CN109444895B - Vibration information positioning method for eliminating interference fading of distributed vibration sensor - Google Patents
Vibration information positioning method for eliminating interference fading of distributed vibration sensor Download PDFInfo
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Abstract
The invention discloses a vibration information positioning method for eliminating interference fading of a distributed vibration sensor, which eliminates the interference fading problem from an algorithm, wherein the algorithm eliminates the interference fading problem by the correlation positioning of signals and a relative value method, and the specific flow is as follows: the acquisition card receives a series of original Rayleigh scattering electric signals, a plurality of scattering curves carry out correlation calculation, the plurality of scattering curves are averaged in a time domain, correlation results are compared with the averaged results in the time domain, and finally the event position is determined. The experimental result shows that the positioning speed can be improved, the event point can be found more easily, and the influence of interference fading is eliminated.
Description
Technical Field
The invention relates to the technical field of distributed optical fiber Rayleigh scattering vibration sensing systems, in particular to a vibration sensor event positioning method and related data processing.
Background
The distributed optical fiber vibration sensor is an optical fiber sensing system which is developed in recent decades and is used for measuring spatial vibration information distribution in real time. After decades of development, the technology is mature. The phi-OTDR distributed optical fiber vibration sensing system utilizes Rayleigh scattering signals, and the disturbance position can be calculated according to the OTDR principle by the following formula:
wherein, Δ t is the time from sending the pulse to receiving the point light signal; c, the speed of light; n is the refractive index of the fiber core.
The phi-OTDR type optical fiber vibration sensing system has the advantages of compact structure, simple demodulation algorithm, high positioning accuracy, high signal-to-noise ratio and the like. However, the problem of interference fading exists, and according to the phi-OTDR principle, a reflected scattering curve is a periodic sawtooth waveform, which means that some parts are at wave crests and have high signal strength, and some parts are at wave troughs and have weak signals. For example, if the variation is 3dB, the variation of the peak of the strong signal is very large, and the variation of the trough of the weak signal is very small, which may possibly ignore the vibration signal of the trough.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the existing distributed vibration sensor vibration information positioning method, the invention provides a correlation demodulation algorithm, aiming at positioning events quickly and well and eliminating the interference fading problem.
The technical scheme adopted by the invention for solving the technical problem is as follows:
the invention provides a vibration information positioning method for eliminating interference fading of a distributed vibration sensor, which comprises the following steps:
s1, a two-dimensional matrix S is formed by a series of original Rayleigh scattering curve signals received by an acquisition card:
wherein m is the number of pulses, n is the number of sampling points, a matrix row vector represents the size of a Rayleigh scattering signal of one pulse along the distance of the optical fiber, and a matrix column vector represents the change of a certain point on the optical fiber along with time;
s2, performing correlation operation on the two-dimensional matrix S to obtain a matrix R:
wherein
Rij＝E[S(i:a+i,j)*S(i+b:a+i+b,j)]-E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]
a is the number of pulses taken in the correlation algorithm, b is the correlation sampling interval,
floor is rounding down; s (i: a + i, j) represents that the jth column in the matrix S is taken out, the data from the ith row to the i + a row are used as a vector, and E () represents the average value of the vector quantity;
s3, averaging a series of original Rayleigh scattering curves in a time domain to obtain a matrix T:
wherein
Tij＝sqrt{E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]}
Sqrt () represents the root number;
s4, calculating a matrix P:
wherein
Pij＝Rij/Tij；
And S5, analyzing the correlation curve of the matrix P, searching for a peak, and positioning an event point at the peak.
The invention also provides a vibration information positioning processor for eliminating interference fading of the distributed vibration sensor, which comprises:
the two-dimensional matrix module is used for forming a two-dimensional matrix S by a series of original Rayleigh scattering electric signals received by the acquisition card:
wherein m is the number of pulses, n is the number of sampling points, a matrix row vector represents the size of a Rayleigh scattering signal of one pulse along the distance of the optical fiber, and a matrix column vector represents the change of a certain point on the optical fiber along with time;
and the correlation operation module is used for performing correlation operation on the two-dimensional matrix S to obtain a matrix R:
wherein
Rij＝E[S(i:a+i,j)*S(i+b:a+i+b,j)]-E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]
a is the number of pulses taken in the correlation algorithm, b is the correlation sampling interval,
floor is rounding down; s (i: a + i, j) represents that the data of the jth column from the ith row to the i + a row in the matrix S are taken out to be used as a vector, and E () represents the average value of the vector quantity;
a time domain averaging module, configured to average multiple scattering curves in a time domain to obtain a matrix T:
wherein
Tij＝sqrt{E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]}
Sqrt () represents the root opening number;
a ratio module for calculating a matrix P:
wherein
Pij＝Rij/Tij；
And the event point acquisition module is used for analyzing the correlation curve of the matrix P, searching a peak and positioning the peak as an event point.
