CN114518128A - Method for obtaining phi-OTDR phase signal by automatically determining reference point - Google Patents

Method for obtaining phi-OTDR phase signal by automatically determining reference point Download PDF

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CN114518128A
CN114518128A CN202111347393.XA CN202111347393A CN114518128A CN 114518128 A CN114518128 A CN 114518128A CN 202111347393 A CN202111347393 A CN 202111347393A CN 114518128 A CN114518128 A CN 114518128A
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event
reference point
noise
phase
distance
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钟镇
邹宁睦
张旭苹
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Changzhou Institute of Technology
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    • G—PHYSICS
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    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
    • G01D5/35354—Sensor working in reflection
    • G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
    • G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
    • G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength
    • G01J9/02—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength by interferometric methods
    • G01J2009/0226—Fibres

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Abstract

The invention provides a method for automatically determining a reference point to acquire a phi-OTDR phase signal, which comprises the following steps: obtaining a sine component and a cosine component of coherent detection data of a phase optical time domain reflectometer after low-pass filtering; acquiring an initial phase and a mode of a phase optical time domain reflectometer; acquiring the sum of the distances of the sampling positions of the optical fibers; calculating a noise floor of the distance sum and a variance of the distance sum noise; determining the number of events according to the noise floor and the variance of the noise and recording the position of each event; determining an interval for each event; determining a candidate range of each event reference point; determining a reference point of the event solving signal according to the candidate range; the phase signal of the event is solved from the reference point. The method can realize the automatic selection of the reference point of the phase optical time domain reflectometer, not only can avoid subjectivity and randomness in manual judgment and improve the accuracy of phase signal detection, but also can enable the phase optical time domain reflectometer to have the automatic detection capability in the process of implementing accurate measurement.

Description

Method for obtaining phi-OTDR phase signal by automatically determining reference point
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a method for automatically determining a reference point to acquire a phi-OTDR phase signal.
Background
Distributed optical fiber sensing technology is gaining more and more attention due to its advantages of convenient deployment and distributed sensing. In order to adapt to the ultra-long distance characteristics of submarine Optical cables, Coherent Optical Time-Domain reflectometers (Coherent Optical Time-Domain reflectometers) with near quantum detection limit effect are available. However, the high coherence of the light source that is the primary factor in determining the detection distance in such devices dramatically affects the detection performance. Therefore, many researchers have been invested in suppressing coherent rayleigh noise. On the other hand, scientists have surprisingly found that the coherent rayleigh noise, which appears in the role of a harmful factor in coherent optical time domain reflectometry, can be used to achieve quantitative detection of the disturbance event acting on the optical fiber. The existing research results reveal that after a high-coherence light source is injected into an optical fiber, a back Rayleigh scattering curve generated in the optical fiber presents a sharp speckle-like pattern, and then phase information of each point of the optical fiber can be solved by the curve. When an external disturbance event acts on the optical fiber, the phase information changes along with the change of the disturbance event, and the change of the phase and the change of the disturbance event do not change along with the change of time in proportion. Instruments and devices operating on this principle are called Phase Optical Time-Domain reflectometers (abbreviated as Φ -OTDRs).
A series of demodulation measures such as quadrature demodulation, hilbert transform, and three-port demodulation are used to perform phase demodulation. In these demodulation measures, the acquisition of the phase signal is dependent on the phase difference of the location points on both sides of the disturbance event. The phase signal can be obtained by a method of continuously subtracting the phases at equal intervals, but this method has the following disadvantages: not only is the difference interval too small, the signal is lost, but also the difference position is at a noise position such as polarization, and an erroneous phase signal is generated. Therefore, it is necessary to accurately determine the proper reference point. However, in the conventional phase optical time domain reflectometer, the selection of the reference point has no clear judgment criterion to select a proper position.
The phase optical time domain reflectometer based on phase change linear distribution provides a method for determining whether a selected reference point is appropriate according to the linear distribution characteristics of phase change, and can accurately solve a phase signal corresponding to a disturbance event. However, here, the confirmation of the reference point is achieved by means of manual judgment. On one hand, due to subjectivity and randomness in manual judgment, the accuracy of a phase signal can be reduced; on the other hand, the manual judgment reduces the automation degree of measurement and influences the sensing efficiency. Moreover, when there are multiple disturbance events on the optical fiber and a reference point needs to be determined for each disturbance event, then a manual judgment needs to be performed for each disturbance event, which greatly reduces the intellectualization of the phase optical time domain reflectometer.
Disclosure of Invention
The invention provides a method for automatically determining a reference point to acquire a phi-OTDR phase signal, which can realize the automatic selection of the reference point of a phase optical time domain reflectometer, avoid the subjectivity and the randomness during the manual judgment, improve the accuracy of phase signal detection, enable the phase optical time domain reflectometer to have the automatic detection capability during the implementation of accurate measurement, and greatly improve the intelligence of the phase optical time domain reflectometer.
