阅读说明：本技术 光纤分布式扰动传感系统扰动信号的定位方法和系统 (Method and system for positioning disturbance signal of optical fiber distributed disturbance sensing system ) 是由 张春熹 马福 马皓钰 王夏霄 刘海霞 宋镜明 于 2019-11-05 设计创作，主要内容包括：本发明公开了一种光纤分布式扰动传感系统扰动信号的定位方法,它包括以下步骤：S1、利用EMD的小波阈值降噪方法对背向瑞利散射光进行降噪处理获得降噪信号；S2、根据系统所采集数据的整体水平进行分段处理,确定不同距离范围段的报警阈值；S3、根据S1中获得的降噪信号和S2中设定的报警阈值,对扰动事件进行定位处理。使得系统不需在引入其他技术的基础上,实现较长的监测距离和较低的误报率。且本方法流程简单,易于实现,成本较低,适合于实际应用。(The invention discloses a method for positioning a disturbance signal of an optical fiber distributed disturbance sensing system, which comprises the following steps: s1, carrying out noise reduction processing on the back Rayleigh scattering light by using a wavelet threshold noise reduction method of EMD to obtain a noise reduction signal; s2, performing segmentation processing according to the overall level of the data acquired by the system, and determining alarm thresholds of different distance range sections; and S3, positioning the disturbance event according to the noise reduction signal obtained in S1 and the alarm threshold set in S2. Therefore, the system can realize longer monitoring distance and lower false alarm rate without introducing other technologies. The method has the advantages of simple process, easy realization and low cost, and is suitable for practical application.)

1. A method for positioning a disturbance signal of an optical fiber distributed disturbance sensing system is characterized by comprising the following steps:

s1, carrying out noise reduction processing on the back Rayleigh scattering light by using a wavelet threshold noise reduction method of EMD to obtain a noise reduction signal;

s2, performing segmentation processing according to the overall level of the data acquired by the system, and determining alarm threshold values of different distance range segments, namely realizing a segmentation threshold value method;

s3, positioning the disturbance event according to the noise reduction signal obtained in S1 and the alarm threshold set in S2: when data in the noise reduction signal exceeds an alarm threshold value, alarming, wherein the relation between the corresponding time t and the position l where the disturbance occurs is that the time t is ct/2n, wherein c is the light speed in vacuum, n is the refractive index of the optical fiber, and t is the acquisition time of the noise reduction signal; and then, calculating a corresponding disturbance position l to realize the positioning of the disturbance event.

2. The method according to claim 1, wherein the step S1 specifically includes the following steps:

s1-1, decomposing the signal into a finite number of intrinsic mode functions IMF components from high frequency to low frequency by EMD;

s1-2, applying wavelet threshold denoising only on the high-frequency IMF component for denoising, and keeping the low-frequency IMF component unchanged;

and S1-3, performing signal reconstruction on the high-frequency IMF component subjected to noise reduction, the low-frequency IMF component without noise reduction and the residual term to obtain a signal subjected to noise reduction.

3. The method for positioning the disturbing signal of the optical fiber distributed disturbance sensing system according to claim 2, wherein in S1-2, the noise reduction processing of the high-frequency IMF component comprises the following steps:

s1-2-1, sequencing the IMF components of the high-frequency to low-frequency inherent mode functions obtained in the S1-1 in sequence;

s1-2-2, determining a high-low frequency threshold value ks;

s1-2-3, performing wavelet threshold denoising processing on the high-frequency IMF component, firstly, obtaining a wavelet coefficient through wavelet decomposition, obtaining a high-frequency coefficient and a low-frequency coefficient according to a set wavelet threshold, and considering the wavelet coefficient as signal information when the wavelet coefficient is greater than the threshold; when the wavelet coefficient is smaller than the threshold value, the wavelet coefficient is considered to be mainly noise; then, threshold quantization is carried out on the high-frequency coefficient according to a threshold function, and finally wavelet reconstruction is carried out to obtain a signal subjected to wavelet threshold denoising processing; while the low frequency IMF component remains unchanged.

4. The method for positioning the disturbing signal of the optical fiber distributed disturbance sensing system according to claim 3, wherein in S1-2-2, the high and low frequency thresholds ks are obtained by:

in the formula (I), the compound is shown in the specification,

5. A positioning system for disturbance signals of an optical fiber distributed disturbance sensing system comprises a light source, a pulse light modulator, an erbium-doped optical fiber amplifier, a circulator, sensing optical fibers, a photoelectric detector and a data acquisition and processing unit, wherein the light source is connected with the erbium-doped optical fiber amplifier through the modulator, the erbium-doped optical fiber amplifier is connected with one end of the circulator, the second end of the circulator is connected with the sensing optical fibers, the third end of the circulator is connected with the data acquisition and processing unit through the photoelectric detector, and disturbance acts on the sensing optical fibers, and the positioning system is characterized in that the data acquisition and processing unit executes the positioning method for the disturbance signals of the optical fiber distributed disturbance sensing system according to any one of claims 1 to 4.

