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

Abstract

The present invention relates to distributed optical fiber strain measurement technology, and specifically to a distributed optical fiber sensing measurement method based on distance domain gating analysis. The method comprises the following steps: S1, respectively acquiring a reference signal and a measurement signal; S2, converting the reference signal and the measurement signal from time domain information to distance domain information via Fast Fourier Transform (FFT) to obtain the length information of the sensing optical fiber; S3, respectively calculating the spatial resolution lengths of the reference signal and the measurement signal to obtain strain information along the optical fiber; S4, accurately analyzing large strain information using a distance gating analysis method; and S5, outputting the strain measurement results. This method effectively avoids the spatial misalignment between the measurement signal and the reference signal caused by changes in the sensing optical fiber length due to strain stretching, thereby overcoming the trade-off between spatial resolution and a wide strain measurement range, and achieving measurement of large strain information with high spatial resolution.

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 response to the shortcomings of the current existing technology, the present invention considers the fundamental problem of the extended optical fiber sensing distance caused by strain stretching, and adopts a method based on distance domain gating analysis to eliminate the problem of reduced correlation between reference signal and measurement signal caused by large strain stretching under high spatial resolution measurement in OFDR technology, thereby realizing large strain measurement at high spatial resolution.

[0006] The technical solutions of the present invention are as follows:

[0007] The distributed optical fiber sensing measurement method based on distance domain gating analysis includes the following steps:

[0008] S1, collects reference signal and measurement signal respectively;

[0009] S2, converting 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 fiber;

[0010] S3, respectively calculating the spatial resolution lengths of the reference signal and the measurement signal to obtain the strain information along the optical fiber;

[0011] S4, accurately analyzing large strain information through distance domain gating analysis, determining the distance domain gating factor, and slidingly selecting a reference signal set with the same length but different distances from the corresponding position of the reference signal at a fixed position of the measurement signal. These reference signal sets and the measurement signal are then inverse Fourier transformed, and the transformed reference signal sets and the measurement signal are sequentially cross-correlated, obtaining the cross-correlation results for that position as a parallel two-dimensional graph;

[0012] S5, output the strain measurement results.

[0013] In order to better implement the present invention, a further technical solution is:

[0014] S1 is specifically:

[0015] 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 the strain information generated by stretching the sensing optical fiber, and the Rayleigh scattering signal data after stretching is collected by the distributed optical fiber strain measurement system.

[0016] S3 is specifically:

[0017] The sensing fiber is divided into several distance segments according to the spatial resolution, where the definition of spatial resolution can be expressed as: ,in, express The amount of Rayleigh scattering inherent in represents the speed of light, represents the refractive index of the optical fiber, Indicates the tuning range of the laser.

[0018] S4 is specifically:

[0019] S41, distance domain gating factor It can be defined as: , Greater than 1, where represents the sliding length on the distance domain, Indicates that the spatial resolution is divided into share;

[0020] S42, for a fixed position of the measurement signal, the reference signal at the corresponding position is Slide the length to select A set of analyzable reference signals of the same length but at different distances are obtained, and these reference signal sets and the measurement signal are subjected to inverse Fourier transform;

[0021] S43, performing cross-correlation calculation on the reference signal set after inverse Fourier transformation and the measurement signal in sequence, and obtaining the cross-correlation results of the position in parallel as a two-dimensional graph;

[0022] S44, repeating S42-S43, obtaining the cross-correlation results of each corresponding position of the measurement signal and arranging them in a two-dimensional graph until the entire sensing optical fiber is completed, thereby obtaining the strain information of different positions of the sensing optical fiber.

[0023] S5 is specifically:

[0024] By acquiring the strain information at different positions of the sensing optical fiber, the strain information along the sensing optical fiber is analyzed.

