Method for analyzing long-distance strain data of distributed fixed-point strain optical cable

Abstract

This invention discloses a method for analyzing long-distance strain data of distributed fixed-point strain optical cables, comprising the following steps: S1, acquiring a set of first data and a set of second data for the effective detection segment of the optical cable, and subtracting them to obtain a set of strain difference values; S2, generating a first position-strain difference curve; S3, dividing the first position-strain difference curve into multiple sequentially connected intervals based on peak noise points; S4, dividing each interval of the optical cable into multiple sequentially connected sub-segments based on the fixed-point spacing; S5, acquiring a set of strain difference values ​​for each sub-segment of the optical cable, and selecting the average value of the strain difference values ​​at the non-endpoint positions of the sub-segment; S6, generating a second position-strain difference curve, and further generating the distance-displacement curve of the optical cable based on this. This invention employs a step-by-step screening mechanism to extract effective points, preserving true strain information while eliminating sampling bias, achieving data denoising, and overcoming the limitation of not being able to comprehensively denoise.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber, in particular to a distributed fixed-point strain optical cable long-distance strain data analysis method. BACKGROUND

[0002] With the progress of modern engineering technology, optical fiber sensing technology is widely used in structural health monitoring, civil engineering, energy pipeline detection and other fields. Distributed optical fiber sensor has important advantages, such as long-distance, real-time and continuous measurement, especially suitable for large-scale structural health monitoring system. At present, the fixed-point structure strain optical cable is widely used in long-distance tunnel, pipe gallery, slope and other engineering due to its characteristics of anti-local crack, displacement direct conversion and data homogenization.

[0003] Since the distributed optical fiber sensor measures the strain or temperature distribution along the optical fiber, the sampling data is usually discrete, and the time interval of each sampling point may vary. The non-uniformity of sampling interval or noise in signal transmission process will cause noise points or inaccurate measurement results in the data. These noise points will affect the reliability of the data, so that the precision and accuracy are reduced when extracting strain and displacement parameters. Figures 1 to 4 As shown in the figure, due to the influence of spatial resolution and sampling interval, sampling point offset may occur near the fixed-point position of the optical cable, and sharp noise points may occur in the strain difference.

[0004] In the data analysis, the traditional technology adopts signal denoising method, such as wavelet transform, filter or interpolation method algorithm, which usually needs more assumptions and prerequisites. In actual application, it is difficult to completely eliminate these interference factors. Especially for fixed-point structure optical cable, the noise is usually caused by the sampling deviation between adjacent two fixed-point sections, so it is difficult to effectively eliminate this specific type of noise interference by using traditional denoising method. SUMMARY

[0005] Therefore, the present application provides a distributed fixed-point strain optical cable long-distance strain data analysis method, which can reliably remove the influence of distributed data noise and obtain real and reliable strain and displacement data.

[0006] To solve the above technical problems, the present application provides a distributed fixed-point strain optical cable long-distance strain data analysis method, comprising the following steps:

[0007] S1, obtaining a group of first data and a group of second data of the effective detection section of the optical cable, wherein the first data is the initial state value after the optical cable is laid, the second data is the value after the optical cable is strained, and the difference between the first data and the second data is obtained. A group of strain difference values of the effective detection section of the optical cable is obtained as the strain difference value before screening;

[0008] S2, generate a first position-strain difference curve with the positions of the effective detection section of the optical cable as the abscissa and the strain difference before screening as the ordinate;

[0009] S3, divide the first position-strain difference curve into a plurality of interval sections connected in turn according to the peak noise points, and an interval section between two adjacent peak noise points, wherein the peak noise points are positions with strain difference exceeding a preset range;

[0010] S4, divide each interval section of the optical cable into a plurality of de sub-sections connected in turn according to the fixed point distance, wherein the fixed point distance is the length of a single fixed point section of the optical cable, and wherein the number of sub-sections in each interval section is P≈(X2-X1) / L, P is a natural number greater than 0, X1 is the abscissa of the smaller end of the interval section, X2 is the abscissa of the larger end of the interval section, and L is the fixed point distance;

[0011] S5, obtain the strain difference of each position of each sub-section, and select the average value of the strain difference of the non-end point positions of the sub-section as the strain difference after screening;

[0012] S6, generate a second position-strain difference curve with the positions of the effective detection section of the optical cable as the abscissa and the strain difference after screening as the ordinate, and take the second position-strain difference curve as the actual position-strain difference curve of the optical cable, and further generate the distance-displacement curve of the optical cable.

