CN111780857B - Multi-point disturbance positioning detection method of P-OTDR system based on harmonic accumulation - Google Patents
Multi-point disturbance positioning detection method of P-OTDR system based on harmonic accumulation Download PDFInfo
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Abstract
The invention discloses a harmonic accumulation-based multipoint disturbance positioning detection method for a P-OTDR system, which comprises the following steps: continuously collecting multiple periods of back Rayleigh scattering signals, and performing fast Fourier transform on the back scattering signals at each position to obtain the change condition of the power spectrum of the back scattering signals along the position of the optical fiber; finding out a first frequency component with amplitude which obviously jumps from a certain optical fiber position from the frequency spectrum, and regarding the first frequency component as a basic frequency; extracting a basic frequency smaller than a specific frequency and a distribution curve of a harmonic frequency of the basic frequency along the position of the optical fiber; and accumulating the extracted curves to be used as a final positioning curve, wherein the position of the amplitude jump in the curve is the final disturbance position. The invention does not need to improve or cooperatively operate the hardware system of the traditional P-OTDR system, and has no harsh application condition, thereby not only realizing the distinguishing and positioning of the multi-point same-frequency disturbance, but also avoiding the report missing problem caused by the traditional positioning scheme when the multi-point different-frequency disturbance is positioned.
Description
Technical Field
The invention relates to the technical field of perimeter security and protection, in particular to a multipoint disturbance positioning detection method.
Background
Since the last 70 s, optical sensing technology has been greatly advanced with the practical use of optical fibers and the development of optical communication technology. Light propagates through an optical fiber and is accompanied by a series of physical phenomena such as interference, refraction, and scattering. When the external environment of the optical fiber changes, the characteristic parameters of the optical fiber, such as the polarization state, the phase, the amplitude, the frequency and the like, of the light beam also change correspondingly. The optical fiber sensor utilizes the property, takes the optical fiber as a sensing element, and finds the relationship between the external environment and the changes by monitoring the changes of information such as polarization amplitude, phase, frequency and the like when light is transmitted in the optical fiber, thereby realizing long-distance sensing distributed along the optical fiber.
Based on the difference of scattering mechanisms, the polarized optical time domain reflectometry (P-OTDR) technology can be further classified into P-OTDR technology based on backward rayleigh scattering, P-OTDR technology based on spontaneous and stimulated brillouin scattering, P-OTDR technology based on spontaneous and stimulated raman scattering, and the like, while the P-OTDR technology based on backward rayleigh scattering is widely concerned and applied in the distributed optical fiber vibration sensing field by virtue of its higher signal-to-noise ratio advantage, and the P-OTDR technology is one of the representative technologies of P-OTDR technology based on backward rayleigh scattering.
The P-OTDR technology uses the polarization state of optical wave to realize sensing based on backward Rayleigh scattering signals, and the sensing signals are formed by backward Rayleigh scattering light original paths along the line when the detection pulse is transmitted by the optical fiber. When there is a disturbance at a certain position, the polarization state of the rayleigh scattered signal after the position is affected by the disturbance, thereby causing a polarization superposition effect. The effect can cause the superposition crosstalk of multiple disturbance events, so that the P-OTDR system cannot accurately distinguish the multiple disturbance events.
The multi-point disturbance positioning algorithm of the P-OTDR system at the present stage is mainly based on a spectrum analysis method, and has the problems of complex implementation process, harsh application conditions and the like. The patent "CN 201610032900.3" uses the phase change of the rayleigh scattering signal spectrum to distinguish the multi-point co-frequency disturbance, but only two points can perform co-frequency disturbance, so the application condition is limited by the number of disturbance points. Patent "CN 201810389171.6" utilizes polarization controller constantly to adjust the initial polarization state of input light wave, then utilizes the distribution curve of the frequency along the optic fibre position of rayleigh scattering signal when fast Fourier transform obtains different input light wave polarization states, last with the spectrum stack along the optic fibre that obtains when different input polarization states together fix a position, this kind of scheme does not have the restriction of disturbance point quantity, nevertheless because need constantly change the polarization state of input light wave and carry out a lot of collection, therefore the corresponding real-time of system can receive the restriction, and the implementation process is comparatively complicated. Therefore, a simple, reliable and easy-to-implement P-OTDR multi-point disturbance monitoring scheme is urgently needed to be proposed.
