CN115808190B - OFDR spatial resolution improvement method and system based on full-phase FFT - Google Patents
OFDR spatial resolution improvement method and system based on full-phase FFT Download PDFInfo
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Abstract
The invention discloses an OFDR space resolution improving method and system based on full-phase FFT, the method utilizes the optical fiber sensing technology based on OFDR to obtain time domain signal sequence, and (3) obtaining a frequency domain signal sequence by adopting a data preprocessing algorithm based on full-phase FFT, and demodulating the frequency domain signal sequence to obtain a distribution curve of an environmental parameter to be detected along the length direction of the optical fiber. After the time domain signal period is prolonged by the data preprocessing algorithm based on the full-phase FFT, all possible cases are truncated by using a window function, and then the signal sequences under all the truncated cases are subjected to FFT, summed and averaged to obtain a full-phase preprocessing result. The spectrum leakage in each cut-off mode is counteracted after summation and average, so that spectrum broadening caused by spectrum leakage phenomenon in the data processing process is effectively restrained, and the spatial resolution of the optical fiber sensing technology based on OFDR is improved.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing, and particularly relates to an OFDR spatial resolution improving method and system based on full-phase FFT (Fast Fourier Transformation, fast Fourier transform).
Background
The optical fiber distributed sensing technology based on optical frequency domain reflection (OFDR, optical Frequency Domain Reflectometry) has excellent performance in the aspects of spatial resolution, sensitivity, signal to noise ratio and the like, and is widely applied to the fields of aerospace, petrochemical industry, civil engineering, perimeter security and the like. The technology adopts a tunable laser with narrow linewidth, wavelength scanning light emitted by a light source is divided into two paths, the two paths respectively enter a reference arm and a measuring arm, local oscillation light of the reference arm and a backward Rayleigh scattering signal returned by an optical fiber to be measured in the measuring arm generate beat frequency, and the frequency and phase information of a time domain beat frequency signal are respectively utilized to process and obtain position and environment parameter information carried in the optical fiber. Where the spatial resolution of the OFDR depends on the frequency resolution during fourier transformation and the ambient parameter resolution depends on the wavelength resolution during phase information processing.
The prior art provides an OFDR strain signal demodulation method based on discrete Fourier transform (DFT, discrete Fourier Transformation), which obtains the position information of each scattering point in the optical fiber by utilizing the obtained frequency domain signal of the DFT algorithm after obtaining the OFDR time domain signal. And further processing by adopting a cross-correlation algorithm to obtain the strain information carried in the optical fiber. The efficient implementation mode of the DFT is a Fast Fourier Transform (FFT) algorithm, and the steps of time domain sampling, data truncation, frequency domain sampling and the like are needed. Data truncation may result in the presence of other frequency components in the signal spectrum, i.e., the presence of spectral leakage. The signal energy leaks to the whole frequency band from the original single spectral line, the frequency spectrum is widened, and the spatial resolution is further deteriorated.
Aiming at the problem of spectrum leakage in the FFT algorithm, the prior art provides an OFDR vibration signal demodulation method based on windowed FFT. After OFDR time domain signals are obtained, the time domain signal sequences are windowed, namely a smooth window function is used for replacing a rectangular window function to conduct signal interception, and FFT is conducted on the windowed signals to obtain frequency domain signals, so that position information of each scattering point of the optical fiber is obtained. And further obtaining vibration information carried in the optical fiber through phase demodulation. In this method, windowing of the time-domain signal sequence is equivalent in the frequency domain to replacing the rectangular window fourier spectrum with the other window fourier spectrum and convolving with the signal spectrum. The attenuation of the first side lobe of the spectrum of a common window function such as a triangular window, a hamming window, a hanning window, etc. is larger than that of a rectangular window, so that the spectrum leakage of the sequence after windowing is suppressed. However, the main lobe bandwidth of the window function spectrum is also larger than that of a rectangular window, and because of a plurality of dense frequency components in the OFDR system, adjacent spectrum components can overlap due to main lobe broadening, so that the spatial resolution is degraded.
