Information recovery method of distributed optical fiber sensing based on wavelet decomposition in optical frequency domain scattering

Abstract

The method for recovering information of optical frequency domain scattering distributed optical fiber sensing based on wavelet decomposition belongs to the field of distributed optical fiber sensing technology; the method uses wavelet decomposition as a spatial / spectral domain analysis tool for distributed optical fiber sensing, and repeatedly performs wavelet decomposition on distributed optical fiber sensing signals or targeted wavelet decomposition on positions of interest. The coefficients of wavelet decomposition correspond to the reflectivity or scattering spectra of sensing units at different positions, and the two reflectivity or scattering spectra before and after the strain or temperature change at the same spatial position are cross-correlated and calculated to obtain the spectral offset of each spatial position, thereby obtaining the distributed strain or temperature. The present invention has the characteristics of being able to independently set spatial resolution and spectral resolution, and is not affected by the mutual restriction relationship between the two. Under the same spatial resolution, the strain / temperature resolution is higher, and the distributed sensing local information of a certain section of optical fiber position of interest can also be recovered, greatly improving the demodulation speed.

Description

Technical Field

[0001] The invention belongs to the technical field of distributed optical fiber sensing, and in particular relates to an optical frequency domain scattering distributed optical fiber sensing information demodulation method based on wavelet decomposition. Background Art

[0002] Distributed fiber optic sensing technology based on optical frequency domain scattering (OFDR) has become a typical high-precision fiber optic distributed sensing technology due to its high spatial resolution, spectral resolution and continuous measurement characteristics, and has received widespread attention in the measurement of distributed temperature and strain.

[0003] With the increasing application of OFDR distributed sensing technology, the demand for OFDR technology's sensing density, sensing accuracy and continuous sensing has developed rapidly in recent years. The traditional method uses a weak fiber grating string as the sensing fiber. Only the area where the fiber grating is written on the fiber has the ability to sense strain or temperature, while the ordinary fiber area does not have the sensing ability and has a measurement "dead zone". Therefore, it still belongs to quasi-distributed sensing and cannot achieve true distributed sensing.

[0004] In recent years, with the in-depth study of fiber scattering phenomenon, spontaneous Rayleigh scattering in optical fiber has gradually attracted attention. The reason for spontaneous Rayleigh scattering in optical fiber is that when manufacturing optical fiber, there are impurities and slight differences in refractive index distribution inside the optical fiber. It can be considered as a stable and unchanging random period equivalent weak grating, and its reflection spectrum is related to the period distribution of the equivalent weak grating. It is a local optical fiber spectral characteristic similar to a "fingerprint". When the local optical fiber is subjected to strain or temperature, the period and refractive index of the equivalent weak grating will change accordingly, so the local "fingerprint" spectrum of the optical fiber will also shift accordingly. Therefore, the demodulation of temperature or strain information and spatial position information can be achieved by using OFDR and Rayleigh scattering spectrum sensing technology.

[0005] At present, demodulation algorithms based on short-time Fourier transform are often used to restore OFDR sensing information. After the OFDR sensing signal is Fourier transformed, the sensing position can be distinguished by frequency, and the position information of the reflection point can be demodulated; and the envelope of the frequency-modulated reflection signal represents the spectrum of the position, the signal in the distance domain is windowed, and the spectral information of each position is extracted by sliding, and the spectrum is obtained by inverse Fourier transform, and the spectral frequency shift is calculated by spectral cross-correlation to obtain strain or temperature information. However, the method of slidingly extracting spectral information after windowing the signal in the distance domain in this algorithm will significantly weaken the spectral resolution. Since the product of the spatial resolution and strain / temperature resolution of the OFDR distributed sensing model is a constant, the algorithm will actually significantly increase this constant, so it is necessary to sacrifice a certain spatial resolution to increase the smaller strain or temperature that can be measured. There is a mutual constraint relationship between spatial resolution and spectral resolution.

