CN117268581A - High-precision Raman temperature demodulation method and device for monitoring dam and pipeline - Google Patents
High-precision Raman temperature demodulation method and device for monitoring dam and pipeline Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
- G01K11/324—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres using Raman scattering
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
- F17D—PIPE-LINE SYSTEMS; PIPE-LINES
- F17D5/00—Protection or supervision of installations
- F17D5/02—Preventing, monitoring, or locating loss
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- G01M3/00—Investigating fluid-tightness of structures
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Abstract
The invention relates to the field of temperature safety detection in distributed optical fiber sensing technology, in particular to a high-precision Raman temperature demodulation method and device for monitoring a dam and a pipeline, wherein the demodulation method comprises the following steps of: s1, carrying out differential reconstruction on an acquired chaotic Raman back-scattered light signal to obtain a reconstructed Raman scattered signal; s2, carrying out cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal twice to obtain twice cross-correlation signals, calculating derivatives of the twice cross-correlation signals, and determining starting points and end points of a temperature change area according to the derivatives; s3, calculating the temperature along the optical fiber according to the correlation peak value of the two cross-correlation signals. The invention can realize centimeter-level high spatial resolution on long distance by utilizing differential reconstruction, and amplify effective chaotic Raman scattering signals by utilizing the autocorrelation characteristic of chaotic pulse laser and through secondary cross correlation operation, thereby improving the signal-to-noise ratio of the system.
Description
Technical Field
The invention relates to the field of temperature safety detection in distributed optical fiber sensing technology, in particular to a high-precision Raman optical fiber temperature demodulation method and device for dam and pipeline leakage monitoring, which improve the signal-to-noise ratio of a chaotic Raman distributed optical fiber sensing system based on a multi-order differential reconstruction chaotic correlation method.
Background
Pipe network transportation is a pulse for national modern industry and national economy development. The leakage of the pipeline is the most important disease threatening the safety of the pipeline network, and is often caused by gradual expansion of micro leakage, when the pipeline is in a micro leakage state (the leakage aperture is smaller than 20 mm), especially the leakage of a pinhole, the length of an optical fiber influenced by the leakage area is often smaller than the spatial resolution of a system, so that weak temperature change information of the leakage area is submerged in environmental temperature noise in the length corresponding to the spatial resolution, the temperature change characteristics generated by the micro leakage are difficult to identify, and finally, a good opportunity for early discovery and early treatment is lost, so that serious disaster accidents such as pipe network explosion or harmful medium leakage are extremely likely to be caused. In addition, the water conservancy transportation engineering is a public service system for ensuring that national or regional socioeconomic activities are efficiently and normally carried out. Therefore, realizing the safety monitoring of the dam and ensuring the safe running of traffic become important strategic demands of the country and the place.
The traditional Raman distributed optical fiber sensing technology is a distributed sensing method for acquiring temperature information by utilizing the Raman back scattering effect in the optical fiber, and has important application in pipeline leakage and dam safety monitoring. However, the principle of pulse optical time domain reflection is limited to only achieve meter-scale spatial resolution, so that temperature change generated by micro leakage is difficult to accurately detect, and serious disaster hidden danger is caused.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a high-precision Raman temperature demodulation method and device for dam and pipeline monitoring, which are based on a multi-order differential reconstruction chaos correlation method, uses chaos light to replace traditional pulse laser to enter a sensing optical fiber, carries out multi-order differential reconstruction operation on a Raman back scattering signal, carries out cross-correlation operation on the differential reconstructed signal and a chaos pulse reference signal, so as to realize centimeter-level high spatial resolution on a long sensing distance, and simultaneously improves the signal-to-noise ratio of a system.