Disclosure of Invention
Aiming at the defects or improvement demands of the prior art, the invention provides an OFDR spatial resolution improving method and system based on full-phase FFT, and aims to solve the problem of degradation of spatial resolution caused by spectrum leakage phenomenon in the OFDR signal processing process.
To achieve the above object, according to a first aspect of the present invention, there is provided an OFDR spatial resolution enhancement method based on an all-phase FFT, including:
S1, respectively acquiring a time domain reference signal before an environmental parameter to be detected acts on an OFDR-based distributed optical fiber sensor and a measurement signal after the environmental parameter to be detected acts on the distributed optical fiber sensor;
S2, respectively carrying out full-phase FFT preprocessing on the time domain reference signal and the measurement signal as signals to be processed as follows: performing period prolongation on the signal to be processed to obtain an initial sequence; all possible truncations are carried out on the initial sequence by adopting a window function with a first preset length, so that all possible sequences are obtained; summing and averaging all possible sequences after FFT to obtain a target signal, and extracting the position information of each scattering point of the optical fiber from the target signal;
And S3, demodulating the frequency domain reference signal and the measurement signal which are subjected to the full-phase FFT preprocessing according to the position information to obtain a distribution curve of the environmental parameter to be detected along the length direction of the optical fiber.
According to a second aspect of the present invention, there is provided an OFDR spatial resolution enhancement system based on an all-phase FFT, comprising: a computer readable storage medium and a processor;
The computer-readable storage medium is for storing executable instructions;
the processor is configured to read executable instructions stored in the computer readable storage medium and perform the method according to the first aspect.
In general, the above technical solutions conceived by the present invention, compared with the prior art, enable the following beneficial effects to be obtained:
The invention discloses an OFDR space resolution improving method and system based on full-phase FFT, the method utilizes the optical fiber sensing technology based on OFDR to obtain time domain signal sequence, and (3) obtaining a frequency domain signal sequence by adopting a data preprocessing algorithm based on full-phase FFT, and demodulating the frequency domain signal sequence to obtain a distribution curve of an environmental parameter to be detected along the length direction of the optical fiber. After the time domain signal period is prolonged by the data preprocessing algorithm based on the full-phase FFT, all possible cases are truncated by using a window function, and then the signal sequences under all the truncated cases are subjected to FFT, summed and averaged to obtain a full-phase preprocessing result. The spectrum leakage in each cut-off mode is counteracted after summation and average, so that spectrum broadening caused by spectrum leakage phenomenon in the data processing process is effectively restrained, and the spatial resolution of the optical fiber sensing technology based on OFDR is improved.
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FIG. 1 is a flowchart of an OFDR spatial resolution enhancement method based on full phase FFT according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an OFDR-based optical fiber sensing technique;
FIG. 3 is a flowchart of a data preprocessing method based on full phase FFT according to an embodiment of the present invention;
FIG. 4 is a second flowchart of an OFDR spatial resolution enhancement method based on full phase FFT according to the present invention;
FIG. 5 is a diagram of an OFDR-based optical fiber environment parameter measurement device;
FIG. 6 is a block diagram of a data preprocessing algorithm based on full phase FFT according to an embodiment of the invention;
fig. 7 is a comparison chart of OFDR spectra corresponding to a plurality of reflection points in an optical fiber sensing link, which are obtained by respectively adopting FFT, windowed FFT (hanning window) and full-phase FFT provided by the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The embodiment of the invention provides an OFDR spatial resolution improvement method based on full-phase FFT, as shown in figure 1, comprising the following steps:
s1, respectively acquiring a time domain reference signal before an environmental parameter to be measured acts on the distributed optical fiber sensor based on the OFDR and a measurement signal after the environmental parameter to be measured acts on the distributed optical fiber sensor.
Specifically, an optical fiber sensing technology based on OFDR is utilized to respectively acquire a time domain reference signal sequence I r (n) and a measurement signal sequence I m (n) before and after the action of an environmental parameter.
The external environment parameters to be measured include, but are not limited to, temperature, strain or vibration.
