CN112683418A - Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement - Google Patents
Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement Download PDFInfo
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Abstract
The invention discloses a Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement, which comprises the following steps: automatic calibration: calculating the length of the optical fiber and an attenuation function; denoising data: the signal-to-noise ratio of the signal is improved by combining the advantages of accumulated denoising and wavelet threshold denoising; and (3) data compensation: a dispersion elimination algorithm based on Linear interpolation calculation is adopted, double-path signals are synchronized, and a data fitting method is adopted to realize an attenuation compensation algorithm; data demodulation: and carrying out numerical calculation such as ratio, logarithm and the like on the two paths of optical signals to demodulate temperature data. The Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement has the characteristics of high response speed, high precision and excellent performance.
Description
Technical Field
The invention relates to the field of optical fiber sensing, in particular to a Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement.
Background
In the field of distributed temperature measurement systems, the application of optical technology plays an important role in the field. With the improvement and improvement of performance of the fiber optics by countless scientists for decades, the fiber optics is not only an important communication medium, but also a key sensing device, and is gradually applied to monitoring systems of some environmental parameters. In a distributed optical fiber sensing system, an optical signal propagates along an optical fiber, and the optical fiber can be used as a medium for optical propagation to convey a communication signal and can also be used as a sensing medium to reflect the change condition of the external environment by detecting the change of the optical signal. With the development of optical fiber communication in recent years, temperature measurement systems using optical fibers as sensing media are being used in real life. Compared with the traditional electronic sensing system, the optical fiber sensing system has great advantages. From the aspect of hardware properties, most of the optical fibers are made of quartz materials, are soft in texture, good in flexibility, capable of being bent at will, corrosion-resistant, light in weight and small in size, provide convenience for installation in engineering, are very high in practicability and are suitable for different scenes. Meanwhile, light is used as a communication or sensing signal, so that the defect of poor anti-interference capability of an electric signal can be made up, and the transmission, demodulation and restoration of the signal are facilitated. The optical signal is used for transmitting data, a power supply is not required to be introduced, safer guarantee is provided for some flammable and explosive field occasions, and the optical fiber application scene is very wide.
Distributed optical fiber temperature measurement technology is based on optic fibre scattering effect to a whole optic fibre is the novel sensing technology of sensing carrier, can measure the temperature of all points on the optic fibre, is applicable to remote transmission, and a plurality of sensor networks in the field of traditional electronic sensing cover the temperature measurement region in other words, and this the chaotic problem of circuit and the data processing that the multisensor arouses that has significantly reduced go up the disorderly shortcoming of data volume, also greatly reduced material cost. Generally, a complete distributed optical fiber temperature measurement system generally only needs one common multimode optical fiber, the multimode optical fiber is laid at a position to be monitored, a host system is used for collecting optical signals, processing data and the like, and then the temperature of an area covered on the whole optical fiber can be obtained. In conclusion, the distributed optical fiber temperature measurement system has the advantages of electromagnetic interference resistance, light weight, corrosion resistance, long-term use, stable system and the like, so that the distributed optical fiber temperature measurement technology is made in the field of temperature measurement, and a new idea and a new method are provided for the temperature measurement technology.
