Method for estimating installation path of optical cable for communication

Abstract

5 10 20 25 28 35 30 18 D ec 2 02 5 A B S T R A C T 2 0 2 5 2 8 3 5 3 0 1 8 D e c 2 0 2 5 1 / 9 FIGURES [Fig 1] 1 / 9 FIGURES 51 4 2 8 3 7 6 20 25 28 35 30 18 D ec 2 02 5 D e c 2 0 2 5 2 0 2 5 2 8 3 5 3 0 1 8 4 2 8 3 7 6

Description

CROSS-REFERENCE TO RELATED APPLICATION 5

[0001] This application claims priority to Korean Patent Application No. KR 10-2024-0194275 filed on 23 December 2024, the contents of which are incorporated by reference in their entirety. BACKGROUND 10

[0002] The present disclosure relates to a sensing technology and sensing method for detecting an installation path of an optical cable, and more particularly, to a method for estimating a position and path of an optical cable installed underground using distributed acoustic sensing (DAS) technology.

[0003] At the time when Internet communication became widespread, an 15 optical cable infrastructure for communication was built on a large scale. In the process of hastily installing communication lines, information about the position, that is, the path, of the underground optical cable for communication is not accurately recorded, and thus there is a problem that the path of the optical cable cannot be accurately identified at this time. Although some records of the path remain, they 20 contain numerous errors and have also been lost. In addition, as underground lifelines are increased and maintenance such as repairs to optical cables are performed, there have been instances where the optic cable paths have been altered. For various other reasons, accurate and systematic information about the optical cable paths currently managed by private telecommunications companies and the 2025283530   18 Dec 2025 government is currently lacking.

[0004] From the perspective of digital informatization of nation's basic infrastructure, it is important to accurately identify the position and path of optical cables for communication. Furthermore, accurately identifying the position of 5 optical cables is crucial for maintaining optical cables as well as for industrial purposes.

[0005] A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge 10 as at the priority date of any of the claims. SUMMARY

[0006] An aspect of the present disclosure provides a method for estimating an installation path of an optical cable for communication to identify a position at 15 which the optical cable for communication is installed a path thereof using distributed acoustic sensing technology.

[0007] Other unspecified objects of the present disclosure will be further considered within the scope that can be readily inferred from the detailed description and effects thereof below. 20

[0008] In accordance with an exemplary embodiment of the present invention, a method for estimating an installation path of an optical cable for communication to identify a path of the optical cable for communication installed underground and comprises: (a) defining a plurality of points by setting arbitrary points at regular intervals from an arbitrary origin in the long optical cable, (b) 2025283530   18 Dec 2025 repeatedly performing a light sensing process with a time difference, in which light is emitted to one end of the optical cable for communication in an environment where elastic waves are applied to an area where the optical cable is estimated to be installed from at least three vibration sources whose positions are known and a 5 backscattered light signal generated by the emitted light being scattered at each point along the optical cable and then returning to the end of the optical cable, is received, (c) forming an output signal by extracting the backscattered light signal for each point through signal processing on the backscattered light signal continuously returned from each point along the optical cable in the optical sensing process, (d) 10 acquiring time series vibration signal data containing phase information of the elastic wave for each of the plurality of points along the optical cable by aligning a plurality of output signals formed for each point during the plurality of optical sensing processes in the order of optical sensing time, (e) identifying elastic wave arrival time of each elastic wave, which is the time it takes for the elastic wave to be 15 propagated from the vibration source to the plurality of points along the optical cable, using the time series vibration signal data, and (f) estimating a position and path of the optical cable by calculating position information for each of the plurality of points using the elastic wave arrival times from the at least three vibration sources to the plurality of points. 20

[0009] In an embodiment of the present invention, a reference point may be designated among the plurality of points along the optical cable, relative difference values of arrival times at which the same elastic wave phase information may appear at sequentially adjacent points starting from the reference point are respectively identified, and the elastic wave arrival time at a specific point may be calculated by 2025283530   18 Dec 2025 accumulating the relative difference values of the arrival times at the respective points on a path from the reference point to the specific point. Here, the elastic wave arrival time at the reference point may be set to approximately 0 and an operation is performed. 5

[0010] In an embodiment of the present invention, the origin may be a point from which light is emitted, and the reference point may be set as a first point closest to the point from which light is emitted.