[0006] In addition, the improved information recovery algorithm based on short-time Fourier transform extracts the signal in the distance domain, uses zero padding to extend the length of the extracted signal to the data length of the complete signal, and then performs inverse Fourier transform to obtain the spectrum. The zero padding operation enables the extracted signal to achieve spectrum refinement, so that the spectral resolution is not weakened, and can achieve the constant value of the product of the spatial resolution and strain resolution of the OFDR distributed sensing model. However, the Rayleigh scattering spectrum obtained by the algorithm through the zero padding operation is not the original, true spectrum, and it is easy to demodulate the wrong spectral information, affecting the measurement accuracy of strain or low temperature.

[0007] In summary, although OFDR sensing technology has achieved distributed measurement of temperature and strain, its sensing information recovery algorithm either weakens the spectral resolution, resulting in low strain or temperature resolution; or it easily demodulates erroneous spectral information, affecting the measurement accuracy of strain or temperature. Summary of the invention

[0008] In order to overcome the problem of low strain or temperature resolution of the above-mentioned OFDR distributed sensing information recovery method, the present invention proposes a method for recovering distributed optical fiber sensing information based on wavelet decomposition and optical frequency domain scattering, which demodulates distributed sensing information from data collected by the OFDR instrument. The distributed sensing information recovery method based on wavelet decomposition has the ability to characterize the local characteristics of the signal in both the distance domain and the spectral domain, thereby recovering the spatial position information and spectral information carried by the sensing signal. The distributed sensing information recovery method based on wavelet decomposition will not cause the problem of weakened spectral resolution during the strain or temperature information recovery process, thereby achieving improved strain or temperature resolution at the same spatial resolution. The multi-resolution analysis characteristics of the wavelet decomposition sensing information recovery method overcome the problem of mutual restriction between spatial resolution and spectral resolution caused by windowing of the short-time Fourier transform algorithm. In addition, the method can perform focused analysis based on a certain section of a spatial region of interest, greatly improving the demodulation speed.

[0009] Technical solution of the present invention

[0010] A method for recovering uniform spatial resolution information of optical frequency domain scattering distributed optical fiber sensing based on wavelet decomposition, characterized in that the method comprises the following steps:

[0011] Step 1: The quotient of the optical frequency domain scattering distributed optical fiber sensing length and the wavelet decomposition series corresponds to the spatial resolution of the distributed sensing. The wavelet decomposition series is set according to the requirements of the spatial resolution.

[0012] Step 2: Before the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data is subjected to wavelet decomposition. The sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively.

[0013] Step 3, repeat step 2 to continue to perform wavelet decomposition on the signal after each wavelet decomposition until the wavelet decomposition level set in step 1 is reached, and each obtained wavelet level corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensor, which serves as the reference spectrum before stress or temperature action;

[0014] Step 4: After the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data obtained each time is subjected to wavelet decomposition according to the above steps 2 to 3, and each obtained wavelet series corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensing, which is used as the measurement spectrum after the stress or temperature is applied;

[0015] Step 5, cross-correlation calculation is performed on the reference spectrum and the measured spectrum of the same order obtained in Step 3 and Step 4, and the shift of the cross-correlation peak in the cross-correlation result represents the shift of the reflection or scattering spectrum of the sensing unit corresponding to the spatial position of the wavelet of the order;

[0016] Step 6: Repeat step 5 to obtain the spectral offset of each level of wavelet, i.e., each spatial position sensing unit;

[0017] Step 7: According to the relationship between the spectral offset and the strain or temperature, the strain or temperature of each spatial position sensing unit is calculated to complete the method for recovering uniform spatial resolution information of optical frequency domain scattering distributed optical fiber sensing.

[0018] The wavelet decomposition method used may be Meyer, dBN, or Triband wavelet.

[0019] A method for recovering local spatial range information of optical frequency domain scattering distributed optical fiber sensing based on wavelet decomposition, characterized in that the method comprises the following steps:

[0020] Step 1: The quotient of the optical frequency domain scattering distributed optical fiber sensing length and the wavelet decomposition series corresponds to the spatial resolution of the distributed sensing. The wavelet decomposition series is set according to the requirements of the spatial resolution.

[0021] Step 2: Before the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data is subjected to wavelet decomposition. The sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively.