The U.S. space agency proposes a temperature two-way demodulation method using Raman Stokes light as reference light and Raman Anti-Stokes light as signal light, and the DTS system is successfully applied to the field of aviation. A Zhang Xuan team of China measurement university provides a design scheme of a distributed optical fiber Raman temperature measurement system, the system integrates the technologies of a double-channel photoelectric detection technology, a self-calibration technology, sampling average processing and the like, a DTS system is developed, the adopted temperature measurement optical fiber is 1km optical fiber, the experimental result shows that the temperature precision is +/-2 ℃, the temperature resolution is 0.1 ℃, the temperature measurement interval is 0-120 ℃, and the measurement time is not more than 40 s. Although the distributed optical fiber temperature measurement technology is relatively mature, with the increasing progress of technology, the performance of the existing system cannot meet the requirement of higher precision, and there are some technical difficulties and disadvantages, such as: the temperature measurement precision is not high, the transmission distance is short, the temperature sensitive performance is not high, the acquisition speed is slow, and the like.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement. The specific technical scheme is as follows:
the invention provides a Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement, which comprises the following steps:
s1, automatic calibration: utilizing an automatic peak-searching algorithm to automatically calibrate the optical fiber parameters and calculating an attenuation compensation function f (x);
s2, data denoising: collecting two-way spectrum signals of Raman Stokes light and anti-Stokes light in an optical fiber, and processing the two-way spectrum signals by adopting an accumulation denoising algorithm and a wavelet threshold denoising algorithm to obtain demodulation signals;
s3, data compensation: processing the demodulated signal by using the attenuation compensation function and a Linear interpolation algorithm to compensate light intensity attenuation and eliminate dispersion to obtain a compensation signal;
s4, data demodulation: demodulating the compensation signal according to the relationship between the light intensity and the temperature of the Raman Stokes light and the anti-Stokes light to obtain a temperature distribution function T, wherein the relationship between the light intensity and the temperature is
In the formula of Us(T) is the intensity of Raman Stokes light, Uas(T) is the intensity of the anti-Stokes light, KO is the photoelectric influence factor, Ks(L) is the light mutation loss coefficient of Raman Stokes light, Kas(L) is the light mutation loss coefficient of anti-Stokes light, KsCoefficient of dependence of scattering cross section for Raman Stokes light, KasCoefficient of dependence of the scattering cross section for anti-Stokes light, vsIs the Raman Stokes light frequency, vasFor anti-Stokes light frequencies,. phi.e. the incident light flux,. alpha.0Is the loss factor of incident light, alphasIs the loss factor of Raman Stokes light, alphaasIs the loss factor of anti-Stokes light, L is the length of the optical fiber, Rs(T) is the Boltzmann factor of Raman Stokes light, Ras(T) is the Boltzmann factor of the anti-Stokes light.
Further, in step S4, the temperature distribution function T is obtained by the following formula:
wherein, I (T) is light intensity ratio, and I (T) is Uas(T)/Us(T), h is planck constant; Δ v is the amount of frequency shift, K is the Boltzmann constant, T0To scale the temperature on the fiber loop, I (T)0) To scale the ratio of light intensity at the fiber loop.
Further, in step S4, boltzmann factors of the raman stokes light and anti-stokes light
Further, in step S1, the fiber parameters include the fiber length, and the fiber length is automatically calculated by using an automatic peak-finding algorithm to locate the positions of the first fresnel scattering peak and the last fresnel scattering peak.
Further, in step S2, the wavelet threshold denoising algorithm includes at least one of a coif3 wavelet basis algorithm, a maximum minimum threshold algorithm, a soft threshold algorithm, and a six-layer decomposition algorithm.
Further, in step S2, the cumulative denoising algorithm is accumulated more than or equal to 15000 times, and the cumulative number is less than or equal to 17000 times.
Further, the attenuation compensation function is obtained by the following formula:
wherein alpha iss(l) Attenuation coefficient, alpha, of distance from starting point l of Raman Stokes lightas(l) The attenuation coefficient is the distance l from the starting point of the anti-stokes light.
Further, the attenuation coefficient of the distance from the starting point/, is obtained by the following formula:
wherein α (l) is an attenuation coefficient at a distance l from the starting point, pi (l) is a light intensity before attenuation at the distance l from the starting point, and po (l) is a light intensity after attenuation at the distance l from the starting point.
Further, the attenuation compensation function is obtained by the following formula:
R(l)＝RAT(l)×10-f(x)
wherein R isAT(l) For the ratio of the two-way voltages before attenuation at a distance l from the starting point, i.e.