The technical scheme adopted by the invention is as follows:
the invention provides a method for automatically determining a reference point to acquire a phi-OTDR phase signal, which comprises the following steps: obtaining coherent detection data I of the phase optical time domain reflectometerD(ii) a Detecting the coherent detection data IDAfter the coherent detection data are converted into a two-dimensional array E (M, N), orthogonal demodulation components of coherent detection data are obtained according to the two-dimensional array E (M, N), wherein the orthogonal demodulation components comprise I components and Q components, M is the number of times of optical pulse transmission, the value range of M is recorded as 1-N, N is the number of points of optical fiber sampling, N is recorded as 1-N, and M, N is a positive integer; respectively passing the I component and the Q component through the same low-pass filter to obtain an I 'sine component and a Q' cosine component of a zero-frequency term; acquiring the initial phase of the phase optical time domain reflectometer according to the zero frequency term I 'sine component and the Q' cosine component
Figure RE-GDA0003603859690000031
And modulo P (m, n); at any optical fiber sampling position, acquiring the distance of a mode P (m, n) between any two optical pulse emission times, and accumulating and summing the acquired distances to acquire the phase optical time domain reflectometer at the positionThe sum of the distances h (n) from the fiber sampling locations; calculating a distance sum h _ noise _ base (n) of h (n) and calculating a variance S of the distance sum noise; determining the number of events according to the distance sum h (n), the noise base h _ noise _ base (n), the distance and the variance S of the noise and recording the position n of each eventnumber_event(ii) a According to the position n of each eventnumber_eventDetermine an interval [ L ] for each eventnumber_event，Rnumber_event](ii) a According to the interval [ L ] of each eventnumber_event，Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef，Lnumber_event](ii) a According to the candidate range [ L ] of the event reference pointnumber_event-SRef，Lnumber_event]Determining a reference point n for an event-resolved signaly_number_event(ii) a From reference point n of the signaly_number_eventSolving for the phase signal phi' (m, n) of the eventnumber_event)。
According to one embodiment of the invention, the distance and the noise floor h _ noise _ base (n) of h (n) are calculated according to the following steps: obtaining the maximum value and the minimum value of the distance sum h (n) at each optical fiber sampling position, and calculating the average value of the maximum value and the minimum value of the distance sum h (n)
Figure RE-GDA0003603859690000032
The sum h (n) of the distances at the sampling positions of the optical fiber is larger than the average value
Figure RE-GDA0003603859690000033
The remaining distance sum is marked as h _ noise (n'); and fitting h _ noise (n') by adopting a linear function with parameters, and acquiring the distance and the noise floor h _ noise _ base (n) of h (n) according to the fitted linear curve.
According to one embodiment of the invention, the distance and the variance S of the noise of h (n) are calculated according to the following steps: calculating the average value of h _ noise (n), and after all the h _ noise (n') are subtracted from the average value, summing all the differences after being squared to obtain the variance S of the distance and the noise of h (n).
According to one embodiment of the invention, determining the number of events according to the distance sum h (n), the noise floor h _ noise _ base (n), the distance sum and the variance S of the noise, and recording the position n of each eventnumber_eventThe method comprises the following steps: n is to beumber_eventThe value of (b) is cleared, and the following calculation is performed from small to large according to the value of n: clearing the value of the temporary variable; computing
Figure RE-GDA0003603859690000041
Determine if there is
Figure RE-GDA0003603859690000042
If so, the temporary variable is counted from zero; if not, clearing the temporary variable count value; when the temporary variable count value is larger than the number N corresponding to the half pulse widthhalf_pulseAnd adding 1 to the value of the number _ event, and marking the current fiber sampling position point as the position n of the eventnumber_event。
According to one embodiment of the invention, the position n is located according to each eventnumber_eventDetermine an interval [ L ] for each eventnumber_event，Rnumber_event]The method comprises the following steps: each event is located at the position nnumber_eventThe distance sum of the left and right sides of (a) and the area continuously larger than the noise floor h _ noise _ base (n) is recorded as the interval [ L ] of each eventnumber_cvent，Rnumber_event]。
According to one embodiment of the invention, the interval [ L ] according to each eventnumber_event，Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef，Lnumber_event]The method comprises the following steps: if the sequence number of the event currently processed is 1, if the interval starting point L of the event1Is less than the number N corresponding to the half pulse widthhalf_pulseTwice of, then 1 st event reference point adjustment range SRefIs equal to L1(ii) a If L is1Not less than Nhalf_pulseTwice of, then 1 st event reference point adjustment range SRefIs equal to Nhalf_pulseTwice of; if the sequence number of the currently processed event is not 1, if Lnumber_eventAnd Rnumber_event-1Is less than Nhalf_pulseTwice, then the adjustment range S of the current event reference pointRefIs equal to Lnumber_evAnd Rnumber_event-1If L is different from Lnumber_eventAnd Rnumber_event-1Is not less than Nhalf_pulseTwice, then the adjustment range S of the current event reference pointRefIs equal to Nhalf_pulseTwice of; if the sequence number of the event to be processed currently is X, the data fitting region is [ R ]X，RFiber_end]， RFiber_endCorresponding to the number of sampling points at the end of the optical fiber, and let LX+1＝RFiber_end(ii) a If the sequence number of the current event to be processed is not X, the data fitting area is [ R ]number_event，Lnumber_event+1]Wherein, the value range of the number _ event is a natural number field [1, X]And X is the maximum value of the number of events.
According to one embodiment of the present invention, the candidate range [ L ] of the reference point is determined according to the eventnumber_event-SRef，Lnumber_event]Determining a reference point n for an event-resolved signaly_umber_eventThe method comprises the following steps: for the number _ event, in the interval [ L ]number_event-SRef，Lnumber_event]At each optical fiber sampling position nyThe following calculations were performed: section (n)y，Lnumber_event+1]At each fiber position and fiber sampling position nyThe difference is made to the initial phase, then the phase unwrapping is made to the difference result in the direction of increasing the number of pulse transmission, and the phase change phi (m, n) is further solvedz)，nzIndicates the interval (n)y，Lnumber_event+1]The sequence numbers from small to large in the above, then in the data fitting interval [ R ]number_event，Lnumber_event+1]And fitting the data of the phase change of each pulse by using a linear function with parameters to obtain the standard deviation sigma (m, n)y) The sum of the standard deviations of all pulses is recordedσ′(ny) Finally, the interval [ L ]number_event-SRef，Lnumber_event]Sum of upper standard deviations σ' (n)y) Optical fiber sampling position n corresponding to minimum valueyIs selected as the reference point ny_number_event。
According to one embodiment of the invention, reference point n is based on a signaly_number_eventSolving for the phase signal phi' (m, n) of the eventnumber_event) The method comprises the following steps: reference point n from said signaly_number_eventAnd corresponding phase change phi (m, n)z) Fitting with a linear function with parameters to obtain the phase signal phi' (m, n) of the eventnumber_event)。
According to one embodiment of the invention, the light source frequency fluctuation of the phase optical time domain reflectometer is less than 50 kHz.