[0022] Step 3, repeat step 2 to continue to perform wavelet decomposition on the signal after each wavelet decomposition until the wavelet decomposition level set in step 1 is reached, and each obtained wavelet level corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensor, which serves as the reference spectrum before stress or temperature action;

[0023] Step 4: After the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data obtained each time is subjected to wavelet decomposition, and the distributed sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively.

[0024] Step 5: Select the wavelet series that contains a certain local sensing range to be analyzed from the wavelet decomposition results of the previous step and continue to decompose;

[0025] Step 6, repeat step 5 until the spatial resolution of the local sensing range to be analyzed reaches the set value, and each obtained wavelet series corresponds to the reflection or scattering spectrum information of a sensing unit in a local sensing range to be analyzed of the optical frequency domain scattering distributed optical fiber sensor, which is used as the measurement spectrum after the stress or temperature action;

[0026] Step 7, cross-correlation calculation is performed on the reference spectrum and the measured spectrum of the same order obtained in Step 3 and Step 6, and the shift of the cross-correlation peak in the cross-correlation result represents the shift of the reflection or scattering spectrum of the sensing unit within a local sensing range to be analyzed corresponding to the wavelet of this order;

[0027] Step 8: Repeat step 7 to obtain the spectral offset of each level of wavelet, that is, each spatial position sensing unit within a certain local sensing range to be analyzed;

[0028] Step 9: According to the relationship between the spectral offset and the strain or temperature, the strain or temperature of each spatial position sensing unit within a local sensing range to be analyzed is calculated to complete the local spatial range information recovery method of optical frequency domain scattering distributed optical fiber sensing.

[0029] The wavelet decomposition method used may be Meyer, dBN, or Triband wavelet.

[0030] The advantages of the present invention are: mathematically there is no mutual restriction relationship between spatial resolution and spectral resolution. Under the condition of the same spatial resolution, the spectral resolution can be improved to obtain higher strain or temperature resolution; the distributed sensing local information of a certain section of optical fiber position of interest can be restored, greatly improving the demodulation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the wavelet decomposition process in the method for recovering information of uniform spatial sensing in optical frequency domain scattering based on wavelet decomposition;

[0032] Figure 2 It is a schematic diagram of the wavelet decomposition process in the method for recovering spatial sensing information in the local range of optical frequency domain scattering based on wavelet decomposition;

[0033] Figure 3It is a schematic diagram of the reflection or scattering spectrum of a certain spatial position obtained from the distributed sensing information data of the optical frequency domain scatterometer;

[0034] Figure 4 It is a schematic diagram of wavelength shift obtained after cross-correlation calculation of reflection or scattering spectra at the same spatial position before and after strain or temperature change. DETAILED DESCRIPTION

[0035] The specific implementation of the present invention is further described in detail below with reference to the accompanying drawings:

[0036] A method for recovering uniform spatial resolution information of optical frequency domain scattering distributed optical fiber sensing based on wavelet decomposition, characterized in that the method comprises the following steps:

[0037] Step 1: The quotient of the optical frequency domain scattering distributed optical fiber sensing length and the wavelet decomposition series corresponds to the spatial resolution of the distributed sensing. The wavelet decomposition series is set according to the requirements of the spatial resolution.

[0038] Step 2: Before the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data is subjected to wavelet decomposition. The sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively.

[0039] Step 3, repeat step 2 to continue to perform wavelet decomposition on the signal after each wavelet decomposition until the wavelet decomposition level set in step 1 is reached, and each obtained wavelet level corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensor, which serves as the reference spectrum before stress or temperature action;

[0040] Step 4: After the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data obtained each time is subjected to wavelet decomposition according to the above steps 2 to 3, and each obtained wavelet series corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensing, which is used as the measurement spectrum after the stress or temperature is applied;

[0041] Step 5, cross-correlation calculation is performed on the reference spectrum and the measured spectrum of the same order obtained in Step 3 and Step 4, and the shift of the cross-correlation peak in the cross-correlation result represents the shift of the reflection or scattering spectrum of the sensing unit corresponding to the spatial position of the wavelet of the order;

[0042] Step 6: Repeat step 5 to obtain the spectral offset of each level of wavelet, i.e., each spatial position sensing unit;

[0043] Step 7: According to the relationship between the spectral offset and the strain or temperature, the strain or temperature of each spatial position sensing unit is calculated to complete the method for recovering uniform spatial resolution information of optical frequency domain scattering distributed optical fiber sensing.