[0025] The beneficial effects of the present invention are:

[0026] 1. The distributed optical fiber strain sensing measurement method based on distance domain gating analysis proposed in this 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;

[0027] 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 capability of large strain, and improve the accuracy of external strain analysis and positioning;

[0028] 3. The measurement method of the present invention effectively improves the accuracy of distributed optical fiber sensing systems in detecting strain intensity and enhances the detection performance of distributed optical fiber sensing systems working in complex environments. It can be widely applied to tunnel monitoring, bridge inspection, water conservancy and hydropower, aerospace stress monitoring and other fields;

[0029] 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 less calculation amount, shorter analysis time and higher analysis efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of a distributed optical fiber large strain measurement system based on distance domain gating analysis used in the present invention;

[0031] Figure 2 is a data processing flow chart of the present invention;

[0032] Figure 3 This is a graph showing the variation of spectral shift with optical fiber length obtained by using a measurement method in the prior art;

[0033] Figure 4 This is a graph showing the change in spectral shift versus optical fiber length obtained using the measurement method of an embodiment of the present application;

[0034] Figure 5 This is a diagram showing the processing results obtained using the OFDR measurement method based on correlation spectrum self-compensation in the existing technology;

[0035] Figure 6 This is a diagram of the processing results obtained using the measurement method of an embodiment of the present application. DETAILED DESCRIPTION

[0036] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in a variety of different configurations.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely intended to represent selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention.

[0038] refer to Figure 2 This embodiment uses a distributed fiber optic sensing measurement method based on distance domain gating analysis to effectively avoid the spatial mismatch between the measurement signal and the reference signal caused by changes in the sensing fiber length due to strain stretching. This overcomes the trade-off between spatial resolution and a wide strain measurement range, and enables the measurement of large strain information at high spatial resolution. The specific steps are as follows:

[0039] (1) After the sensing fiber is laid, the distributed optical fiber strain measurement system collects a set of Rayleigh scattering signal data, which serves as a reference signal.

[0040] (2) The sensing optical fiber is stretched to generate strain information, and the Rayleigh scattering signal data after stretching is collected using a distributed optical fiber strain measurement system. This data is called the measurement signal.

[0041] (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 fiber can be obtained.

[0042] (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 spatial resolution can be expressed as ,

[0043] in, express The amount of Rayleigh scattering inherent in represents the speed of light, represents the refractive index of the optical fiber, Indicates the tuning range of the laser.

[0044] (5) In order to accurately analyze large strain information, the distance domain gating factor is further introduced , which can be defined as: , Greater than 1, where represents the sliding length on the distance domain, Indicates that the spatial resolution is divided into share, Small values ​​mean fewer cycles, but key information may be ignored. The larger the value, the more cycles, and the longer the processing time. Figure 4 In the embodiment The value is 20.

[0045] (6) After determining the range domain gating factor, for a fixed position of the measurement signal, the reference signal at the corresponding position is Slide the length to select A reference signal set of the same length but different distance positions that can be analyzed is obtained, and these reference signal sets and the measurement signal are subjected to inverse Fourier transform, and the transformed reference signal set and the measurement signal are cross-correlated in sequence to obtain the cross-correlation results of the position in parallel two-dimensional graphics.

[0046] (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.

[0047] (8) By obtaining the strain information at different positions of the sensing optical fiber, the strain information along the sensing optical fiber is analyzed.

[0048] Figure 1 The distributed fiber-optic 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 split into two parts by coupler 1 (10 / 90 optical coupler), 10% of which is incident on an unbalanced Mach-Zehnder triggered interferometer to provide a trigger signal for the acquisition card, and the remaining light enters coupler 2; then coupler 2 (1 / 99 optical coupler) is divided into two parts, of which 1% of the output is adjusted by polarization controller 1 so that the "p" and "s" light components have the same power, and 99% enters the sensing fiber detection through a circulator and polarization controller 2. The sensing fiber is a standard single-mode fiber; then the interference signal obtained by combining the Rayleigh scattering signal with the 1% laser output from coupler 3 (50 / 50 optical coupler) is decomposed into "p" and "s" components by a polarization beam splitter; finally, the "p" and "s" lights are collected by the acquisition card.