The invention also provides a
The optical fiber vibration sensing system comprises a laser, a pulse modulator, an optical amplifier, a circulator, a photoelectric detector, a collecting card and a processor which are connected in sequence, wherein one port of the circulator is also connected with an optical fiber to be detected;
laser emitted by a laser is modulated by a pulse modulator, modulated light is amplified by an optical amplifier, amplified signal light enters an optical fiber to be detected through a circulator, rayleigh scattered light reflected by the optical fiber to be detected is subjected to photoelectric conversion through a photoelectric detector, and a Rayleigh scattered electric signal is collected by a collection card; processing the Rayleigh scattering electric signal through a processor, eliminating interference fading and positioning an event point; the processor is the vibration information positioning processor in the technical scheme.
According to the technical scheme, the laser is a narrow linewidth laser, the output power is 13mw, and the wavelength is 1550.12 nm.
According to the technical scheme, the pulse modulator is an optical fiber coupling acousto-optic modulator.
In connection with the above technical solution, the amplifier is an EDFA erbium-doped fiber amplifier.
According to the technical scheme, the detector is a PD photoelectric converter.
And connecting the technical scheme, wherein the optical fiber to be detected is a single-mode optical fiber.
The present invention also provides a computer readable storage medium having a computer program executable by a processor, the computer program executing the steps of the vibration information positioning method for eliminating interference fading of the distributed vibration sensor according to the above technical solution.
The invention has the following beneficial effects: the invention provides an event positioning method for eliminating interference fading, which averagely eliminates random noise on a time domain through a Rayleigh scattering curve; through the calculation of the relative quantity, the influence of a sawtooth interference waveform on the external excitation change is avoided, the influence of interference fading is eliminated, the positioning speed can be improved, and an event point can be found more easily. The method of the invention can also be used in other distributed sensors involving the principle of interference. For example, an Optical Frequency Domain Reflectometer (OFDR) and a distributed optical fiber sensing technology based on the Brillouin scattering principle can also avoid the interference fading problem by using the method.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic representation of an embodiment of the present invention
A distributed optical fiber vibration sensing system;
FIG. 2 is a flow chart of an event locating method for processing data in the spatial domain according to an embodiment of the present invention;
FIG. 3 is an event locator curve according to an embodiment of the present invention, the left graph is absolute values, and the right graph is processed relative values.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
According to a one-dimensional impulse response model:
assuming that at time t =0, a coherent light pulse is incident into the fiber with a pulse width W and a frequency v, the light wave e (t) that is backscattered rayleigh at the incident end of the fiber can be represented as
Wherein a is i And τ i Respectively, the amplitude and round trip time of the ith scattered wave, N the total number of scattering points, alpha the attenuation constant of the optical fiber, c the speed of light in vacuum, N f Representing the refractive index of the fiber. Wherein
Round trip time of ith scattering point and distance z from incident section of fiber i Can be expressed as tau i ＝2n f z i And c, the ratio of the total weight to the total weight. The backscattered light power can therefore be expressed as follows
p(t)＝|e(t)| 2 ＝p 1 (t)+p 2 (t)
Wherein phi ij ＝2πv(τ i -τ j ) And represents the phase difference between the ith and jth scattering points. In the above formula p 1 (t) represents the sum of the respective scattered powers of the N scattering points, this term not varying with the temperature or strain of the fiber, nor with the laser frequency. And p is 2 (t) shows the result of interference between different scattering points, so that the rayleigh scattered echoes exhibit an interference fading waveform. At p 2 (t) there is a term cos (. Phi.) in the expression ij ) Wherein the phase difference between adjacent scattering points is ij Proportional to the frequency v, refractive index n of the laser f Distance s between scattering points ij ＝z i -z j The relationship can be expressed as phi ij ＝4πvn f s ij And c, the ratio of the total weight to the total weight. Thus the interference term p 2 (t) is v, n f And s ij A function of n, and n f And s ij Depending on the change in temperature and strain of the fiber.
Of system interest is p 2 (t) from p 2 It can be seen in (t) that the phase time domain signal has a correlation characteristic because of the delay of the light intensity signal due to the phase.
As shown in FIG. 1, is
The system comprises a laser, a pulse modulator, an optical amplifier, a circulator, a photoelectric detector, a collection card and a processor which are connected in sequence, wherein one port of the circulator is also connected with an optical fiber to be detected.
