CN108917636B - A kind of distributive fiber optic strain demodulation method based on subset window adaption algorithm - Google Patents
A kind of distributive fiber optic strain demodulation method based on subset window adaption algorithm Download PDFInfo
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- CN108917636B CN108917636B CN201811013846.3A CN201811013846A CN108917636B CN 108917636 B CN108917636 B CN 108917636B CN 201811013846 A CN201811013846 A CN 201811013846A CN 108917636 B CN108917636 B CN 108917636B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
Abstract
The invention discloses a kind of distributive fiber optic strain demodulation methods based on subset window adaption algorithm provided by the invention, this method is by establishing the theoretical model of strain calculation precision and proposing that a kind of effective evaluation Rayleigh scattering composes the parameter of quality, it joined adaptive subset window algorithm in strain demodulation method, the algorithm can scientifically calculate the length of subset window, and make length adjustment automatically by the superiority and inferiority that Rayleigh scattering in evaluation subset composes quality and do not need manually to be intervened.This distributive fiber optic strain demodulation method based on subset window adaption algorithm can not only reduce the experience needs to user, but also the precision of strain measurement can be improved, to improve the popularization of engineering field application.
Description
Technical field
The present invention relates to monitoring structural health conditions field more particularly to a kind of distributed light based on subset window adaption algorithm
Fibre strain demodulation method.
Background technique
Optical frequency domain reflection technology (Optical Frequency Domain Reflectometry, OFDR) is distributed light
Fibre measurement and developing direction emerging in sensing technology.More traditional optical time domain reflection method (Optical Time Domain
Reflectometry, OTDR), OFDR has the features such as signal-to-noise ratio is high, and spatial resolution is high, high sensitivity.Based on Rayleigh scattering
Distributed strain measurement mainly by cross-correlation analysis calculate tested optical fiber in strain occur front and back Rayleigh scattering spectrum partially
Shifting amount, to obtain corresponding strain information.
During actual measurement, the precision of strain measurement is influenced by many factors, such as the size of signal-to-noise ratio, subset window
Length, the selection etc. of interpolating function.Wherein the selection of the processing of noise, interpolating function can be adjusted according to measurement demand
Demodulating algorithm software is to meet the needs of user is to measurement accuracy.And the definition for subset window length, usually it is based on by user
Have measurement experience roughly to provide, and the length of subset window has the reliability of cross-correlation calculation and the precision of strain measurement
Critical impact.In general, the length of subset window is longer, the difference for including in measurement Subset and the characteristic information of other subsets
More, the cross-correlation analysis result obtained in this way is more reliable.But the length of subset window is longer, reaction structure is locally latent
It is poorer in the ability of strain information, that is, the decline of strain measurement accuracy.Therefore, based on the considerations of the above two o'clock, son
The length selection for collecting window should be the smaller the better on the basis of meeting cross-correlation calculation reliability.Due to traditional distribution type fiber-optic
Subset window is substantially the regular length defined by user based on certain experience in strain demodulation method, and subset window length
The range for directly determining the reference Rayleigh scattering spectrum and measurement Rayleigh scattering spectrum for doing cross-correlation analysis, to cross-correlation calculation
Reliability and strain calculation precision have very important influence.And this roughly estimation mode lacks scientific and foundation
Property, the precision of strain measurement may be damaged.
Summary of the invention
According to problem of the existing technology, the invention discloses a kind of distributed light based on subset window adaption algorithm
Fibre strain demodulation method, comprising the following steps: S1: it is composed using the Rayleigh scattering in optical frequency domain reflectometer method acquisition tested optical fiber
Data information, wherein Rayleigh scattering modal data information includes composing and measuring Rayleigh scattering spectrum with reference to Rayleigh scattering；
S2: the requirement according to user to measurement spatial resolution will compose and measure Rayleigh scattering with reference to Rayleigh scattering and compose nothing
It is truncated into aliasing K subset, wherein calculating the optimal subset window length for composing each subset with reference to Rayleigh scattering
S3: by optimal subset window obtained in S2It is auspicious to measuring in distance domain
Sharp scattering spectra and reference Rayleigh scattering spectrum re-start truncation, obtain the measurement Subset in K new distance domains and refer to subset；
S4: measurement Subset in distance domain that S3 is obtained and inverse Fourier transform is carried out with reference to subset and zero padding is to same
Data length I measurement Subset and transforms to spectral domain with reference to subset at this time, on spectral domain each group measurement Subset and with reference to subset into
Row cross-correlation analysis obtains the spectrum offset amount Δ F of every group of subset；
S5: the spectrum offset amount of every group of subset in S4 is converted into the strain information ε that measurement Rayleigh scattering composes each subset.
