Method for measuring buried depth of buried optical cable based on DAS vibration signal delay

Abstract

The invention discloses a buried optical cable burial depth measurement method based on DAS vibration signal delay, and the method specifically comprises the following steps: S1, determining the meter number of a to-be-measured point of a buried optical cable, selecting a to-be-measured burial depth place in a ground surface range, and generating a ground surface vibration source with fixed amplitude and frequency by using a fixed-frequency vibration generation device; the DAS host is used for monitoring, and the strongest vibration point in the to-be-measured optical cable area is recorded as the meter number of the to-be-measured optical cable; s2, determining the accurate position of the earth surface of a to-be-measured point; s3, using a fixed frequency vibration generation device to generate vibration at the determined accurate position of the ground surface of the point to be measured, and recording vibration time domain signals of each sampling point near the buried optical cable through a DAS host; and S4, based on the obtained vibration time domain signal of each sampling point, calculating and obtaining the burial depth of the buried optical cable to be measured. Through delay amount acquisition and calculation, the calculation precision is improved, and the interference of environmental factors is effectively eliminated; the optical cable is used as a sensor, and adaptability is high.

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 DAS vibration signal delay. 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] Optical cables carry massive amounts of data exchange and are an essential carrier of data security, requiring effective operation and maintenance to ensure efficient and continuous operation. This necessitates accurately determining the burial depth of underground optical cables to facilitate rapid excavation and repair when necessary.

[0004] Among the many positioning methods, the distributed optical fiber positioning method, which uses the optical cable itself as a sensor, has wide applicability, long sensing distance, and reduced demand for external equipment, and shows great promise. However, current positioning technologies still have shortcomings.

[0005] Distributed fiber optic temperature measurement methods, such as those disclosed in patents CN119167057A and CN112444218A, are relatively simple to operate, but require the temperature to change stably and significantly with burial depth, making them less universally applicable.

[0006] In comparison, using distributed optical fiber vibration sensing (DAS) technology and vibration signals that can propagate effectively in most media to determine burial depth has wider applicability. For example, patent CN115014234A discloses a DAS+wave vibration excitation submarine cable burial depth measurement scheme, which uses statistical analysis data of natural wave vibration over a period of time to calculate the burial depth of the optical cable without the need for manual sampling. However, its characteristics are not suitable for underground optical cables with few or no natural vibration sources, and the measurement and calibration are also slower.

[0007] Patent CN119471785A discloses a scheme for determining the burial depth of underground optical cables by combining DAS technology with an additional vibration source and sensor. It incorporates a second vibration sensing device that synchronously senses artificially generated vibration signals with the optical fiber. Through certain adjustments and feedback, the distance from the vibration source to the second vibration sensing device is ultimately equal to the burial depth of the optical cable; this method is simple and direct to operate and calculate. However, the second vibration sensing device introduces additional engineering work and costs.

[0008] Patent KR102392287B1 discloses a scheme for determining the burial depth of underground optical cables based on artificial vibration sources and DAS technology. It eliminates the need for a second vibration sensing device, instead simultaneously exciting the vibration source and acquiring vibration information via DAS. It analyzes the delay in the vibration signal from the source to various points on the optical cable to calculate the burial depth. However, accurate delay acquisition requires strict time synchronization between the vibration source and the DAS system, which is difficult to implement, especially in environments with poor time signals. Furthermore, the time-domain waveforms at various points on the DAS system are complex and easily affected by other factors, making accurate delay calculation challenging. 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 DAS vibration signal delay. This invention achieves higher accuracy through delay measurement and calculation, effectively eliminating interference from environmental factors. It utilizes the optical cable itself as a sensor, eliminating the need to deploy other measurement hardware at the measurement site, and is unaffected by changes in soil conditions and other environmental factors, thus exhibiting 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 DAS vibration signal delay, the method specifically includes the following steps:

[0012] S1. Determine the meter length of the buried optical cable to be measured. Select the location of the burial depth to be measured within the surface area. Use a fixed frequency vibration generator to generate a surface vibration source with fixed amplitude and frequency. Use the DAS host to monitor the vibration sensing of each point of the optical cable to be measured. The point with the strongest vibration in the area of ​​the optical cable to be measured is recorded as the meter length of the optical cable to be measured, and is used as the location of the optical cable at the depth to be measured.

