Method for measuring buried depth of buried optical cable based on distributed optical fiber vibration sensing

Abstract

The invention discloses a buried optical cable burial depth measuring method based on distributed optical fiber vibration sensing, and the method specifically comprises the following steps: S1, determining a to-be-measured point of a buried optical cable, selecting a plurality of sampling points at a to-be-measured burial depth place, and generating a ground surface vibration source with a fixed amplitude at the sampling points by using a vibration generation tool; the DAS host is used for monitoring the vibration intensity of each point of the to-be-measured optical cable, and the point with the highest vibration intensity is selected as the to-be-measured point of the buried optical cable; s2, determining an optical cable ground surface position right above the buried optical cable to be measured; and S3, setting a plurality of optical cable sections at a buried optical cable measurement point, using the vibration generation tool again at the ground surface position right above the optical cable in the S2 to generate vibration, recording the vibration amplitude of the optical cable sections through the DAS host, and calculating to obtain the buried depth of the to-be-measured optical cable. The optical cable is used as a sensor, and other measurement hardware does not need to be deployed on a measurement site; the method is not influenced by changes of environmental factors such as soil texture, and is high in adaptability.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber sensing and optical communication technology, and in particular relates to a method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing. Background Technology

[0002] Optical fiber cables are a crucial medium for high-bandwidth, low-latency data exchange in the information age, making their health extremely important. Underground optic cables are a common deployment method. Information about their burial depth can indicate geological risks such as surrounding subsidence and facilitates accurate excavation by maintenance personnel during line inspections, reducing workload and improving efficiency. Therefore, accurately determining the burial depth of optical cables is of great significance for ensuring the safety of optical cables and data assets.

[0003] Because optical fibers have a small diameter and contain almost no conductors, conventional methods for determining the burial depth of pipelines, such as ground-penetrating radar and electromagnetic methods, are not applicable. However, optical fibers are characterized by carrying their own information. By utilizing distributed optical fiber sensing, with the optical fiber itself as the sensing medium, information about the surrounding environment can be sensed at various points along the cable. Using distributed optical fiber sensing as the basic sensing source to assist in determining burial depth is expected to significantly reduce measurement difficulty, reduce additional engineering work, and reduce the need for external sensing equipment.

[0004] A common method for determining fiber optic burial depth is to use distributed fiber optic temperature sensing (DTS) to infer the burial depth at different locations by utilizing the temperature changes corresponding to different burial depths, as disclosed in patents CN119167057A and CN112444218A. This method is relatively simple to operate, but the dependence of burial depth on temperature changes over time, and the temperature difference may be so small as to be lower than the temperature sensing accuracy of the DTS, thus limiting the accuracy and consistency of the burial depth calculation.

[0005] Distributed fiber optic vibration sensing (DAS) technology is used to determine burial depth because vibration signals can propagate effectively in any environment and are not limited by changes in temperature, making it more adaptable. Unfortunately, current DAS-based burial depth measurement schemes, while having made some breakthroughs, all have many shortcomings in terms of ease of use and universality.

[0006] Patent CN115014234A discloses a scheme for determining the burial depth of submarine cables based on wave vibration excitation and DAS technology. Its key feature is that it requires no external sensors or auxiliary operations; the burial depth of the optical cable can be monitored based on statistical analysis of vibration energy at various points along the cable. However, it is primarily designed for submarine optical cables and is not suitable for buried optical cables with a limited number of natural vibration sources that are unevenly distributed. Furthermore, the method of statistically analyzing vibration energy requires a considerable amount of time, which is not conducive to quickly determining the burial depth of optical cables.

[0007] Patent CN119471785A discloses a scheme for determining the burial depth of underground optical cables based on artificial vibration sources and DAS technology. It involves setting up a second vibration sensing device outside the vibration-sensing optical cable, and then artificially creating controlled vibration events on the ground surface, i.e., artificial vibration sources. By repeatedly adjusting the positions of the artificial vibration source and the second vibration sensing device, the vibration sensed by the optical cable is eventually made strongest at this point, and the vibration sensed by the optical cable is completely synchronized with the vibration sensed by the second vibration sensing device. At this point, the distance from the vibration source to the second vibration sensing device equals the burial depth, requiring no complex calculations and making the operation relatively simple. However, the need to set up a second vibration sensing device is cumbersome and not conducive to deployment in field environments.

