demodulation device for dam and pipeline monitoring, comprising: a pulsed chaotic light source, a beam splitter, a wavelength division multiplexer, a sensing fiber, a photodetector, a data acquisition card, and a computing unit. The pulsed chaotic laser emitted by the pulsed chaotic light source is split into two beams by the beam splitter. One beam serves as a reference beam and is detected by the photodetector. The other beam serves as the detection beam and enters the sensing fiber after passing through the wavelength division multiplexer. In the sensing fiber, the generated chaotic Raman backscattered anti-Stokes light is output by the wavelength division multiplexer and detected by the photodetector. The photodetector sends the detected reference light signal and the Raman backscattered anti-Stokes light signal to the data acquisition card. The data acquisition card sends the acquired data to the computing unit, which is used for:

[0019] Differential reconstruction is performed on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal;

[0020] Two cross-correlation operations are performed on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals. The derivatives of the two cross-correlation signals are calculated, and the starting and ending positions of the temperature change region are determined based on the derivatives.

[0021] The temperature along the optical fiber is calculated based on the correlation peak-to-peak values ​​of the two cross-correlation signals. The calculation formula is as follows:

[0022]

[0023] Where T represents the temperature of the temperature-varying region, h is Planck's constant, Δν is the Raman frequency shift, k is the Boltzmann constant, P is the input power, and R... a (T0) represents the value of the temperature modulation function of the anti-Stokes light at ambient temperature T0, C peak1 C represents the peak-to-peak value of a single correlation. peak2 The peak value of the second correlation peak is represented by s, which represents the intensity ratio of the probe light to the reference light, and P is the peak value of the second correlation peak. r (j) and P r (j+1) represents the power of the j-th and (j+1)-th data points of the reference signal, I a (n) is the anti-Stokes intensity.

[0024] The pulsed chaotic light source includes a laser, an optical fiber coupler, a circulator, an attenuator, a polarization controller, a pulsed light modulator, and an erbium-doped fiber amplifier.

[0025] The laser emitted by the laser is split into two paths after passing through an optical fiber coupler. One path passes through a polarization controller and attenuator, then through a circulator and another optical fiber coupler, and returns to the laser along the original path, causing it to output chaotic laser light. The other path outputs chaotic laser light through a circulator. A pulsed light modulator is used to modulate the chaotic laser light output through the circulator into pulsed chaotic light, and an erbium-doped fiber amplifier is used to amplify the power of the pulsed chaotic light.

[0026] The beam splitter is a 1×2 fiber coupler with a splitting ratio of 1:99, where 1% of the beam is used as the reference beam and 99% is used as the probe beam.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. This invention achieves centimeter-level high spatial resolution over long distances by incident chaotic pulsed laser light into a sensing fiber and utilizing differential reconstruction. Furthermore, by utilizing the autocorrelation characteristics of chaotic pulsed laser light and performing secondary cross-correlation operations, the effective chaotic Raman scattering signal is amplified, thereby improving the system's signal-to-noise ratio.

[0029] 2. This invention modulates conventional pulsed laser light into chaotic pulsed light through a feedback loop consisting of an attenuator and a polarization controller. The pulsed light emitted by the pulsed laser is split into two beams after passing through an optical fiber coupler. One beam returns to the pulsed laser after passing through an attenuator, a polarization controller, and an optical circulator, causing it to output chaotic pulsed light. Then, after being amplified by an erbium-doped fiber amplifier, it becomes chaotic pulsed laser light for sensing, thus realizing high-precision measurement of chaotic Raman temperature. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of the chaotic Raman distributed optical fiber sensing device used in Embodiment 1 of the present invention;

[0031] Figure 2 This is a schematic diagram of a high-precision Raman temperature demodulation device for dam and pipeline monitoring provided in Embodiment 2 of the present invention;

[0032] In the diagram: 1-Laser, 2-Optical splitter, 3-Circulator, 4-Attenuator, 5-Polarization controller, 6-Pulsed light modulator, 7-Erbium-doped fiber amplifier, 8-1×2 fiber coupler, 9-Wavelength division multiplexer, 10-Sensing fiber, 11-Photodetector, 12-Acquisition card, 13-Computing unit, 14-Pulsed chaotic light source. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] Embodiment 1 of this invention provides a high-precision Raman temperature demodulation method for dam and pipeline monitoring. It effectively improves the system signal-to-noise ratio through quadratic correlation compression. In addition, by analyzing the shape of the first chaotic scattering correlation signal and using function differentiation, the starting position of the temperature change zone is accurately located, ultimately achieving precise positioning and demodulation with centimeter-level ultra-high spatial resolution.