[0013] Further, in step S3, the preset range is 100-200με.

[0014] Further, in step S4, the fixed point distance is 0.5-5m.

[0015] Further, in step S4, the number of sub-sections in each interval section is calculated according to the rounding principle.

[0016] Further, in step S5, the strain difference after screening does not include the strain difference of the end points of each sub-section and N1 positions on each side of the end points, and N1 is a natural number greater than 0.

[0017] Further, N1 is 1-4.

[0018] Further, in step S5, the strain difference after screening includes the strain difference of the midpoint of the sub-section and N2 positions closest to the midpoint, wherein N2≤N3-2N1-1, N3 is the number of positions corresponding to each strain difference of the sub-section, and N2 and N3 are natural numbers greater than 0.

[0019] Further, the selection method of the nth midpoint position is X1+(2n-1)*(X2-X1) / (L*P), wherein P is a natural number greater than 0, X1 is the horizontal coordinate of the smaller coordinate end of the interval segment, X2 is the horizontal coordinate of the larger coordinate end of the interval segment, and L is the fixed point distance.

[0020] Further, N2 is an even number.

[0021] Further, the strain difference value after screening is the average value of the strain difference values of the midpoint of the subsegment and N2 / 2 positions on each side of the midpoint.

[0022] The above technical solutions of the present application have the following advantages compared with the prior art: the distributed fixed-point strain optical cable long-distance strain data analysis method of the present application adopts a step-by-step screening mechanism to extract effective points, which not only retains real strain information but also eliminates sampling bias, realizes data denoising, and overcomes the limitations of wavelet transform, filter or interpolation methods that cannot comprehensively denoise. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the accompanying drawings.

[0024] Figure 1 is a schematic diagram of a distance-strain curve without spatial distribution influence;

[0025] Figure 2 is a schematic diagram of a distance-strain curve with spatial distribution influence;

[0026] Figure 3 is a schematic diagram of a distance-strain curve of multiple tests;

[0027] Figure 4 is a schematic diagram of a distance-strain difference curve with spatial distribution influence or multiple tests;

[0028] Figure 5 is a schematic diagram of the first position-strain difference curve disclosed by the present application;

[0029] Figure 6 is a schematic diagram of a sharp noise point on the first position-strain difference curve disclosed by the present application;

[0030] Figure 7 is a schematic diagram of two interval segments of the first position-strain difference curve disclosed by the present application;

[0031] Figure 8 is a schematic diagram of the selected screening strain value on the first position-strain difference curve disclosed by the present application;

[0032] Figure 9A schematic diagram of a second position-strain difference curve disclosed by the present application;

[0033] Figure 10 A schematic diagram of a distance-displacement curve disclosed by the present application. DETAILED DESCRIPTION

[0034] The present application will be further described below with reference to the drawings and specific embodiments, so that those skilled in the art can better understand the present application and implement it, but the embodiments are not limiting to the present application.

[0035] Referring to Figures 5 to 10 An embodiment of the method for analyzing long-distance strain data of a distributed fixed-point strain optical cable disclosed by the present application is shown.

[0036] The method for analyzing long-distance strain data of a distributed fixed-point strain optical cable comprises the following steps:

[0037] S1, obtaining a first group of data and a second group of data of an effective detection section of the optical cable, wherein the first data is the initial state value after the optical cable is laid, the second data is the value after the optical cable is strained, and the first data and the second data are subtracted to obtain a group of strain difference values of the effective detection section of the optical cable as the strain difference values before screening;

[0038] S2, taking the position of the effective detection section of the optical cable as the horizontal coordinate and the strain difference values before screening as the vertical coordinate to generate a first position-strain difference curve;

[0039] S3, dividing the first position-strain difference curve into a plurality of interval sections connected in sequence according to the sharp peak noise points, and one interval section between two adjacent sharp peak noise points, and the sharp peak noise points are the positions where the strain difference values exceed the preset range;

[0040] S4, dividing each interval section of the optical cable into a plurality of sub-sections connected in sequence according to the fixed-point spacing, and the fixed-point spacing is the length of a single fixed-point section of the optical cable, wherein the number of sub-sections P in each interval section is approximately (X2-X1) / L, P is a natural number greater than 0, X1 is the horizontal coordinate of the smaller end of the interval section, X2 is the horizontal coordinate of the larger end of the interval section, and L is the fixed-point spacing;

[0041] S5, obtaining the strain difference value of each position of each sub-section, and selecting the average value of the strain difference values of the non-end point positions of the sub-section as the strain difference values after screening;

[0042] S6, taking the position of the effective detection section of the optical cable as the horizontal coordinate and the strain difference values after screening as the vertical coordinate to generate a second position-strain difference curve as the actual position-strain difference curve of the optical cable, and further generating a distance-displacement curve of the optical cable.

