Existing communication optical fiber positioning method based on earthquake arrival time double difference

Abstract

An existing communication optical fiber positioning method based on earthquake arrival time double difference comprises the steps that firstly, a DAS system is arranged at one end of an existing communication optical fiber and communicated, secondly, a plurality of monitoring points are evenly arranged in the length direction of the optical fiber, at least two earthquake sources are selected on the periphery, and the time when earthquake waves reach the monitoring points is collected through the DAS system, and thirdly, the time when the earthquake waves reach the monitoring points is collected through the DAS system. The method comprises the following steps: step 1, taking two adjacent monitoring points as a group of monitoring point pairs, calculating travel time difference from the same seismic source to the group of monitoring point pairs, then calculating to obtain double-difference travel time of different seismic sources, and covering all the monitoring point pairs, step 4, based on the double-difference travel time and a linear relation of relative positions of the adjacent monitoring points, establishing linear relation expressions of each group, summarizing to form an overdetermined linear equation set, and 5, solving the equation set to obtain the relative space relation of adjacent monitoring points, combining the absolute coordinates of one end of the optical fiber, and deriving the absolute coordinates of all the monitoring points through vector superposition to complete positioning. Therefore, the positioning speed is high, and the precision can be guaranteed.

Description

Technical Field

[0001] This invention relates to an existing optical fiber positioning method, belonging to the field of optical fiber seismographs, and particularly to an existing optical fiber positioning method based on the time difference of earthquake arrival. Background Technology

[0002] In the field of earthquake monitoring, utilizing existing optical fibers in conjunction with distributed acoustic sensing (DAS) systems has become an important direction for constructing high-density earthquake sensor networks. When external vibrations (such as seismic waves) are transmitted to existing optical fibers, they cause changes in the physical properties of the fibers, such as changes in refractive index and length. The DAS system transmits optical signals into the fiber and receives and demodulates the changes in scattered light signals caused by these changes in physical properties in real time, thereby achieving distributed vibration monitoring of the entire fiber optic cable to achieve the purpose of earthquake monitoring.

[0003] However, when using existing communication optical fibers as seismic sensors, the primary task is to accurately locate the fibers and determine the absolute positions of each monitoring point within them. Currently, locating existing communication optical fibers mainly relies on artificially induced vibration. This method requires manually striking the fiber to generate vibration signals, then combining these signals with vibration differences recorded by the DAS system to deduce the specific location of the striking point within the fiber. Subsequently, the overall direction of the fiber is pieced together through multiple striking points and repeated positioning. However, this process requires large-scale excavation, and the point-by-point operation is extremely time-consuming and labor-intensive, resulting in slow positioning speed and difficulty in guaranteeing accuracy.

[0004] Chinese patent application No. 202110689398.4, filed on June 22, 2021, discloses a positioning method, device, electronic device, and storage medium. The method involves: responding to a positioning request for an object to be positioned, performing positioning correction processing on the object to be positioned to obtain target positioning information. The positioning correction processing includes: obtaining intermediate positioning information based on velocity measurement data after updating initial positioning information, and iteratively correcting the intermediate positioning information using obtained satellite observation data and feature point coordinate data to obtain the target positioning information, and then presenting the target positioning information corresponding to the object to be positioned on an operable page. Although this patent achieves positioning of the object to be positioned by fusing satellite observation data, inertial sensor data, and image feature point data, it still has the following drawbacks:

[0005] This design is highly dependent on satellite signals. In actual earthquake monitoring scenarios, especially in complex terrain or urban environments, satellite signals are easily blocked or interfered with, which still results in slow positioning speed and difficulty in guaranteeing accuracy.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this patent application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects and problems of slow positioning speed and difficulty in guaranteeing accuracy in the existing technology, and to provide an existing optical fiber positioning method based on earthquake arrival time difference with faster positioning speed and guaranteed accuracy.

[0008] To achieve the above objectives, the technical solution of the present invention is: a positioning method for existing optical fiber communication based on earthquake arrival time difference, the method comprising the following steps:

[0009] Step 1: Deploy a DAS system at one end of the existing communication fiber optic cable and connect the DAS system to the existing communication fiber optic cable;

[0010] Step 2: First, set up multiple monitoring points evenly along the length of the existing communication fiber optic cable. Then, select at least two seismic sources around the existing communication fiber optic cable and collect the time when the seismic waves generated by each seismic source arrive at each monitoring point through the DAS system.

[0011] Step 3: Each pair of adjacent monitoring points forms a monitoring point pair. Based on the arrival time of the collected seismic waves at each monitoring point, for each monitoring point pair, first calculate the travel time difference from the same seismic source to the monitoring point pair, and then calculate the double difference travel time corresponding to different seismic sources based on the travel time difference. Repeat the calculation of travel time difference and double difference travel time for all monitoring point pairs to finally obtain the double difference travel time of all monitoring point pairs.