Disclosure of Invention
The invention aims to provide a multipoint disturbance positioning detection method of a P-OTDR system based on harmonic accumulation, which does not need to improve or cooperatively operate a hardware system of the traditional P-OTDR system and has no harsh application conditions, not only can realize the distinguishing and positioning of multipoint same-frequency disturbance, but also can avoid the problem of missed report caused by the traditional positioning scheme during the positioning of multipoint different-frequency disturbance.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a multipoint disturbance positioning detection method of a P-OTDR system based on harmonic accumulation comprises the following steps:
(1) continuously acquiring m backward Rayleigh scattering curves with n points by using a data acquisition card, and reconstructing the m curves into an m x n matrix L, wherein each row of the matrix L represents the variation condition of Rayleigh scattering light power along with the position of an optical fiber;
(2) performing fast Fourier transform processing of k points on each column of data in the matrix L to obtain a power spectrum of the Rayleigh scattering signal at each position; then reconstructing the result of the fast Fourier transform at each position into a k-n matrix Fou, thereby obtaining the distribution condition of each component of the power spectrum along the position of the optical fiber;
(3) searching each line of data of the matrix Fou according to the sequence of the frequencies from small to large by using a threshold method, namely searching the distribution curve of each frequency component along the position of the optical fiber, searching for the frequency component of which the first amplitude has obvious mutation from a certain position, and recording the frequency at the moment as F0，F0The frequency of the first disturbance point is obtained;
(4) extracting the frequency F-Fmax F from the matrix Fou0Wherein Fmax is the highest order of harmonic frequency;
(5) and accumulating and summing all the extracted curves, wherein the curve obtained after summation is a final positioning curve, and the position where each amplitude value in the positioning curve is subjected to mutation is the external disturbance position.
Further, each curve is normalized by 0-1 before summing the distribution curves of the eligible frequency components along the fiber position.
Further, according to the characteristic that the signal-to-noise ratio of the positioning signal increases first and then decreases along with the increase of Fmax, the size of the parameter Fmax is adjusted to dynamically adjust the signal-to-noise ratio of the positioning signal at each disturbance position.
Further, after obtaining the distribution curves of the frequency components along the optical fiber, the distribution curves of several frequency components are selected, and then the summation of the distribution curves is used as the final positioning curve.
Compared with the prior art, the scheme of the invention has the beneficial effects that:
(1) the implementation of the scheme of the invention does not need to improve and cooperate with a hardware system, the implementation is simple, and the response speed is high;
(2) according to the scheme of the invention, the distribution curve of the specific frequency component is selected for positioning, so that the introduction of noise frequency components is reduced, and the signal-to-noise ratio of the positioning result is higher;
(3) the scheme of the invention realizes the differentiation of multi-point disturbance by utilizing the characteristic that the power spectrum of each position contains the linear superposition component of the disturbance frequency before the position, does not need to implement different positioning schemes aiming at different disturbance conditions, does not have the limitation of the differentiation number of disturbance points, and has higher practicability.
(4) The scheme of the invention realizes the differentiation of the multi-point disturbance by utilizing the characteristic that the power spectrum of each position contains the linear superposition component of the disturbance frequency before the position, and can avoid the problem of report missing caused by the traditional positioning scheme when the disturbance positioning of different frequencies of multiple points is carried out.
Drawings
FIG. 1 is a schematic diagram of a P-OTDR system;
FIG. 2 is a flow chart of a method of the present invention;
FIG. 3 is a graph of the distribution of the frequency spectrum of a back Rayleigh scattered signal along an optical fiber during co-frequency disturbance;
FIG. 4 is a graph of the distribution of 10Hz, 30Hz, and 60Hz components along the fiber during co-frequency perturbation;
FIG. 5 is a plot of the location of the inventive arrangements for co-frequency disturbances;
FIG. 6 is a graph of the distribution of the frequency spectrum of a back Rayleigh scattered signal along an optical fiber during different frequency disturbances;
FIG. 7 is a plot of the location of a conventional spectral location method for perturbations at different frequencies;
fig. 8 is a plot of the location of the inventive arrangement for perturbations at different frequencies.
Detailed Description
The technical solution and the advantages of the present invention will be described in detail with reference to the accompanying drawings.
By adopting the P-OTDR system shown in FIG. 1, a laser emits 1000 groups of inspection optical pulses in a period of 1ms, and a single-mode fiber of 2km is used as a sensor to sense external vibration. The whole scheme is shown in figure 2. Respectively applying 3 same-frequency disturbing signals of 10Hz at 1km, 1.3km and 1.6km, continuously sampling a backscattering curve by a data acquisition card at the rate of 250MHz, and then reconstructing 1000 collected curves into a matrix L by a PC (personal computer), wherein each row of the matrix L represents the change condition of Rayleigh scattered light power along with the position of an optical fiber.
And performing fast Fourier transform processing of 1000 points on each column of data in the matrix L, thereby obtaining a power spectrum of the Rayleigh scattering signal at each position. The results of the fast fourier transform at each location are then reconstructed into a matrix Fou, resulting in the distribution of each component of the power spectrum along the fiber location, as shown in fig. 3. As can be seen from the graph, the 10Hz, 20Hz … 70Hz, etc. components show distinct amplitude jumps at different disturbance positions.