The reference Rayleigh scattering of the S2 composes the optimal subset window length of each subset specifically in the following way:
S21. the noise variance σ (η) calculated with reference to Rayleigh scattering spectrum passes through according to required strain calculation precision σ (d)
FormulaFind out the threshold value Q for the Rayleigh scattering spectrum signal intensity gradient summation that data length is Lt；
S22. the threshold value q of average subset signals intensity gradient sum is calculatedt=Qt/ K, K are subset quantity；
S23., each subset is set and unifies initial window lengthTo Rayleigh scattering
Spectrum signal carries out Fourier transformation, and data are transformed into distance domain from spectral domain, and with the initial subset window length of each subsetIt will be away from
The reference Rayleigh scattering spectrum of delocalization is truncated into K subset；
S24., K subset is carried out to inverse Fourier transform again and domain data of the zero padding to length for I, data are according to subset
Interior average signal strength gradient calculation formulaWhereinFor son
Signal intensity gradient in collection,For signal strength in subset, average signal strength gradient δ=[δ in each subset is calculated1,
δ2,δ3,...,δk]；
S25. according to formulaIt calculates in initial subset window lengthUnder each subset signal intensity gradient and
S26. with kth (k=1,2 ..., K) a subset for, judge inequalityIt is whether true；If set up,If invalid, makeS is that subset window extends fixed step size value, according to formulaNew q is calculatedk, continue to judge inequality qk≥qtIt is whether true, until occurringMake qk≥qtIt sets up, thenIter isThe number of iterations.
By adopting the above-described technical solution, a kind of distributed light based on subset window adaption algorithm provided by the invention
Fibre strain demodulation method, this method is by establishing the theoretical model of strain calculation precision and proposing a kind of effective evaluation Rayleigh scattering
The parameter for composing quality joined adaptive subset window algorithm in strain demodulation method, which can scientifically calculate subset
The length of window, and length adjustment is made by the superiority and inferiority that Rayleigh scattering in evaluation subset composes quality automatically and does not need manually to carry out
Intervene.This distributive fiber optic strain demodulation method based on subset window adaption algorithm can not only reduce the warp to user
Demand is tested, and the precision of strain measurement can be improved, to improve the popularization of engineering field application.
Detailed description of the invention
In order to illustrate the technical solutions in the embodiments of the present application or in the prior art more clearly, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is only this
The some embodiments recorded in application, for those of ordinary skill in the art, without creative efforts,
It is also possible to obtain other drawings based on these drawings.
Fig. 1 is in the present invention for obtaining the optical frequency domain reflectometer schematic diagram of Rayleigh scattering spectrum signal
Fig. 2 is the optimal subset window length computation flow chart in the present invention by taking k-th of subset as an example
Fig. 3 is the present invention according to the optimal subset window N being calculatedoptExist to the Rayleigh scattering modal data of reference and measurement
Distance domain carries out the schematic diagram for being truncated into K subset.