[0013] S2, determine the accurate location of the test point on the ground surface, move the fixed frequency vibration generating device used in S1 to the location until the vibration amplitude of the optical cable position at the depth to be measured in the signal analyzed by the DAS host is the largest. At this time, the location of the fixed frequency vibration generating device is the accurate location of the test point on the ground surface.

[0014] S3, a fixed-frequency vibration generator is used to generate vibration at the precise location on the ground surface of the determined test point, and the vibration time-domain signal of each sampling point near the buried optical cable is recorded by the DAS host.

[0015] S4. Calculate the burial depth of the underground optical cable to be measured based on the vibration time-domain signals of each sampling point.

[0016] Furthermore, in S3, the DAS host records the vibration time-domain signal of the underground optical cable sampling point as follows: the measured length of the underground optical cable is determined as the original sampling point, and a first sampling point and a second sampling point are respectively set on the underground optical cable from the original sampling point towards the DAS host. The original sampling point, the first sampling point and the second sampling point are evenly set.

[0017] Furthermore, after the sampling points are set, the vibration time-domain signal of each sampling point is acquired through the DAS host, and the original vibration response of the original sampling points is set as follows.

[0018] A1(Δt·i),

[0019] Set the vibration response of the first sampling point as...

[0020] A2(Δt·i),

[0021] Set the vibration response of the second sampling point as follows:

[0022] A3(Δt·i),

[0023] After the DAS host has collected the signals from each sampling point, a 100Hz cosine signal is generated.

[0024] B0 = cos(200π·Δt·i),

[0025] Where i is the data frame number sampled by the DAS system host, with values ​​of 0, 1, 2, ..., Δt is the pulse repetition period transmitted by the DAS host, the 100Hz component in A1 comes from the vibration source, and the other frequency components are environmental interference.

[0026] Furthermore, during sampling by the DAS host, the data of each sampling point is automatically synchronized, and the signals of the original sampling point and the first sampling point are collected simultaneously, avoiding the complexity and error of additional time synchronization.

[0027] Furthermore, the burial depth of the underground optical cable is calculated from the delay information obtained at each sampling point as follows:

[0028]

[0029] T2-T1 is numerically equal to the difference in time between the original sampling point and the first sampling point when a 100Hz vibration propagates from the ground surface directly above the buried optical cable. T3-T2 is numerically equal to the difference in time between the first sampling point and the second sampling point when a 100Hz vibration propagates from the ground surface directly above the buried optical cable.

[0030] Dividing the two equations and eliminating the unknown variable v, we get:

[0031]

[0032] The burial depth h of the underground optical cable can be obtained from the above formula;

[0033] Where T1, T2, and T3 are the original sampling point delay values, the first sampling point delay value, and the second sampling point delay value, respectively; v is the vibration propagation velocity; and d0 is the interval distance between adjacent sampling points.

[0034] Based on the above technical solution, the method for determining the burial depth of underground optical cables based on DAS vibration signal delay, as proposed in this invention, has achieved the following technical effects through practical application:

[0035] 1. The present invention provides a method for determining the burial depth of underground optical cables based on DAS vibration signal delay. The delay measurement and calculation are relatively accurate, effectively eliminating the interference of environmental factors. The optical cable itself is used as a sensor, eliminating the need to deploy other measurement hardware at the measurement site. It is not affected by changes in environmental factors such as soil quality and has high adaptability. Attached Figure Description

[0036] Figure 1 This is a diagram of the overall sensing structure of the system in an embodiment of the present invention, which is a method for determining the burial depth of underground optical cables based on DAS vibration signal delay.

[0037] Figure 2 This is a diagram illustrating the specific implementation steps of the method for determining the burial depth of an underground optical cable based on DAS vibration signal delay, as described in this invention.

[0038] Figure 3 This is a schematic diagram of the sampling point layout at the burial depth measurement location in the method for determining the burial depth of underground optical cables based on DAS vibration signal delay according to the present invention. Detailed Implementation

[0039] 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.