Uas' (l) is the anti-Stokes light intensity before attenuation, Us' (l) is the Stokes light intensity before attenuation; r (l) is the ratio of the two-way voltages after attenuation at a distance of l from the starting point, i.e.
Uas(l) For attenuated anti-Stokes light intensity, Us(l) Is the attenuated stokes light intensity.
Further, the attenuation compensation function is modified by a data fitting algorithm in step S3.
The technical scheme of the invention has the beneficial effects that:
a. the de-noising and compensation processing greatly improves the detection precision;
b. the limitation of the accumulation times improves the interest rate response speed;
c. the comprehensive performance is excellent.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic flow chart of a method of an embodiment of the present invention;
FIG. 2 is a schematic diagram of a calibration flow in an embodiment of the invention;
FIG. 3 is a schematic interface diagram of an anti-Stokes light intensity curve in an embodiment of an example of the invention;
FIG. 4 is a schematic diagram of a raw signal demodulation temperature profile interface in an embodiment of an example of the invention;
FIG. 5 is a schematic interface diagram of a temperature profile after 16000 accumulations in an embodiment of an example of the invention;
FIG. 6 is a schematic diagram of a temperature curve interface after wavelet denoising in an embodiment of the present invention;
FIG. 7 is a schematic diagram of a two-pass light intensity curve interface before and after dispersion cancellation in an embodiment of an example of the invention;
FIG. 8 is a schematic diagram of a two-pass light intensity curve interface before and after attenuation compensation in an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood and more clearly understood by those skilled in the art, the technical solutions of the embodiments of the present invention will be described in detail and completely with reference to the accompanying drawings. It is to be understood that the described embodiments are merely exemplary of a portion of the invention and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. In addition, the terms "comprises" and "comprising," and any variations thereof, in the description and claims of this invention, are intended to cover a non-exclusive inclusion, such that a process, method, apparatus, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In an embodiment of the present invention, there is provided a two-way demodulation method of raman scattering light with optical fiber distributed temperature measurement, as shown in fig. 1, including the following steps:
s1, automatic calibration: utilizing an automatic peak-searching algorithm to automatically calibrate the optical fiber parameters and calculating an attenuation compensation function f (x);
s2, data denoising: collecting two-way spectrum signals of Raman Stokes light and anti-Stokes light in an optical fiber, and processing the two-way spectrum signals by adopting an accumulation denoising algorithm and a wavelet threshold denoising algorithm to obtain demodulation signals;
s3, data compensation: processing the demodulated signal by using the attenuation compensation function and a Linear interpolation algorithm to compensate light intensity attenuation and eliminate dispersion to obtain a compensation signal; the attenuation compensation function may be obtained by the following equation:
wherein alpha iss(l) Attenuation coefficient, alpha, of distance from starting point l of Raman Stokes lightas(l) The attenuation coefficient is the distance l from the starting point of the anti-stokes light.
Wherein the attenuation coefficient of the distance from the starting point /) can be obtained by the following formula:
wherein α (l) is an attenuation coefficient at a distance l from the starting point, pi (l) is a light intensity before attenuation at the distance l from the starting point, and po (l) is a light intensity after attenuation at the distance l from the starting point.
Alternatively, the attenuation compensation function is obtained by the following formula:
R(l)＝RAT(l)×10-f(x)
wherein R isAT(l) For the ratio of the two-way voltages before attenuation at a distance l from the starting point, i.e.
Uas' (l) is the anti-Stokes light intensity before attenuation, Us' (l) is the Stokes light intensity before attenuation; r (l) is the ratio of the two-way voltages after attenuation at a distance of l from the starting point, i.e.
Uas(l) For attenuated anti-Stokes light intensity, Us(l) Is the attenuated stokes light intensity.