[0043] In the above step S1, the first data is the strain-free size of the optical cable, which needs to be collected after the distributed optical fiber installation is completed and before the structure is stressed, as a reference value, and needs to ensure that the optical fiber is not affected by external forces (no stretching / compression) at this time, otherwise the reference error will be introduced. The second data is the real-time size data collected after the structure is stressed, which needs to match the collection position and sampling frequency of the first data completely to avoid distortion of the difference value caused by asynchronous sampling. The pre-screening strain difference is calculated by "second data - first data", and at this time, the pre-screening strain difference contains sharp peak noise.

[0044] In the above step S2, the discrete pre-screening strain difference data is converted into a first position-strain difference two-dimensional curve, which intuitively presents the data distribution characteristics and provides a basis for subsequent noise identification and interval segment division. The first position-strain difference curve may present the characteristics that most positions are stable and local positions suddenly jump, and these jump points are the sharp peak noise (the convex points in the figure). Figure 6

[0045] In the above step S3, the sharp peak noise is identified and used as the segmentation boundary of the interval segment, and the first position-strain difference curve is divided into multiple continuous interval segments. The sharp peak noise is defined as the position where the strain difference exceeds the preset range, and the preset range needs to be set according to the scene. The interval segment between the adjacent two sharp peak noises is an interval segment, and the strain difference in the interval segment is within the preset range, and the data continuity is good, which is an effective data unit for analysis.

[0046] In the above step S4, each interval segment is divided into multiple equal-length subsegments according to the fixed-point interval. The essence is to convert the continuous interval segment into multiple "small units" that can be independently analyzed, and the "small unit" is the subsegment.

[0047] In the above step S5, the strain difference of the selected point in each subsegment is further screened, and the boundary noise that may be left at the end point of the subsegment is excluded. Figure 8

[0048] In the above step S6, the second position-strain difference curve is reconstructed through the screened data. The curve has eliminated the sharp peak noise and boundary interference, and can reflect the real strain distribution of the distributed optical fiber. Through calculation, the distance-displacement curve of the optical cable is obtained, and finally the conversion from strain monitoring to displacement state evaluation is realized.

[0049] ​​Specifically, the method first obtains the original strain distribution through difference calculation, generating an initial curve containing noise points. The curve is divided into multiple independent interval segments through threshold identification, ensuring that each interval segment only contains continuous effective data segments. The interval segments are evenly divided according to the actual fixed point spacing of the optical fiber, so that the sub-segment length corresponds to the physical structure of the optical cable. After removing the boundary area data within the sub-segment, the strain values of the middle stable area are retained for curve reconstruction.

[0050] Through the above technical solution, the effective points are extracted by using the step-by-step screening mechanism, which not only retains the true strain information but also eliminates the sampling bias, realizes data denoising, and overcomes the limitations of wavelet transform, filter or interpolation method that cannot comprehensively denoise.

[0051] In this embodiment, in step S3, the preset range is 100-200με.

[0052] In the above, the preset range refers to the strain change value threshold interval for judging sharp peak noise points, which can be determined by the calibration data of the optical fiber strain sensor combined with engineering experience. This range is set based on the actual strain response range of optical fiber materials in engineering applications, which not only considers the typical range of sensor measurement error, but also covers the normal strain fluctuation allowed by structural safety monitoring. Among them, micro-strain is the unit of strain measurement, and 1με corresponds to a change of one ten-thousandth of the length of the optical fiber. This magnitude selection can effectively distinguish between true strain and noise signals.

[0053] Specifically, when the strain change value of the optical fiber at a certain position exceeds 100-200με, the system determines that the point is a sharp peak noise point and performs interval division. By setting the lower threshold to 100με, small deviations caused by uneven sampling intervals can be filtered out; by setting the upper threshold to 200με, larger strain changes that may indicate structural abnormalities are retained, avoiding the misremoval of effective signals.