[0040] Example 1

[0041] A method for determining the burial depth of underground optical cables based on DAS vibration signal delay, the method specifically includes the following steps:

[0042] S1. Determine the meter length of the buried optical cable to be measured. Select the location of the burial depth to be measured within the surface area. Use a fixed frequency vibration generator to generate a surface vibration source with fixed amplitude and frequency. Use the DAS host to monitor the vibration sensing of each point of the optical cable to be measured. The point with the strongest vibration in the area of ​​the optical cable to be measured is recorded as the meter length of the optical cable to be measured, and is used as the location of the optical cable at the depth to be measured.

[0043] S2, determine the accurate location of the test point on the ground surface, move the fixed frequency vibration generating device used in S1 to the location until the vibration amplitude of the optical cable position at the depth to be measured in the signal analyzed by the DAS host is the largest. At this time, the location of the fixed frequency vibration generating device is the accurate location of the test point on the ground surface.

[0044] S3, a fixed-frequency vibration generator is used to generate vibration at the precise location on the ground surface of the determined test point, and the vibration time-domain signal of each sampling point near the buried optical cable is recorded by the DAS host.

[0045] S4. Calculate the burial depth of the underground optical cable to be measured based on the vibration time-domain signals of each sampling point.

[0046] The specific method for the DAS host to record the vibration time-domain signal of the underground optical cable sampling point in S3 is as follows: the measured length of the underground optical cable is determined as the original sampling point, and a first sampling point and a second sampling point are respectively set on the underground optical cable from the original sampling point towards the DAS host. The original sampling point, the first sampling point and the second sampling point are evenly set.

[0047] After the sampling points are set, the vibration time-domain signal of each sampling point is acquired through the DAS host, and the original vibration response of the original sampling point is set as follows.

[0048] A1(Δt·i),

[0049] Set the vibration response of the first sampling point as...

[0050] A2(Δt·i),

[0051] Set the vibration response of the second sampling point as follows:

[0052] A3(Δt·i),

[0053] After the DAS host has collected the signals from each sampling point, a 100Hz cosine signal is generated.

[0054] B0 = cos(200π·Δt·i),

[0055] By performing cross-correlation calculations, the delay of the 100Hz component at each sampling point relative to the generated 100Hz cosine signal is obtained; the burial depth of the underground optical cable is calculated based on the delay information obtained from each sampling point.

[0056] Where i is the data frame number sampled by the DAS system host, with values ​​of 0, 1, 2, ..., Δt is the pulse repetition period transmitted by the DAS host, the 100Hz component in A1 comes from the vibration source, and the other frequency components are environmental interference.

[0057] When the DAS host samples, the data of each sampling point is automatically synchronized. The signals of the original sampling point and the first sampling point are collected at the same time, avoiding the complexity and error of additional time synchronization.

[0058] The burial depth of the underground optical cable is calculated from the delay information obtained from each sampling point as follows:

[0059]

[0060] T2-T1 is numerically equal to the difference in time between the original sampling point and the first sampling point when a 100Hz vibration propagates from the ground surface directly above the buried optical cable. T3-T2 is numerically equal to the difference in time between the first sampling point and the second sampling point when a 100Hz vibration propagates from the ground surface directly above the buried optical cable.

[0061] Dividing the two equations and eliminating the unknown variable v, we get:

[0062]

[0063] The burial depth h of the underground optical cable can be obtained from the above formula;

[0064] Where T1, T2, and T3 are the original sampling point delay values, the first sampling point delay value, and the second sampling point delay value, respectively; v is the vibration propagation velocity; and d0 is the interval distance between adjacent sampling points.

[0065] Example 2

[0066] The overall sensing structure of the system is as follows Figure 1 As shown. The components are described below.

[0067] The DAS system's 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 provide the cable length at each point. Each time a light pulse is emitted, the host 100 records the vibration amplitude at various points on the optical cable 101 under test at that moment, forming a data frame. The recording period of the data frame is the repetition period of the detection light pulse emitted by the DAS system, with a typical value of 0.5ms.