Specific embodiment
To keep technical solution of the present invention and advantage clearer, with reference to the attached drawing in the embodiment of the present invention, to this
Technical solution in inventive embodiments carries out clear and complete description:
A kind of distributive fiber optic strain demodulation method based on subset window adaption algorithm as shown in FIG. 1 to FIG. 3；Specifically
The following steps are included:
S1: using the Rayleigh scattering modal data information in optical frequency domain reflectometer method acquisition tested optical fiber, wherein Rayleigh dissipates
Penetrating modal data information includes composing and measuring Rayleigh scattering spectrum with reference to Rayleigh scattering；
S2: the requirement according to user to measurement spatial resolution will compose and measure Rayleigh scattering with reference to Rayleigh scattering and compose nothing
It is truncated into aliasing K subset, wherein calculating the optimal subset window length for composing each subset with reference to Rayleigh scattering
S3: by optimal subset window obtained in S2It is auspicious to measuring in distance domain
Sharp scattering spectra and reference Rayleigh scattering spectrum re-start truncation, obtain the measurement Subset in K new distance domains and refer to subset；
S4: measurement Subset in distance domain that S3 is obtained and inverse Fourier transform is carried out with reference to subset and zero padding is to same
Data length I measurement Subset and transforms to spectral domain with reference to subset at this time, on spectral domain each group measurement Subset and with reference to subset into
Row cross-correlation analysis obtains the spectrum offset amount Δ F of every group of subset；
S5: the spectrum offset amount of every group of subset in S4 is converted into the strain information ε that measurement Rayleigh scattering composes each subset.
Further, the optimal subset window length that the reference Rayleigh scattering of the S2 composes each subset is specifically used such as lower section
Formula:
S21. the noise variance σ (η) calculated with reference to Rayleigh scattering spectrum passes through according to required strain calculation precision σ (d)
FormulaFind out the threshold value Q for the Rayleigh scattering spectrum signal intensity gradient summation that data length is Lt；
S22. the threshold value q of average subset signals intensity gradient sum is calculatedt=Qt/ K, K are subset quantity；
S23., each subset is set and unifies initial window lengthTo Rayleigh scattering
Spectrum signal carries out Fourier transformation, and data are transformed into distance domain from spectral domain, and with the initial subset window length of each subsetIt will be away from
The reference Rayleigh scattering spectrum of delocalization is truncated into K subset；
S24., K subset is carried out to inverse Fourier transform again and domain data of the zero padding to length for I, data are according to subset
Interior average signal strength gradient calculation formulaWhereinFor son
Signal intensity gradient in collection,For signal strength in subset, average signal strength gradient δ=[δ in each subset is calculated1,δ2,
δ3,...,δk]；
S25. according to formulaIt calculates in initial subset window lengthUnder each subset signal intensity gradient and
S26. with kth (k=1,2 ..., K) a subset for, judge inequalityIt is whether true；If set up,If invalid, makeS is that subset window extends fixed step size value, according to formulaNew q is calculatedk, continue to judge inequality qk≥qtIt is whether true, until occurringMake qk≥qtIt sets up, thenIter isThe number of iterations.
Embodiment:
The first step, the optical frequency domain reflectometer shown using Fig. 1 (OFDR) acquire reference of one group of tested optical fiber under unstressed
Rayleigh scattering modal data and one group of measurement Rayleigh scattering spectrum under stress, fiber lengths are 22 meters, and data length L is
450000。
Second step calculates the optimal subset window that each subset is composed with reference to Rayleigh scattering
1. the noise with reference to Rayleigh scattering spectrum signal is calculated according to required strain calculation precision σ (d)=0.008
Variances sigma (η)=4, passes through formulaQ is calculatedt=6.25 × 104, and it is set as threshold value；
2. according to formula qt=Qt/ K, be arranged subset quantity K=1500, be calculated subset average signal strength gradient and
Threshold value qt=41.7；
3. each subset, which is arranged, unifies initial window lengthRayleigh is dissipated
It penetrates spectrum signal and carries out Fourier transformation (FFT), data are transformed into distance domain from spectral domain, are truncated into K=1500 son with subset window
Collection；
4. each subset is carried out to inverse Fourier transform (IFFT) domain data that simultaneously zero padding is 1000 to data length again,
According to formulaBe calculated average signal strength gradient δ in each subset=[, 0.11,
0.136,...,0.126]；
5. according to formulaBy taking the 2nd subset as an example, calculate in initial subset window lengthLower letter
Number intensity gradient and
6. judging inequalityMake N2=310, being provided with subset window extension fixed step size value S is 10, again basis
FormulaNew q is calculatedk=42.3, judgement obtains inequality q at this timek≥qtIt sets up,
Then
7. being obtained with the 2nd subsetMethod it is identical, successively obtainFinally obtain this
The optimal subset window set N of group Rayleigh scattering spectrum signalopt=[380,310,300 ..., 340].