Laser emitted by a laser is modulated by a pulse modulator, modulated light is amplified by an optical amplifier, amplified signal light enters an optical fiber to be detected through a circulator, rayleigh scattered light reflected by the optical fiber to be detected is subjected to photoelectric conversion through a photoelectric detector, and a Rayleigh scattered electric signal is collected by a collection card; and processing the Rayleigh scattering electric signal through a processor to eliminate interference fading and locate an event point.
The processor mainly comprises:
the two-dimensional matrix module is used for forming a two-dimensional matrix S by a series of original Rayleigh scattering electric signals received by the acquisition card:
wherein m is the number of pulses, n is the number of sampling points, a matrix row vector represents the size of a Rayleigh scattering signal of one pulse along the distance of the optical fiber, and a matrix column vector represents the change of a certain point on the optical fiber along with time;
and the correlation operation module is used for performing correlation operation on the two-dimensional matrix S to obtain a matrix R, and the purpose of the correlation operation is to extract a disturbance signal:
wherein
Rij＝E[S(i:a+i,j)*S(i+b:a+i+b,j)]-E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]
a is the number of pulses taken in the correlation algorithm, b is the correlation sampling interval,
floor is rounding down; s (i: a + i, j) represents that the data of the jth column from the ith row to the i + a row in the matrix S are taken out to be used as a vector, and E () represents the average value of the vector quantity;
the time domain averaging module is used for averaging a series of Rayleigh scattering curves in a time domain, and the averaging aims at eliminating random noise to obtain a matrix T:
wherein
Tij＝sqrt{E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]}
Sqrt () represents the root number;
a ratio module for calculating a matrix P:
wherein
Pij = Rij/Tij, the effect of interference fading can be eliminated by phase comparison;
and the event point acquisition module is used for analyzing the correlation curve of the matrix P, searching a peak and positioning the peak as an event point.
In the preferred embodiment of the invention, the laser is a narrow linewidth laser with the output power of 13mw and the wavelength of 1550.12nm, the pulse modulator is an ancient (Gooch & Housego, translation amount of 200 MHz) optical fiber coupling acousto-optic modulator, the amplifier is an EDFA erbium-doped fiber amplifier, the detector is a PD photoelectric converter, the optical fiber for testing is a single-mode optical fiber, and the length is 8Km. The repetition frequency of the adopted pulse light is 10kHz, the pulse width is 100ns, 100 Rayleigh scattering curves are collected at the sampling rate of 100M/s, and each curve has 10000 points.
As shown in fig. 2, the method for positioning vibration information by a processor to eliminate interference fading for a distributed vibration sensor specifically includes:
s1, forming a two-dimensional matrix by 100 original Rayleigh scattering electric signals collected by the collection clamping.
m =100 is the number of pulses, n =10000 is the number of points (determined by the sampling rate of the acquisition card and the length of the optical fiber), a matrix row vector represents the size of the distance of a rayleigh scattering signal of one pulse along the optical fiber, and a matrix column vector represents the change of a certain point on the optical fiber along with time;
s2, carrying out correlation operation on a series of Rayleigh scattering signals to obtain a matrix R
Wherein
Rij＝E[S(i:a+i,j)*S(i+b:a+i+b,j)]-E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]
a is the number of pulses taken in the correlation algorithm, 50 in this embodiment, and b is the correlation sampling interval, 20 in this embodiment.
floor is rounded down and is 3 in this example. S (i: a + i, j) means that the data of the jth column, ith row to i +50 th row in the matrix S is taken out as a vector. E () represents an average value of the vector quantity;
the left graph in fig. 3 is the curve processed in step S2, and it can be seen from the graph that the event point can be found by the correlation operation at 5.04km, but the signal of the non-event point is uneven and very uneven.
S3, averaging a plurality of scattering curves in time domain
Wherein
Tij＝sqrt{E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]}
sqrt represents the root number;
s4, comparing the correlation result with the time domain average result
Wherein
Pij＝Rij/Tij；
And S5, analyzing a correlation curve of the relative quantity, and positioning the peak as an event point.
The right graph in fig. 3 is the curve processed in step S4, and it can be seen from the graph that after the processing, the event point can be found to be 5.04km, and simultaneously the signal ratio is improved by 3dB (compared with step S2), and the signals of other non-event points are uniform, so that the interference fading problem is eliminated.
The present invention also provides a computer readable storage medium having a computer program executable by a processor, the computer program executing the steps of the vibration information positioning method for eliminating interference fading of the distributed vibration sensor of the above embodiment.
In summary, the main advantages of the invention are:
(1) The interference fading problem of the sensing system is avoided. Through the calculation of relative quantity, the influence of sawtooth-shaped interference waveforms on external excitation change is avoided.