The invention has the beneficial effects that:
the invention can realize the automatic selection of the reference point of the phase optical time domain reflectometer, not only can avoid subjectivity and randomness in manual judgment and improve the accuracy of phase signal detection, but also can enable the phase optical time domain reflectometer to have the capability of automatic detection when implementing accurate measurement, and greatly improve the intelligence of the phase optical time domain reflectometer.
Drawings
FIG. 1 is a schematic diagram of a phase optical time domain reflectometer according to one embodiment of the present invention;
FIG. 2 is a schematic illustration of data collected by an oscilloscope according to one embodiment of the present invention;
FIG. 3 is a waterfall plot of data collected by an oscilloscope according to one embodiment of the invention;
fig. 4 is a flow diagram of a method of automatically determining a reference point to acquire a phi-OTDR phase signal, according to an embodiment of the present invention;
FIG. 5 is a superimposed graph of the modulus values of coherently detected data according to one embodiment of the present invention;
FIG. 6 is a waterfall plot of the modulus of coherently detected data according to one embodiment of the present invention;
FIG. 7 is a distribution plot of the sum of distances of coherently detected data according to one embodiment of the present invention;
FIG. 8 is a plot of distance-summed noise floor plots for coherent detection data in accordance with one embodiment of the present invention;
FIG. 9 is a distribution plot of distance sums indicative of noise floor and variance for coherent detection data according to one embodiment of the present invention;
FIG. 10 is a schematic of the variance and calculation of coherent detection data according to one embodiment of the present invention;
FIG. 11 is a diagram of a phase signal solution for coherently detected data according to one embodiment of the present invention;
fig. 12 is a functional block diagram of a method of automatically determining a reference point to acquire a phi-OTDR phase signal according to one embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the 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, it will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Theoretically, in a phase optical time domain reflectometer, if the frequency fluctuation of the laser is less than 50kHz, the phase change in the region of action of the perturbation event will be characterized by a linear profile along the length of the fiber. At this time, if the calculated phase change is processed by a data fitting method to further solve the phase signal corresponding to the event, it is necessary to know the position of the event, select an appropriate reference point on the left side of the event, and then perform data fitting in the right area of the event. However, due to polarization fading, rayleigh fading, false unwrapping, etc., the corresponding location becomes a bad noise point during the dephasing process. Some pre-processing methods may eliminate some of these noise points, but not all of them are guaranteed to be eliminated, and the data fitting method is used to reduce the influence of noise location points.
However, it is emphasized that the premise of using the data fitting method is that the correctly solved phase change after a perturbation event must exhibit linear behavior. However, in practical systems, the linear characteristic also has a more fundamental condition that the position of the reference point must avoid the position point where the polarization fading, rayleigh fading, unwrapping error, etc. are located. However, on the other hand, there are many location points where the region before the disturbance event is not an obvious noise point. Due to factors such as thermal noise of the detector, noise exists at all sampling positions of the optical fiber, and even if the noise is very slight, the noise is always present. Thus, a most suitable location point must be selected from these many possibilities as a reference point.
For differential demodulation, the method of quadrature demodulation is the preferred method for obtaining the minimum distortion level demodulated signal. In the process of quadrature demodulation, the quadrature demodulation component is obtained before the initial phase of the winding is acquired. After low-pass filtering, the root, i.e. the modulus, of the sum of the squares of the corresponding sine and cosine components also varies with the phase. Therefore, when a disturbance event acts on the optical fiber, the phase of the corresponding optical fiber sampling position not only changes along with the change of the pulse emission times, but also changes relative to the phases at two sides of the disturbance event.
Under ideal conditions, neither the phase nor the modulus before the perturbation event will change. Both the phase and the modulus change in the region of action of the perturbation event. While the phase changes in the direction of increasing pulse number following the region of action of the disturbance event along with the changes accumulated in the disturbance region, the phase does not change in the fiber length direction as long as there are no other disturbance events to the right of the disturbance event. Accordingly, the modulus value to the right of the perturbation event does not change due to the occurrence of the perturbation event. Therefore, when a disturbance event occurs, the module values of the two sides of the disturbance event area can not be changed, and only the module value of the disturbance event area is changed. And calculating the distance of the module values at different pulse moments for any point of optical fiber sampling positions, and calculating the sum of various calculation combinations, namely the distance sum. Obviously, the sum of the distances on both sides of the perturbation event zone tends towards zero, whereas the sum of the distances within the perturbation event zone may deviate significantly from zero. Based on the principle, the accurate positioning of the disturbance event can be realized, so that an accurate basis is provided for determining the reference point selection area. After the selected area of the reference point is determined, each optical fiber sampling position point of the area is used as a candidate reference point, the difference between the winding initial phase on the optical fiber position point behind the candidate reference point and the winding initial phase on the candidate reference point is obtained to obtain the winding differential phase, and then the winding differential phase is unwound to obtain the unfolded differential phase.
The unwrapped differential phase has no linear characteristic over the length of the fiber due to the non-uniform distribution of the fiber's refractive index along the length of the fiber. Therefore, the phase change having a linear characteristic is further solved. Also, even if the phase change exhibits linear characteristics along the optical fiber length direction due to the presence of noise factors such as polarization fading, rayleigh fading, and unwinding error, the curve is not a curve without an abnormal point such as a burr. Obviously, the more the phase change along the fiber direction conforms to the linear characteristic, the closer the solution result is to the true value, and the corresponding candidate reference point is the reference point to be searched. The smaller the standard deviation of data fitting is, the closer the fitted data is to a real primary curve is, the better the fitting effect is predicted, and the fitted curve can better represent a real value. Therefore, the standard deviation can be fitted by a primary curve to judge whether the candidate reference point is good or bad.