As shown in fig. 2, the principle of the optical fiber sensing technology based on OFDR is as follows: the continuous sweep light output by the tunable laser 1 enters the coupler 2 and then is split into two beams, one beam enters the reference arm to become reference light. The other beam enters the optical fiber to be measured 3 in the signal arm, and the light entering the optical fiber to be measured can generate Rayleigh scattering. The backward scattered signal light in the reference light and the optical fiber to be measured reaches the photosensitive surface of the photodetector 4 through different paths of the coupler 2 to interfere. The interference light carries the frequency difference and the phase difference of the two beams of light, and is detected on the surface of the photoelectric detector to obtain an OFDR time domain signal sequence comprising a time domain reference sequence and a measurement signal.
S2, respectively carrying out full-phase FFT preprocessing on the time domain reference signal and the measurement signal as signals to be processed as follows: performing period prolongation on the signal to be processed to obtain an initial sequence; all possible truncations are carried out on the initial sequence by adopting a window function with a first preset length, so that all possible sequences are obtained; summing and averaging all possible sequences after FFT to obtain a target signal, and extracting the position information of each scattering point of the optical fiber from the target signal; the target signal includes a frequency domain reference signal and a measurement signal after full phase FFT preprocessing.
Specifically, a data preprocessing algorithm based on full-phase FFT is adopted to respectively perform spectrum analysis on a time domain reference signal and a measurement signal, so as to obtain a frequency domain reference signal and a measurement signal (including the position information of each scattering point of the optical fiber) after full-phase preprocessing, and further obtain the position information of each scattering point of the optical fiber.
The data preprocessing algorithm based on the full-phase FFT comprises the following steps: firstly, carrying out period prolongation on a time domain signal sequence, then carrying out truncation of all possible conditions on the time sequence after period prolongation by utilizing a window function with a certain length, and finally, respectively carrying out post-FFT summation and average on the sequences under all the truncation conditions to obtain a frequency domain reference signal and a measurement signal after full-phase pretreatment, namely obtaining the position information of each scattering point of the optical fiber.
As shown in fig. 3, the data preprocessing method based on the full-phase FFT includes steps of truncation, cyclic shift, FFT, summation averaging and the like. The total length of the input time domain signal sequence I (N) is N, firstly, the time domain signal sequence I (N) is subjected to periodic extension, then, the signals after periodic extension are truncated by using a window function W (N) with the same length of N, and all truncation conditions are traversed by carrying out cyclic shift on the window function. And finally, respectively carrying out FFT (fast Fourier transform) summation and average on the sequences under all cut-off conditions to obtain a full-phase preprocessing result X (z), and obtaining the position information of each scattering point of the optical fiber. All-phase preprocessing is performed on the time-domain reference signal I r (n) and the measurement signal I m (n), so as to obtain a frequency-domain reference signal X r (z) and a measurement signal X m (z) respectively.
Period extension has a variety of ways, but it is contemplated that overlapping of the effective signals may occur if the extension period is less than the original signal sequence length; if the extension period is larger than the original signal sequence, the signal quality is reduced because the effective signal is selected to be in the area without the effective signal when the signal is cut off. Based on this, preferably, the extension period in the embodiment of the present invention is the original sequence length of the signal to be processed; namely, the period extension in the step S2 takes the original time domain signal sequence length as the period, and the period extension is performed by directly repeating the sequence.
The first preset length can be set according to actual requirements, but considering that in general cases, when the time domain signal is converted into the frequency domain signal by utilizing FFT, the length of the signal sequence before and after conversion is unchanged; if the length of the truncated window is different from that of the original signal, the length of the processed signal is different from that of the original signal, which is unfavorable for subsequent data processing. Based on this, preferably, in the embodiment of the present invention, the first preset length is an original sequence length of a signal to be processed; that is, in the step S2, the signal after the period extension is truncated by using a length window having the same length as the original signal sequence, so that the period length of the signal after the period extension is equal to the period length of the signal after the period extension is truncated, and the sequences under all the truncation conditions are subjected to post-FFT summation and average.
Preferably, window functions for data truncation during full phase data preprocessing include, but are not limited to, rectangular windows, hanning windows, hamming windows, and the like.
And S3, demodulating the frequency domain reference signal and the measurement signal which are subjected to the full-phase FFT preprocessing according to the position information to obtain a distribution curve of the environmental parameter to be detected along the length direction of the optical fiber.