[0044] The wavelet decomposition method used may be Meyer, dBN, or Triband wavelet.

[0045] A method for recovering local spatial range information of optical frequency domain scattering distributed optical fiber sensing based on wavelet decomposition, characterized in that the method comprises the following steps:

[0046] Step 1: The quotient of the optical frequency domain scattering distributed optical fiber sensing length and the wavelet decomposition series corresponds to the spatial resolution of the distributed sensing. The wavelet decomposition series is set according to the requirements of the spatial resolution.

[0047] Step 2: Before the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data is subjected to wavelet decomposition. The sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively.

[0048] Step 3, repeat step 2 to continue to perform wavelet decomposition on the signal after each wavelet decomposition until the wavelet decomposition level set in step 1 is reached, and each obtained wavelet level corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensor, which serves as the reference spectrum before stress or temperature action;

[0049] Step 4: After the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data obtained each time is subjected to wavelet decomposition, and the distributed sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively.

[0050] Step 5: Select the wavelet series that contains a certain local sensing range to be analyzed from the wavelet decomposition results of the previous step and continue to decompose;

[0051] Step 6, repeat step 5 until the spatial resolution of the local sensing range to be analyzed reaches the set value, and each obtained wavelet series corresponds to the reflection or scattering spectrum information of a sensing unit in a local sensing range to be analyzed of the optical frequency domain scattering distributed optical fiber sensor, which is used as the measurement spectrum after the stress or temperature action;

[0052] Step 7, cross-correlation calculation is performed on the reference spectrum and the measured spectrum of the same order obtained in Step 3 and Step 6, and the shift of the cross-correlation peak in the cross-correlation result represents the shift of the reflection or scattering spectrum of the sensing unit within a local sensing range to be analyzed corresponding to the wavelet of this order;

[0053] Step 8: Repeat step 7 to obtain the spectral offset of each level of wavelet, that is, each spatial position sensing unit within a certain local sensing range to be analyzed;

[0054] Step 9: According to the relationship between the spectral offset and the strain or temperature, the strain or temperature of each spatial position sensing unit within a local sensing range to be analyzed is calculated to complete the local spatial range information recovery method of optical frequency domain scattering distributed optical fiber sensing.

[0055] The wavelet decomposition method used may be Meyer, dBN, or Triband wavelet.

[0056] The working process of the present invention is as follows:

[0057] Before the temperature or strain acts on the sensing optical fiber, the swept light source of the optical frequency domain scattering distributed optical fiber sensing system performs a frequency sweep and measures the time domain interference sensing signal of the sensing optical fiber as a reference signal. Then, after the temperature or strain acts on the sensing optical fiber, the swept light source of the optical frequency domain scattering distributed optical fiber sensing system performs a frequency sweep again and measures the time domain interference sensing signal of the sensing optical fiber as a measurement signal. The reference signal and the measurement signal are processed according to the optical frequency domain scattering distributed optical fiber sensing uniform spatial resolution information recovery method based on wavelet decomposition or the optical frequency domain scattering distributed optical fiber sensing local spatial range information recovery method based on wavelet decomposition of the present invention to obtain temperature or strain information along different spatial positions of the sensing.

[0058] The innovative points and technical effects of the optical frequency domain scattering distributed sensing information recovery algorithm based on wavelet transform are: in the process of distributed sensing information recovery, the algorithm does not weaken the spectral resolution, and can improve the temperature or strain resolution under the same spatial resolution; the algorithm can adjust the spatial resolution, temperature or strain resolution as needed, overcoming the problem that traditional algorithms can only achieve single resolution / resolution analysis; the algorithm can perform local sensing information recovery on a certain section of optical fiber position of interest, greatly improving the demodulation speed.