As shown in fig. 1, in the phase optical time domain reflectometer, a high-coherence laser light source LD emits continuous light, which is divided into two paths of light of 90:10 by a coupler OC1, an upper path L1 uses continuous light having an optical power of 90% as signal light, and a lower path L2 uses continuous light having an optical power of 10% as reference light. The signal light is modulated by an Acousto-Optic Modulator AOM (Acousto-Optic Modulator) with 40MHz frequency shift, the modulated signal light becomes pulse light, and the pulse light is amplified by an erbium Doped Fiber amplifier edfa (erbium Doped Fiber amplifier) and injected into the optical Fiber. Due to the existence of the rayleigh scattering effect, a part of the light returns to the fiber injection port, and the returned backward rayleigh scattering light enters the coupler OC2 together with the reference light after passing through the circulator. Since the subsequent photodetector bpd (balance photo electric detector) is a balanced detector, the coupler OC2 employs a split ratio of 50: 50. The back rayleigh scattered light and the reference light are incident on the photosensitive surface of the balanced detector BPD via the coupler OC2, and the differential current generated by the BPD is directly converted into a voltage and then enters the oscilloscope osc (oscilloscope)). The modulation work of the acousto-optic modulator AOM is completed by sending a modulation signal to the driving driver by the pulse signal generator PG, and the synchronous signal of the oscilloscope OSC is also provided by the pulse signal generator PG. During data acquisition of the oscilloscope OSC, the frequency fluctuation of the laser light emitted from the laser light source LD is kept within 50 kHz.
A sine wave was applied to the pzt (piezoelectric ceramics) drive shown in fig. 1. The data collected by the oscilloscope is shown in fig. 2. Since only the Fiber length (Fiber length) and the Electrical signal (i.e., the signal displayed on the oscilloscope screen) are shown, we cannot see any information about the vibration applied by the PZT from this figure.
The collected data shown in fig. 2 is displayed as a waterfall graph shown in fig. 3 on a two-dimensional plane of the length of the optical fiber and the Time (Time, Time corresponding to the change of the number of pulses). From fig. 3 alone, the signal hardly changes with time. Thus, information about the vibration event is also not available from fig. 3.
Based on this, as shown in fig. 4, the present invention provides a method for automatically determining a reference point to obtain a Φ -OTDR phase signal, including the following steps:
s1, obtaining coherent detection data I of phase optical time domain reflectometerD。
S2, coherent detection data IDAfter the data is converted into a two-dimensional array E (M, N), orthogonal demodulation components of coherent detection data are obtained according to the two-dimensional array E (M, N), wherein the orthogonal demodulation components comprise I components and Q components, M is the number of times of optical pulse transmission, the value range of M is recorded as 1-N, M is less than or equal to M, N is the number of points of optical fiber sampling, the sampling position of the optical fiber can also be directly marked, the value range of N is recorded as 1-N, N is less than or equal to N, and M, N is a positive integer.
And S3, respectively passing the I component and the Q component through the same low-pass filter to obtain an I 'sine component and a Q' cosine component of a zero-frequency term.
Specifically, although the oscilloscope OSC collects data every time an optical pulse is transmitted according to an instruction of a trigger pulse when collecting data, the data is stored as continuous one-dimensional data, and therefore, coherent detection data I to be collected is first collected according to a period of the number of sampling pointsDAnd converting the optical pulse into a two-dimensional array E (M, N) which is convenient for subsequent processing, wherein M is the number of times of optical pulse emission, the value range of M is recorded as being more than or equal to 1 and less than or equal to M, N is the number of points of optical fiber sampling, and the value range of N is recorded as being more than or equal to 1 and less than or equal to N. Because the frequency shift of the acousto-optic modulator is 40MHz, the coherent detection result is an intermediate frequency signal of 40MHz, and the corresponding trigonometric function is multiplied by the intermediate frequency signal by combining the frequency shift of 40MHz and the sampling rate of 500MSa/s to obtain an I component and a Q component. Wherein the sine function and the cosine function have the same factor, all of which are
Figure RE-GDA0003603859690000111
I.e. 0.08 n.
An fir (finite Impulse response) low pass filter can then be used with a passband gain of 1 and a passband bandwidth of 5 MHz. Then, the filter is used for filtering the I component and the Q component respectively, and due to the fact that the filter is a low-pass filter, only the required zero-frequency term I 'sine component and Q' cosine component are reserved as a result of filtering.
S4, obtaining the initial phase of the phase optical time domain reflectometer according to the I 'sine component and the Q' cosine component of the zero frequency term
Figure RE-GDA0003603859690000112
And modulo P (m, n).
Specifically, the initial phase can be obtained by performing arc tangent operation after dividing the zero frequency term I 'sine component by the Q' cosine component
Figure RE-GDA0003603859690000113
The result of the arctangent operation takes into account the quadrant in which the I 'sine component and the Q' cosine component are located, so that the initial phase is distributed over [ - π, π]Within the range of (1). Nevertheless, if the actual value of the phase signal exceeds [ - π, π]Is still folded within the range, so that the initial phase is distributed in [ - π, π]A winding value within a range of (a). And performing square operation on the I 'sine component and the Q' cosine component, adding the components and then squaring to obtain the model P (m, n) of the phase optical time domain reflectometer.
If the calculated modulus values are embodied in fig. 5 and 6, respectively, it can be seen that the modulus values appear clearly distinct from other regions at about 1.2km, regardless of the plane from which it can be seen, and in fig. 5, at about 1.2km, the modulus values are much denser; in fig. 6, at about 1.2km, the modulus value changes significantly with time.
And S5, acquiring the distance of the mode P (m, n) between any two optical pulse emission times at any optical fiber sampling position, and accumulating and summing the acquired distances to acquire the distance sum h (n) of the phase optical time domain reflectometer at the optical fiber sampling position.