Specifically, there are two signal demodulation methods, one is to perform signal demodulation based on the wavelength shift amount of the fiber rayleigh scattering spectrum, and the other is to perform signal demodulation based on the phase change amount of the scattered light.
When signal demodulation is performed based on the wavelength drift amount of the fiber Rayleigh scattering spectrum, the flow of the OFDR spatial resolution improvement method based on the full-phase FFT provided by the embodiment of the invention is shown in figure 4.
Firstly, segmenting a frequency domain signal sequence obtained after full-phase pretreatment, taking a frequency domain signal in a certain length window for IFFT to obtain a Rayleigh scattering spectrum, further detecting the wavelength drift amount of the Rayleigh scattering spectrum corresponding to the length window compared with a reference spectrum, and obtaining an external environment parameter corresponding to the length window. By moving the length window along the length of the optical fiber, a distribution curve of the environmental parameter along the length of the optical fiber is obtained, that is, the step S3 includes:
s31, segmenting the frequency domain reference signal by adopting a window function with a second preset length, and respectively performing IFFT on each segmented frequency domain reference signal and the measurement signals in the corresponding length window to obtain a reference Rayleigh scattering spectrum and a measurement Rayleigh scattering spectrum in each length window.
Specifically, the frequency domain reference signal obtained in the step S2 is segmented by utilizing a window with a certain length, and IFFT is carried out on signals in the window with the same position in the frequency domain reference signal and the measured signal, so that a reference Rayleigh scattering spectrum and a measured Rayleigh scattering spectrum corresponding to the length window are obtained.
That is, the frequency domain signal obtained in S2 is equally divided into K segments by using a length window, and the rayleigh scattering spectrum corresponding to the length window of the K segment is obtained by IFFT.
Dividing the frequency domain signal into K segments, selecting a length window with the length delta z of the K (K is N +, K is less than or equal to K) segment, and referring to the frequency domain reference signal in the length windowAnd measuring signalsPerforming IFFT to obtain the reference Rayleigh scattering spectrum corresponding to the length windowAnd measuring Rayleigh scattering spectra
Preferably, the formula is as follows:
s32, detecting wavelength drift amount of the reference Rayleigh scattering spectrum and the measured Rayleigh scattering spectrum to obtain a distribution curve of the environmental parameter to be detected along the length direction of the optical fiber.
Specifically, wavelength drift amount detection is carried out on the reference Rayleigh scattering spectrum and the measured Rayleigh scattering spectrum corresponding to the length window, when the external environment parameter difference exists between the two groups of data, the Rayleigh scattering spectrum drifts, and the environment parameter corresponding to the length window is determined through the wavelength drift amount;
that is, the reference Rayleigh scattering spectrum corresponding to the kth segment length window And measuring Rayleigh scattering spectrumAnd detecting wavelength drift amount, and when external environment parameter difference exists between the two groups of data, measuring the drift of the Rayleigh scattering spectrum relative to the reference Rayleigh scattering spectrum, and further determining an environment parameter p (z k) corresponding to a k section length window through the wavelength drift amount.
Preferably, the Rayleigh scattering spectrum wavelength drift amount detection algorithm comprises, but is not limited to, a cross correlation algorithm, a least square method, a least Euclidean distance method and the like.
Preferably, the equation for detecting the wavelength drift amount of the Rayleigh scattering spectrum by using the cross-correlation algorithm is as follows:
Where the function conv represents the cross-correlation algorithm, Is a cross-correlation spectrum. The function match represents finding the position of a certain value in the array, i.e. finding the position of the maximum value in the cross-correlation spectrum. K p is an external environment parameter-wavelength drift coefficient, and can be obtained through scaling.
And (3) moving a length window along the length direction of the optical fiber, and repeating the steps S31 and S32 to obtain the distribution curve of the environmental parameter to be measured along the length direction of the optical fiber.
That is, by moving the length window along the length direction of the optical fiber so that k traverses the [1, k ] section, the distribution curve p (z) of the environmental parameter along the length direction can be obtained by repeating S31 and S32.