[0054] Through the above technical solution, the judgment threshold of sharp peak noise points is set in the range of 100-200με, making the noise identification have engineering applicability.

[0055] In this embodiment, in step S4, the fixed point spacing is 0.5-5m.

[0056] In the above, the fixed point spacing is 0.5-5 meters, which is the physical distance range between two adjacent fixed points on the fixed point cable, i.e. the distance measured along the cable laying path from one physical fixed point to the next physical fixed point is between 0.5 meters and 5 meters. These "physical fixed points" are key positions for the fixed point cable to form a fixed point structure, and eventually form a monitoring pattern with a data segment of 0.5-5 meters. The above fixed point spacing is, for example, 0.5m, 1m, 1.5m, 2m, 2.5m, 3m, 3.5m, 4m, 4.5m or 5m.

[0057] By the technical solution, the fixed-point interval is set as 0.5-5 m, so that slight changes in the optical cable coverage area can be ensured not to be missed.

[0058] In the embodiment, in step S4, the number of sub-sections in each interval section is determined according to the rounding principle.

[0059] In the above, the rounding principle refers to rounding the decimal part according to the value when the ratio of the interval section length to the fixed-point interval has a decimal part, for example, rounding up when the decimal part is greater than or equal to 0.5, and rounding down when the decimal part is less than 0.5. The rounding function or algorithm in mathematical operations can be used to achieve this, for example, the calculation result can be processed by using the built-in rounding function of a programming language. This feature converts the theoretical number of sections into an integer, solves the contradiction that non-integer sub-sections cannot be divided in actual engineering, and ensures the realizability of sub-section division.

[0060] Specifically, when the ratio of the interval section length to the fixed-point interval has a decimal part, directly discarding or rounding up may cause the total length of the sub-sections to deviate greatly from the actual length of the interval section. By rounding, the effective data loss caused by directly truncating the decimal part in the traditional method is avoided, and the problem of sub-section length exceeding the actual interval caused by rounding up is also prevented, thereby providing an accurate interval division basis for subsequent screening of strain change values at non-endpoint positions.

[0061] By the technical solution, the number of sections is dynamically adjusted by the rounding principle, so that the matching degree of the total length of the sub-sections to the actual length of the interval section is optimized, and the cumulative error caused by unreasonable division is effectively reduced.

[0062] In the embodiment, in step S5, the screened strain difference values do not include the strain difference values at the endpoints of each sub-section and N1 positions on each side of the endpoints, and N1 is a natural number greater than 0.

[0063] In the above, the endpoints of the sub-sections refer to the two boundary positions at which each sub-section starts and ends on the coordinate axis, and the N1 positions on each side of the endpoints refer to N1 consecutive measurement points extending from the endpoints to the interior of the sub-section along the optical fiber axis.

[0064] Specifically, after the sub-sections are divided, abnormal strain values are prone to occur at the endpoints of each sub-section and the adjacent regions. By excluding the data at the endpoints and N1 positions on each side of the endpoints, the local measurement deviation between adjacent sections of the fixed-point structure optical cable can be eliminated. For example, when N1 is 3, 3 measurement points are removed from each end of each sub-section, and the strain data in the middle stable region is retained.

[0065] By the technical solution, abnormal data affected by sampling deviation near the endpoints is directly eliminated, noise at the endpoints is avoided from being misjudged as structural deformation, and measurement error is reduced.

[0066] In this embodiment, N1 is 1-4.

[0067] In the above, the value range of N1 is determined by experimental verification based on the physical characteristics of the fixed-point optical cable and the distribution law of the sampling deviation, which functions to eliminate abnormal data interference at the junction of adjacent fixed-point segments due to mechanical installation errors or environmental mutations. The 1-4 positions on each side of the endpoint refer to 1-4 measurement points extending outward from the endpoint along the length direction of the optical fiber. For example, N1 is 1, 2, 3, or 4. When N1 is 3, the 3 positions on each side of the endpoint refer to the three continuous measurement points extending outward from the endpoint along the length direction of the optical fiber.

[0068] Through the above technical solution, by limiting the exclusion range of N1, the accurate positioning and elimination of noise points in the junction area are realized, and the problem of excessive exclusion of effective data leading to the expansion of the monitoring blind area is avoided.