In particular, for any point n on the fiberxAnd solving the distance of the module values corresponding to all the two pulses in the M pulses (solving the curve P (M, n)x) The distance of any two points above), these distances are summed, called the location point nxA distance sum h (n)x) Due to nxIs any value of N in the natural number domain [1, N]There is a sum of distances h (n), and the sum of distances h (n) at all fiber sampling locations is shown in FIG. 7. In the undisturbed region of the fiber, the phase and, correspondingly, the modulus do not change over time. Thus, the distance values calculated by the modulus values at different pulse times are close to zero, and the sum of the calculated distances should also be close to zeroThe value is obtained. At the fiber location where vibration occurs, the phase of the fiber is disturbed and accordingly the modulus changes with time, and the calculated distance sum is necessarily much larger than zero. Since the distance is non-negative, the sum of the distances calculated therefrom must also be far from zero.
S6, calculating the distance and the noise base h _ noise _ base (n) of h (n) and calculating the variance S of the distance and the noise.
Further, according to an embodiment of the present invention, the distance sum h _ noise _ base (n) of h (n) is calculated according to the following steps: obtaining the maximum value and the minimum value of the distance sum h (n) at each optical fiber sampling position, and calculating the average value of the maximum value and the minimum value of the distance sum h (n)
Figure RE-GDA0003603859690000121
The sum h (n) of the distances at the sampling positions of the optical fiber is larger than the average value
Figure RE-GDA0003603859690000122
The remaining distance sum is marked as h _ noise (n'); and fitting h _ noise (n') by using a linear function with parameters, and acquiring the distance sum h _ noise _ base (n) of the noise floor h (n) according to the fitted linear curve.
Calculating the distance and the variance S of the noise of h (n) according to the following steps: calculating the average value of h _ noise (n '), subtracting the average value from all h _ noise (n'), and summing the squared differences to obtain the distance and the variance S of the noise of h (n).
Specifically, in order to obtain the distance and accurate noise floor calculation result, the numerical values of the distance and the noise which are obviously not noise are eliminated. When the distance sum is used for judging the position of the event, the module value of the event area is obviously far away from the zero value, and the characteristic is used for eliminating the distance sum and the area corresponding to the vibration event in the curve as far as possible. Searching the maximum value and the minimum value of the distance sum h (n), and averaging the maximum value and the minimum value
Figure RE-GDA0003603859690000134
As a reference, the distance is then determinedSum of ions is less than
Figure RE-GDA0003603859690000135
The positions of the optical fibers are reserved, the reserved positions of the optical fibers are regarded as positions where the noise exists, and the values of the distance sum calculated on the positions of the optical fibers are regarded as the noise of the distance sum. Then, a fitting operation is performed on the noise data by using a linear band parameter function, the fitting algorithm is a least square method, and a linear curve obtained by fitting is regarded as a noise bottom, as shown by a straight line Q1 in FIG. 8. After the first order curve is calculated, the variance of the noise data is further calculated, and a straight line Q2 in fig. 9 is the sum of the noise floor and the variance.
S7, determining the number of events according to the distance sum h (n), the noise floor h _ noise _ base (n), the distance and the variance S of the noise and recording the position n of each eventnumber_event。
Further, according to an embodiment of the present invention, the number of events is determined according to the distance sum h (n), the noise floor h _ noise _ base, the distance and the variance S of the noise, and the position n of each event is recordednumber_eventThe method comprises the following steps: and clearing the number _ event, and calculating according to the value of n from small to large as follows:
clearing the value of the temporary variable; computing
Figure RE-GDA0003603859690000131
Determine if there is
Figure RE-GDA0003603859690000132
Figure RE-GDA0003603859690000133
If so, counting the temporary variable from zero; if not, resetting the temporary variable count value; when the temporary variable count value is larger than the number N corresponding to the half pulse widthhalf_pulseAnd adding 1 to the value of the number _ event, and marking the current optical fiber sampling position point as the position n of the eventnumber_event。
Specifically, in the method of continuously differencing and solving the phase information, the phase information is often obtained firstAnd obtaining the phase information, and then judging the number of the events according to the phase information or the joint phase information. In the method of the present invention, the number of events is determined independently of the phase. And before obtaining the phase information, firstly solving the number of the events, then locking a certain event, and solving the phase information. When an event is applied to the fiber, the values of the distance sum h (n) will deviate significantly from the value zero. However, due to the presence of noise, the distance sum h (n) will have a value slightly higher than zero even in areas of the fiber that are not subject to external disturbances. Calculating h (n) and
Figure RE-GDA0003603859690000141
the sampling points with positive difference are continuous and accumulated to be more than the number N corresponding to the half pulse widthhalf_pulseWhen the number of events is 1 added from zero, the fiber sampling position point n is at this timenumber_eventThe mark is the position of the event, and every time the number _ event value is updated, the number of sampling points with positive difference, i.e. the temporary variable, is accumulated from zero again only after the negative difference occurs.
In one embodiment of the present invention, as shown in fig. 9, the number of events is 1, and the position of the event is 1073.2m (ignoring the conversion between the fiber sampling position, the number of sampling points, and the sampling interval).
S8, according to the position n of each eventnumber_eventDetermine an interval [ L ] for each eventnumber_event,Rnumber_event]。
Further, according to an embodiment of the present invention, the location n is determined according to each eventnumber_eventDetermine an interval [ L ] for each eventnumber_event,Rnumber_event]The method comprises the following steps: each event is located at the position nnumber_eventThe distance sum of the left and right sides of (a) and the area continuously larger than the noise floor h _ noise _ base (n) is recorded as the interval [ L ] of each eventnumber_event,Rnumber_event]。
That is, for the number _ event, the sampling location point mnumber_eventH (n) on the left and right sides is continuously greater thanThe area of h _ noise _ base (n) is marked as the area [ L ] of the number _ event acting on the optical fibernumber_event，Rnumber_event]。
The disturbance event acting on the optical fiber has a certain distance in space, and the position of the action of the finally detected disturbance event is slightly larger than the length of the area where the disturbance event actually acts, due to the influence of the width of the optical pulse. In the actual process, the influence of the optical pulse width is ignored when calculating the disturbance event region.