S4, data demodulation: demodulating the compensation signal according to the relationship between the light intensity and the temperature of the Raman Stokes light and the anti-Stokes light to obtain a temperature distribution function T, wherein the relationship between the light intensity and the temperature is
In the formula of Us(T) is the intensity of Raman Stokes light, Uas(T) is the intensity of the anti-Stokes light, KO is the photoelectric influence factor, Ks(L) is the light mutation loss coefficient of Raman Stokes light, Kas(L) is the light mutation loss coefficient of anti-Stokes light, KsCoefficient of dependence of scattering cross section for Raman Stokes light, KasCoefficient of dependence of the scattering cross section for anti-Stokes light, vsIs the Raman Stokes light frequency, vasFor anti-Stokes light frequencies,. phi.e. the incident light flux,. alpha.0Is the loss factor of incident light, alphasIs the loss factor of Raman Stokes light, alphaasIs the loss factor of anti-Stokes light, L is the length of the optical fiber, Rs(T) is the Boltzmann factor of Raman Stokes light, Ras(T) is the Boltzmann factor of the anti-Stokes light.
Step S4 may add another inspection algorithm as shown in fig. 1, check whether the result meets the requirement, if yes, complete the temperature measurement; if not, the process returns to step S2 to start the process, and the steps of re-sampling, data collection and calculation are performed.
In step S4, the Boltzmann factor of the Raman Stokes light and the Boltzmann factor of the anti-Stokes light are
In step S4, the temperature distribution function T can be obtained by the following formula:
wherein, I (T) is light intensity ratio, and I (T) is Uas(T)/Us(T), h is planck constant; Δ v is the amount of frequency shift, K is Boltzmann constantAmount, T0To scale the temperature on the fiber loop, I (T)0) To scale the light intensity ratio at the fiber loop, the fiber loop is located 10m from the fiber start in this embodiment.
In one embodiment of the present invention, in step S1, the optical fiber parameter includes an optical fiber length, and the optical fiber length is automatically calculated by locating the positions of the first fresnel scattering peak and the last fresnel scattering peak using an automatic peak finding algorithm, and more specifically, as shown in fig. 2, step S1 includes: the method comprises the following substeps of starting automatic calibration, data acquisition, accumulated denoising, wavelet denoising, Fresnel scattering peak searching, dispersion elimination and attenuation function calculation. In addition, in the whole process of the technical solution of the present invention, a determination algorithm as shown in fig. 1 may be added after step S1 to determine whether the calibration result meets the requirement, if not, the calibration result is re-calibrated, and if so, the next step is performed.
In one embodiment of the present invention, in step S2, the wavelet threshold denoising algorithm includes at least one of coif3 wavelet basis algorithm, maximum minimum threshold algorithm, soft threshold algorithm, and six-layer decomposition algorithm, which greatly improves the signal-to-noise ratio.
In an embodiment of the present invention, in step S2, the accumulation number of the accumulation denoising algorithm is greater than or equal to 15000 times, and the accumulation number is less than or equal to 17000 times, preferably 16000 times, which can achieve both higher accuracy and time saving.
Further, the attenuation compensation function is modified by a data fitting algorithm in step S3.
The following provides a specific operation that the present solution achieves:
the demodulation algorithm design is carried out by adopting Python language, and the method mainly comprises four main processes of automatic calibration, data denoising pretreatment, data signal compensation and data demodulation as shown in figure 1.
The automatic calibration process further comprises: several processes of data acquisition, denoising processing, data compensation, automatic calculation of the fiber length, etc. are shown in fig. 2. The denoising preprocessing comprises the following steps: and (4) denoising by combining two denoising advantages of accumulated average denoising and wavelet threshold denoising. The data signal compensation includes: a dispersion elimination algorithm based on Linear numerical calculation and an attenuation compensation algorithm designed by adopting a data fitting method. The data demodulation is mainly to calculate the ratio, logarithm and the like on the value according to the relation between the Raman scattering light and the temperature, and then the temperature can be demodulated.
