Distributed optical fiber sensing measurement method based on distance domain gating analysis

Abstract

The invention relates to a distributed optical fiber strain measurement technology, in particular to a distributed optical fiber sensing measurement method based on distance domain gating analysis, and the method comprises the following steps: S1, respectively collecting a reference signal and a measurement signal; s2, converting time domain information of the reference signal and the measurement signal into distance domain information through fast Fourier transform, and obtaining length information of the sensing optical fiber; s3, respectively calculating the spatial resolution lengths of the reference signal and the measurement signal, and obtaining the strain information along the optical fiber; s4, large strain information is accurately analyzed through a range gating analysis method; and S5, outputting a strain measurement result. According to the invention, the problem that the measurement signal and the reference signal do not correspond to each other in spatial position due to the length change of the sensing optical fiber caused by strain stretching can be effectively avoided, so that the balance between the spatial resolution and the wide strain measurement range is overcome, and the measurement of large strain information under high spatial resolution is realized.

Description

Technical Field

[0001] The present invention relates to a distributed optical fiber strain measurement technology, and in particular to a distributed optical fiber sensing measurement method based on distance domain gating analysis. Background Art

[0002] In distributed fiber-optic sensing, optical fiber serves as both the sensing medium and the transmission medium for measurement. By utilizing the propagation characteristics of light waves in optical fibers, including Raman scattering, Rayleigh scattering, and Brillouin scattering, real-time monitoring of the external environment along the length of the fiber is achieved. Distributed fiber-optic sensing technology offers advantages such as strong resistance to electromagnetic interference, relatively simple structure, high spatial resolution, and long sensing distance. Based on these advantages, the technology is being gradually applied in a growing number of fields, such as bridge safety monitoring, civil engineering inspections, underground fire alarms in tunnels, and geological surveys, playing a significant role in social development. Optical frequency domain reflectometry (OFDR), a representative distributed fiber-optic sensing system, boasts advantages such as light weight, compact size, high sensitivity, strong resistance to electromagnetic interference, and high spatial resolution. It can continuously measure changes in external physical quantities such as strain, vibration, and temperature along the length of the fiber.

[0003] The OFDR system has the characteristics of high spatial resolution, and its system spatial resolution can reach the millimeter level. Therefore, it has very important applications in high-precision monitoring fields such as aerospace. However, when the measurement spatial resolution is improved or when measuring large strains, the cross-correlation between the reference signal and the test signal will be greatly reduced, resulting in multiple peaks and false peaks in the cross-correlation results, and incorrect results cannot be obtained. Patents CN113218320 and CN119737880 have successively reported solutions to large strain analysis. However, for patent CN113218320, it analyzes specific strain measurement values to compensate for subsequent position strain information. This will result in the difficulty of accurately measuring subsequent positions once an error in the strain measurement occurs, making this method less robust and stable. Patent CN119737880 makes up for the shortcomings of patent CN113218320 to a certain extent and improves the stability of large strain measurement. However, the use of a large range of reference spectrum for analysis and measurement requires the use of a large-span reference spectrum cyclic measurement, which greatly increases the analysis time. At the same time, this method does not fundamentally consider the distance domain position error caused by strain stretching.

[0004] Therefore, how to effectively improve the strain measurement range of the OFDR system at high spatial resolution remains an important problem that needs to be solved urgently. Summary of the Invention

[0005] In view of the deficiencies of the current existing technologies, the present invention considers from the fundamental problem of the elongation of the fiber optic sensing distance caused by strain stretching, and adopts a distance-domain gated analysis method to eliminate the problem of reduced correlation between the reference signal and the measurement signal caused by large strain stretching in high-spatial-resolution measurement of the OFDR technology, so as to achieve the measurement of large strain at high spatial resolution.