(2) The sensitivity of the sensor is improved. And the sensitivity is improved by adopting related ideas.
(3) The universality is good. The method can also be used in other distributed sensors involving the principle of interference. For example, optical frequency domain reflectometer OFDR, the distributed optical fiber sensing technology based on the brillouin scattering principle also has the problem of interference fading, and the method can also avoid the problem.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (9)
1. A vibration information positioning method for eliminating interference fading by a distributed vibration sensor is characterized by comprising the following steps:
s1, a two-dimensional matrix S is formed by a series of original Rayleigh scattering curve signals received by an acquisition card:
wherein m is the number of pulses, n is the number of sampling points, a matrix row vector represents the size of a Rayleigh scattering signal of one pulse along the distance of the optical fiber, and a matrix column vector represents the change of a certain point on the optical fiber along with time;
s2, performing correlation operation on the two-dimensional matrix S to obtain a matrix R:
wherein
Rij＝E[S(i:a+i,j)*S(i+b:a+i+b,j)]-E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]
a is the number of pulses taken in the correlation algorithm, b is the correlation sampling interval,
floor is rounding down; s (i: a + i, j) represents that the jth column in the matrix S is taken out, the data from the ith row to the i + a row are used as a vector, and E () represents the average value of the vector quantity;
s3, averaging a series of original Rayleigh scattering curves in a time domain to obtain a matrix T:
wherein
Tij＝sqrt{E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]}
Sqrt () represents the root number;
s4, calculating a matrix P:
wherein
Pij＝Rij/Tij；
And S5, analyzing the correlation curve of the matrix P, searching for a peak, and positioning an event point at the peak.
2. A vibration information positioning processor for eliminating interference fading of a distributed vibration sensor, comprising:
the two-dimensional matrix module is used for forming a two-dimensional matrix S by a series of original Rayleigh scattering electric signals received by the acquisition card:
wherein m is the number of pulses, n is the number of sampling points, a matrix row vector represents the size of a Rayleigh scattering signal of one pulse along the distance of the optical fiber, and a matrix column vector represents the change of a certain point on the optical fiber along with time;
and the correlation operation module is used for performing correlation operation on the two-dimensional matrix S to obtain a matrix R:
wherein
Rij＝E[S(i:a+i,j)*S(i+b:a+i+b,j)]-E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]
a is the number of pulses taken in the correlation algorithm, b is the correlation sampling interval,
floor is rounding down; s (i: a + i, j) represents that the data of the jth column from the ith row to the i + a row in the matrix S are taken out to be used as a vector, and E () represents the average value of the vector quantity;
a time domain averaging module, configured to average multiple scattering curves in a time domain to obtain a matrix T:
wherein
Tij＝sqrt{E[S(i:a+i,j)]*E[S(i+b:a+i+b,j)]}
Sqrt () represents the root opening number;
a ratio module for calculating a matrix P:
wherein
Pij＝Rij/Tij；
And the event point acquisition module is used for analyzing the correlation curve of the matrix P, searching a peak and positioning the peak as an event point.
3. A kind of
The optical fiber vibration sensing system is characterized by comprising a laser, a pulse modulator, an optical amplifier, a circulator, a photoelectric detector, a collecting card and a processor which are connected in sequence, wherein one port of the circulator is also connected with an optical fiber to be detected;
laser emitted by a laser is modulated by a pulse modulator, modulated light is amplified by an optical amplifier, amplified signal light enters an optical fiber to be detected through a circulator, rayleigh scattered light reflected by the optical fiber to be detected is subjected to photoelectric conversion through a photoelectric detector, and a collecting card collects Rayleigh scattered electric signals; processing the Rayleigh scattering electric signal through a processor, eliminating interference fading and positioning an event point; the processor is a vibration information positioning processor as recited in claim 2.
4. Seed according to claim 3
The optical fiber vibration sensing system is characterized in that the laser is a narrow linewidth laser, the output power is 13mw, and the wavelength is 1550.12 nm.
5. Seed according to claim 3
The optical fiber vibration sensing system is characterized in that the pulse modulator is an optical fiber coupling acousto-optic modulator.
6. Seed according to claim 3
The optical fiber vibration sensing system is characterized in that the amplifier is an EDFA erbium-doped fiber amplifier.
7. Seed according to claim 3
The optical fiber vibration sensing system is characterized in that the detector is a PD photoelectric converter.
8. The seed of claim 3
The optical fiber vibration sensing system is characterized in that the optical fiber to be detected is a single-mode optical fiber.
9. A computer-readable storage medium having a computer program executable by a processor, the computer program performing the steps of the distributed vibration sensor interference fading canceling vibration information locating method according to claim 1.
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