The first step is as follows: and (6) automatic calibration. A raman anti-stokes light profile is collected as shown in figure 3. Since the optical fiber is welded and connected by flanges at the beginning and the end, Fresnel scattering occurs at the beginning and the end. The automatic calculation of the optical fiber length can be completed by positioning the positions of the original Fresnel scattering peak and the final Fresnel scattering peak by using an automatic peak-finding algorithm, so that the automatic calibration is completed. Meanwhile, a signal is collected once in the calibration process, and an attenuation compensation function f (x) is calculated.
The second step is that: and (5) denoising. The denoising processing mainly combines the accumulation average denoising and the wavelet threshold denoising. The most common natural noise is white Gaussian noise, the noise is normally distributed and meets the zero-mean characteristic, the noise can be well eliminated after accumulation average processing, and calculation time is saved while the noise is well eliminated by 16000 accumulation times. In order to further improve the signal-to-noise ratio, a wavelet threshold denoising algorithm is adopted after accumulation average denoising. After the signal is subjected to wavelet transformation, the signal is transformed from a time domain to a wavelet domain, the correlation of the signal on a time domain is eliminated, and the local characteristic of the signal can be shown. In the wavelet domain, the wavelet coefficient of the effective signal is large, the wavelet coefficient of the noise signal is small, and the small wavelet coefficient is processed, so that the noise can be well reduced. In the invention, the coif3 wavelet basis, the maximum and minimum threshold, the soft threshold method and the 6-layer decomposition are used for realizing the wavelet de-noising processing, and finally the demodulation signal with higher signal-to-noise ratio is obtained.
The third step: and (6) compensating data. The compensation algorithm mainly comprises two algorithms of attenuation compensation and dispersion elimination. Light propagates in an optical fiber and can have certain attenuation, in the actual demodulation process, due to different attenuation speeds of dual-path optical signals, a demodulation ratio curve is in a certain attenuation trend, and the relationship between signals before and after attenuation can be obtained according to an attenuation formula:
alpha (l) is the attenuation coefficient at a distance l from the starting point, Pi(l)，Po(l) The light intensity before and after attenuation at a distance l from the starting point. Through numerical theoretical calculation, the following relation exists between the two-path voltage ratio before and after attenuation:
R(l)、RAT(l) The ratio of the two paths of light before attenuation at a distance of l from the starting point
The following relationship can be obtained:
lg(RAT(l))＝lg(R(l))+f(x)。
in practical situations, the optical fiber is set at the same temperature, lg (r (l)) can be regarded as a constant, and the ratio of the voltage before attenuation is subjected to logarithmic operation, and then data fitting is performed to obtain a ratio curve expression. Subtracting constant term in function expression to obtain attenuation coefficient function f (x), and calculating to obtain attenuation voltage ratio
R(l)＝RAT(l)×10-f(x)。
Due to the fact that the Stokes light and the anti-Stokes light have different wavelengths, two-way signal acquisition is asynchronous, certain position deviation exists, and the errors are more obvious along with the increase of the distance. The Fresnel scattering peaks at the tail ends of the two paths of signals are not in the same position on the signals. In order to eliminate different signal influences caused by chromatic dispersion, a Linear interpolation algorithm is proposed.