Claims

1. A method for recovering uniform spatial resolution information of distributed optical fiber sensing based on wavelet decomposition of optical frequency domain scattering, characterized in that The method comprises the following steps: Step 1: The quotient of the optical frequency domain scattering distributed optical fiber sensor length and the wavelet decomposition series corresponds to the spatial resolution of the distributed sensor. The wavelet decomposition series is set according to the requirements of the spatial resolution. Step 2: Before the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data is subjected to wavelet decomposition. The sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively. Step 3, repeat step 2 to continue to perform wavelet decomposition on the signal after each wavelet decomposition until the wavelet decomposition level set in step 1 is reached, and each obtained wavelet level corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensor, which serves as the reference spectrum before stress or temperature action; Step 4: After the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data obtained each time is subjected to wavelet decomposition according to the above steps 2 to 3, and each obtained wavelet series corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensing, which is used as the measurement spectrum after the stress or temperature is applied; Step 5, cross-correlation calculation is performed on the reference spectrum and the measured spectrum of the same order obtained in Step 3 and Step 4, and the shift of the cross-correlation peak in the cross-correlation result represents the shift of the reflection or scattering spectrum of the sensing unit corresponding to the spatial position of the wavelet of the order; Step 6: Repeat step 5 to obtain the spectral offset of each wavelet level, i.e., each spatial position sensing unit; Step 7: Calculate the strain or temperature of each spatial position sensing unit based on the relationship between the spectral offset and the strain or temperature, and complete the method for recovering uniform spatial resolution information of optical frequency domain scattering distributed optical fiber sensing.

2. The method according to claim 1, characterized in that: The wavelet decomposition methods used are Meyer, dBN, and Triband wavelets.

3. A method for recovering local spatial range information of optical frequency domain scattering distributed optical fiber sensing based on wavelet decomposition, characterized in that The method comprises the following steps: Step 1: The quotient of the optical frequency domain scattering distributed optical fiber sensor length and the wavelet decomposition series corresponds to the spatial resolution of the distributed sensor. The wavelet decomposition series is set according to the requirements of the spatial resolution. Step 2: Before the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data is subjected to wavelet decomposition. The sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively. Step 3, repeat step 2 to continue to perform wavelet decomposition on the signal after each wavelet decomposition until the wavelet decomposition level set in step 1 is reached, and each obtained wavelet level corresponds to the reflection or scattering spectrum information of each spatial position sensing unit of the optical frequency domain scattering distributed optical fiber sensor, which serves as the reference spectrum before stress or temperature action; Step 4: After the stress or temperature is applied, the optical frequency domain scattering distributed optical fiber sensing data obtained each time is subjected to wavelet decomposition, and the distributed sensing data is divided into high-frequency and low-frequency parts, which correspond to the reflection or scattering spectrum information of the first half and the second half of the sensing optical fiber, respectively. Step 5: Select the wavelet series that contains a certain local sensing range to be analyzed from the wavelet decomposition results of the previous step and continue to decompose; Step 6, repeat step 5 until the spatial resolution of the local sensing range to be analyzed reaches the set value, and each obtained wavelet series corresponds to the reflection or scattering spectrum information of a sensing unit in a local sensing range to be analyzed of the optical frequency domain scattering distributed optical fiber sensor, which is used as the measurement spectrum after the stress or temperature action; Step 7, cross-correlation calculation is performed on the reference spectrum and the measured spectrum of the same order obtained in Step 3 and Step 6, and the shift of the cross-correlation peak in the cross-correlation result represents the shift of the reflection or scattering spectrum of the sensing unit within a local sensing range to be analyzed corresponding to the wavelet of this order; Step 8: Repeat step 7 to obtain the spectral offset of each level of wavelet, that is, each spatial position sensing unit within a certain local sensing range to be analyzed; Step 9: According to the relationship between the spectral offset and the strain or temperature, the strain or temperature of each spatial position sensing unit within a local sensing range to be analyzed is calculated to complete the local spatial range information recovery method of optical frequency domain scattering distributed optical fiber sensing.

4. The method according to claim 3, characterized in that: The wavelet decomposition methods used are Meyer, dBN, and Triband wavelets.

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