[0011] In an embodiment of the present invention, an area where the optical cable is estimated to be installed may be divided into a plurality of grids. 10          Equation 1 N ^(d Xpn-tY n=l Equation 2 s — e d = s ■------- |s- e|

[0012] (Here, N is the number of vibration sources, which is approximately 3 15 or more, Pn is a reciprocal of an apparent elastic wave propagation speed approximation at the position of optical cable of n-th vibration source, t is the elastic wave arrival time, and d is defined by Equation 2 above, where s is ae position vector of a grid point from the reference point, and e is a position vector of the vibration source from the reference point.) 20

[0013] In an embodiment of the present invention, a value at which a value of Equation 1 above is minimum may be used to calculate the position of a specific point along the optical cable. 2025283530   18 Dec 2025

[0014] In an embodiment of the present invention, the vibration source may be an earthquake. BRIEF DESCRIPTION OF THE DRAWINGS 5

[0015] Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

[0016] FIG. 1 is a schematic diagram illustrating a distributed acoustic sensing system; 10

[0017] FIG. 2 is a schematic flowchart of a method for estimating an installation path of an optical cable for communication according to an embodiment of the present invention;

[0018] FIG. 3 is a diagram showing an area where both an optical cable is estimated to be installed and a vibration source; 15

[0019] FIG. 4 is an enlarged view of an area where the optical cable is installed in FIG. 3;

[0020] FIG. 5 is a diagram for describing a situation where the propagation speed of seismic waves affects the optical cable;

[0021] FIG. 6 shows backscattering light signals received in some sections of 20 the optical cable through a plurality of optical sensing;

[0022] FIG. 7 shows time series vibration signal data of points along the optical cable;

[0023] The upper graph of FIG. 8 shows relative difference values in elastic wave arrival times for points, and the lower graph shows the elastic wave arrival 2025283530   18 Dec 2025 times; and

[0024] FIG. 9 is a diagram for describing a method for calculating position coordinates for each point along an optical cable in the present invention.

[0025] It is to be understood that the accompanying drawings are provided 5 for reference only to help understand the technical concept of the present invention, and the scope of the present invention is not limited thereto. DETAILED DESCRIPTION OF EMBODIMENTS

[0026] In describing the present invention, when it is determined that the 10 detailed description of related known functions that are obvious to those skilled in the art may unnecessarily obscure the gist of the present invention, a detailed description thereof will be omitted.

[0027] The present invention relates to a method for estimating a position and path of an optical cable for communication installed underground using distributed 15 acoustic sensing technology.

[0028] As described in the BACKGROUND paragraph, optical cables for communication are installed in a network form across the country, but for various reasons, accurate information on the position and path of the optical cables is not accurately provided. Even in terms of maintenance and repair of optical cables, the 20 position and path information of the optical cables should be accurately checked but in order to utilize optical cables industrially for various purposes, the position and path information should be identified first. One of the industrial uses of optical cables is in distributed acoustic sensing systems (DAS). That is, if optical cables for communication are used as optical fiber sensors, which are important components in 2025283530   18 Dec 2025 DAS systems, it is possible to estimate the epicenter of an earthquake and to detect whether blasting is occurring during construction work, for example. In addition, if optical cables are installed under the road, vibration caused by overloaded vehicles can be tracked. In addition, when optical cable for communications is utilized as 5 DAS, various industrial uses are possible.

[0029] A distributed sound sensing technology will be briefly described with reference to FIG. 1.

[0030] FIG. 1 is a schematic diagram of a distributed acoustic sensing system (DAS). Referring to FIG. 1, the distributed acoustic sensing system basically 10 includes a light source 1, an optical fiber 2, and a photodetector 3. The optical fiber is laid long and placed in close contact with a target to be measured (e.g., the ground). Laser light emitted from a light source is converted into a light pulse through an optical modulator 4 and transmitted to the optical fiber 2 through an optical circulator 5. The optical signal travels forward along the optical fiber, but at 15 each point along the optical fiber where the light passes, a reflected signal exists that is reflected back due to light scattering. That is, the light propagating through the optical fiber collides with molecules within the optical fiber and scatters, thereby generating a reflected signal (backscattered light) in the opposite direction. The backscattered light returning from the optical fiber is guided to an optical amplifier 6 20 through the optical circulator. In the optical amplifier, the backscattered light is amplified and transmitted to the photodetector 3 through an amplified spontaneous emission filter 7. In the photodetector 3, the backscattered light is converted into an electrical signal. Finally, a digital converter 8 converts the electrical signal (analog signal) into a digital signal. The processing circuit (not shown) processes and 2025283530   18 Dec 2025 analyzes the digital signal. For reference, below, components of the DAS system excluding the light source and optical fiber are collectively referred to as the 'interrogator'.