In one embodiment of the invention, the perturbation events comprise one, which in turn only requires the effect of one perturbation event to be resolved. If a plurality of disturbance events exist, the solution is carried out in sequence. H (n and h _ noise _ base (n)) are differentiated, and a fiber sampling position L with a negative difference value for the first time appears on the left side of the fiber position 1073.2m when viewed from the fiber position 1073.2m to two sidesnumber_event1053.2m, the first negative difference occurring on the right side of the optical fiber position 1073.2mnumber_event1094.6 m. [1053.2m, 1094.6m]I.e. the area where the disturbance event acts on the fibre.
S9, according to the interval [ L ] of each eventnumber_event，Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef，Lnumber_event]。
Further, according to the interval [ L ] of each eventnumber_event，Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef，Lnumber_event]The method comprises the following steps:
if the sequence number of the currently processed event is 1, if the interval start point L of the event1Is less than the number N corresponding to the half pulse widthhalf_pulseTwice, then the adjustment range S of the 1 st event reference pointRefIs equal to L1(ii) a If L is1Not less than Nhalf_pulsTwice of, then 1 st event reference point adjustment range SRefIs equal to Nhalf_pulsTwice of; if the sequence number of the currently processed event is not 1, if Lnumber_eventAnd Rnumber_event-1Is less than Nhalf_pulseTwice, then the adjustment range S of the current event reference pointRefIs equal to Lnumber_eventAnd Rnumber_event-1If L is different from Lnumber_eventAnd Rnumber_event-1Is not less than Nhalf_pulseTwice, then the adjustment range S of the current event reference pointRefIs equal to Nhalf_pulseTwice of;
if the sequence number of the event to be processed currently is X, the data fitting region is [ R ]X，RFiber_end]， RFiber_endCorresponding to the number of sampling points at the end of the optical fiber, and let LX+1＝RFiber_end(ii) a If the sequence number of the current event to be processed is not X, the data fitting area is [ R ]number_event，Lnumber_event+1]Wherein, in the process,
Figure RE-GDA0003603859690000161
the value range of (1) is a natural number field]And X is the maximum value of the number of events.
In this example, the number of events is only 1, and the start point L of the interval of events is1Number N greater than half pulse widthhalf_pulseTwice, therefore, the reference points are selected to have a region [1053.2m-200 x 0.2m, 1053.2m]And the region of data fitting is naturally [1094.6m, 2000m ]]。
S10, according to the candidate range [ L ] of the event reference pointnumber_event-SRef，Lnumber_event]Determining a reference point n of an event solution signaly_number_event。
Further, according to the candidate range [ L ] of the event reference pointnumber_event-SRef，Lnumber_event]Determining a reference point n for an event-resolved signaly_number_eventThe method specifically comprises the following steps:
for the number _ event, in the interval [ L ]number_event-SRef，Lnumber_event]At each optical fiber sampling position nyThe following calculations were performed: will interval (n)y，Lnumber_event+1]Each optical fiber position onInitial phase position and optical fiber sampling position nyThe difference is made to the initial phase, then the phase unwrapping is made to the difference result in the direction of increasing the number of the pulse transmission, and the phase change phi (m, n) is further solvedz)，nzIndicates the interval (n)y，Lnumber_event+1]The sequence numbers from small to large in the above, then in the data fitting interval [ R ]number_event，Lnumber_event+1]And fitting the data of the phase change of each pulse by using a linear function with parameters to obtain the standard deviation sigma (m, n)y) The sum of the standard deviations of all pulses is denoted as σ' (n)y) Finally, the interval [ L ]number_event-SRef，Lnumber_event]Sum of upper standard deviations σ' (n)y) Optical fiber sampling position n corresponding to minimum valueyIs selected as the reference point ny_number_event。
Specifically, within the candidate range of the event reference point determined at S9, the respective fiber sampling positions are sequentially taken as candidate reference points from the fiber sampling position 1013.2m to the fiber sampling position 1053.2 m. For each candidate reference point, the initial phase of the unwound phase at each fiber sampling position after the candidate reference point is differenced from the initial phase of the unwound phase at the candidate reference point. Then, each optical fiber sampling position behind the candidate reference point is unwrapped according to the pulse emission direction, and the unwrapped differential phase is obtained. In order to eliminate the problem of irregular initial phase along the optical fiber caused by uneven distribution of refractive index, the differential phase corresponding to each pulse is made different from the reference phase. The reference phase may select the differential phase corresponding to the initial pulse. In the invention, in order to reduce the error of single sampling, the average value of the differential phases corresponding to a plurality of times of pulses is used for replacing the differential phase corresponding to the initial pulse as the reference phase. The phase change is the result of the difference between the differential phase corresponding to each pulse and the reference phase. Next, data fitting is performed on the calculated phase change for each optical pulse using a linear function with parameters. One pulse corresponds to the standard deviation obtained by one-time fitting, and the 1000 standard deviations are accumulated to obtain the standard deviation sum corresponding to the candidate reference point. As shown in fig. 10, different candidate reference points correspond to different standard deviation sums, and in fig. 10, the abscissa is the fifth fiber sampling position from the small coordinate to the large coordinate, that is, the fifth candidate reference point.
Overall, as the distance between the candidate reference point and the disturbance event decreases, the standard deviation in fig. 10 decreases. On the other hand, this indicates that the position of the disturbance event is successfully determined by the determination in step S7. On the other hand, the reason for the overall decreasing trend is mainly that the closer the candidate reference point is to the disturbance event, the smaller the influence of the accumulated noise before the disturbance event. However, simply choosing a reference point arbitrarily to the left of the disturbance event affects the accuracy of the measurement. In the 105 th candidate reference point in fig. 10, the sum of the standard deviations of both sides is reduced. Therefore, the final reference point is not the optimal choice simply determined by the length of the distance between the candidate reference point and the disturbance event. In this embodiment, the candidate reference point corresponding to the standard deviation and the minimum value is selected as the final reference point, ny_number_eventExactly the 200 th candidate reference point.