[0049] The same sensing fiber was measured using the existing measurement method and the measurement method of the present invention. The strain information was applied in the range of 10.3m-10.6m at the fiber position. The strain range was 1000με-10000με, and the strain interval was 1000με. The analysis results obtained without using the method of the present invention are as follows: Figure 3 As shown, it can be seen that when the present invention is not used for analysis, many spike abnormal values ​​appear, and it is difficult to distinguish the specific value of the strain information and the strain application range. Figure 4 From the analysis results obtained using the present invention, it can be seen that, through the technology of the present invention, the strain distribution range can be clearly analyzed, abnormal information can be eliminated, and the strain information along the optical fiber can be effectively obtained.

[0050] The OFDR measurement method based on the self-compensation of the correlation spectrum in the prior art and the measurement method of the present invention were used to analyze the same section of the sensing fiber. The fiber position was selected to be 10-10.7m, the range of applied strain information was 10000με, and the spatial resolution was 2mm. The processing results of the prior art and the present application are shown in Figure 2. Figure 5-6As shown, when processing the same section of sensing fiber, strain information along the fiber can be effectively obtained. The prior art analysis took 102.745697 seconds, while the present application analysis took 38.241451 seconds, representing only the time required for this experiment. This application does not start with adjustments in the frequency and time domains, but instead fundamentally considers the distance domain error caused by stretching. Therefore, the waveform is more regular than the prior art, eliminating the need for a large-scale frequency domain search and requiring fewer steps. This application is faster and more efficient.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A distributed optical fiber sensing measurement method based on distance domain gating analysis, characterized by: The steps include: S1, collects reference signal and measurement signal respectively; S2, converting 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 fiber; S3, respectively calculating the spatial resolution lengths of the reference signal and the measurement signal to obtain the strain information along the optical fiber; S4, accurately analyzing large strain information through distance gating analysis, determining the distance domain gating factor, and slidingly selecting a set of reference signals with the same length but different distances from the corresponding position of the reference signal at a fixed position of the measurement signal. These reference signal sets and the measurement signal are then inverse Fourier transformed, and cross-correlations are calculated between the transformed reference signal sets and the measurement signal in sequence, obtaining the cross-correlation results for that position as a parallel two-dimensional graph; S5, output strain measurement results; Among them, S3 is specifically, The sensing fiber is divided into several distance segments according to the spatial resolution, where the definition of spatial resolution can be expressed as: ,in, express The amount of Rayleigh scattering inherent in represents the speed of light, represents the refractive index of the optical fiber, Indicates the tuning range of the laser; S4 is specifically: S41, distance domain gating factor It can be defined as: , Greater than 1, where represents the sliding length on the distance domain, Indicates that the spatial resolution is divided into share; S42, for a fixed position of the measurement signal, the reference signal at the corresponding position is Slide the length to select A set of analyzable reference signals of the same length but at different distances are obtained, and these reference signal sets and the measurement signal are subjected to inverse Fourier transform; S43, performing cross-correlation calculation on the reference signal set after inverse Fourier transformation and the measurement signal in sequence, and obtaining the cross-correlation results of the position in parallel as a two-dimensional graph; S44, repeating S42-S43 to obtain the cross-correlation results of each corresponding position of the measurement signal and arrange them in a two-dimensional graph until the entire sensing optical fiber is completed.

2. The distributed optical fiber sensing measurement method based on distance domain gating analysis according to claim 1, characterized in that: S1 is specifically: 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 the strain information generated by stretching the sensing optical fiber, and the Rayleigh scattering signal data after stretching is collected by the distributed optical fiber strain measurement system.

3. The distributed optical fiber sensing measurement method based on distance domain gating analysis according to claim 1, characterized in that: S5 is specifically: By acquiring the strain information at different positions of the sensing optical fiber, the strain information along the sensing optical fiber is analyzed.

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