[0031] In a normal state where no external forces are acting on the target 5 object, the backscattered light signal exhibits a consistent pattern. However, when an external influence such as vibration acts on the target object and optical fiber, the magnitude, frequency, and phase of the scattered light change, and thus the backscattered light exhibits a pattern different from the normal state. In this way, by detecting that the signal of backscattered light appears different from the normal state 10 due to external actions such as vibration, it is possible to infer that an event such as an earthquake has occurred.

[0032] As described above, by using fiber optic sensors, backscattered light signals that are scattered and returned from all points of the optical fiber can be obtained, and the fiber optic sensors have spatial resolution in units of at least 0.2 m, 15 which yields an effect similar to that of vibration sensors such as geophones or hydrophones installed at 0.2 m intervals.

[0033] To apply DAS technology, the position of the optical fiber sensor should be known precisely. In addition, in order to use the optical cable for communication as an optical fiber of the DAS system, information on the position 20 and path of the optical cable should be accurately secured, as described above. The present invention provides a method for identifying the position of an optical cable using DAS technology.

[0034] Hereinafter, a method for estimating an installation path of an optical cable communication according to an embodiment of the present invention will be 2025283530   18 Dec 2025 described in detail with reference to the drawings.

[0035] FIG. 2 is a schematic flowchart of a method for estimating an installation path of an optical cable for communication according to an embodiment of the present invention, FIG. 3 illustrates an area where both the optical cable is 5 estimated to be installed and the vibration source, and FIG. 4 is an enlarged view of the area where the optical cable is installed in FIG. 3.

[0036] Referring to the drawing, first, an area A where an optical cable for communication is estimated to be installed is set. The area may be set arbitrarily, but in this example, it is set as a rectangular shape with a width and height of 10 approximately several kilometers. Although the entire path of an optical cable F is not identified, important points such as the starting point, ending point, and hub where the optical cable is connected are known. Based on the information on these important points, a boundary line of the area A where the optical cable F is estimated to be installed may be set. 15

[0037] Then, a specific point along the optical cable that is already known is set as the origin, and a light source and interrogator are installed at the origin. In this example, the origin is designated as the starting or ending point of the optical cable.

[0038] Light generated from the light source is converted into a laser pulse and then emitted to the optical cable. Hereinafter, ‘light’ is used interchangeably 20 with the ‘laser pulse’. Light L propagates through the optical cable F, and backscattered light R continuously generated at each point returns to the interrogator.

[0039] Back-scattered light is continuously received from the point in time when the light is emitted, and and the time between the point in time when the light is emitted and the point in time when the backscattered light is finally received is 2025283530   18 Dec 2025 calculated. By multiplying the time difference between the point in time when the light was emitted and the point in time when the backscattered light was last received by the speed of the optical signal, the total length of the optical cable whose path is to be estimated may be identified. However, calculating the distance of the optical 5 cable is not a necessary process, but it helps improve the accuracy of optical cable path estimation.

[0040] In addition, arbitrary points P are set at regular intervals from the origin. For example, the points may be set in units of approximately 5 m. The first point is the point closest to the origin where the interrogator is connected to the 10 optical cable F. If the optical cable is approximately 10 km long, approximately 2,001 points are set. In addition, a section division point T can be optionally set at intervals of a plurality of points.