In order to solve the technical problems, the invention adopts the following technical scheme: a high-precision Raman temperature demodulation method for dam and pipeline monitoring is realized based on a chaotic Raman distributed optical fiber sensing device, and the chaotic Raman distributed optical fiber sensing device comprises the following components: the device comprises a pulse chaotic light source, a beam splitter, a wavelength division multiplexer, a sensing optical fiber, a photoelectric detector and an acquisition card, wherein pulse chaotic laser emitted by the pulse chaotic light source is split into two beams after passing through the beam splitter, one beam is detected by the photoelectric detector as reference light, the other beam is detected by the detection light after passing through the wavelength division multiplexer and enters the sensing optical fiber, the generated chaotic Raman backward anti-Stokes scattered light is detected by the photoelectric detector after being output by the wavelength division multiplexer, and the photoelectric detector sends a detected reference light signal and a Raman backward anti-Stokes scattered light signal to the acquisition card; the demodulation method comprises the following steps:
s1, carrying out differential reconstruction on an acquired chaotic Raman back-scattered light signal to obtain a reconstructed Raman scattered signal;
s2, carrying out cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal twice to obtain twice cross-correlation signals, calculating derivatives of the twice cross-correlation signals, and determining starting points and end points of a temperature change area according to the derivatives;
s3, calculating the temperature along the optical fiber according to the correlation peak value of the two cross-correlation signals, wherein the calculation formula is as follows:
wherein T represents temperature of a temperature change region, h is Planck constant, deltav is Raman frequency shift, k is Boltzmann constant, P is fiber inlet power, R a (T 0 ) Representing the temperature modulation function of anti-Stokes light at ambient temperature T 0 The value of C peak1 Represents the peak value of the primary correlation peak, C peak2 The peak value of the secondary correlation peak is represented, s represents the light intensity ratio of the detection light to the reference light, and P r (j) And P r (j+1) represents the power of the jth and jth+1th data points of the reference signal, I a And (n) is the anti-Stokes intensity.
In the step S2, a point where the first derivative of the twice cross-correlation signal is zero is taken as a start point of the temperature change region, and a point where the second derivative is zero and the third derivative is not zero is taken as an end point of the temperature change region.
In the step S1, the calculation formula of the differential reconstruction is as follows:
I c (n)＝I a ((n+1)·L f )-I a (n·L f )；
wherein I is c (n) represents the n-th sample data after reconstruction, I a ((n+1)·L f ) And I a (n·L f ) Light intensity information of the (n+1) th and the (n) th sampling data of the chaotic Raman back scattering signal are respectively represented.
In the step S2, the specific method for performing the cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic raman anti-stokes signal twice to obtain the twice cross-correlation signal is as follows:
s201, performing cross-correlation operation on a chaotic pulse reference signal and a reconstructed chaotic Raman anti-Stokes signal to obtain a primary cross-correlation signal;
s202, performing cross-correlation operation on the chaotic pulse reference signal and the primary cross-correlation signal again to obtain a secondary cross-correlation signal.
In addition, the invention also provides a high-precision Raman temperature demodulation device for monitoring the dam and the pipeline, which comprises the following components: the device comprises a pulse chaotic light source, a light splitter, a wavelength division multiplexer, a sensing optical fiber, a photoelectric detector, an acquisition card and a calculation unit, wherein pulse chaotic laser emitted by the pulse chaotic light source is divided into two beams after passing through the light splitter, one beam is detected by the photoelectric detector as reference light, the other beam enters the sensing optical fiber after passing through the wavelength division multiplexer as detection light, the generated chaotic Raman backward anti-Stokes scattered light is detected by the photoelectric detector after being output by the wavelength division multiplexer, the photoelectric detector transmits a detected reference light signal and a Raman backward anti-Stokes scattered light signal to the acquisition card, the acquisition card transmits acquired data to the calculation unit, and the calculation unit is used for:
carrying out differential reconstruction on the acquired chaotic Raman back-scattered light signals to obtain reconstructed Raman scattered signals;
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, calculating derivatives of the twice cross-correlation signals, and determining starting points and end points of a temperature change area according to the derivatives;
according to the correlation peak value of the two cross-correlation signals, the temperature along the optical fiber is calculated, and the calculation formula is as follows:
wherein T represents temperature of a temperature change region, h is Planck constant, deltav is Raman frequency shift, k is Boltzmann constant, P is fiber inlet power, R a (T 0 ) Representing anti-siThe temperature modulation function of the Toxose light is at ambient temperature T 0 The value of C peak1 Represents the peak value of the primary correlation peak, C peak2 The peak value of the secondary correlation peak is represented, s represents the light intensity ratio of the detection light to the reference light, and P r (j) And P r (j+1) represents the power of the jth and jth+1th data points of the reference signal, I a And (n) is the anti-Stokes intensity.
The pulse chaotic light source comprises a laser, an optical fiber coupler, a circulator, an attenuator, a polarization controller, a pulse light modulator and an erbium-doped optical fiber amplifier;
the laser emitted by the laser is divided into two paths after passing through the optical fiber coupler, one path of the laser returns to the laser along the original path after passing through the polarization controller and the attenuator and then passes through the circulator and the optical fiber coupler, so that the laser outputs chaotic laser, the other path of the laser outputs the chaotic laser through the circulator, the pulse optical modulator is used for modulating the chaotic laser output by the circulator into pulse chaotic light, and the erbium-doped optical fiber amplifier is used for amplifying the power of the pulse chaotic light.