[0036] like Figure 1 As shown, the demodulation method in this embodiment uses a chaotic Raman distributed fiber optic sensing device, which includes: a pulsed chaotic light source 14, a beam splitter 8, a wavelength division multiplexer 9, a sensing fiber 10, a photodetector 11, and a data acquisition card 12. The pulsed chaotic laser emitted by the pulsed chaotic light source is split into two beams after passing through the beam splitter 8. One beam is used as a reference beam and detected by the photodetector 11. The other beam is used as a probe beam and enters the sensing fiber 10 after passing through the wavelength division multiplexer 9. In the sensing fiber 10, the chaotic Raman backscattered anti-Stokes light generated is output by the wavelength division multiplexer 9 and detected by the photodetector 11. The photodetector 11 sends the detected reference light signal and the Raman backscattered anti-Stokes light signal to the data acquisition card 12.

[0037] Specifically, in this embodiment, the wavelength of the pulsed chaotic light source is 1550nm. The beam splitter 8 is a 1×2 fiber coupler with a splitting ratio of 1:99. One 1% path serves as a reference light and is detected by the photodetector 1; the remaining 99% path passes through the wavelength division multiplexer 9 and enters the sensing fiber 10. The Raman backscattered anti-Stokes light with a wavelength of 1450nm generated in the sensing fiber 10 is output from the wavelength division multiplexer 9 and detected by the photodetector 11. Finally, the reference signal and the Raman backscattered signal are acquired by the acquisition card 12. The obtained chaotic pulse reference signal and chaotic Raman anti-Stokes scattering signal are differentially reconstructed and processed to obtain the temperature information along the fiber.

[0038] Specifically, the demodulation method in this embodiment is as follows: differential reconstruction is performed on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal; two cross-correlation operations are performed on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal, and the first and second derivatives of the correlated signal are calculated. The point where the first derivative is zero corresponds to the starting point of the hot spot region, and the point where the second derivative is zero and the third derivative is not zero corresponds to the ending point of the temperature change region; the temperature T along the optical fiber can be calculated based on the correlation peak value.

[0039] Specifically, the demodulation method in this embodiment includes the following steps:

[0040] S1. Differential reconstruction is performed on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal.

[0041] In step S1, the calculation formula for differential reconstruction is:

[0042] I c (n)=I a ((n+1)·L f )-I a (n·L f (1)

[0043] Among them, I c (n) represents the nth sampled data after differential reconstruction, I a ((n+1)·L f ) represents the light intensity information of the (n+1)th sample data of the chaotic Raman backscattering signal, I a (n·L f L represents the light intensity information of the nth sample data of the chaotic Raman backscattering signal. f Indicates the unit sampling length.

[0044] S2. Perform two cross-correlation operations on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals. Calculate the derivatives of the two cross-correlation signals and determine the starting and ending positions of the temperature change region based on the derivatives.

[0045] Specifically, in step S2, the method for performing two cross-correlation operations on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals is as follows:

[0046] S201. Perform cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain a first cross-correlation signal;

[0047] S202. Perform cross-correlation operation again on the chaotic pulse reference signal and the first cross-correlation signal to obtain the second cross-correlation signal.

[0048] Furthermore, in step S2, the point where the first derivative of the two cross-correlation signals is zero is taken as the starting point of the temperature change region, and the point where the second derivative is zero and the third derivative is not zero is taken as the ending point of the temperature change region.