[0041] In addition, an estimated installation area A of the optical cable is divided into a plurality of grids C. The higher the resolution of the grid, the more 15 advantageous it is for estimating the installation path of the optical cable later, but it has the disadvantage of increasing the amount of computation. Accordingly, considering the size of the estimated installation area A, the grid spacing can be set to several meters or tens of meters, and the resolution can also be changed during the process of estimating the path. 20

[0042] Once the above preparations are completed, light sensing is performed continuously and repeatedly by emitting light from the light source and receiving backscattered light. From the point in time when the light is emitted, backscattered light begins to be received continuously. For example, it is assumed that the optical cable is approximately 50 km. Since the optical signal travels at a speed equal to the 2025283530   18 Dec 2025 speed of light divided by the refractive index of the optical cable (3x108m s ^ 1.5 = 2x108m s), if the optical fiber is approximately 50 km, the backscattered light begins to flow in immediately from the point in time when the light is emitted, and it takes approximately the same amount of time for a signal to return from the last point 5 located at approximately 50 km as the time it takes for light to travel approximately 100 km (approximately 500 ps). That is, an optical signal is emitted once and the backscattered light is received for approximately 500 ps. Then, light can be transmitted and received approximately 2,000 times per second without overlapping transmission and reception of light. It is capable of approximately 2,000 optical 10 sensing operations per second. Of course, the frequency of emitting light from the light source may be adjusted to a lower level. For example, in this example, optical sensing can be performed at approximately 1,000 times / second. Optical sensing is performed for a certain period of time in the above manner.

[0043] In addition, while performing optical sensing, elastic waves are 15 individually applied at different times to the estimated optical cable installation area (A) through at least three vibration sources whose positions are known. In this example, five vibration sources e1 to e5 are used as shown in FIG. 3, but for convenience of description, an example in which three vibration sources are used is described. In this specification, elastic waves, vibrations, and seismic waves are all 20 used interchangeably. A plurality of vibration sources are located outside the estimated optical cable installation area A as shown in FIG. 3. Artificial vibration means such as gunpowder blasting may also be used as the vibration source, but even a naturally occurring earthquake may be used as the vibration source under the condition that the position of the epicenter and the occurrence time of the earthquake 2025283530   18 Dec 2025 are known. In South Korea, earthquakes of magnitude approximately 2 or greater occur approximately 70 times a year, and micro-earthquakes of magnitude approximately 2 or less occur much more frequently. Since seismic information can be obtained through a network of seismographs, it is also possible to use earthquakes 5 as a vibration source. However, since it is impossible to predict whether an earthquake will occur in advance, if an earthquake occurs while performing regular optical sensing, the position and occurrence time of the earthquake can be identified and used as a vibration source.

[0044] The speed at which vibrations propagate through the ground varies 10 depending on the type of elastic wave and the medium. P waves travel at approximately 5 to 8 km / s, and S waves travel at approximately 3 to 4 km / s. In addition, the wavelength of seismic waves is long. Referring to FIG. 5, the seismic wave generated from a vibration source E are propagated in a concentric circle, and even if the seismic waves reach a radius R1 centered on the vibration source, the 15 optical cable F is not affected by the vibration. When the seismic wave progresses to the R2 radius, the seismic wave affects the points on the optical cable F located on the R2 concentric circle as well as points within the wavelength of the seismic wave. That is, vibration is applied to a plurality of points indicated as Pr2 in FIG. 5. Since optical sensing occurs very frequently more than several hundred times per second, 20 optical sensing may be performed at Pr2 points while vibration is applied. When the seismic wave propagates further and exceeds the R2 radius and the point in time when the the wavelength of the seismic wave no longer is reached, the Pr2 points no longer experience any applied vibration. At the point in time when vibration is applied to the Pr2 points, the waveform of the backscattered light generated at those 2025283530   18 Dec 2025 points changes to an abnormal state, and returns to a normal state after the seismic wave passes. In addition, when the vibration propagates to a point at radius R3, the same effect occurs at points located on the R3 concentric circle and at a plurality of points Pr3 near the concentric circle within the seismic wave wavelength range. 5 Once the vibration propagates to the point at radius R4 and completely passes through the optical cable F, the optical sensing signal at all points along the optical cable returns to its normal state. That is, as the vibration passes, the vibration is applied to at different points along the optical cable with a time difference and then disappears. That is, at each point along the optical cable, abnormal backscattered 10 light is generated with a time difference according to the arrival time of the vibration. Although the backscattered light generated under the applied vibration was generated at different point in times, its waveforms appear similar to each other. That is, the waveform of the backscattered light generated while vibration is applied to the Pr2 points at the first point in time and the waveform of the backscattered light generated 15 while vibration is applied to the Pr3 points at the second point in time with a time difference exhibit similar patterns.

[0045] The present invention identifies changes in the waveform of backscattered light at each point along an optical cable and subsequently estimates the path of the optical cable through computation. This will be described in detail 20 later.