[0006] The technical solution of the present invention is as follows: A distributed optical fiber sensing measurement method based on distance-domain gated analysis, comprising the following steps: S1, respectively collect a reference signal and a measurement signal; S2, convert the reference signal and the measurement signal from time-domain information into distance-domain information through fast Fourier transform to obtain the length information of the sensing optical fiber; S3, respectively calculate the spatial resolution lengths of the reference signal and the measurement signal to obtain the strain information along the optical fiber; S4, accurately analyze the large strain information through the distance-domain gated analysis method, determine the distance-domain gating factor, for a certain fixed position of the measurement signal, slide at the corresponding position of the reference signal to select a set of reference signals at different distance positions with the same length, perform inverse Fourier transform on these sets of reference signals and the measurement signal, and perform cross-correlation calculation on the transformed sets of reference signals and the measurement signal in sequence to obtain the cross-correlation result at this position and list a two-dimensional graph; S5, output the strain measurement result.

[0007] In order to better implement the present invention, a further technical solution is: S1 is specifically: The reference signal is a set of Rayleigh scattering signal data collected by a distributed optical fiber strain measurement system after laying the sensing optical fiber; the test signal is to stretch the sensing optical fiber to generate strain information, and use the distributed optical fiber strain measurement system to collect the Rayleigh scattering signal data after stretching.

[0008] S3 is specifically: Divide the sensing optical fiber into several distance segments according to the spatial resolution, and the definition of the spatial resolution can be expressed as: , where represents the number of Rayleigh scatterings inherent in represents the speed of light, represents the refractive index of the optical fiber, represents the tuning range of the laser.

[0009] S4 is specifically: S41, the distance-domain gating factor can be defined as: , Greater than 1, where represents the sliding length in the distance domain, represents dividing the spatial resolution into parts; S42. For a certain fixed position of the measurement signal, the reference signal slides at the corresponding position in accordance with length in sequence to select sets of reference signals with the same length but different distance positions for analysis. These sets of reference signals and the measurement signal are subjected to inverse Fourier transform; S43. The sets of reference signals and the measurement signal after inverse Fourier transform are subjected to cross-correlation calculation in sequence to obtain the cross-correlation result at this position and list a two-dimensional graph; S44. Repeat S42 - S43 to obtain the cross-correlation results and list two-dimensional graphs at each corresponding position of the measurement signal until the entire sensing optical fiber is completed, and the strain information at different positions of the sensing optical fiber can be obtained.

[0010] S5 specifically is Analyze the strain information along the sensing optical fiber through the strain information at different positions of the obtained sensing optical fiber.

[0011] The beneficial effects of the present invention are: 1. The distributed optical fiber strain sensing measurement method based on distance domain gating analysis proposed by the present invention can greatly improve the strain measurement range of the system under high spatial resolution measurement, and realize high spatial resolution and large strain measurement of the OFDR system; 2. The measurement method of the present invention can further eliminate the spatial mismatch phenomenon at the rear end of the strain stretching position caused by large strain stretching, enhance the analysis ability of large strains, and improve the accuracy of external strain analysis and positioning; The measurement method of the present invention effectively improves the accuracy of detecting the strain intensity of the distributed optical fiber sensing system, improves the detection performance of the distributed optical fiber sensing system in complex environments, and can be widely applied to fields such as tunnel monitoring, bridge detection, water conservancy and hydropower, and aerospace stress monitoring; 4. Compared with the measurement methods of the prior art, the present application can fundamentally solve the problem of distance domain position error caused by strain stretching, with a smaller amount of calculation, a shorter required analysis time, and a higher analysis efficiency. Description of the Drawings

[0012] Figure 1 Schematic diagram of the distributed optical fiber large strain measurement system based on distance domain gating analysis used in the present invention; Figure 2 Data processing flowchart of the present invention; Figure 3 Graph of the change of spectral shift with optical fiber length obtained by using the measurement method of the prior art; Figure 4 It is a graph showing the variation of spectral shift with fiber length obtained by using the measurement method of the embodiment of the present application; Figure 5 It is a processing result graph obtained by using the prior art OFDR measurement method based on correlation spectrum self-compensation; Figure 6 It is a processing result graph obtained by using the measurement method of the embodiment of the present application. Detailed implementation manners

[0013] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Usually, the components of the embodiments of the present invention described and shown here can be arranged and designed in various different configurations.