S11, according to the reference point ny_number_eventSolving for the phase signal phi' (m, n) of the eventnumber_event)。
Further in accordance with an embodiment of the present invention, reference point n is based on a signaly_number_eventSolving for the phase signal phi' (m, n) of the eventnumber_event) The method comprises the following steps: according to reference point ny_number_eventAnd corresponding phase change phi (m, n)z) Fitting with a linear function with parameters to obtain the phase signal phi' (m, n) of the eventnumber_event)。
Specifically, the un-unwrapped initial phase at each fiber sampling position after the 200 th candidate reference point is subtracted from the un-unwrapped initial phase at the candidate reference point, and the subsequent data processing procedure is consistent with that in S10 until the calculated phase change is obtained. And fitting the calculated phase change corresponding to each pulse along the length direction of the optical fiber by using a linear function with parameters to obtain a fitted phase change curve. Then, a curve of the phase change at the 200 th candidate reference point in the pulse number change direction is solved as a phase signal to be solved, which can be specifically referred to as fig. 11, in which the horizontal axis of fig. 11 is time and the vertical axis is a phase signal.
In order to make the understanding of the present invention more clear to those skilled in the art, the principle of a method for automatically determining the reference point acquisition of a Φ -OTDR phase signal according to the present invention will be described below with reference to the block diagram shown in fig. 12.
As shown in fig. 12, the process of the phase signal acquisition method includes: coherent detection data I for obtaining phase optical time domain reflectometerDThen obtaining coherent detection data IDOrthogonal mediation I component and Q component, further obtaining zero frequency term I 'sine component and Q' cosine component according to the orthogonal mediation component I component and Q component, and further obtaining initial phase of phase optical time domain reflectometer according to the zero frequency term I 'sine component and Q' cosine component
Figure RE-GDA0003603859690000191
And modulo P (m, n). Then, the sum h (n) of the distances between the mode values at different pulse times at any fiber position is solved.
Further, a noise floor h _ noise _ base (n) and a variance S are calculated according to the distance sum value h (n). Determining the number of events by comparing the distance sum h (n) with the noise floor plus the variance sum value and recording the position n of each eventnumber_eventAnd then determining an interval [ L ] of each eventnumber_event，Rnumber_event]According to the interval [ L ] of each eventnumber_event，Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef，Lnumber_event]. For reference point candidate region [ Lnumber_event-SRef，Lnumber_event]At any point above, the fit data is processed to a range [ R ]number_event，Lnumber_event+1]Fitting the phase change corresponding to each light pulse, and recording the sum of the fitted standard deviations corresponding to the pulses obtained by fitting, corresponding to the sum of the standard deviationsThe fiber position on the minimum reference point candidate area is finally determined as the reference point ny_number_event. Finally, according to the reference point ny_number_eventSolving for the phase signal phi (m, n) of the eventnumber_event)。
Therefore, automatic selection of the reference point is realized, subjectivity and randomness in manual judgment are avoided, and the quantitative measurement function of the phase optical time domain reflectometer based on data fitting has the capability of automatic detection.
In summary, according to the method for obtaining a phase signal of a Φ -OTDR by automatically determining a reference point according to the embodiments of the present invention, based on a distance and an interval in which an event can be effectively searched, and then, a fitting standard deviation is effectively used to determine a phase difference solution reference point, so as to solve an accurate phase signal on the basis, thereby realizing accurate positioning and accurate display of the event, avoiding subjectivity and randomness during manual judgment, improving accuracy of phase signal detection, enabling a phase optical time domain reflectometer to have an automatic detection capability during accurate measurement, and greatly improving intelligence of the phase optical time domain reflectometer.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, various steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system.
It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.
In addition, functional units in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.
The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (9)

1. A method for automatically determining a reference point to acquire a Φ -OTDR phase signal, comprising the steps of:
obtaining coherent detection data I of the phase optical time domain reflectometerD；
The coherent detection data IDAfter the coherent detection data are converted into a two-dimensional array E (M, N), orthogonal demodulation components of coherent detection data are obtained according to the two-dimensional array E (M, N), wherein the orthogonal demodulation components comprise I components and Q components, M is the number of times of optical pulse transmission, the value range of M is recorded as 1-N, N is the number of points of optical fiber sampling, N is recorded as 1-N, and M, N is a positive integer;
respectively passing the I component and the Q component through the same low-pass filter to obtain an I 'sine component and a Q' cosine component of a zero-frequency term;
acquiring the initial phase of the phase optical time domain reflectometer according to the zero frequency term I 'sine component and the Q' cosine component
Figure FDA0003354694470000011
And modulo P (m, n);
acquiring the distance of a mode P (m, n) between any two optical pulse emission times at any optical fiber sampling position, and accumulating and summing the acquired distances to acquire the distance sum h (n) of the phase optical time domain reflectometer at the optical fiber sampling position;
calculating a distance sum h _ noise _ base (n) of h (n) and calculating a variance S of the distance sum noise;
determining the number of events and recording the position n of each event according to the distance, h (n), the noise floor h _ noise _ base (n), the distance and the variance S of the noisenumber_event；
According to the position n of each eventnumber_eventDetermine an interval [ L ] for each eventnumber_event,Rnumber_event]；
According to the interval [ L ] of each eventnumber_event,Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef,Lnumber_event]；
According to the candidate range [ L ] of the event reference pointnumber_event-SRef,Lnumber_event]Determining a reference point n for an event-resolved signaly_number_event；
According to reference point ny_number_eventSolving for the phase signal phi' (m, n) of the eventnumber_event)。
2. A method for automatic reference point determination for acquisition of a Φ -OTDR phase signal according to claim 1, characterized in that said distance and the noise floor h _ noise _ bas of h (n) are calculated according to the following steps:
obtaining the maximum value and the minimum value of the distance sum h (n) at each optical fiber sampling position, and calculating the average value of the maximum value and the minimum value of the distance sum h (n)
Figure FDA0003354694470000021
The sum h (n) of the distances at the sampling positions of the optical fiber is larger than the average value
Figure FDA0003354694470000022
The remaining distance sum is marked as h _ noise (n');
and fitting h _ noise (n') by adopting a linear function with parameters, and acquiring the distance and the noise floor h _ noise _ base (n) of h (n) according to the fitted linear curve.