[0046] As described above, during the optical sensing process, signal processing is performed on the backscattered light signals continuously reflected back from each point along the optical cable, and the backscattered light signals are extracted for each point to form an output signal. It will be described in detail with 2025283530   18 Dec 2025 reference to FIG. 6. FIG. 6 shows the signal received from the backscattered light that returned from a section between the approximately 10 km point and the approximately 10.10 km point along the optical cable with the light source as the starting point, after performing three optical sensing operations. 5

[0047] Immediately after the light is emitted, backscattered light begins to be received and continues to be received for a certain period of time. Since backscattered light signals are received sequentially from points closer to the light source in the optical cable, signals received earlier originate from points nearer to the source, while signals received later originate from points farther away from the light 10 source. To put it more accurately, using the time at which the backscattered light was received (the time from emission of light emission to reception of backscattered light) and the speed of the optical signal (2x108 m / s) mentioned above, it is possible to know at which point along the optical cable each backscattered light signal was generated. That is, each point on the X-axis in FIG. 6 is the time at which the 15 backscattered light was received, and it also indicates the point in the optical cable at which the backscattered light was generated. If the backscattered light reception signal is cut into segments at regular intervals along the X-axis, the backscattered light output signal can be extracted for each point along the optical cable. In the present invention, optical sensing is performed multiple times either continuously or 20 intermittently to generate an output signal for each turn.

[0048] In this way, after performing light sensing continuously a plurality of times in an environment where vibration is applied from a vibration source and generating an output signal for a plurality of points along the optical cable through signal processing, time series vibration signal data is acquired for each point. That 2025283530   18 Dec 2025 is, when the output signals generated at each point along the optical cable during a plurality of optical sensing are aligned in order according to the optical sensing executions, time series vibration signal data is formed. For example, by sequentially listing the output signals generated at point P14 as indicated by the dotted box B in 5 FIG. 6, vibration signal data over time at point P14 can be created.

[0049] The time series vibration signal data of each point reveals the result of elastic waves acting due to vibration, i.e. elastic wave phase information. FIG. 7 shows the time series vibration signal data for each point. In FIG. 7, the X-axis represents time T, the Y-axis represents the distance Y of the optical cable from the 10 origin, and time series vibration signal data D for each point from P1 to Pn is shown.

[0050] The time series vibration signal data D of each point contains a portion where the waveform is deformed by the influence of vibration, unlike the waveform in a normal state, i.e., a portion where elastic wave phase information W appears. In addition, the time at which the elastic wave phase information appears at 15 each point is different. This is because the time at which the vibration acts differs at each point. In the present invention, the arrival time of elastic waves from a vibration source to each point is determined using vibration signal data D for each point. The exact meaning of elastic wave arrival time and how to determine the arrival time will be described in detail below. 20

[0051] On the other hand, if the length of the optical cable is short, the elastic wave phase information appears in the same or very similar form at all points. Therefore, by taking the elastic wave phase information that appears at one point as a reference, a waveform having the same form as the reference can be found in the time series vibration signal data of the remaining points. Although this method is not 2025283530   18 Dec 2025 excluded in the present invention, it is needed to improve the above method when conditions change, such as when the length of the optical cable increases. That is, when the length of the optical cable is extended to lengths of tens of kilometers or more, such as in optical cables for communication, deformation appears in the elastic 5 wave phase information as the distance from the vibration source increases. Referring to FIG. 7, it may be seen that the shape of the elastic wave phase information shown at the upper end is deformed as it moves toward the lower end. This deformation occurs as the elastic wave propagates through the ground. In FIG. 7, the elastic wave phase information of point P1 has a triangle shape pointed 10 upwards, whereas the elastic wave phase information of point Pn has a polygonal shape pointed downwards. This is because although it is the same acoustic wave generated from a single vibration source, its phase is deformed during the process of propagation through the ground. If the elastic wave phase information at point P1 is fixed as the only reference, a problem arises in that the same elastic wave phase 15 information cannot be detected in the vibration signal data at points such as Pn-2, Pn-1, and Pn.