[0049] S3. Calculate the temperature along the optical fiber based on the correlation peak-to-peak values ​​of the two cross-correlation signals. The calculation formula is as follows:

[0050]

[0051] Where T represents the temperature of the temperature variation region, C peak1 C represents the peak-to-peak value of a single correlation. peak2 The peak value of the second correlation peak is represented by s, the intensity ratio of the probe light to the reference light is represented by h, Planck's constant is represented by Δν, Raman frequency shift is represented by k, Boltzmann constant is represented by Pr, the reference signal power is represented by P, and the input power is represented by P. r (j) and P r (j+1) represents the power of the j-th and (j+1)-th data points of the reference signal, R a (T) represents the modulation function of the anti-Stokes light at ambient temperature T. o The value of I a (n) is the anti-Stokes intensity.

[0052] Specifically, in this invention, the demodulation and positioning principles of temperature measurement in the embodiments of the invention are described below.

[0053] 1. Acquisition process of chaotic Raman anti-Stokes signal and chaotic pulse reference signal.

[0054] The expression for the collected chaotic Raman anti-Stokes light intensity is:

[0055]

[0056] Where I a (L) is the intensity of the chaotic Raman anti-Stokes light; P is the incident power; L is the position of the sensing fiber; K a These represent coefficients related to the backscattering cross section of the anti-Stokes beam; S is the backscattering factor of the optical fiber; and ν is the incident light frequency. Represents the pulsed laser flux coupled into the optical fiber; α0, α a , respectively, are the loss coefficients of the incident light and the an-Stokes light per unit length of the optical fiber, and L represents the position in the optical fiber.

[0057] Let the constant term in formula (1) For C1, the formula simplifies to:

[0058] I a (L)=C1·P·R a (T)·exp[-(α0+α a )L] (4)

[0059] R a (T) is the temperature modulation function with respect to anti-Stokes light:

[0060]

[0061] For example, at a sampling rate of 10 Gs / s, that is, taking one step forward and collecting one point every 0.1 ns (i.e., collecting one point every 1 cm); for example, when the temperature change zone is 10 cm long, it corresponds to 10 sampling intervals; to simplify the representation of the difference formula, the sampling interval is understood as a sampling step of n steps. L = nL f L f Step size (unit sampling length);

[0062] Therefore, equation (4) can be rewritten as:

[0063] I a (L)=I a (n·L f )=C1·P·R a (T)·exp[-(α0+α a )n·L f (6)

[0064] 2. Differential reconstruction process of Raman backscattered signal.

[0065] Since the attenuation coefficients of two adjacent points are similar, they are approximately the same after subtraction, and therefore are unified as a constant C; thus, the expression for the chaotic Raman anti-Stokes light intensity after differential reconstruction is:

[0066] I c (n)=I a((n+1)·L f )-I a (n·L f )=C[P(n+1)·R a (T n+1 )-P(n)·R a (T n (7)

[0067] 3. The differential reconstructed signal and the reference signal undergo correlation compression operations.

[0068] The chaotic signal is mainly concentrated in the high-level portion of the reference signal, while the chaotic signal in the low-level portion of the reference signal is relatively weak and fluctuates around 0. Therefore, for the correlated signal, the high-level portion of the reference signal has the greatest impact on the correlation result. Thus, in this embodiment, the correlation operation only considers the high-level portion of the reference signal. For the reference signal, the number of data points corresponding to the pulse width is m, while the differential signal I... c The number of data points in (n) is n, determined by the fiber length and sampling step. The total length of the sequence after cross-correlation of the two signals is (m+n-1), however, the first (m-1) and last (m-1) data points of this sequence are invalid data, and there are a total of (n-m+1) valid data points. The value of the i-th component of the valid cross-correlation data (valid data is when the pulse is completely within the differential signal during the correlation operation) is:

[0069]

[0070] In the formula, Pr is the reference signal power and P is the input fiber power. Theoretically, there is a 1:s relationship between the two, so equation (8) can be rewritten as:

[0071]

[0072] Due to the periodicity of the pulse, i can be understood as the pulse moving forward i steps, so Pr(j)≈Pr(i+j), and the above formula can be transformed into:

[0073]

[0074] The maximum correlation peak value can only be generated when the entire temperature change region enters the pulse. Therefore, the maximum correlation peak value C peak1 The expression is:

[0075]

[0076] 4. Temperature demodulation process corresponding to quadratic correlation operation

[0077] Compare the primary correlation signal I1 with the reference signal P rBy performing correlation calculations, we can obtain the results of quadratic correlation.