The fourth step: the signal demodulation is mainly derived according to a theoretical formula between Raman scattering light and temperature, and a relation function between derivatives is obtained for demodulation. Raman scattered light is very sensitive to temperature changes, where the intensity of stokes and anti-stokes light is related to temperature by:
wherein KO is a photoelectric influence factor, and K (L) is a light mutation loss coefficient; k is the relevant coefficient of the scattering cross section; v is frequency; Φ e is the incident light flux; alpha is the optical loss coefficient; l is the length of the optical fiber; usually, the value of k (l) is not fixed and the loss factor of the two-way light is different, but the ratio is usually a fixed value. R (T) is the Boltzmann factor, which can be expressed as:
h is the Planck constant; Δ v is the amount of frequency shift; k is Boltzmann constant; t is expressed as absolute temperature. When the temperature changes, the factor also changes, causing the light intensity to change. In order to eliminate the influence of parameters such as loss coefficient, the two optical signals are subjected to phase division processing
In the actual measurement process, a reference temperature is required to be introduced as a reference for temperature demodulation. At the initial end 10m of the optical fiber, a 10m optical fiber ring is wound as a reference optical fiber and the temperature T on the reference optical fiber is obtained0And I (T)0) And the temperature can be demodulated by numerical calculation
A specific operational flow of an embodiment of the present invention is provided below, where the method may be operated on a computer having a display screen that displays the results of the calculations of fig. 3-8 at different stages of the algorithm during execution of the algorithm. Hardware optical paths and circuits are connected as follows. Firstly, calibration is carried out, the length of an optical fiber is positioned according to the position of a Fresnel scattering peak, then accumulation and wavelet denoising are carried out to reduce noise, then a Linear interpolation algorithm is carried out to eliminate dispersion, and finally an attenuation function is calculated through curve fitting for 5 times, as shown in FIG. 3:
f(x)＝3.089*10-21x5-6.07*10-17x4+4.237*10-13x3-1.24*10-9x2+6.139*10-6x。
and after the calibration is finished, the acquisition process can be carried out.
In the invention, two denoising algorithms of accumulation average denoising and wavelet threshold denoising are combined. Firstly, 16000 cumulative mean de-noising is used, as shown in fig. 4, the temperature obtained by demodulation before cumulative mean is obtained, and fig. 5 is the temperature obtained by demodulation after cumulative 16000 times. As shown in table 1, the error gradually decreases as the number of accumulations increases. The signal-to-noise ratio after 16000 times of accumulation is 1.6 times of the signal-to-noise ratio after 1000 times of accumulation, and the error fluctuation range is reduced from +/-5 ℃ to +/-1.5 ℃.
TABLE 1 cumulative average denoised SNR comparison
After the accumulated average denoising, a wavelet threshold denoising method is used for denoising, and the wavelet denoising processing is realized by using a coif3 wavelet basis, a maximum and minimum threshold, a soft threshold method and 6-layer decomposition.
TABLE 2 cumulative mean denoising with combined wavelet denoising signal-to-noise ratio and standard deviation comparison
As shown in fig. 6, which is a temperature curve after wavelet denoising, after the wavelet threshold denoising, the signal-to-noise ratio is further improved, the standard deviation is reduced, and when the optical fiber is at the same temperature, the upper and lower temperature are only 0.5 ℃ floating, which is better than the effect of single use cumulative denoising.
And performing data compensation after denoising algorithm. Firstly, a Linear interpolation algorithm is adopted for dispersion elimination. As shown in fig. 7, the graph (a) shows that the fresnel scattering peak at the tail end of the original dual-path optical signal has a large deviation, which is due to the asynchronization of the dual-path light caused by the dispersion effect, and the graph (b) shows that the fresnel scattering peak of the dual-path light is visually observed to be synchronized by the dual-path curve after interpolation calculation. Then, the attenuation compensation algorithm is adopted, and the attenuation compensation function f (x) obtained by calibration is subjected to numerical calculation:
R(l)＝RAT(l)×10-f(x)，
the curve after attenuation compensation can be obtained. As shown in fig. 8, graphs (a) and (b) are temperature curves before and after the attenuation compensation.