[0069] In this embodiment, in step S5, the strain difference values after screening include the strain difference values of the midpoint of the subsegment and the N2 positions closest to the midpoint, wherein N2≤N3-2N1-1, N3 is the number of positions corresponding to each strain difference value of the subsegment, and N2 and N3 are natural numbers greater than 0.

[0070] In the above, the midpoint of the subsegment is the geometric center position of the subsegment formed after the fixed-point interval is divided, which is used to avoid the area near the endpoint affected by the adjacent interval segment. The N2 positions closest to the midpoint refer to the measurement points selected symmetrically from the midpoint position to both sides, for example, the N2 data points closest to the midpoint are selected by a sorting algorithm to ensure that the data selection is concentrated in the stable area of the subsegment. The constraint condition of N3-2N1-1 is to limit the upper limit of the number of intermediate data points after excluding N1 positions on each side of the endpoint, for example, when the total number of positions of the subsegment is 21 and N1=3, the maximum value of N2 is 21-6-1=14, and this calculation method guarantees the mathematical feasibility of data screening.

[0071] Specifically, after the subsegment division is completed, each subsegment contains strain change values corresponding to multiple measurement positions. By positioning the midpoint and selecting N2 positions adjacent to it, the possible peak noise points at the connection of the adjacent interval segments at both ends of the subsegment can be effectively avoided. By the constraint of N2≤N3-2N1-1, it is ensured that there are still a sufficient number of intermediate position data available for analysis after excluding N1 positions on each side of the endpoint.

[0072] Through the above technical solution, by limiting the data selection range of the intermediate stable area, the accuracy of strain data analysis is improved.

[0073] In this embodiment, N2 is an even number. The strain difference value after screening is the average of the strain difference values of the midpoint of the subsegment and the N2 / 2 positions on each side of the midpoint.

[0074] In the above text, the strain difference value after filtering is the average of the strain difference values ​​at the midpoint of the segment and at N2 positions on both sides of the midpoint (a total of N2+1 data points). The even number of N2 ensures that the data points are evenly distributed with the midpoint as the center of symmetry, avoiding local deviations caused by an imbalance in the number of data points on one side.

[0075] Specifically, after determining the midpoint within a sub-segment, half the number of positions (N2) are selected from the midpoint on both sides. For example, when N2 is 12, six positions are selected on each side from the midpoint. This symmetrical selection method ensures that the selected strain change values ​​are far from the endpoints and the noise areas near the endpoints, while also covering the relatively stable area in the middle of the sub-segment. Since the number of selections on both sides is equal, spatial weight shifts caused by too many or too few data points on one side are not introduced during data processing, thereby improving the spatial balance of the strain data.

[0076] By using the above technical solution, and by symmetrically selecting data points near the midpoint, the introduction of measurement errors in the endpoint region is avoided, and the spatial continuity of the selected data is ensured, thus providing a reliable data foundation for the subsequent generation of high-precision actual distance-strain difference curves.

[0077] Example 1: The distributed fixed-point strain sensing optical cable data analysis method consists of 5 specific steps:

[0078] To obtain the strain change value, select a set of initial value data, subtract the initial value data from the subsequent test data;

[0079] The data is segmented, and the location of peak noise points in long-distance data is located based on the strain difference between two sets of data. The strain threshold ε is usually designed to be 100-200με. The entire length of data is divided into intervals based on the located peak noise points. Each interval is further segmented according to the fixed point spacing of the optical cable (usually 0.5-5m). The distance between adjacent noise points is X2-X1 and X3-X2, and the fixed point spacing is L. Then, these two intervals are divided into segments P1 and P2, where P1 is (X2-X1) / L (rounded to the nearest integer) and P2 is (X3-X2) / L (rounded to the nearest integer).

[0080] Center point selection: Based on the segmentation of each interval, select the center point of each segment. For the interval X1-X2, take X1 as the base point and (X2-X1) / (L*P1) as the step size. Then, the position of the first center point in this interval is X1+1*(X2-X1) / (L*P1), the position of the second center point is X1+3*(X2-X1) / (L*P1), and the position of the nth center point is X1+(2n-1)*(X2-X1) / (L*P1).