[0008] Patent KR102392287B1 also discloses a scheme for determining the burial depth of underground optical cables based on artificial vibration sources and DAS technology. It simultaneously excites the vibration source and collects vibration information via DAS, utilizing the different delays in the vibration signals sensed at various points on the optical cable to determine the burial depth. Besides the DAS system and artificial vibration source, it eliminates the need for a second vibration sensing device, further simplifying the measurement process. However, converting the delay into burial depth requires the velocity of the underground environment. Since velocity varies significantly with precipitation, soil conditions, etc., the mechanical wave propagation velocity of the underground environment must also be measured each time the burial depth is measured, which is still not simple enough. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the existing technology. This invention provides a method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing. This invention utilizes the optical cable itself as a sensor, eliminating the need to deploy other measurement hardware at the measurement site. The engineering implementation and calculation are simple, fast, and relatively accurate. It is not affected by changes in environmental factors such as soil conditions and has high adaptability.

[0010] To achieve the above-mentioned objectives, the technical solution provided by this invention patent is as follows:

[0011] A method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing, the method specifically includes the following steps:

[0012] S1. Determine the test point of the buried optical cable. Select the burial depth to be measured within the ground surface area. Select multiple sampling points at the burial depth to be measured. Use a vibration generation tool to generate a surface vibration source with a fixed amplitude at the sampling points. Use the DAS host to monitor the vibration intensity of each point of the optical cable to be measured and give the optical cable length at each sampling point. Select the point with the strongest vibration intensity as the test point of the buried optical cable.

[0013] S2, select the test point location in S1, select multiple measurement locations, use the vibration generation tool to generate vibration until the DAS host senses the maximum vibration amplitude at the test point optical cable, and record the vibration location at this time as the optical cable surface location directly above the test buried optical cable.

[0014] S3: Set up multiple optical cable sections at the underground optical cable measurement point. In S2, use a vibration generation tool to generate vibration again at the optical cable surface location. Record the vibration amplitude of the optical cable section through the DAS host, and calculate the burial depth of the optical cable to be measured.

[0015] Furthermore, the vibration generation tool generates a surface vibration source with a fixed amplitude at each landing point. The vibration emitted by this source is captured by the buried optical cable section under test and then sensed by the DAS host.

[0016] Furthermore, the optical cable near the measurement point of the buried optical cable is divided into a first optical cable segment, a second optical cable segment, and a third optical cable segment in sequence from the side farther away from the DAS host to the side closer to the DAS host. The center point of the first optical cable segment is the burial depth measurement point of the buried optical cable. The center point of the first optical cable segment is the determined measurement point of the buried optical cable. The distance between the center point of the second optical cable segment and the center point of the first optical cable segment, and the distance between the center point of the second optical cable segment and the center point of the third optical cable segment are equal, both being d0. The lengths of the three optical cable segments are equal, all being L1. Here, L1 is the gauge length of the DAS system, which is a known fixed parameter of the system; d0 is a known quantity set by the user, usually the sampling interval of the DAS system.

[0017] Furthermore, the burial depth of the optical cable to be measured is calculated by solving the following equation:

[0018]

[0019] In the above formula, P1, P2, and P3 are the vibration energies sensed by the DAS system in the first, second, and third optical cable sections, respectively. h is the burial depth of the underground optical cable at the measured point x0, which is the only unknown quantity. The required burial depth of the optical cable can be obtained by solving h using the numerical solution method of the equation.

[0020] Based on the above technical solution, the method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing, as proposed in this invention, has achieved the following technical effects through practical application:

[0021] 1. The present invention provides a method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing. By utilizing the optical cable itself as a sensor, there is no need to deploy other measurement hardware at the measurement site, thus reducing the workload of engineering implementation.

[0022] 2. The engineering implementation and calculation are simple, fast, and relatively accurate.