The optical splitter is a 1×2 optical fiber coupler, and the splitting ratio is 1:99, wherein 1% of the paths are used as reference light, and 99% of the paths are used as detection light.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, the chaotic pulse laser is incident into the sensing optical fiber, the differential reconstruction is utilized, the centimeter-level high spatial resolution on a long distance can be realized, and the effective chaotic Raman scattering signal is amplified by utilizing the autocorrelation characteristic of the chaotic pulse laser through the secondary cross-correlation operation, so that the signal-to-noise ratio of the system is improved.
2. The invention modulates the traditional pulse laser into the chaotic pulse light through the feedback loop formed by the attenuator and the polarization controller, the pulse light emitted by the pulse laser is divided into two beams after passing through the optical fiber coupler, one beam returns to the pulse laser through the attenuator and the polarization controller optical circulator to output the chaotic pulse light, and then the chaotic pulse laser for sensing is obtained after the output of the chaotic pulse light is amplified by the erbium-doped optical fiber amplifier, so that the measurement of the chaotic Raman temperature with high precision is realized.
Drawings
Fig. 1 is a schematic structural diagram of a chaotic raman distributed optical fiber sensing device adopted in the first embodiment of the present invention;
fig. 2 is a schematic structural diagram of a high-precision raman temperature demodulation device for monitoring a dam and a pipeline according to a second embodiment of the present invention;
in the figure: the device comprises a 1-laser, a 2-light splitter, a 3-circulator, a 4-attenuator, a 5-polarization controller, a 6-pulse light modulator, a 7-erbium-doped fiber amplifier, an 8-1×2 fiber coupler, a 9-wavelength division multiplexer, a 10-sensing fiber, an 11-photoelectric detector, a 12-acquisition card, a 13-calculation unit and a 14-pulse chaotic light source.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments; all other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
The first embodiment of the invention provides a high-precision Raman temperature demodulation method for monitoring a dam and a pipeline, which effectively improves the signal to noise ratio of a system through a secondary correlation compression method, and in addition, precisely positions the initial position of a temperature change area by analyzing the shape of a primary chaotic scattering related signal in a function derivation way, thereby finally realizing the precise positioning and demodulation of centimeter-level ultrahigh spatial resolution.
As shown in fig. 1, the chaotic raman distributed optical fiber sensing device adopted in the demodulation method of the present embodiment includes: the device comprises a pulse chaotic light source 14, a light splitter 8, a wavelength division multiplexer 9, a sensing optical fiber 10, a photoelectric detector 11 and an acquisition card 12, wherein pulse chaotic laser emitted by the pulse chaotic light source is divided into two beams after passing through the light splitter 8, one beam is detected by the photoelectric detector 11 as reference light, the other beam is detected by the wavelength division multiplexer 9 and enters the sensing optical fiber 10 as detection light, and after being output by the wavelength division multiplexer 9, the generated chaotic Raman backward anti-Stokes scattered light is detected by the photoelectric detector 11, and the photoelectric detector 11 transmits a detected reference light signal and a Raman backward anti-Stokes scattered light signal to the acquisition card 12.
Specifically, in this embodiment, the wavelength of the pulsed chaotic light source is 1550nm. The spectroscope 8 is a 1×2 fiber coupler, and its spectroscope ratio is 1:99, wherein 1% of one path is used as reference light to be detected by the photodetector 1; 99% of the light passes through the wavelength division multiplexer 9 and then enters the sensing optical fiber 10, and Raman backward anti-Stokes scattered light with the wavelength of 1450nm generated in the sensing optical fiber 10 is output from the wavelength division multiplexer 9 and detected by the photoelectric detector 11; finally, the reference signal and the raman back-scattered signal are acquired by the acquisition card 12. And carrying out differential reconstruction and correlation processing on the obtained chaotic pulse reference signal and the chaotic Raman anti-Stokes scattering signal to obtain temperature information along the optical fiber.