[0052] Accordingly, in the present invention, a method for comparing the reference elastic wave phase information with the phase information of adjacent points is adopted instead of fixing the reference elastic wave phase information to a 20 single value. That is, a method in which, in FIG. 7, with the elastic wave phase information at point P1 as the reference, the same phase information is detected at point P1, and similarly, phase information at point P3 is detected using the phase information at point P1, is adopted. Changes in phase information occur gradually over time, and thus phase information shows almost the same shape in adjacent 2025283530   18 Dec 2025 vibration signal data, making them easy to detect. By identifying the same phase information between adjacent points in this way, even if the phase of elastic waves is distorted as the time it takes for the elastic wave to propagate and the distance over which the elastic wave propagates in very long optical cables increase, the point in 5 time when the elastic wave acts on each point can be accurately identified.

[0053] Hereinafter, a method for determining the arrival time of elastic waves from the vibration source to each point along the optical cable will be described in detail.

[0054] Referring to FIG. 7, in this example, a reference point is set in the 10 optical cable. For example, the point closest to the light source (almost the point where the light source is installed) is set as a reference point SP. In FIG. 7, point P1 becomes the reference point in this example. For reference, the reference point closest to the light source may be regarded substantially the same as the origin where the light source is installed. 15

[0055] The elastic wave propagation time from the vibration source E to the reference point SP is set to 0. Of course, there is a physical propagation time from the vibration source to the reference point, but there is no problem in estimating the position coordinates of each point even if the elastic wave propagation time to the reference point is set to 0. 20

[0056] In this example, a relative difference value in the elastic wave arrival time between the reference point P1 and the adjacent point P2 is calculated. That is, when referring to the time series vibration signal data of P1 and P2 in FIG. 7, the time at which elastic wave phase information appears is slightly different. However, as described above, since elastic waves have long wavelengths, the elastic wave 2025283530   18 Dec 2025 phase information also appears for a long time over a certain period of time. Therefore, it is difficult to specify at which point elastic wave phase information appears based on only one vibration signal data, and the time when elastic wave phase information appears can only be set to a wide range. However, by using a 5 method that compares two vibration signal data, it is possible to determine the point in time when elastic wave phase information appears.

[0057] By moving the P2 time series vibration signal data slightly along the time axis T, the point where the similarity (correlation) of waveform between the P1 time series vibration signal data and the P2 time series vibration signal data is 10 greatest can be found.

[0058] For example, in FIG. 7, by fixing the P1 vibration signal data on the time axis and slightly moving the P2 vibration signal data to the left, a point in time at which the waveforms of the two vibration signal data appear almost similar over time can be found. By finding this point in time, the time at which elastic wave 15 phase information appears in the P2 vibration signal data can be found by determining how much it has moved along the time axis from the original P2 vibration signal data. Rather than individually identifying at which point or section elastic wave phase information appears in the P1 and P2 vibration signal data, the difference between the time at which elastic wave phase information appears in the 20 P2 time series vibration signal data and the time at which elastic wave phase information appears in the P1 vibration signal data, i.e., the ‘relative difference value (time) in arrival time’, is determined through a comparison of the similarity (correlation) of waveform between the P1 vibration signal data and the P2 vibration signal data. 2025283530   18 Dec 2025

[0059] In the above manner, elastic wave phase information is sequentially detected for each point and the relative difference value in arrival time compared to adjacent points is calculated. With the P2 time series vibration signal data as a reference, the relative difference value at which elastic wave phase information 5 appears in the P3 time series vibration signal data is calculated.

[0060] For example, at point P2 in FIG. 7, since the elastic wave phase information appears later than at point P1, a positive relative difference value is obtained. However, at point Pn-2, since the elastic wave phase information appears earlier than at point Pn-1, a negative relative difference value is obtained. For 10 reference, in FIG. 7, positive difference values are indicated by 'f and negative difference values are indicated by '|', and the size of the arrow increases as the relative difference value increases.

[0061] As described above, after sequentially calculating all the relative difference values in arrival times at adjacent points from the reference point, the 15 elastic wave arrival time at a specific point is calculated by accumulating the relative difference values at the respective points along a path from the reference point to the specific point.

[0062] In the upper graph of FIG. 8, the X-axis represents each point P of the optical cable and the Y-axis represents the relative difference value in arrival time 20 TD, and in the lower graph of FIG. 8, the X-axis represents each point P of the optical cable and the Y-axis represents the elastic wave arrival time AD. As mentioned previously, the elastic wave propagation time at the reference point SP is set to 0.