[0081] The average point number is determined, and the determined center point is taken as the starting point, and the point number N2 is selected to the two sides to bring the calculation average value, N2 is an even number, and the N2 value is determined according to the data point number between the fixed points. Generally, the principle is that 3 data points on the edge of each section of fixed points are deducted, and then the first section of valid data in the X1-X2 interval is the average value of the strain values corresponding to the first center point and N2 / 2 measurement points on the left and right.

[0082] Processing software development, according to the above processing steps, the special distributed fixed point strain cable data processing software is developed, and the parameter setting includes: the starting and ending position of the limited section, the segmented length (i.e. the fixed point spacing L), the segmented strain threshold value ε, and the average point number selection quantity N2 / 2 on one side of the center point.

[0083] Obviously, the above embodiments are only examples for clearly illustrating, and are not limited to the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments cannot be exhausted, and the obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for analyzing long-range strain data of a distributed fixed-point strain optical cable, characterized in that, The method comprises the following steps: S1, obtaining a first set of data and a second set of data of an effective detection section of the optical cable, wherein the first data is a value in an initial state after the optical cable is laid, the second data is a value after the optical cable is strained, and the first data and the second data are subtracted to obtain a set of strain difference values of the effective detection section of the optical cable as pre-screening strain difference values; S2, generating a first position-strain difference curve with the position of the effective detection section of the optical cable as the horizontal coordinate and the pre-screening strain difference values as the vertical coordinate; S3, dividing the first position-strain difference curve into a plurality of interval sections connected in sequence according to the sharp peak noise points, and one interval section is between two adjacent sharp peak noise points, and the sharp peak noise points are positions where the strain difference values exceed a preset range; S4, dividing each interval section of the optical cable into a plurality of sub-sections connected in sequence according to a fixed point distance, wherein the fixed point distance is the length of a single fixed point section of the optical cable, the number of sub-sections in each interval section is P≈(X2-X1) / L, P is a natural number greater than 0, X1 is the horizontal coordinate of the smaller end of the interval section, X2 is the horizontal coordinate of the larger end of the interval section, and L is the fixed point distance; S5, obtaining a set of strain difference values of each sub-section of the optical cable, and selecting the average value of the strain difference values of the non-end point positions of the sub-section as the post-screening strain difference values, wherein the post-screening strain difference values do not include the strain difference values of the end points of each sub-section and N1 positions on each side of the end points, and N1 is a natural number greater than 0; S6, generating a second position-strain difference curve with the position of the effective detection section of the optical cable as the horizontal coordinate and the post-screening strain difference values as the vertical coordinate, and the second position-strain difference curve is taken as the actual position-strain difference curve of the optical cable, and a distance-displacement curve of the optical cable is further generated according to the actual position-strain difference curve.

2. The method of claim 1, wherein the distributed fixed-point strain optical cable long-range strain data is analyzed by, In step S3, the preset range is 100-200με.

3. The method of claim 1, wherein the distributed fixed-point strain optical cable long-range strain data is analyzed by, In step S4, the fixed point distance is 0.5-5m.

4. The method of claim 1, wherein the distributed fixed-point strain optical cable long-range strain data analysis method is characterized by, In step S4, the number of sub-sections in each interval section is calculated according to the rounding principle.

5. The method of claim 1, wherein the distributed fixed-point strain optical cable long-range strain data analysis method is characterized by, N1 is 1-4.

6. The method of claim 1, wherein the distributed fixed-point strain optical cable long-range strain data analysis method is characterized by, In step S5, the post-screening strain difference values include the strain difference values of the midpoint of the sub-section and N2 positions closest to the midpoint, wherein N2≤N3-2N1-1, N3 is the number of positions corresponding to each strain difference value of the sub-section, and N2 and N3 are natural numbers greater than 0.

7. The method of claim 6, wherein the distributed fixed-point strain optical cable long-range strain data is analyzed by, The selection method of the nth midpoint position is X1+(2n-1)*(X2-X1) / (L*P), wherein P is a natural number greater than 0, X1 is the horizontal coordinate of the smaller end of the interval section, X2 is the horizontal coordinate of the larger end of the interval section, and L is the fixed point distance.

8. The method of claim 7, wherein the distributed fixed-point strain optical cable long-range strain data is analyzed by, N2 is an even number.

9. The method of claim 8, wherein the distributed fixed-point strain optical cable long-range strain data is analyzed by, The post-screening strain difference values are the average values of the strain difference values of the midpoint of the sub-section and N2 / 2 positions on each side of the midpoint.

Images