Technical Field

The invention belongs to the field of optical fiber distributed disturbance sensors, and particularly relates to a phi-OTDR optical fiber distributed disturbance sensing system signal processing method based on an EMD wavelet threshold denoising method and a segmented threshold method.

Background

The optical fiber distributed optical fiber sensing system based on the phase-sensitive optical time domain reflectometer (phi-OTDR) adopts pulse light with narrow line width and low frequency drift, detects backward Rayleigh scattered light generated in the optical fiber within a fixed pulse width through a photoelectric detector, and achieves monitoring and positioning of a disturbance position through subsequent data processing.

The sensing distance of the traditional phi-OTDR optical fiber distributed disturbance sensing system can only reach about 26km generally, and the influence of nonlinear effect and the like limits the sensing distance to have the problem of low false alarm rate of remote monitoring. In order to increase the sensing distance, the existing scheme not only increases the system cost but also increases the complexity of the system by introducing a novel amplification technology and the like. In order to reduce the false alarm rate, an Empirical Mode Decomposition (EMD) method and a wavelet threshold denoising method are generally adopted, and the EMD denoising method discards part of high-frequency components from the decomposed components, so that the method discards part of useful information of a high-frequency band while removing noise signals, thereby possibly causing serious distortion of useful signals; the wavelet threshold denoising method has the same defects, and discards useful signals while discarding noise signals, so how to effectively remove the noise signals and reduce distortion of real signals is more important for monitoring at longer distance and reducing false alarm rate.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a phi-OTDR optical fiber distributed disturbance sensing system signal processing method based on an EMD wavelet threshold denoising method and a segmented threshold method aiming at the defects of the prior art, which can realize the monitoring of a long distance of 50km and effectively remove noise signals.

The technical scheme is as follows:

the invention firstly discloses a method for positioning a disturbance signal of an optical fiber distributed disturbance sensing system, which is characterized by comprising the following steps:

s1, carrying out noise reduction processing on the back Rayleigh scattering light by using a wavelet threshold noise reduction method of EMD to obtain a noise reduction signal;

s2, performing segmentation processing according to the overall level of the data acquired by the system, and determining alarm threshold values of different distance range segments, namely realizing a segmentation threshold value method;

s3, positioning the disturbance event according to the noise reduction signal obtained in S1 and the alarm threshold set in S2: when data in the noise reduction signal exceeds an alarm threshold value, alarming, wherein the relation between the corresponding time t and the position l where the disturbance occurs is that the time t is ct/2n, wherein c is the light speed in vacuum, n is the refractive index of the optical fiber, and t is the acquisition time of the noise reduction signal; and then, calculating a corresponding disturbance position l to realize the positioning of the disturbance event.

Preferably, the S1 specifically includes the following steps:

s1-1, decomposing the signal into a finite number of intrinsic mode functions IMF components from high frequency to low frequency by EMD;

s1-2, applying wavelet threshold denoising to the high-frequency IMF component only to perform denoising, and keeping the low-frequency IMF component unchanged;

and S1-3, performing signal reconstruction on the high-frequency IMF component subjected to noise reduction, the low-frequency IMF component without noise reduction and the residual term to obtain a signal subjected to noise reduction.

Preferably, in S1-2, the noise reduction processing of the high-frequency IMF component includes the following steps:

s1-2-1, sequencing the IMF components of the high-frequency to low-frequency inherent mode functions obtained in the S1-1 in sequence;

s1-2-2, determining a high-low frequency threshold value ks;

s1-2-3, performing wavelet threshold denoising processing on the high-frequency IMF component, firstly, obtaining a wavelet coefficient through wavelet decomposition, obtaining a high-frequency coefficient and a low-frequency coefficient according to a set wavelet threshold, and considering the wavelet coefficient as signal information when the wavelet coefficient is greater than the threshold; when the wavelet coefficient is smaller than the threshold value, the wavelet coefficient is considered to be mainly noise; then, threshold quantization is carried out on the high-frequency coefficient according to a threshold function, and finally wavelet reconstruction is carried out to obtain a signal subjected to wavelet threshold denoising processing; while the low frequency IMF component remains unchanged.

Preferably, in S1-2-2, the high and low frequency thresholds ks are obtained by the following formula:

in the formula (I), the compound is shown in the specification,

n is the length of the signal x (t), C_k(t) is the k-th IMF component of signal x (t) decomposed by EMD.