Specifically, the demodulation method of the present embodiment is: carrying out differential reconstruction on the acquired chaotic Raman back-scattered light signals to obtain reconstructed Raman scattered signals; performing cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal twice, and solving a first derivative and a second derivative of the correlated signal, wherein a point with zero first derivative corresponds to a hot spot area starting point, and a point with zero second derivative and non-zero third derivative corresponds to a temperature area end point position; based on the correlation peak-to-peak value, the fiber temperature T along the line can be calculated.
Specifically, the demodulation method of the present embodiment specifically includes the following steps:
s1, carrying out differential reconstruction on the acquired chaotic Raman back scattering optical signals to obtain reconstructed Raman scattering signals.
In the step S1, the calculation formula of the differential reconstruction is as follows:
I c (n)＝I a ((n+1)·L f )-I a (n·L f )；(1)
wherein I is c (n) represents the nth sampled data after differential reconstruction, I a ((n+1)·L f ) Indicating chaotic Raman backward dispersionLight intensity information of (n+1) th sampling data of the emission signal, I a (n·L f ) Light intensity information representing nth sampling data of chaotic Raman back scattering signal, L f Representing the unit sample length.
S2, performing cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal twice to obtain two cross-correlation signals, calculating derivatives of the two cross-correlation signals, and determining the starting point and the end point of the temperature change area according to the derivatives.
Specifically, in the step S2, the specific method for performing the cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic raman anti-stokes signal twice to obtain the twice cross-correlation signal is as follows:
s201, performing cross-correlation operation on a chaotic pulse reference signal and a reconstructed chaotic Raman anti-Stokes signal to obtain a primary cross-correlation signal;
s202, performing cross-correlation operation on the chaotic pulse reference signal and the primary cross-correlation signal again to obtain a secondary cross-correlation signal.
Further, in the step S2, a point where the first derivative of the twice cross-correlation signal is zero is taken as a start point of the temperature change region, and a point where the second derivative is zero and the third derivative is not zero is taken as an end point of the temperature change region.
S3, calculating the temperature along the optical fiber according to the correlation peak value of the two cross-correlation signals, wherein the calculation formula is as follows:
wherein T represents the temperature of the temperature change region, C peak1 Represents the peak value of the primary correlation peak, C peak2 S represents the light intensity ratio of the detection light to the reference light, h represents the Planck constant, deltav represents the Raman frequency shift, k represents the Boltzmann constant, pr represents the reference signal power, P represents the fiber-in power, P r (j) And P r (j+1) represents the power of the jth and jth+1th 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 below，I a And (n) is the anti-Stokes intensity.
In particular, in the present invention, the demodulation and positioning principle of temperature measurement in the embodiment of the present invention is described below.
1. And a chaotic Raman anti-Stokes signal and chaotic pulse reference signal acquisition process.
The acquired chaotic Raman anti-Stokes light intensity expression is:
wherein I is a (L) is the chaotic raman anti-stokes light intensity; p is the incident power; l is the position of the sensing optical fiber; k (K) a Respectively, coefficients related to the anti-stokes light back-scatter cross-section; s is the backscattering factor of the fiber; v is the frequency of the incident light;representing the pulse laser flux coupled into the fiber; alpha 0 、α a The loss coefficients of the incident light and an-Stokes light per unit length of the optical fiber, respectively, L represents the position in the optical fiber.
Let the constant term in formula (1)Is C 1 I.e. the formula reduces to:
I a (L)＝C 1 ·P·R a (T)·exp[-(α 0 +α a )L] (4)
R a (T) is a temperature modulation function with anti-stokes light:
for example, at a sampling rate of 10 Gs/s. I.e. 0.1ns (i.e. one point is collected every 1 cm) one step forward, one point is collected; for example: when the length of the temperature change area is 10cm, corresponding to 10 sampling intervals; for convenience in expressing the difference formula, we will takeThe sample interval is understood to be the sampling step n steps. L= n L f ，L f Step length (unit sampling length);
therefore, the formula (4) is rewritten as:
I a (L)＝I a (n·L f )＝C 1 ·P·R a (T)·exp[-(α 0 +α a )n·L f ] (6)
2. and carrying out differential reconstruction processing on the Raman back-scattered signals.
Because the attenuation coefficients of two adjacent points are similar and are approximately the same after difference, the attenuation coefficients are unified as a constant C; the expression of the chaotic raman anti-stokes light intensity after differential reconstruction is:
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)
3. and carrying out a related compression operation process on the differential reconstruction signal and the reference signal.