[0023] 3. It is not affected by changes in environmental factors such as soil quality and has high adaptability. Attached Figure Description

[0024] Figure 1 This is a diagram of the overall sensing structure of the system in an embodiment of the method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing according to the present invention.

[0025] Figure 2 This diagram illustrates the specific implementation steps of the method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing, as described in this invention.

[0026] Figure 3 This is a schematic diagram of vibration sensing near the burial depth measurement location in a method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing, according to the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and effects of this invention clearer, specific examples are provided below. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of this invention.

[0028] Example 1

[0029] The overall sensing structure of the system in the method for determining the burial depth of underground optical cables based on distributed fiber optic vibration sensing is as follows: Figure 1 As shown:

[0030] The DAS system detection host 100 (hereinafter referred to as DAS host 100) emits detection light pulses and receives Rayleigh scattered light containing vibration information. It can quantitatively sense the vibration intensity at various points along the optical cable 101 under test and give the length of the optical cable at each point.

[0031] The optical cable under test, 101, is partially or entirely located below the ground surface.

[0032] The optical cable section 102 of the optical cable to be tested, located in the area to be tested, is below the ground surface 103 of the section to be tested, at an unknown depth. Its approximate route is given by information such as the mileage markers at the time of cable laying, but the specific route is uncertain.

[0033] The vibration generation tool 104 is a heavy object such as a hammer. When 104 is dropped from a fixed height at different positions on the ground surface 103, a ground vibration source with a fixed amplitude can be generated at each landing point. The vibration emitted by this vibration source can be captured by the buried optical cable section 102 and then sensed by the DAS host 100.

[0034] like Figure 2As shown, the method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing includes the following steps:

[0035] S1: Determine the test point of the buried optical cable. First, roughly select the location where the burial depth needs to be measured within the range of the ground surface 103, such as a certain optical cable mileage marker. Use the vibration generation tool 104 to generate a ground vibration source with a fixed amplitude at this location. When the vibration propagates, the DAS host 100 can measure the vibration intensity at each sampling point of the optical cable 101 to be tested and give the optical cable length at each sampling point. Take the point with the strongest vibration within the range of section 102 and record its length as x0, as the test point.

[0036] S2: Near the test point selected by the vibration generation tool 104 in S1, repeatedly adjust the position and use the vibration generation tool 104 to generate vibration until the DAS host 100 senses the maximum vibration amplitude at the meter x0 of the optical cable under test 101. Record the location where the vibration is generated at this time as 105. It should be located directly above the meter x0 of the optical cable under test 101, because the distance from the applied vibration to meter x0 is the shortest, so the energy is the strongest.

[0037] S3: Multiple fiber optic cable segments are set at the underground fiber optic cable measurement point, ranging from the furthest point from the DAS host to the closest point, including the first fiber optic cable segment 106, the second fiber optic cable segment 107, and the third fiber optic cable segment 108. In S2, vibration is generated again at the fiber optic cable surface location 105 using a vibration generation tool. The vibration amplitude measured near meter number x0 is recorded by the DAS host 100. The burial depth of the fiber optic cable at meter number x0 is calculated through algorithm analysis.

[0038] Detailed algorithm analysis methods are provided by Figure 3 Help and instructions; Figure 3 middle:

[0039] same Figure 1 102 is the optical cable section of the optical cable 101 to be tested in the area to be tested at the burial depth.

[0040] same Figure 1 103 represents the surface near the area to be measured.

[0041] same Figure 1 104 is a vibration generation tool.

[0042] As described in S2, the ground location 105 of the optical cable is the ground surface directly above the optical cable length x0, which is determined by S1 and S2.

[0043] The vibration amplitude sensed by the DAS system 100 at each point on the optical cable 101 under test is the sum of the vibration energy experienced by the optical cable within a length of L1 / 2 before and after that point. L1 is the gauge length of the DAS system 100, which is a known quantity.

[0044] Therefore, the first optical cable section 106 represents the optical cable section of the DAS system 100 for sensing vibration energy at the meter number x0. Its starting and ending meter numbers are x0 - L1 / 2 and x0 + L1 / 2 respectively.