Searching each line of data of Fou by using a threshold method according to the sequence of frequencies from small to large, namely searching the distribution curve of each frequency component along the position of the optical fiber, searching for the frequency component with the first amplitude having obvious mutation from a certain position, and recording the frequency at this moment as F0The frequency at this time is the frequency of the first disturbance point. As can be seen from FIG. 3, the frequency of the first disturbance point is F in this embodiment0＝10Hz。
Extracting a frequency F (F ═ Fmax × (F)) from the Fou0Fmax is the highest order of harmonic frequencies) along the fiber position. The extracted frequency component curve contains different external disturbance position information, fig. 4 shows the distribution curves of 10Hz, 30Hz and 60Hz components along the optical fiber, and it can be seen from the figure that the three curves can just distinguish three disturbance points respectively. Fmax in this example is 10.
All the extraction curves are summed up, and the resulting curve after summation is the final positioning curve, as shown in fig. 5. As can be seen from the figure, the amplitudes of the positioning curves obtained by direct accumulation have jump at positions of 1km, 1.3km and 1.6km, so that three same-frequency disturbances can be effectively distinguished. Preferably, when the qualified frequency curves are normalized and then accumulated, the signal-to-noise ratio of the positioning curve in fig. 5 is significantly further improved.
Next, different frequency perturbations of 10Hz, 15Hz and 20Hz were applied to 1km, 1.3km and 1.6km, respectively, and then the processing steps of the above scheme were repeated. Fig. 6 shows the distribution of each component of the power spectrum along the fiber position under different frequency disturbances, and it can be seen that the frequency components of 5Hz, 10Hz, 15Hz, 20Hz, 25Hz, 30Hz … …, etc. exhibit distinct amplitude jumps at different disturbance positions. Fig. 7 shows three positioning curves obtained by directly using components of 10Hz, 15Hz, and 20Hz according to the conventional spectrum positioning method, and it can be seen from the diagram that the 10Hz and 15Hz curves can effectively position the first disturbance and the second disturbance, but the 20Hz curve cannot position the third disturbance point, and obvious false alarm occurs. Fig. 8 shows the positioning curve obtained by the solution of the present invention, and it can be seen from the diagram that the curves obtained by direct accumulation or normalized accumulation can perform positioning distinction on three different frequency disturbances, but the signal-to-noise ratio of the positioning curve of the preferred solution is significantly higher.
The above embodiments are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modifications made on the basis of the technical scheme according to the technical idea of the present invention fall within the protection scope of the present invention.
Claims (4)
1. A multipoint disturbance positioning detection method of a P-OTDR system based on harmonic accumulation is characterized by comprising the following steps:
(1) continuously acquiring m backward Rayleigh scattering curves with n points by using a data acquisition card, and reconstructing the m curves into an m x n matrix L, wherein each row of the matrix L represents the variation condition of Rayleigh scattering light power along with the position of an optical fiber;
(2) performing fast Fourier transform processing of k points on each column of data in the matrix L to obtain a power spectrum of the Rayleigh scattering signal at each position; then reconstructing the result of the fast Fourier transform at each position into a k-n matrix Fou, thereby obtaining the distribution condition of each component of the power spectrum along the position of the optical fiber;
(3) searching each line of data of the matrix Fou according to the sequence of the frequencies from small to large by using a threshold method, namely searching the distribution curve of each frequency component along the position of the optical fiber, searching for the frequency component of which the first amplitude has obvious mutation from a certain position, and recording the frequency at the moment as F0，F0The frequency of the first disturbance point is obtained;
(4) extracting a fundamental frequency F from the matrix Fou0A curve of distribution of all harmonic frequency components along the fiber position;
(5) and accumulating and summing all the extracted curves, wherein the curve obtained after summation is a final positioning curve, and the position where each amplitude value in the positioning curve is subjected to mutation is the external disturbance position.
2. The method of claim 1, wherein the method comprises: each curve is normalized by 0-1 before summing the distribution curves of the eligible frequency components along the fiber position.
3. The method of claim 1, wherein the method comprises: and according to the characteristic that the signal-to-noise ratio of the positioning signal is increased and then decreased along with the increase of Fmax, adjusting the size of the parameter Fmax to dynamically adjust the signal-to-noise ratio of the positioning signal at each disturbance position, wherein Fmax represents the highest order of the harmonic frequency.
4. The method of claim 1, wherein the method comprises: after obtaining the distribution curves of the frequency components along the optical fiber, the distribution curves of several frequency components are selected, and then the summation of the distribution curves is used as the final positioning curve.
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