[0078]

[0079] The maximum correlation peak value can be obtained in the temperature variation region:

[0080]

[0081] Further simplification yields:

[0082]

[0083] To facilitate calculation, take P. r The average value of (j) but and Since they are approximately equal, quadratic correlation can increase the peak value of the correlation peak. times, that is:

[0084]

[0085] but:

[0086]

[0087] According to equations (16) and (6), we have:

[0088]

[0089] After rearranging equation (17), the relationship between the measured temperature and the peak value of the second correlation is obtained as follows:

[0090]

[0091] Combined with R as (T)=[exp(hΔν / kT)-1] -1 Temperature information in the temperature change region is extracted, and its demodulation equation is shown in formula (19).

[0092]

[0093] In the formula, h is Planck's constant, Δν is the Raman frequency shift, k is Boltzmann's constant, all of which are constants, and P r For the reference signal power, P r (j) is the reference signal power at point j. P is the input fiber power, measured by a power meter, and C... peak1 C represents the peak-to-peak value of a single correlation. peak2 R represents the peak value of the second correlation peak, s represents the intensity ratio of the probe light to the reference light, and R represents the intensity ratio of the probe light to the reference light. a(T0) is the temperature modulation function of the anti-Stokes light, which is related to the room temperature T0 and can be obtained by formula (5). a (n) is the anti-Stokes light intensity, obtained through measurement.

[0094] Example 2

[0095] like Figure 2 As shown, Embodiment 2 of the present invention provides a high-precision Raman temperature demodulation device for dam and pipeline monitoring, comprising: a pulsed chaotic light source, a beam splitter 8, a wavelength division multiplexer 9, a sensing fiber 10, a photodetector 11, a data acquisition card 12, and a computing unit. The pulsed chaotic laser emitted by the pulsed chaotic light source is split into two beams by the beam splitter 8. One beam serves as a reference beam and is detected by the photodetector 11. The other beam serves as a detection beam and enters the sensing fiber 10 after passing through the wavelength division multiplexer 9. In the sensing fiber 10, the generated chaotic Raman backscattered anti-Stokes light is output by the wavelength division multiplexer 9 and detected by the photodetector 12. The photodetector 11 sends the detected reference light signal and the Raman backscattered anti-Stokes light signal to the data acquisition card 12. The data acquisition card 12 sends the acquired data to the computing unit. The computing unit is used for:

[0096] Differential reconstruction is performed on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal;

[0097] Two cross-correlation operations are performed on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals. The derivatives of the two cross-correlation signals are calculated, and the starting and ending positions of the temperature change region are determined based on the derivatives.

[0098] The temperature along the optical fiber is calculated based on the correlation peak-to-peak values ​​of the two cross-correlation signals. The calculation formula is as follows:

[0099]

[0100] Where T represents the temperature of the temperature-varying region, h is Planck's constant, Δν is the Raman frequency shift, k is the Boltzmann constant (all constants), P is the input power, and R... a (T0) represents the temperature modulation function of the anti-Stokes light at ambient temperature T. o The value below. C peak1 C represents the peak-to-peak value of a single correlation. peak2 The peak value of the second correlation peak is represented by s, which represents the intensity ratio of the probe light to the reference light, and P is the peak value of the second correlation peak. r (j) and P r (j+1) represents the power of the j-th and (j+1)-th data points of the reference signal, I a (n) is the anti-Stokes light intensity, obtained through measurement.