[0014] Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0015] Refer to Figure 2 , in this embodiment, by adopting a distributed optical fiber sensing measurement method based on distance domain gating analysis, it is possible to effectively avoid the problem of non-correspondence in spatial position between the measurement signal and the reference signal caused by the change in the length of the sensing optical fiber due to strain stretching, thereby overcoming the trade-off between spatial resolution and wide strain measurement range and realizing the measurement of large strain information at high spatial resolution. The specific steps are as follows: (1) After laying the sensing optical fiber, a distributed optical fiber strain measurement system collects a set of Rayleigh scattering signal data, which is used as the reference signal.

[0016] (2) Stretch the sensing optical fiber to generate strain information, and use the distributed optical fiber strain measurement system to collect the Rayleigh scattering signal data after stretching, which is called the measurement signal.

[0017] (3) After collecting the measurement signal, the collected reference signal and measurement signal are converted from time domain information to distance domain information through fast Fourier transform, and the length information of the sensing optical fiber can be obtained.

[0018] (4) In order to obtain the strain information along the optical fiber, the sensing optical fiber needs to be divided into several distance segments according to the spatial resolution. The definition of the spatial resolution can be expressed as , where, represents The amount of Rayleigh scattering inherent in represents the speed of light, represents the refractive index of the optical fiber, represents the tuning range of the laser.

[0019] (5) To accurately analyze the large strain information, a distance domain gating factor is further introduced, which can be defined as: , is greater than 1, where represents the sliding length in the distance domain, represents dividing the spatial resolution into parts, Taking a small value results in fewer loop iterations, but key information may be ignored. Taking a large value leads to more loop iterations and a relatively increased processing time. In the appended Figure 4 embodiment takes the value of 20.

[0020] (6) After determining the distance domain gating factor, for a certain fixed position of the measurement signal, the reference signal slides successively at the corresponding position according to the length to select an analyzable set of reference signals at the same length but different distance positions. The inverse Fourier transform is performed on these sets of reference signals and the measurement signal, and the cross-correlation calculation is successively performed on the transformed sets of reference signals and the measurement signal to obtain the cross-correlation result and a two-dimensional graph at this position.

[0021] (7) Repeat step (6) for different positions of the measurement signal until the entire sensing optical fiber is completed, and the strain information at different positions of the sensing optical fiber can be obtained.

[0022] (8) Analyze the strain information along the sensing optical fiber by the strain information at different positions of the obtained sensing optical fiber.

[0023] Figure 1The distributed optical fiber large strain measurement system based on distance domain gating analysis shown in the figure includes: the continuous laser output of the tunable laser source is divided into two parts by coupler 1 (10 / 90 optical coupler). 10% of the light is incident on an unbalanced Mach-Zehnder trigger interferometer to provide a trigger signal for the acquisition card, and the remaining light enters coupler 2. Then coupler 2 (1 / 99 optical coupler) divides the light into two parts. Among them, 1% of the output is adjusted by polarization controller 1 to make the "p" and "s" light components have the same power, and 99% enters the sensing optical fiber for detection through the circulator and polarization controller 2. The sensing optical fiber is a standard single-mode optical fiber. Then the Rayleigh scattering signal and the interference signal obtained by combining 1% of the laser output from coupler 3 (50 / 50 optical coupler) are decomposed into "p" and "s" components by the polarization beam splitter. Finally, the "p" and "s" lights are collected by the acquisition card.

[0024] Using the existing measurement method and the measurement method of the present invention to measure the same sensing optical fiber, strain information is applied in the range of 10.3 m - 10.6 m of the optical fiber position, the strain change range is 1000 με - 10000 με, and the strain interval is 1000 με. The analysis results obtained without using the method of the present invention are as Figure 3 shown. It can be seen that when the analysis of the present invention is not used, many spike outliers appear, and it is difficult to distinguish the specific values of the strain information and the strain application range. Figure 4 The analysis results obtained by using the present invention are shown. It can be seen that through the technology of the present invention, the strain distribution range can be clearly analyzed, and abnormal information is also eliminated, and the strain information along the optical fiber can be effectively obtained.