Step 3, by each subset optimal subset window N obtained in step 2opt=[380,310,300 ..., 340] away from
Be truncated in delocalization to measurement Rayleigh scattering spectrum and with reference to Rayleigh scattering spectrum, obtain measurement Subset in 1500 distance domains and
With reference to subset.
Step 4 carries out inverse Fourier transform simultaneously by the measurement Subset in distance domain obtained in step 3 and with reference to subset
Zero padding is to 1000 length, and measurement Subset and reference subset transform to spectral domain at this time.Each group measurement Subset and reference on spectral domain
Subset carries out cross-correlation analysis, obtains the spectrum offset amount Δ F of every group of subset.
Step 5, the spectrum offset amount Δ F of every group of subset is fibre strain spirit by formula ε=Δ F/K, K in step 4
Sensitivity coefficient is converted to the strain information ε of final each subset.
The foregoing is only a preferred embodiment of the present invention, but scope of protection of the present invention is not limited thereto,
Anyone skilled in the art in the technical scope disclosed by the present invention, according to the technique and scheme of the present invention and its
Inventive concept is subject to equivalent substitution or change, should be covered by the protection scope of the present invention.
Claims (1)
1. a kind of distributive fiber optic strain demodulation method based on subset window adaption algorithm, comprising the following steps:
S1: using the Rayleigh scattering modal data information in optical frequency domain reflectometer method acquisition tested optical fiber, wherein Rayleigh scattering is composed
Data information includes composing and measuring Rayleigh scattering spectrum with reference to Rayleigh scattering；
S2: the requirement according to user to measurement spatial resolution will compose and measure Rayleigh scattering spectrum with reference to Rayleigh scattering without aliasing
Ground is truncated into K subset, wherein calculating the optimal subset window length for composing each subset with reference to Rayleigh scattering
S3: by optimal subset window obtained in S2Measurement Rayleigh is dissipated in distance domain
It penetrates spectrum and re-starts truncation with reference to Rayleigh scattering spectrum, obtain the measurement Subset in K new distance domains and refer to subset；
S4: measurement Subset in distance domain that S3 is obtained and inverse Fourier transform is carried out with reference to subset and zero padding is to same data
Length I, measurement Subset and reference subset transform to spectral domain at this time, carry out to each group measurement Subset on spectral domain and with reference to subset mutual
Correlation analysis obtains the spectrum offset amount Δ F of every group of subset；
S5: the spectrum offset amount of every group of subset in S4 is converted into the strain information ε that measurement Rayleigh scattering composes each subset；
The reference Rayleigh scattering of the S2 composes the optimal subset window length of each subset specifically in the following way:
S21. the noise variance σ (η) calculated with reference to Rayleigh scattering spectrum passes through formula according to required strain calculation precision σ (d)Find out the threshold value Q for the Rayleigh scattering spectrum signal intensity gradient summation that data length is Lt；
S22. the threshold value q of average subset signals intensity gradient sum is calculatedt=Qt/ K, K are subset quantity；
S23., each subset is set and unifies initial window lengthRayleigh scattering is composed and is believed
Number Fourier transformation is carried out, data are transformed into distance domain from spectral domain, and with the initial subset window length of each subsetBy distance domain
Reference Rayleigh scattering spectrum be truncated into K subset；
S24., K subset is carried out to inverse Fourier transform again and domain data of the zero padding to length for I, data are according in subset
Average signal strength gradient calculation formulaWhereinFor in subset
Signal intensity gradient,For signal strength in subset, average signal strength gradient δ=[δ in each subset is calculated1,δ2,
δ3,...,δk]；
S25. according to formulaIt calculates in initial subset window lengthUnder each subset signal intensity gradient and
S26. with kth (k=1,2 ..., K) a subset for, judge inequalityIt is whether true；If set up,If invalid, makeS is that subset window extends fixed step size value, according to formulaNew q is calculatedk, continue to judge inequality qk≥qtIt is whether true, until occurringMake qk≥qtIt sets up, thenIter isThe number of iterations.
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