[0101] Specifically, in this embodiment, the pulsed chaotic light source includes a laser 1, an optical fiber coupler 2, a circulator 3, an attenuator 4, a polarization controller 5, a pulsed light modulator 6, and an erbium-doped fiber amplifier 7. The laser emitted by the laser 1 is split into two paths after passing through the optical fiber coupler 2. One path passes through the polarization controller 5 and the attenuator 4, then through the circulator 3 and the optical fiber coupler 2, and returns to the laser 1 along the original path, causing it to output chaotic laser light. The other path outputs chaotic laser light through the circulator 3. The pulsed light modulator 6 is used to modulate the chaotic laser light output through the circulator 3 into pulsed chaotic light, and the erbium-doped fiber amplifier 7 is used to amplify the power of the pulsed chaotic light.

[0102] Specifically, in this embodiment, the fiber coupler 2 is a 1×2 fiber coupler with a splitting ratio of 50:50. The continuous light emitted by the laser 1 with a center wavelength of 1550nm is split into two paths after passing through the 50:50 fiber coupler 2. One continuous beam passes through attenuator 4, polarization controller 5, circulator 3, and fiber coupler 2 before returning to laser 1, forming a single feedback structure. This modulates the traditional continuous beam into chaotic continuous beam. The other output chaotic continuous beam, after passing through circulator 3, enters pulse modulator 6 and is modulated into chaotic pulse beam. After being amplified by erbium-doped fiber amplifier 7, it is split into two beams (1:99) by beam splitter 8. The 1% beam serves as a reference signal and is detected by a photodetector; the 99% beam passes through a wavelength division multiplexer (WDM) and enters the sensing fiber. The WDM 9 outputs Raman backscattered anti-Stokes light with a wavelength of 1450 nm from the C-end, which is detected by photodetector 11. Finally, acquisition card 12 collects the reference signal and Raman backscattered signal and sends them to computing unit 13. Computing unit 13 performs differential reconstruction and related processing on the obtained chaotic pulse reference signal and chaotic Raman anti-Stokes scattering signal to obtain temperature information along the fiber.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision Raman temperature demodulation method for dam and pipeline monitoring, characterized in that, Based on a chaotic Raman distributed fiber optic sensing device, the chaotic Raman distributed fiber optic sensing device includes: a pulsed chaotic light source (14), a beam splitter (8), a wavelength division multiplexer (9), a sensing fiber (10), a photodetector (11), and a data acquisition card (12). The pulsed chaotic laser emitted by the pulsed chaotic light source (14) is split into two beams by the beam splitter (8). One beam is used as a reference beam and detected by the photodetector (11). The other beam is used as a detection beam and enters the sensing fiber (10) after passing through the wavelength division multiplexer (9). In the sensing fiber (10), the generated chaotic Raman backscattered anti-Stokes light is output by the wavelength division multiplexer (9) and detected by the photodetector (11). The photodetector (11) sends the detected reference light signal and the Raman backscattered anti-Stokes light signal to the data acquisition card (12). The demodulation method includes the following steps: S1. Perform differential reconstruction on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal; S2. Perform two cross-correlation operations on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals. Calculate the derivatives of the two cross-correlation signals and determine the starting and ending positions of the temperature change region based on the derivatives. S3. Calculate the temperature along the optical fiber based on the correlation peak-to-peak values ​​of the two cross-correlation signals. The calculation formula is as follows: Where T represents the temperature of the temperature-varying region, h is Planck's constant, Δν is the Raman frequency shift, k is the Boltzmann constant, P is the input power, and R... a (T0) represents the value of the temperature modulation function of the anti-Stokes light at ambient temperature T0, C peak1 C represents the peak-to-peak value of a single correlation. peak2 The peak value of the second correlation peak is represented by s, which represents the intensity ratio of the probe light to the reference light, and P is the peak value of the second correlation peak. r (j) and P r (j+1) represents the power of the j-th and (j+1)-th data points of the reference signal, I a (n) is the anti-Stokes intensity.

2. The high-precision Raman temperature demodulation method for dam and pipeline monitoring according to claim 1, characterized in that, In step S2, the point where the first derivative of the two cross-correlation signals is zero is taken as the starting point of the temperature change region, and the point where the second derivative is zero and the third derivative is not zero is taken as the ending point of the temperature change region.