3. A method for automatic reference point determination for acquisition of a Φ -OTDR phase signal according to claim 2, characterized in that said distance and the variance S of the noise of h (n) are calculated according to the following steps:
calculating the average value of h _ noise (n '), subtracting the average value from all h _ noise (n'), and summing the squared differences to obtain the variance S of the distance and the noise of h (n).
4. A method for automatically determining a reference point to acquire a Φ -OTDR phase signal according to claim 3, wherein the number of events is determined according to the distance sum h (n), noise floor h _ noise _ base (n), variance S of distance sum noise and the number of events is recorded and the position n of each event is recordednumber_eventThe method comprises the following steps: and clearing the value of the number _ event, and calculating the following values according to the value of n from small to large:
clearing the value of the temporary variable;
computing
Figure FDA0003354694470000031
Determine if there is
Figure FDA0003354694470000032
If so, the temporary variable is counted from zero;
if not, resetting the temporary variable count value;
when the temporary variable count value is larger than the number N corresponding to the half pulse widthhalf_pulseAnd adding 1 to the value of the number _ event, and marking the current fiber sampling position point n as the position n of the eventnumber_event。
5. Method for acquiring a Φ -OTDR phase signal with automatic reference point determination according to claim 1, characterized in that, according to the position n where each event is locatednumber_eventDetermine an interval [ L ] for each eventnumber_event,Rnumber_event]The method comprises the following steps:
each event is located at the position nnumber_eventThe distance sum of the left side and the right side of the noise floor h _ noise _ base (n) is continuously larger than the interval of each event [ Lnumber_event,Rnumber_event]。
6. Method for acquiring a Φ -OTDR phase signal with automatic reference point determination according to claim 5, characterized in that the interval [ L ] of each event is determined according tonumber_event,Rnumber_event]Determining a candidate range for each event reference point Lnumber_event-SRef,Lnumber_event]The method comprises the following steps:
if the sequence number _ event of the currently processed event is 1, if the interval start point L of the event is 11Is less than the number N corresponding to the half pulse widthhalf_pulseTwice of, then 1 st event reference point adjustment range SRefIs equal to L1(ii) a If L is1Not less than Nhalf_pulseTwice, then the adjustment range S of the 1 st event reference pointRefIs equal to Nhalf_pulseTwice of; if the sequence number of the currently processed event is not 1, if Lnumber_eventAnd Rnumber_event-1Is less than Nhalf_pulseTwice, then the adjustment range S of the current event reference pointRefIs equal to Lnumber_eventAnd Rnumber_event-1If L is different from Lnumber_eventAnd Rnumber_event-1Is not less than Nhalf_pulseTwice, then the adjustment range S of the current event reference pointRefIs equal to
Figure FDA0003354694470000041
Twice of;
if the sequence number of the current event to be processed is X, the region where the data is fitted is [ R ]X,RFiber_end]，RFiber_endCorresponding to the number of sampling points at the end of the optical fiber, and let LX+1＝RFiber_end(ii) a If the sequence number of the current event to be processed is not X, the data fitting area is [ R ]number_event,Lnumber_event+1]Wherein, in the step (A),
Figure FDA0003354694470000042
the value range of (1) is a natural number field]And X is the maximum value of the number of events.
7. Method for acquiring a Φ -OTDR phase signal with automatic reference point determination according to claim 6, characterized in that said candidate range of said event reference point [ L [ ] -Lnumber_event-SRef,Lnumber_event]Determining a reference point n of an event solution signaly_number_eventThe method comprises the following steps:
for the number _ event, in the interval [ L ]number_event-SRef,Lnumber_event]At each optical fiber sampling position nyThe following calculations were performed: section (n)y_number_event,Lnumber_event+1]At each fiber position and the fiber sampling position nyThe difference is made to the initial phase, then the phase unwrapping is made to the difference result in the direction of increasing the number of pulse transmission, and the phase change phi (m, n) is further solvedz)，nzIndicates the interval (n)y,Lnumber_event+1]The number of sequences from small to large, then in the data fitting interval [ R ]number_event,Lnumber_event+1]The data fitting is carried out on the phase change of each pulse by using a linear function with parameters, and the standard deviation sigma (m, n) is obtained by fittingy) The sum of the standard deviations of all pulses is denoted as σ' (n)y) Finally, the interval [ L ]number_event-SRef,Lnumber_event]Sum of upper standard deviations σ' (n)y) Optical fiber sampling position n corresponding to minimum valueyIs selected as the reference point ny_number_event。
8. A method of obtaining a Φ -OTDR phase signal by automatically determining the reference point according to claim 7, characterized in that the reference point n is used as a basis for determining the phase of the Φ -OTDR signaly_number_eventSolving for the phase signal phi' (m, n) of the eventnumber_event) The method comprises the following steps:
according to the reference point ny_number_eventAnd corresponding phase change phi (m, n)z) Fitting with a linear function with parameters to obtain the phase signal phi' (m, n) of the eventnumber_event)。
9. A method for automatic determination of reference point acquisition of a phi-OTDR phase signal according to any of claims 1-8, characterized in that,
the light source frequency fluctuation of the phase optical time domain reflectometer is less than 50 kHz.
CN202111347393.XA 2021-11-15 2021-11-15 Method for obtaining phi-OTDR phase signal by automatically determining reference point Pending CN114518128A (en)

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