The chaotic signal is mainly concentrated in the high level part of the reference signal, while the chaotic signal in the low level part of the reference signal is relatively weak and fluctuates around 0, so that the high level part of the reference signal has the greatest influence on the result after correlation for the correlated signal, and therefore, in the embodiment, the correlation operation only considers the high level part of the reference signal. For the reference signal, the number of data points corresponding to the pulse width is m, and the differential signal I c The number of data points of (n) is n, which is determined by the length of the optical fiber and the sampling step. The total length of the sequence after the cross correlation operation of the two signals is (m+n-1), however, the front (m-1) and back (m-1) data points of the sequence are invalid data, and the number of valid data is n-m+1. The value of the ith component of the cross-correlation valid data (valid data is that the pulse is completely within the differential signal during the correlation operation) is:
in the formula, pr is reference signal power, P is fiber-in power, and the relationship between Pr and P is 1:s exists in theory, so that the formula (8) can be rewritten as follows:
since i can be understood as the pulse has moved forward by i steps due to the periodic nature of the pulse, pr (j) ≡Pr (i+j), the above equation can be translated into:
when the whole temperature change area enters the pulse, the maximum correlation peak value can be generated, so the maximum correlation peak value C peak1 The expression of (2) is:
4. temperature demodulation process corresponding to secondary correlation operation
Will once correlate signal I 1 With reference signal P r Performing correlation operation to obtain secondary correlation result
The maximum correlation peak-to-peak value can be obtained in the temperature change region:
further simplifying and obtaining:
taking P for convenient calculation r (j) Average value of (2)Then->And (3) withApproximately equal, therefore, the secondary correlation allows the correlation peak to be lifted +.>Doubling, namely:
then:
according to the formulas (16) and (6), there are:
after the formula (17) is finished, the relationship between the measured temperature and the secondary correlation peak value is as follows:
binding R as (T)＝[exp(hΔν/kT)-1] -1 Temperature information of the temperature mutation area is extracted, and a demodulation equation is shown in a formula (19).
Where h is the Planck constant, deltav is the Raman frequency shift, k is the Boltzmann constant, both are constant, P r For reference signal power, P r (j) Is the reference signal power at point j. P is the power of the incoming fiber, which is measured by a power meter, C peak1 Represents the peak value of the primary correlation peak, C peak2 The peak value of the secondary correlation peak is represented, s represents the probe light and the referenceThe light intensity ratio of the test light, R a (T 0 ) Is a temperature modulation function of anti-Stokes light and is equal to the room temperature T 0 In relation, can be obtained by the formula (5), I a And (n) is the anti-Stokes light intensity, as measured.
Example two
As shown in fig. 2, a second embodiment of the present invention provides a high-precision raman temperature demodulation device for monitoring a dam and a pipeline, which includes: the device comprises a pulse chaotic light source, a light splitter 8, a wavelength division multiplexer 9, a sensing optical fiber 10, a photoelectric detector 11, an acquisition card 12 and a calculation unit, wherein pulse chaotic laser emitted by the pulse chaotic light source is divided into two beams after passing through the light splitter 8, one beam is detected by the photoelectric detector 11 as reference light, the other beam enters the sensing optical fiber 10 after passing through the wavelength division multiplexer 9 as detection light, the generated chaotic Raman backward anti-Stokes scattered light is detected by the photoelectric detector 12 after being output by the wavelength division multiplexer 9 by the sensing optical fiber 10, the photoelectric detector 11 transmits a detected reference light signal and a Raman backward anti-Stokes scattered light signal to the acquisition card 12, the acquisition card 12 transmits acquisition data to the calculation unit, and the calculation unit is used for:
carrying out differential reconstruction on the acquired chaotic Raman back-scattered light signals to obtain reconstructed Raman scattered signals;
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, calculating derivatives of the twice cross-correlation signals, and determining starting points and end points of a temperature change area according to the derivatives;
according to the correlation peak value of the two cross-correlation signals, the temperature along the optical fiber is calculated, and the calculation formula is as follows:
wherein T represents temperature of a temperature change area, h is Planck constant, deltav is Raman frequency shift, k is Boltzmann constant, both are constant values, P is fiber inlet power, R a (T 0 ) Representing temperature modulation of anti-Stokes lightThe system function is at the ambient temperature T o The following values. C (C) peak1 Represents the peak value of the primary correlation peak, C peak2 The peak value of the secondary correlation peak is represented, s represents the light intensity ratio of the detection light to the reference light, and P r (j) And P r (j+1) represents the power of the jth and jth+1th data points of the reference signal, I a And (n) is the anti-Stokes light intensity, as measured.