[0068] The optical cable under test 101 receives vibrations at various points along its length. In this embodiment, its length does not exceed 50km.

[0069] 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.

[0070] When the fixed-frequency vibration generating device 104 is deployed on the ground, it generates a continuous vibration signal at a fixed single frequency and fixed amplitude at the deployment point. The vibration signal propagates underground in the form of a spherical wave, is captured by the buried optical cable section 102, and then sensed by the DAS host 100. The vibration frequency is set to 100Hz; obviously, other vibration values ​​can be selected and subsequent calculations adjusted according to the actual situation.

[0071] Specific working methods are as follows: Figure 2 .

[0072] Step 201: Determine the measurement depth in meters. First, roughly select the location to be measured within the surface area 103, such as a fiber optic cable mileage marker. Use a fixed-frequency vibration generator 104 to generate a surface vibration source with a fixed amplitude and frequency at this location. The DAS host 100 monitors the vibration sensing at various points on the fiber optic cable 101 under test. Select the point with the strongest 100Hz vibration within the section 102, record its meter length as x0, and use it as the point for measuring the depth.

[0073] Step 202: Locate the precise location of the test point. Near the location where the fixed-frequency vibration generator 104 was used in the previous step, repeatedly adjust the placement of 104 until the vibration amplitude at 100Hz at point 0 (meters x 0) of the optical cable under test, as analyzed by the DAS host 100, is the largest. Record this location as 105; it will be discussed later. Figure 3 The details are marked in the text. The shortest distance to the optical cable under test is 101 meters x0, so it should be located directly above meter x0, which is the accurate location of the test point on the ground.

[0074] Step 203: Record the vibration response. Vibration is generated again at point 105 using the fixed-frequency vibration generator 104, and the vibration time-domain signal of each sampling point near meter x0 is recorded by the DAS host 100.

[0075] Step 204: Calculate the burial depth: Calculate the burial depth of the optical cable at point x0 using algorithm analysis.

[0076] The detailed principles of algorithm analysis, using Figure 3 The diagram is accompanied by an explanation. Figure 3 middle:

[0077] 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.

[0078] 103 represents the surface area near the area to be measured.

[0079] 104 is a device for generating vibration at a fixed frequency.

[0080] As described in step 202, location 105 is the ground surface directly above the fiber optic cable length x0, determined through steps 201 and 202.

[0081] Sampling point 106 is a sampling point of DAS system 100, with a meter value of x0, located directly below location 105. This is also the location where the burial depth of the optical cable needs to be determined. The unknown burial depth is denoted as h. When executing step 203, let the original vibration response at this point be A1(Δt·i), where i is the data frame sequence number sampled by the DAS system host 100, taking values ​​of 0, 1, 2, ...; Δt is the pulse repetition period transmitted by the DAS system. The 100Hz component in A1 comes from the vibration source, and the other frequency components are environmental interference.

[0082] Sampling point 107 is the adjacent sampling point after sampling point 106 (approaching the direction of DAS system 100), separated from sampling point 106 by the spatial sampling interval d0 of DAS system 100. The typical value of d0 is 1m, which is a known quantity. Let the vibration response of this point in step 203 be A2(Δt·i). When the DAS system host 100 samples, the data of each sampling point is automatically synchronized, and A2(0) and A1(0) are collected simultaneously, avoiding the complexity and error of additional time synchronization.

[0083] Sampling point 108 is the adjacent sampling point after sampling point 107, with a distance of d0 from sampling point 107 and a distance of 2d0 from sampling point 106. The vibration response of this point in step 203 is A3(Δt·i).

[0084] After all signals are acquired, a 100Hz cosine signal B0 = cos(200π·Δt·i) is artificially generated. Using a correlation algorithm, the delays of the 100Hz components in A1, A2, and A3 relative to B0 are calculated, denoted as T1, T2, and T3 respectively. The correlation method effectively filters out stray vibration interference from the environment, retaining only the useful 100Hz signal generated by the fixed-frequency vibration generator 104, and calculates the delays with relatively high accuracy.