[0045] The spatial sampling interval for the DAS system 100 to sense vibration along the optical cable is d0, which is also a known quantity; the second optical cable section 107 represents the section corresponding to the previous sampling point of x0 for the DAS system 100, its central meter number is x0 - d0, and the starting and ending meter numbers are x0 - L1 / 2 - d0 and x0 + L1 / 2 - d0 respectively; the third optical cable section 108 represents the section corresponding to the two previous sampling points of x0, its central meter number is x0 - 2d0, and the starting and ending meter numbers are x0 - L1 / 2 - 2d0 and x0 + L1 / 2 - 2d0 respectively.

[0046] Let the energies sensed by the first optical cable section 106, the second optical cable section 107, and the third optical cable section 108 be P1, P2, and P3 respectively; from Figure 3 It is not difficult to see that P1 - P2 corresponds to the energy difference sensed by the first optical cable section 106 and the second optical cable section 107, that is, the energy of the section from the meter number x0 + L1 / 2 - d0 to x0 + L1 / 2 minus the energy of the section from the meter number x0 - L1 / 2 - d0 to x0 - L1 / 2; the vibration propagates from the optical cable surface position 105 to the underground in the form of a spherical wave, and usually d0 << L1, which can be regarded as a single point; accordingly, the following formula can be listed:

[0047]

[0048] Among them, K is an unknown proportionality coefficient, which is determined by factors such as the on-site soil quality and is a fixed value. h is the buried depth of the optical cable at the meter number x0.

[0049] Similarly:

[0050]

[0051] Dividing the above two formulas and eliminating the proportionality coefficient K, we can get:

[0052]

[0053] Except for the buried depth h in the above formula, all are known quantities (fixed parameters or measured values), and the buried depth h of the待测 optical cable 101 at the meter number x0 can be solved by conventional numerical methods.

[0054] 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. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing, characterized in that, The method specifically includes the following steps: S1. Determine the test point of the buried optical cable. Select the burial depth to be measured within the ground surface area. Select multiple sampling points at the burial depth to be measured. Use a vibration generation tool to generate a surface vibration source with a fixed amplitude at the sampling points. Use the DAS host to monitor the vibration intensity of each point of the optical cable to be measured and give the optical cable length at each sampling point. Select the point with the strongest vibration intensity as the test point of the buried optical cable. S2, select the test point location in S1, select multiple measurement locations, use the vibration generation tool to generate vibration until the DAS host senses the maximum vibration amplitude at the test point optical cable, and record the vibration location at this time as the optical cable surface location directly above the test buried optical cable. S3: Set up multiple optical cable sections at the underground optical cable measurement point. In S2, use a vibration generation tool to generate vibration again at the optical cable surface location. Record the vibration amplitude of the optical cable section through the DAS host, and calculate the burial depth of the optical cable to be measured.

2. The method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing according to claim 1, characterized in that, The vibration generation tool generates a ground vibration source with a fixed amplitude at each landing point. The vibration emitted by this source is captured by the buried optical cable section under test and then sensed by the DAS host.

3. The method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing according to claim 1, characterized in that, The buried optical cable near the measurement point is divided into three segments in sequence, from the side furthest from the DAS host to the side closest to the DAS host: a first segment, a second segment, and a third segment. The center point of the first segment is the measurement point for the burial depth of the buried optical cable. The distance between the center points of the second and third segments is equal, both d0. The lengths of the three segments are equal, all L1. L1 is the gauge length of the DAS system, a known fixed parameter. d0 is a known quantity set by the user, typically the sampling interval of the DAS system.

4. The method for determining the burial depth of underground optical cables based on distributed optical fiber vibration sensing according to claim 3, characterized in that, The burial depth of the optical cable to be measured is calculated by solving the following equation: In the above formula, P1, P2, and P3 are the vibration energies sensed by the DAS system in the first, second, and third optical cable sections, respectively. h is the burial depth of the underground optical cable at the measured point x0, which is the only unknown quantity. The required burial depth of the optical cable can be obtained by solving h using the numerical solution method of the equation.

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