Specifically, in this embodiment, the pulse chaotic light source includes a laser 1, an optical fiber coupler 2, a circulator 3, an attenuator 4, a polarization controller 5, a pulse optical modulator 6, and an erbium-doped fiber amplifier 7; the laser emitted by the laser 1 is divided into two paths after passing through the optical fiber coupler 2, one path of the laser returns to the laser 1 along the original path after passing through the polarization controller 5 and the attenuator 4 and then passing through the circulator 3 and the optical fiber coupler 2, so that the laser outputs chaotic laser, the other path of the laser outputs the chaotic laser through the circulator 3, the pulse optical modulator 6 is used for modulating the chaotic laser output through the circulator 3 into pulse chaotic light, and the erbium-doped optical fiber amplifier 7 is used for amplifying the power of the pulse chaotic light.
Specifically, in the present embodiment, the optical fiber coupler 2 has a split ratio of 50:50, said laser 1 emits continuous light having a central wavelength of 1550nm through 50:50, and then split into two paths. One path of continuous light returns to the laser 1 after passing through the attenuator 4, the polarization controller 5, the circulator 3 and the optical fiber coupler 2 to form a single feedback structure, the traditional continuous light is modulated into chaotic continuous light, then the chaotic continuous light output by the other path of continuous light is output by the circulator 3, enters the pulse modulator 6 and is modulated into chaotic pulse light, and is amplified by the erbium-doped optical fiber amplifier 7 and is divided into two paths of 1:99 by the optical splitter 8, wherein 1% of the chaotic continuous light is used as a reference signal to be detected by the photoelectric detector; 99% of the light enters the sensing optical fiber after passing through the wavelength division multiplexer, the wavelength division multiplexer 9 outputs Raman backward anti-Stokes scattered light with the wavelength of 1450nm from the c end, and the Raman backward anti-Stokes scattered light is detected by the photoelectric detector 11; finally, the reference signal and the raman back scattering signal are collected by the collection card 12 and sent to the calculation unit 13. The computing unit 13 carries out differential reconstruction and correlation processing on the obtained chaotic pulse reference signal and the chaotic Raman anti-Stokes scattering signal, and obtains temperature information along the optical fiber.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.
Claims (7)
1. The high-precision Raman temperature demodulation method for dam and pipeline monitoring is characterized by being realized based on a chaotic Raman distributed optical fiber sensing device, wherein the chaotic Raman distributed optical fiber sensing device comprises the following components: the device comprises a pulse chaotic light source (14), a light splitter (8), a wavelength division multiplexer (9), a sensing optical fiber (10), a photoelectric detector (11) and an acquisition card (12), wherein pulse chaotic laser emitted by the pulse chaotic light source (14) is divided into two beams after passing through the light splitter (8), one beam is detected by the photoelectric detector (11) as reference light, the other beam is detected by the wavelength division multiplexer (9) and enters the sensing optical fiber (10), the generated chaotic Raman backward anti-Stokes scattered light is output by the wavelength division multiplexer (9) and then is detected by the photoelectric detector (12), and the photoelectric detector (12) transmits a detected reference light signal and a Raman backward anti-Stokes scattered light signal to the acquisition card (12); the demodulation method comprises the following steps:
s1, carrying out differential reconstruction on an acquired chaotic Raman back-scattered light signal to obtain a reconstructed Raman scattered signal;
s2, carrying out cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic Raman anti-Stokes signal twice to obtain twice cross-correlation signals, calculating derivatives of the twice cross-correlation signals, and determining starting points and end points of a temperature change area according to the derivatives;
s3, calculating the temperature along the optical fiber according to the correlation peak value of the two cross-correlation signals, wherein the calculation formula is as follows:
wherein T represents temperature of a temperature change region, h is Planck constant, deltav is Raman frequency shift, k is Boltzmann constant, P is fiber inlet power, R a (T 0 ) Representing the temperature modulation function of anti-Stokes light at ambient temperature T 0 The value of C peak1 Represents the peak value of the primary correlation peak, C peak2 The peak value of the secondary correlation peak is represented, s represents the light intensity ratio of the detection light to the reference light, and P r (j) And P r (j+1) represents the power of the jth and jth+1th data points of the reference signal, I a And (n) is the anti-Stokes intensity.