In summary, when demodulating a signal based on fiber rayleigh scattering, dividing the frequency domain signal obtained after full-phase pretreatment into K (K e N +) segments, and selecting a frequency domain signal corresponding to a K segment length window from k=1 to perform IFFT to obtain the rayleigh scattering spectrum corresponding to the length window. And further detecting the wavelength drift amount of the Rayleigh scattering spectrum corresponding to the kth section of length window relative to the reference spectrum, and obtaining the external environment parameter corresponding to the length window. And finally, moving a length window along the length direction of the optical fiber to enable k to traverse the [1, K ] interval, and obtaining an environment parameter curve distributed along the length direction.
When demodulating based on the phase variation amount of the scattered light, the step S3 includes:
s31', calculating phase angles corresponding to all scattering points of the optical fiber according to the frequency domain reference signals and the measuring signals after full-phase preprocessing;
And S32', differentiating and deriving the phase angle to obtain a distribution curve of the environmental parameter to be measured along the length direction of the optical fiber.
The method provided by the invention will be further described with a specific example.
And acquiring a time domain reference signal and a measurement signal before and after the action of the environmental parameter by using an OFDR-based optical fiber sensing technology. The technology adopts a tunable laser with narrow linewidth, wavelength scanning light emitted by a light source is divided into two paths, the two paths enter a reference arm and a measuring arm respectively, beat frequency is generated between local oscillation light of the reference arm and a backward Rayleigh scattering signal returned by an optical fiber to be measured in the measuring arm, and a time domain signal obtained by a photoelectric detector carries position and environmental parameter information of the optical fiber. Since the tunable laser inevitably exhibits a nonlinear sweep phenomenon when outputting continuous sweep light, spatial resolution is deteriorated. Therefore, an auxiliary interferometer is added into the optical fiber environment parameter measuring device based on the OFDR to acquire the instantaneous optical frequency information of the laser, and the nonlinear sweep frequency compensation is realized. In addition, the polarization fading phenomenon in the distributed sensing can cause the degradation of the signal-to-noise ratio of the OFDR beat frequency signal, so that the polarization diversity reception is added to inhibit the degradation effect of the polarization fading phenomenon on the signal.
FIG. 5 shows an OFDR-based optical fiber environment parameter measurement device according to an embodiment of the present invention. The tunable laser 1 generates a beam of wavelength-swept light with a wavelength sweep range of 60nm, a sweep speed of 60nm/s and an output power of 8dBm. The beam is split into two beams after passing through the isolator 5 and the coupler 6 (the splitting ratio is 10:90), wherein 10% of the beams enter the auxiliary interferometer and 90% of the beams enter the main interferometer. The auxiliary interferometer consists of a coupler 7 (the splitting ratio is 50:50), a delay optical fiber 8, a Faraday rotator 9 and a Faraday rotator 10. And detecting a time domain signal I REF (n) output by the auxiliary interferometer by using the photoelectric detector 11 to acquire real-time optical frequency information of the laser. The main interferometer comprises a polarization diversity receiving structure, and comprises a coupler 12 (the light splitting ratio is 10:90), a polarization controller 13, a circulator 14, a sensing optical fiber 15, a coupler 16 (the light splitting ratio is 50:50), a polarization beam splitter 17 and a polarization beam splitter 18. 10% of the light passes through the coupler 12 and enters the polarization controller 13 shown in the upper leg, and 90% enters the circulator 14 shown in the lower leg. Time domain reference signals I r,x (n) and I r,y (n) and measurement signals I m,x (n) and I m,y (n) in the x-polarization and y-polarization directions are detected by the balance detector 19 and the balance detector 20, respectively, and passed to the data acquisition and signal processing module 21.
The auxiliary interferometer time domain signal obtained by the device is utilized to carry out nonlinear sweep compensation on the time domain signals in the x-polarization direction and the y-polarization direction of the main interferometer, and the square sum of the signals in the x-polarization direction and the y-polarization direction after compensation is carried out, so that the main interferometer time domain reference signal I r (n) and the measurement signal I m (n) which are subjected to nonlinear sweep compensation and polarization attenuation inhibition are obtained.
The nonlinear sweep frequency compensation method comprises a hardware compensation method and a software compensation method, such as an auxiliary interferometer trigger sampling method, a resampling method, a matched Fourier transform method, a declivity filtering method and the like.