[0085] Numerically, T2-T1 is equal to the difference in time it takes for a 100Hz vibration to propagate from point 105 on the ground to sampling points 107 and 106; similarly, T3-T2 is equal to the difference in time it takes for a 100Hz vibration to propagate from point 105 on the ground to sampling points 108 and 107. Let the vibration propagation speed be v, then the calculation formula can be written as follows.

[0086]

[0087] Dividing the two equations and eliminating the unknown variable v, we get:

[0088]

[0089] Except for the burial depth h, all the quantities in the above formula are known (fixed parameters or measured values). The burial depth h of the optical cable 101 under test at the meter number x0 can be solved by conventional numerical methods.

[0090] 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 DAS vibration signal delay, characterized in that, The method specifically includes the following steps: S1. Determine the meter length of the buried optical cable to be measured. Select the location of the burial depth to be measured within the surface area. Use a fixed frequency vibration generator to generate a surface vibration source with fixed amplitude and frequency. Use the DAS host to monitor the vibration sensing of each point of the optical cable to be measured. The point with the strongest vibration in the area of ​​the optical cable to be measured is recorded as the meter length of the optical cable to be measured, and is used as the location of the optical cable at the depth to be measured. S2, determine the accurate location of the test point on the ground surface, move the fixed frequency vibration generating device used in S1 to the location until the vibration amplitude of the optical cable position at the depth to be measured in the signal analyzed by the DAS host is the largest. At this time, the location of the fixed frequency vibration generating device is the accurate location of the test point on the ground surface. S3, a fixed-frequency vibration generator is used to generate vibration at the precise location on the ground surface of the determined test point, and the vibration time-domain signal of each sampling point near the buried optical cable is recorded by the DAS host. S4. Calculate the burial depth of the underground optical cable to be measured based on the vibration time-domain signals of each sampling point.

2. The method for determining the burial depth of underground optical cables based on DAS vibration signal delay according to claim 1, characterized in that, The specific method for the DAS host to record the vibration time-domain signal of the underground optical cable sampling point in S3 is as follows: the measured length of the underground optical cable is determined as the original sampling point, and a first sampling point and a second sampling point are respectively set on the underground optical cable from the original sampling point towards the DAS host. The original sampling point, the first sampling point and the second sampling point are evenly set.

3. The method for determining the burial depth of underground optical cables based on DAS vibration signal delay according to claim 2, characterized in that, After the sampling points are set, the vibration time-domain signal of each sampling point is acquired through the DAS host, and the original vibration response of the original sampling point is set as follows. A1(Δt·i), Set the vibration response of the first sampling point as... A2(Δt·i), Set the vibration response of the second sampling point as follows: A3(Δt·i), After the DAS host has collected the signals from each sampling point, a 100Hz cosine signal is generated. B0 = cos(200π·Δt·i), Where i is the data frame number sampled by the DAS system host, with values ​​of 0, 1, 2, ..., Δt is the pulse repetition period transmitted by the DAS host, the 100Hz component in A1 comes from the vibration source, and the other frequency components are environmental interference.

4. The method for determining the burial depth of underground optical cables based on DAS vibration signal delay according to claim 3, characterized in that, When the DAS host samples, the data of each sampling point is automatically synchronized. The signals of the original sampling point and the first sampling point are collected at the same time, avoiding the complexity and error of additional time synchronization.

5. The method for determining the burial depth of underground optical cables based on DAS vibration signal delay according to claim 4, characterized in that, The burial depth of the underground optical cable is calculated from the delay information obtained from each sampling point as follows: T2-T1 is numerically equal to the difference in time between the original sampling point and the first sampling point when a 100Hz vibration propagates from the ground surface directly above the buried optical cable. T3-T2 is numerically equal to the difference in time between the first sampling point and the second sampling point when a 100Hz vibration propagates from the ground surface directly above the buried optical cable. Dividing the two equations and eliminating the unknown variable v, we get: The burial depth h of the underground optical cable can be obtained from the above formula; Where T1, T2, and T3 are the original sampling point delay values, the first sampling point delay value, and the second sampling point delay value, respectively; v is the vibration propagation velocity; and d0 is the interval distance between adjacent sampling points.

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