[0063] When referring to the upper graph of FIG. 8, the relative difference 2025283530   18 Dec 2025 value in arrival time TD appears as positive and negative values. A positive value means that the arrival time of the elastic wave at that point in the optical cable was later than the arrival time at the adjacent preceding point, while a negative value means that the arrival time thereof was earlier than at the preceding point. The lower 5 graph of FIG. 8 is the result of accumulating the relative difference values in arrival times. That is, the elastic wave arrival time at that point is the sum of the relative difference values in arrival times of the preceding points.

[0064] In the lower graph of FIG. 8, for point K, the relative difference values TD of the preceding points are all negative values. Accordingly, when all the 10 relative difference values of the preceding points are accumulated, that point has the the largest negative value for the elastic wave arrival time. That is, that point becomes the position where the vibration first arrives in the optical cable. In addition, in the optical cable, the relative difference values in arrival times at points behind point K is mostly positive. Therefore, the elastic wave propagation time of 15 the points behind the point K moves upward-right direction and gradually gets slower, and the point H becomes the position where the elastic wave propagates the latest in the optical cable.

[0065] Through the above process, the elastic wave propagation time, i.e. the time, which is obtained by accumulating the relative differences in the elastic wave 20 propagation time it takes for the elastic wave to arrive each point from the reference point along the optical cable, can be obtained.

[0066] Since the elastic wave propagation time at each point has been determined and the positions of the three vibration sources are already known, the position coordinates of each point along the optical cable can be estimated. 2025283530   18 Dec 2025

[0067] In the present invention, the position of each point along an optical cable is estimated using computer computation.

[0068] FIG. 9 is a diagram for describing a method for calculating position coordinates for each point along an optical cable in the present invention. 5

[0069] Referring to FIG. 9, the estimated optical cable installation area A is divided into a plurality of grids as described above. The spacing between each grid (resolution) can be set to several meters and can be changed in various ways.

[0070] In addition, using Equations 1 and 2 below, the position coordinates for each point are calculated. 10

[0071] Equation 1 N (d x pn -t)2 n=l

[0072]

[0073] Equation 2 s — e d = s-------? s - e

[0074]

[0075] Here, N is the number of vibration sources, which is approximately 3 15 or more, Pn is the reciprocal of the apparent elastic wave propagation speed approximation at the position of the optical cable of the n-th vibration source, and t is the elastic wave arrival time. The d is defined by Equation 2, where s is the position vector of the grid point from the reference point, and e is the position vector of the vibration source from the reference point. 20

[0076] Referring to FIG. 9, the s-e vector represents the vector s-e from the vibration source to the grid point, which is obtained by subtracting the vector e from the vibration source to the grid point from the vector s from the reference point to the 2025283530   18 Dec 2025 grid point. When dividing this vector by its absolute value, the unit vector of the s-e vector is yielded. When the dot product operation is performed on the unit vector of the s-e vector and the s vector, |s|-|s-e|-cos0 is yielded, and this value is defined as d. Here, 0 is the angle formed by the s-e vector and the s vector, and since the s-e vector 5 is a unit vector, its absolute value is approximately 1. When dividing d by the inverse of the elastic wave propagation speed approximation, the theoretical propagation time required for an elastic wave to propagate from the reference point to the corresponding grid point is yielded. In the above manner, the theoretical propagation time between each vibration source and grid point is calculated for all 10 grid points within the estimated optical cable installation area A.

[0077] In Equation 1, t is the elastic wave arrival time at a specific point in the optical cable calculated above. Therefore, the difference between the theoretical propagation time for elastic wave to be propagated from the reference point to the grid point and the elastic wave propagation time at a specific point along the optical 15 cable calculated above is obtained. Squaring in Equation 1 is a measure to convert a negative time difference into a positive value. Then, the above process is performed on each of the three pieces of data generated by applying the three vibration sources to calculate the grid point where the sum of the three time differences is minimized. That is, the grid point where Equation 1 is minimized is calculated. The position of 20 the grid point where the sum of the time differences is minimized is estimated to be the position of a specific point on the optical cable. Since the positions of all grid points within the estimated area are already known, if the grid point corresponding to each point along the optical cable is estimated, the position of each point can be specified. 2025283530   18 Dec 2025

[0078] By specifying the position of all points along the optical cable in the above manner, the entire path of the optical cable can be identified. However, in another example, the calculation is performed only for the previously set section division points T rather than all points along the optical cable, and the path of the 5 optical cable can be estimated by connecting the respective section division points with a straight line. This method is also possible because the path of the optical cable is generally installed in a straight line at the level of several tens of meters. This method has the advantage of reducing computational computation load, and does not significantly compromise accuracy, especially if the section division points 10 are set at short distance intervals.