Fig. 6 is a block diagram of a data preprocessing algorithm based on an all-phase FFT in an embodiment of the present invention. Taking full-phase FFT with data length n=3 as an example, spectrum analysis is performed on all truncated cases with length n=3 including data point I (0), and then summation and averaging are performed to obtain a final full-phase spectrum analysis result. The spectrum leakage in each cut-off mode counteracts most of the spectrum leakage after summation and averaging, thereby achieving the purpose of inhibiting the spectrum leakage. At this time, the full-phase FFT algorithm performs n=3 FFT operations, the calculation amount of the algorithm is obviously increased, and in order to simplify the operation, all input segments are overlapped and then subjected to FFT again according to the superposition and homogeneity of the linear time-invariant system. The full-phase preprocessing is equivalent to weighting [ I (-N), …, I (0), …, I (N) ] by a triangular window with length of 2N-1=5, adding the data items with interval of n=3, that is, implementing cyclic shift addition, and finally performing FFT on the data after the summation and averaging to obtain the frequency domain signal X (z), that is, obtaining the position information of each scattering point of the optical fiber. The above procedure is used to pre-process the time domain reference signal I r (n) and the measurement signal I m (n) to obtain the frequency domain reference signal X r (n) and the measurement signal X m (n), respectively.
Dividing a frequency domain reference signal X r (N) and a measurement signal X m (N) into K sections by utilizing a window with the length of deltaz, selecting a K (K is N +, K is less than or equal to K) section length window from the K section length window, performing IFFT on the frequency domain signal in the window, and obtaining a reference Rayleigh scattering spectrum corresponding to the length windowAnd measuring Rayleigh scattering spectra
A cross-correlation algorithm is adopted to perform the corresponding reference Rayleigh scattering spectrum on the kth section length windowAnd measuring Rayleigh scattering spectrumAnd detecting the wavelength drift amount. When the external environment parameter difference exists between the two groups of data, the environment parameter p (z k) corresponding to the length window is determined through the wavelength drift quantity.
Where the function conv represents the cross-correlation algorithm,Is a cross-correlation spectrum. The function match represents finding the position of a certain value in the array, i.e. finding the position of the maximum value in the cross-correlation spectrum. K p is an external environment parameter-wavelength drift coefficient, and can be obtained through scaling.
By moving the length window along the length direction of the optical fiber, k is traversed over the [1, k ] interval, and the parameter distribution curve p (z) along the length direction can be obtained.
As shown in fig. 7, the data preprocessing algorithm based on the full-phase FFT, the FFT algorithm and the windowed FFT algorithm in the present invention are adopted to respectively obtain OFDR spectrums corresponding to a plurality of reflection points in the optical fiber sensing link. Firstly, the optical fiber environment parameter measuring device based on OFDR shown in fig. 5 in the embodiment of the invention is utilized to obtain a time domain signal, after nonlinear effect compensation and polarization fading inhibition, FFT, windowed FFT and full-phase FFT are respectively adopted to perform data processing to obtain a signal spectrum, and comparison is performed. Taking three adjacent reflection points as an example, in the spectrum obtained by the FFT algorithm, three adjacent reflection peaks are widened under the influence of spectrum leakage, so that the three adjacent reflection peaks cannot be distinguished. When the windowed (hanning window) FFT is adopted, the attenuation of the first side lobe of the spectrum reflection peak is larger, and the spectrum leakage is suppressed. However, the main lobe bandwidth is also increased, and for the reflection peaks corresponding to three adjacent reflection points, main lobe components overlap each other, and the adjacent reflection points still cannot be distinguished. When the data preprocessing algorithm based on the full-phase FFT is adopted, all possible truncation conditions are considered and averaged, and the bandwidth widening of the main lobe is reduced while the amplitude of the side lobe is reduced. The spectrum leakage is suppressed, and the phenomenon of overlapping of adjacent reflection peak spectrums caused by main lobe broadening is avoided to a certain extent. And three adjacent reflection points in the frequency spectrum can be better resolved, and better spatial resolution is obtained.