Finally, data demodulation is carried out, and the data demodulation is used during demodulation
The temperature can be demodulated. The performance indexes of the invention are shown in table 3:
table 3 comparison of system performance indicators herein
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A Raman scattering light double-path demodulation method for optical fiber distributed temperature measurement is characterized by comprising the following steps:
s1, automatic calibration: utilizing an automatic peak-searching algorithm to automatically calibrate the optical fiber parameters and calculating an attenuation compensation function f (x);
s2, data denoising: collecting two-way spectrum signals of Raman Stokes light and anti-Stokes light in an optical fiber, and processing the two-way spectrum signals by adopting an accumulation denoising algorithm and a wavelet threshold denoising algorithm to obtain demodulation signals;
s3, data compensation: processing the demodulated signal by using the attenuation compensation function and a Linear interpolation algorithm to compensate light intensity attenuation and eliminate dispersion to obtain a compensation signal;
s4, data demodulation: demodulating the compensation signal according to the relationship between the light intensity and the temperature of the Raman Stokes light and the anti-Stokes light to obtain a temperature distribution function T, wherein the relationship between the light intensity and the temperature is
In the formula of Us(T) is the intensity of Raman Stokes light, Uas(T) is the intensity of the anti-Stokes light, KO is the photoelectric influence factor, Ks(L) is the light mutation loss coefficient of Raman Stokes light, Kas(L) is the light mutation loss coefficient of anti-Stokes light, KsCoefficient of dependence of scattering cross section for Raman Stokes light, KasCoefficient of dependence of the scattering cross section for anti-Stokes light, vsIs the Raman Stokes light frequency, vasFor anti-Stokes light frequencies,. phi.e. the incident light flux,. alpha.0Is the loss factor of incident light, alphasIs the loss factor of Raman Stokes light, alphaasIs the loss factor of anti-Stokes light, L is the length of the optical fiber, Rs(T) is the Boltzmann factor of Raman Stokes light, Ras(T) is the Boltzmann factor of the anti-Stokes light.
2. The two-way demodulation method according to claim 1, wherein in step S4, the temperature distribution function T is obtained by the following formula:
wherein, I (T) is light intensity ratio, and I (T) is Uas(T)/Us(T), h is planck constant; Δ v is the amount of frequency shift, K is the Boltzmann constant, T0To scale the temperature on the fiber loop, I (T)0) To scale the ratio of light intensity at the fiber loop.
3. The two-way demodulation method according to claim 1, wherein in step S4, boltzmann factors of the raman stokes light and boltzmann factors of the anti-stokes light
4. The dual-channel demodulation method of claim 1, wherein in step S1, the fiber parameters include the fiber length, and the fiber length is automatically calculated by using an automatic peak-finding algorithm to locate the positions of the original and the final fresnel scattering peaks.
5. The dual path demodulation method of claim 1 wherein in step S2, the wavelet threshold denoising algorithm comprises at least one of coif3 wavelet basis algorithm, max-min threshold algorithm, soft threshold algorithm, and six-layer decomposition algorithm.
6. The two-way demodulation method according to claim 1 or 5, wherein in step S2, the accumulation number of times of said accumulation denoising algorithm is greater than or equal to 15000 times, and said accumulation number of times is less than or equal to 17000 times.
7. A dual-path demodulation method as set forth in claim 1 wherein said fading compensation function is obtained by the formula:
wherein alpha iss(l) Attenuation coefficient, alpha, of distance from starting point l of Raman Stokes lightas(l) The attenuation coefficient is the distance l from the starting point of the anti-stokes light.
8. A two-way demodulation method according to claim 7 wherein the attenuation coefficient for the distance/, from the starting point, is obtained by the following equation:
wherein α (l) is an attenuation coefficient at a distance l from the starting point, pi (l) is a light intensity before attenuation at the distance l from the starting point, and po (l) is a light intensity after attenuation at the distance l from the starting point.
9. A dual-path demodulation method as set forth in claim 1 wherein said fading compensation function is obtained by the formula:
R(l)＝RAT(l)×10-f(x)
wherein R isAT(l) For the ratio of the two-way voltages before attenuation at a distance l from the starting point, i.e.
Uas' (l) is the anti-Stokes light intensity before attenuation, Us' (l) is the Stokes light intensity before attenuation; r (l) is the ratio of the two-way voltages after attenuation at a distance of l from the starting point, i.e.
Uas(l) For attenuated anti-Stokes light intensity, Us(l) Is the attenuated stokes light intensity.
10. The dual-path demodulation method of claim 1 wherein the attenuation compensation function is modified by a data fitting algorithm in step S3.
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