The invention also discloses a positioning system of the disturbance signals of the optical fiber distributed disturbance sensing system, which comprises a light source, a pulse light modulator, an erbium-doped optical fiber amplifier, a circulator, a sensing optical fiber, a photoelectric detector and a data acquisition and processing unit, wherein the light source is connected with the erbium-doped optical fiber amplifier through the modulator, the erbium-doped optical fiber amplifier is connected with one end of the circulator, the second end of the circulator is connected with the sensing optical fiber, the third end of the circulator is connected with the data acquisition and processing unit through the photoelectric detector, a disturbance event acts on the sensing optical fiber, and the data acquisition and processing unit executes the positioning method of the disturbance signals of the optical fiber distributed disturbance sensing system disclosed by the invention.

The invention has the advantages of

The invention provides a phi-OTDR optical fiber distributed disturbance sensing system signal processing method based on an EMD wavelet threshold denoising method and a segmented threshold method, so that the system does not need to introduce other technologies and realizes longer monitoring distance and lower false alarm rate.

The invention provides a phi-OTDR optical fiber distributed disturbance sensing system signal processing method based on an EMD wavelet threshold denoising method and a segmented threshold method, which has the advantages of simple process, easy realization and lower cost and is suitable for practical application.

Drawings

Fig. 1 is a schematic structural diagram of a distributed perturbation sensing system of a phi-OTDR fiber according to the present invention.

Fig. 2 is a flowchart of the wavelet threshold denoising method based on EMD according to the present invention.

Detailed Description

The invention is further illustrated by the following examples, without limiting the scope of the invention:

fig. 1 is a schematic diagram of a distributed perturbation sensing system of a Φ -OTDR fiber applied in the present invention, which is also a conventional structure, and includes a light source, a pulse light modulator, an erbium-doped fiber amplifier, a circulator, a sensing fiber, a photodetector, and a data acquisition and processing unit. On the basis of the system, other optical amplification technologies and the like are not introduced to increase the structural complexity and the cost of the system, long-distance monitoring and good noise reduction effect are realized only by changing the subsequent signal processing and noise reduction method, and the false alarm rate is reduced.

The data acquisition and processing unit of the invention is used for executing the following steps:

s1, carrying out noise reduction processing on the back Rayleigh scattering light by using a wavelet threshold noise reduction method of EMD to obtain a noise reduction signal;

s2, performing segmentation processing according to the overall level of the data acquired by the system, and determining alarm thresholds of different distance range segments (determined according to specific experimental data, different systems built in different laboratories and different alarm thresholds; which can be regarded as empirical values, manually set by technicians according to specific working conditions and are known by technicians in the field), namely, implementing a segmentation threshold method;

s3, positioning the disturbance event according to the noise reduction signal obtained in S1 and the alarm threshold set in S2: when data in the noise reduction signal exceeds an alarm threshold value, alarming, wherein the relation between the corresponding time t and the position l where the disturbance occurs is that the time t is ct/2n, wherein c is the light speed in vacuum, n is the refractive index of the optical fiber, and t is the acquisition time of the noise reduction signal; and then, calculating a corresponding disturbance position l to realize the positioning of the disturbance event.

Fig. 2 shows a flowchart of the EMD-based wavelet threshold denoising method in step S1 according to the present invention:

s1-1, EMD decomposition is carried out on the original signal x (t) to obtain a finite number of IMF components C_k(t)；

S1-2, determining a value of ks by using a continuous mean square error criterion;

s1-3, selecting a threshold value and a threshold function of wavelet threshold denoising, and calculating an IMF component C of a high frequency band₁(t)～C_ks(t) threshold value, then for C₁(t)～C_ks(t) performing wavelet threshold denoising treatment, and performing wavelet reconstruction to obtain denoised C₁'(t)～C'_ks(t) a signal;

the signal is reconstructed and the signal is reconstructed,

in the formula, the first term is the high-frequency IMF after noise reduction, the second term is the low-frequency IMF, and the third term is a residual term, and the three terms are added to obtain a signal after noise reduction.

More preferably, in step S1-2, the high and low frequency thresholds ks are obtained by the following formula:

in the formula (I), the compound is shown in the specification,

n is the length of the signal x (t), C_k(t) is the k-th IMF component of the signal x (t) decomposed by EMD, and n is the sum of the high and low frequency IMFs.

The invention provides a phi-OTDR optical fiber distributed disturbance sensing system signal processing and positioning method based on an EMD wavelet threshold denoising method and a segmented threshold method, which has practical application significance for further improving the sensing distance of the system and reducing the false alarm rate of the system.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.