According to the method, the time domain reference signal and the measuring signal before and after the action of the environmental parameters are respectively obtained by using the OFDR-based optical fiber sensing technology. And then, carrying out data preprocessing on the time domain signals by adopting full-phase FFT (fast Fourier transform), and respectively obtaining a frequency domain reference signal and a measurement signal, namely obtaining the position information of each scattering point in the optical fiber. A window of a certain length is then taken from the frequency domain signal and IFFT is performed to obtain a reference and measured rayleigh scattering spectrum. And further detecting wavelength drift amount of the measured Rayleigh scattering spectrum and the reference Rayleigh scattering spectrum to obtain external environment parameters corresponding to the length window. By moving the length window along the length of the fiber, a profile of the environmental parameter along the length of the fiber is obtained. After the time domain signal period is prolonged by the data preprocessing algorithm based on the full-phase FFT, all possible conditions of the signal are truncated by using a window function, spectrum analysis is carried out on all possible truncated conditions of the signal, and a full-phase preprocessing result is obtained after summation and average are carried out. The spectrum leakage in each cut-off mode is counteracted after summation and average, so that spectrum broadening caused by spectrum leakage phenomenon in the data processing process is restrained, and the spatial resolution of the optical fiber sensing technology based on OFDR is effectively improved.
The embodiment of the invention provides an OFDR spatial resolution improving system based on full-phase FFT, comprising the following steps: a computer readable storage medium and a processor;
The computer-readable storage medium is for storing executable instructions;
The processor is configured to read executable instructions stored in the computer readable storage medium and perform a method as in any of the embodiments described above.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (9)
1. An OFDR spatial resolution improving method based on full-phase FFT, which is characterized by comprising the following steps:
S1, respectively acquiring a time domain reference signal before an environmental parameter to be detected acts on an OFDR-based distributed optical fiber sensor and a measurement signal after the environmental parameter to be detected acts on the distributed optical fiber sensor;
s2, respectively carrying out full-phase FFT preprocessing on the time domain reference signal and the measurement signal as signals to be processed as follows: performing period prolongation on the signal to be processed to obtain an initial sequence; all possible truncations are carried out on the initial sequence by adopting a window function with a first preset length, so that all possible sequences are obtained; summing and averaging all possible sequences after FFT to obtain a target signal, and extracting the position information of each scattering point of the optical fiber from the target signal; the target signal comprises a frequency domain reference signal and a measurement signal after full-phase FFT preprocessing;
And S3, demodulating the frequency domain reference signal and the measurement signal which are subjected to the full-phase FFT preprocessing according to the position information to obtain a distribution curve of the environmental parameter to be detected along the length direction of the optical fiber.
2. The method of claim 1, wherein the extension period is an original sequence length of the signal to be processed.
3. The method of claim 1, wherein the first predetermined length is an original sequence length of the signal to be processed.
4. The method of claim 1, wherein the window function is a rectangular window, a hanning window, or a hamming window.
5. The method of claim 1, wherein signal demodulation is based on the amount of wavelength shift of the fiber rayleigh scattering spectrum; or, signal demodulation is performed based on the phase change amount of the scattered light.
6. The method of claim 5, wherein demodulating the signal based on the amount of wavelength shift of the fiber rayleigh scattering spectrum comprises:
Segmenting the frequency domain reference signal by adopting a window function with a second preset length, and respectively performing IFFT on each segmented frequency domain reference signal and the measurement signals subjected to full-phase pretreatment in the corresponding length window to obtain a reference Rayleigh scattering spectrum and a measurement Rayleigh scattering spectrum in each length window;
And detecting wavelength drift amount of the reference Rayleigh scattering spectrum and the measured Rayleigh scattering spectrum to obtain a distribution curve of the environmental parameter to be detected along the length direction of the optical fiber.
7. The method of claim 6, wherein the wavelength drift amount detection is based on a cross-correlation algorithm, a least squares method, or a least euclidean distance method.
8. The method of claim 1, wherein the environmental parameter to be measured is temperature, strain, or vibration.
9. An OFDR spatial resolution enhancement system based on an all-phase FFT, comprising: a computer readable storage medium and a processor;
The computer-readable storage medium is for storing executable instructions;
the processor is configured to read executable instructions stored in the computer readable storage medium and perform the method of any one of claims 1-8.
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