[0079] The present invention can estimate a path of an optical cable installed underground using distributed acoustic sensing technology. The present invention has the advantage of being able to estimate the path of the optical cable extending over a distance of several tens of kilometers very simply and accurately. 15

[0080] By accurately identifying the position and path of the optical cables for communication, the optical cables for communication can be connected to DAS systems for use in various industrial fields, such as detecting earthquake occurrences and detecting blasting in construction sites.

[0081] Meanwhile, it should be noted that even effects not explicitly 20 mentioned herein, but which are expected based on the technical features of the present invention, as well as the effects described in the specification below and their potential effects, shall be treated as described in the specification of the present invention.

[0082] The scope of protection of the present invention is not limited to the 2025283530   18 Dec 2025 description and expression of the embodiments explicitly described above. Furthermore, it should be reiterated that the scope of protection of the present invention cannot be limited by obvious modifications or substitutions in the technical field to which the present invention belongs. 5

[0083] Although the method for estimating an installation path of an optical cable for communication has been described with reference to the specific embodiments, it is not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present invention defined by the 10 appended claims.

[0084] Unless the context requires otherwise, where the terms “comprise”, “comprises”, “comprised” or “comprising” are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other 15 features, integers, steps or components, or group thereof.

Claims

1. A method for estimating an installation path of an optical cable forcommunication to identify a path of the optical cable for communication installed 5 underground, the method comprising:(a) defining a plurality of points by setting arbitrary points at regular intervals from an arbitrary origin in the long optical cable;(b) repeatedly performing a light sensing process with a time difference, in which light is emitted to one end of the optical cable for communication in an10 environment where elastic waves are applied to an area where the optical cable is estimated to be installed from at least three vibration sources whose positions are known and a backscattered light signal generated by the emitted light being scattered at each point along the optical cable and then returning to the end of the optical cable, is received;15           (c) forming an output signal by extracting the backscattered light signal foreach point through signal processing on the backscattered light signal continuously returned from each point along the optical cable in the optical sensing process;(d) acquiring time series vibration signal data containing phase information of the elastic wave for each of the plurality of points along the optical cable by aligning20 a plurality of output signals formed for each point during the plurality of optical sensing processes in the order of optical sensing time;(e) identifying elastic wave arrival time of each elastic wave, which is the time it takes for the elastic wave to be propagated from the vibration source to the2025283530   18 Dec 2025plurality of points along the optical cable, using the time series vibration signal data; and(f) estimating a position and path of the optical cable by calculating position information for each of the plurality of points using the elastic wave arrival times5 from the at least three vibration sources to the plurality of points.

2. The method of claim 1, wherein a reference point is designated among theplurality of points along the optical cable, relative difference values of arrival times at which the same elastic wave phase information appears at sequentially adjacent 10 points starting from the reference point are respectively identified, and the elastic wave arrival time at a specific point is calculated by accumulating the relative difference values of the arrival times at the respective points on a path from the reference point to the specific point.15   3.     The method of claim 2, wherein the elastic wave arrival time at the referencepoint is set to approximately 0.

4. The method of claim 2 or 3, wherein the origin is a point from which light isemitted, and20           the reference point is set as a first point closest to the point from which lightis emitted.

5. The method of any one of claims 2 to 4, wherein an area where the opticalcable is estimated to be installed is divided into a plurality of grids,2025283530   18 Dec 2025Equation 1N^\d Xpn-t)271 = 1Equation 2s — e5 where, N is the number of vibration sources, which is approximately 3 or more, Pn is a reciprocal of an apparent elastic wave propagation speed approximation at the position of optical cable of n-th vibration source, t is the elastic wave arrival time, and d is defined by Equation 2 above, where s is ae position vector of a grid point from the reference point, and e is a position vector of the vibration source from the 10 reference point, anda value at which a value of Equation 1 above is minimum is used to calculate the position of a specific point along the optical cable.

6. The method of any one of claims 1 to 5, wherein the vibration source is an15 earthquake.

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