[0025] Using the existing technology's OFDR measurement method based on correlation spectrum self-compensation and the measurement method of the present invention to analyze the same section of sensing optical fiber, the optical fiber position is selected from 10 - 10.7 m, the applied strain information is 10000 με, and the spatial resolution is 2 mm. The processing results of the existing technology and this application are as Figures 5-6 shown. When processing the same section of sensing optical fiber, the strain information along the optical fiber can be effectively obtained. Among them, the existing technology takes 102.745697 seconds for analysis, and this application takes 38.241451 seconds for analysis, which only represents the time required for this experiment. This application does not start from the adjustment of the frequency domain and time domain, but fundamentally considers the distance domain error caused by stretching. Therefore, the waveform is more regular than the existing technology, without the need for a large-scale frequency domain search, with fewer required steps, faster processing time, and higher efficiency for this application.

[0026] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Any other modifications or equivalent replacements made by those of ordinary skill in the art to the technical solutions of the present invention should be covered within the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solutions of the present invention.

Claims

1. A distributed optical fiber sensing measurement method based on distance domain gating analysis, characterized in that: It includes the following steps: S1. Collect the reference signal and the measurement signal respectively; S2. Convert the reference signal and the measurement signal from time-domain information to distance-domain information through fast Fourier transform to obtain the length information of the sensing optical fiber; S3. Calculate the spatial resolution lengths of the reference signal and the measurement signal respectively to obtain the strain information along the optical fiber; S4. Accurately analyze the large strain information through the distance gating analysis method to determine the distance-domain gating factor. For a certain fixed position of the measurement signal, slide and select a set of reference signals at different distance positions with the same length at the corresponding position of the reference signal. Perform inverse Fourier transform on these sets of reference signals and the measurement signal, and perform cross-correlation calculation on the transformed sets of reference signals and the measurement signal in sequence to obtain the cross-correlation result at this position and list a two-dimensional graph; S5. Output the strain measurement result.

2. The distributed optical fiber sensing measurement method based on distance domain gating analysis according to claim 1, characterized in that: Specifically, S1 is The reference signal is a set of Rayleigh scattering signal data collected by the distributed optical fiber strain measurement system after the sensing optical fiber is laid; the test signal is to stretch the sensing optical fiber to generate strain information, and use the distributed optical fiber strain measurement system to collect the Rayleigh scattering signal data after stretching.

3. The distributed optical fiber sensing measurement method based on distance domain gating analysis according to claim 1, characterized in that: Specifically, S3 is The sensing optical fiber is divided into several distance segments according to the spatial resolution, and the definition of the spatial resolution can be expressed as: , where represents the number of Rayleigh scatterings inherent in the speed of light, the refractive index of the optical fiber, the tuning range of the laser.

4. The distributed optical fiber sensing measurement method based on distance domain gating analysis according to claim 1, characterized in that: Specifically, S4 is S41, distance domain gating factor can be defined as: , greater than 1, where represents the sliding length in the distance domain, represents dividing the spatial resolution into parts; S42, for a certain fixed position of the measurement signal, the reference signal slides and selects in sequence according to the length to obtain sets of reference signals at different positions with the same length and different distances that can be analyzed, and performs inverse Fourier transform on these sets of reference signals and the measurement signal; S43. Perform cross-correlation calculation on the set of reference signals and the measurement signal after inverse Fourier transform in sequence to obtain the cross-correlation result at this position and list a two-dimensional graph; S44. Repeat S42 - S43 to obtain the cross-correlation results at each corresponding position of the measurement signal and list two-dimensional graphs until the entire sensing optical fiber is completed.

5. The distributed optical fiber sensing measurement method based on distance domain gating analysis according to claim 1, wherein: Specifically, S5 is Analyze the strain information along the sensing optical fiber by obtaining the strain information at different positions of the sensing optical fiber.

Images