2. The method according to claim 1, wherein in the step S2, a point where the first derivative of the twice cross-correlation signal is zero is used as a start point of the temperature change region, and a point where the second derivative is zero and the third derivative is not zero is used as an end point of the temperature change region.
3. The high-precision raman temperature demodulation method for monitoring a dam and a pipeline according to claim 1, wherein in the step S1, a calculation formula of differential reconstruction is as follows:
I c (n)＝I a ((n+1)·L f )-I a (n·L f )；
wherein I is c (n) represents the n-th sample data after reconstruction, I a ((n+1)·L f ) And I a (n·L f ) Light intensity information of the (n+1) th and the (n) th sampling data of the chaotic Raman back scattering signal are respectively represented.
4. The high-precision raman temperature demodulation method for monitoring a dam and a pipeline according to claim 1 is characterized in that in the step S2, the specific method for performing cross-correlation operation on the chaotic pulse reference signal and the reconstructed chaotic raman anti-stokes signal twice to obtain two cross-correlation signals is as follows:
s201, performing cross-correlation operation on a chaotic pulse reference signal and a reconstructed chaotic Raman anti-Stokes signal to obtain a primary cross-correlation signal;
s202, performing cross-correlation operation on the chaotic pulse reference signal and the primary cross-correlation signal again to obtain a secondary cross-correlation signal.
5. A high-precision Raman temperature demodulation device for monitoring a dam and a pipeline is characterized by comprising the following components: the device comprises a pulse chaotic light source (14), a light splitter (8), a wavelength division multiplexer (9), a sensing optical fiber (10), a photoelectric detector (11), an acquisition card (12) and a calculation unit, wherein pulse chaotic laser emitted by the pulse chaotic light source (14) is divided into two beams after passing through the light splitter (8), one beam is detected by the photoelectric detector (11) as reference light, the other beam enters the sensing optical fiber (10) after passing through the wavelength division multiplexer (9) as detection light, the generated chaotic Raman backward anti-Stokes scattered light is detected by the photoelectric detector (12) after being output by the wavelength division multiplexer (9), the photoelectric detector (12) transmits detected reference light signals and Raman backward anti-Stokes scattered light signals to the acquisition card (12), the acquisition card (12) transmits acquisition data to the calculation unit (13), and the calculation unit (13) is used for:
carrying out differential reconstruction on the acquired chaotic Raman back-scattered light signals to obtain reconstructed Raman scattered signals;
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, calculating derivatives of the twice cross-correlation signals, and determining starting points and end points of a temperature change area according to the derivatives;
according to the correlation peak value of the two cross-correlation signals, the temperature along the optical fiber is calculated, and the calculation formula is as follows:
wherein T represents temperature of a temperature change region, h is Planck constant, deltav is Raman frequency shift, k is Boltzmann constant, P is fiber inlet power, R a (T 0 ) Representing the temperature modulation function of anti-Stokes light at ambient temperature T 0 The value of C peak1 Represents the peak value of the primary correlation peak, C peak2 The peak value of the secondary correlation peak is represented, s represents the light intensity ratio of the detection light to the reference light, and P r (j) And P r (j+1) represents the power of the jth and jth+1th data points of the reference signal, I a And (n) is the anti-Stokes intensity.
6. The high-precision Raman temperature demodulation device for dam and pipeline monitoring according to claim 5, wherein the pulse chaotic light source (14) comprises a laser (1), an optical fiber coupler (2), a circulator (3), an attenuator (4), a polarization controller (5), a pulse optical modulator (6) and an erbium-doped fiber amplifier (7);
the laser emitted by the laser (1) is divided into two paths after passing through the optical fiber coupler (2), one path of the laser returns to the laser (1) along the original path after passing through the polarization controller (5) and the attenuator (4) after passing through the circulator (3) and the optical fiber coupler (2) so as to output chaotic laser, the other path of the laser outputs the chaotic laser through the circulator (3), the pulse optical modulator (6) is used for modulating the chaotic laser output by the circulator (3) into pulse chaotic light, and the erbium-doped optical fiber amplifier (7) is used for amplifying the power of the pulse chaotic light.
7. The high-precision raman temperature demodulation apparatus for dam and pipeline monitoring according to claim 5, wherein the beam splitter (8) is a 1 x 2 fiber coupler, and the beam splitting ratio is 1:99, wherein 1% of the paths are used as reference light, and 99% of the paths are used as detection light.
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