3. The high-precision Raman temperature demodulation method for dam and pipeline monitoring according to claim 1, characterized in that, In step S1, the calculation formula for differential reconstruction is: I c (n)=I a ((n+1)·L f )-I a (n·L f ); Among them, I c (n) represents the nth sampled data after reconstruction, I a ((n+1)·L f ) and I a (n·L f ) represent the light intensity information of the (n+1)th and nth sampled data of the chaotic Raman backscattering signal, respectively.

4. The high-precision Raman temperature demodulation method for dam and pipeline monitoring according to claim 1, characterized in that, In step S2, the specific method for performing two cross-correlation operations on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals is as follows: S201. Perform cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain a first cross-correlation signal; S202. Perform cross-correlation operation again on the chaotic pulse reference signal and the first cross-correlation signal to obtain the second cross-correlation signal.

5. A high-precision Raman temperature demodulation device for dam and pipeline monitoring, characterized in that, include: The system comprises a pulsed chaotic light source (14), a beam splitter (8), a wavelength division multiplexer (9), a sensing fiber (10), a photodetector (11), a data acquisition card (12), and a computing unit. The pulsed chaotic laser emitted by the pulsed chaotic light source (14) is split into two beams by the beam splitter (8). One beam serves as a reference beam and is detected by the photodetector (11). The other beam serves as a detection beam and enters the sensing fiber (10) after passing through the wavelength division multiplexer (9). In the sensing fiber (10), the generated chaotic Raman-backscattered anti-Stokes light is output by the wavelength division multiplexer (9) and detected by the photodetector (11). The photodetector (11) sends the detected reference light signal and the Raman-backscattered anti-Stokes light signal to the data acquisition card (12). The data acquisition card (12) sends the acquired data to the computing unit (13). The computing unit (13) is used for: Differential reconstruction is performed on the acquired chaotic Raman backscattered light signal to obtain the reconstructed Raman scattering signal; Two cross-correlation operations are performed on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal to obtain two cross-correlation signals. The derivatives of the two cross-correlation signals are calculated, and the starting and ending positions of the temperature change region are determined based on the derivatives. The temperature along the optical fiber is calculated based on the correlation peak-to-peak values ​​of the two cross-correlation signals. The calculation formula is as follows: Where T represents the temperature of the temperature-varying region, h is Planck's constant, Δν is the Raman frequency shift, k is the Boltzmann constant, P is the input power, and R... a (T0) represents the value of the temperature modulation function of the anti-Stokes light at ambient temperature T0, C peak1 C represents the peak-to-peak value of a single correlation. peak2 The peak value of the second correlation peak is represented by s, which represents the intensity ratio of the probe light to the reference light, and P is the peak value of the second correlation peak. r (j) and P r (j+1) represents the power of the j-th and (j+1)-th data points of the reference signal, I a (n) is the anti-Stokes intensity.

6. A high-precision Raman temperature demodulation device for dam and pipeline monitoring according to claim 5, characterized in that, The pulsed chaotic light source (14) includes a laser (1), an optical fiber coupler (2), a circulator (3), an attenuator (4), a polarization controller (5), a pulsed light modulator (6), and an erbium-doped fiber amplifier (7). The laser emitted by the laser (1) is split into two paths after passing through the fiber coupler (2). One path passes through the polarization controller (5), the attenuator (4), the circulator (3), and the fiber coupler (2) before returning to the laser (1) along the original path, causing it to output chaotic laser. The other path outputs chaotic laser through the circulator (3). The pulsed light modulator (6) is used to modulate the chaotic laser output through the circulator (3) into pulsed chaotic light. The erbium-doped fiber amplifier (7) is used to amplify the power of the pulsed chaotic light.

7. A high-precision Raman temperature demodulation device for dam and pipeline monitoring according to claim 5, characterized in that, The beam splitter (8) is a 1×2 fiber coupler with a splitting ratio of 1:99, of which 1% is used as the reference beam and 99% is used as the probe beam.

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