[0012] Step 4: Based on the double-difference travel time of all the monitoring point pairs mentioned above, and combined with the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber, establish a linear relationship describing the relative spatial relationship of the monitoring point pair. The relative spatial relationship of the monitoring point pair includes the relative distance and direction of adjacent monitoring points. Then, summarize all the linear relationships corresponding to all monitoring point pairs to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as the unknown.

[0013] Step 5: First, use numerical methods to solve the above overdetermined linear equations to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication fiber; then, combine the absolute coordinates of one end of the existing communication fiber, and derive the absolute coordinates of all monitoring points on the existing communication fiber by vector superposition of the relative spatial relationships between adjacent monitoring points, thereby completing the positioning of the existing communication fiber.

[0014] In the first step, deploying a DAS system at one end of an existing communication optical fiber and connecting the DAS system with the existing communication optical fiber means: selecting the start or end of the existing communication optical fiber as the installation point, physically connecting the optical fiber at the installation point to the optical interface of the DAS system, and fixing the DAS system at the installation point to form a path for optical signal transmission.

[0015] In the second step, the earthquake source includes natural earthquake sources and artificial earthquake sources.

[0016] In the second step, the phrase "uniformly setting up multiple monitoring points along the length of the existing communication optical fiber" means: setting up multiple monitoring points along the length of the existing communication optical fiber, with equal spacing between adjacent monitoring points;

[0017] In the second step, selecting at least two seismic sources around the existing communication fiber means selecting two or more seismic sources that meet the propagation path conditions, wherein the propagation path of the seismic waves generated by the seismic sources to each monitoring point on the existing communication fiber is consistent, and the location of the seismic sources ensures that the seismic waves cover all monitoring points on the existing communication fiber.

[0018] In the second step, the acquisition of the arrival time of seismic waves generated by each earthquake source at each monitoring point by the DAS system mentioned above refers to the following: the DAS system transmits optical signals and receives backscattered light generated by the vibration of seismic waves in the existing communication optical fiber, demodulates the changes in the scattered light signals, identifies the time when the seismic waves arrive at multiple monitoring points on the existing communication optical fiber, and records and stores the seismic wave arrival time data corresponding to each monitoring point.

[0019] The distance between adjacent monitoring points is 1-100 meters.

[0020] In the third step, based on the arrival time of the acquired seismic waves at each monitoring point, for each pair of monitoring points, the travel time difference from the same seismic source to the pair is first calculated, and then the double-difference travel time corresponding to different seismic sources is calculated based on the travel time difference. The calculation of travel time difference and double-difference travel time is repeated for all monitoring point pairs. Finally, the double-difference travel time of all monitoring point pairs is obtained as follows: for any pair of monitoring points on the existing communication optical fiber, namely monitoring point k and monitoring point l, and any two different seismic sources, namely seismic source i and seismic source j, based on the DAS system... The arrival times of the collected seismic waves at each monitoring point are calculated by first determining the travel time difference Δtikl = tkl - tki from seismic source i to monitoring point k and monitoring point l in the same group, where tki is the arrival time from seismic source i to monitoring point k and tkl is the arrival time from seismic source i to monitoring point l. Simultaneously, the travel time difference Δtjkl = tkl' - tki' from seismic source j to monitoring point k and monitoring point l in the same group is also calculated, where tki' is the arrival time from seismic source j to monitoring point k and tkl' is the arrival time from seismic source j to monitoring point l.

[0021] Then, the difference between the two travel times is used to calculate the corresponding double-difference travel time ΔΔtklij=Δtjkl-Δtikl for this group of monitoring points, so as to eliminate the systematic deviation in the process of seismic wave propagation;

[0022] Then, the above calculations are performed on all monitoring point pairs on the existing communication optical fiber one by one, and finally the double difference travel time corresponding to each monitoring point pair is obtained.

[0023] In the fourth step, based on the double-difference travel time of all the aforementioned monitoring point pairs, and combining the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, a linear relationship describing the relative spatial relationship of each monitoring point pair is established for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber. The relative spatial relationship of the monitoring point pairs includes the relative distance and direction of adjacent monitoring points. Then, all the linear relationships corresponding to all monitoring point pairs are summarized to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as unknowns. This means that for the double-difference travel time corresponding to each monitoring point pair obtained in the third step, based on the assumption that the propagation speed of seismic waves in the medium of this region remains constant, and combined with the absolute coordinates of the seismic source, the propagation speed of seismic waves to the set of monitoring point pairs is calculated. The direction components of the monitoring point pairs are identified. Based on this, it is determined that there is a direct proportional relationship between the relative spatial distance between adjacent monitoring points and the double-difference travel time, and the relative direction of adjacent monitoring points is reflected by the direction parameter determined based on the direction components in the linear expression. Subsequently, according to the direct proportional relationship and the direction parameter, the double-difference travel time of this set of monitoring point pairs is transformed into a linear expression that simultaneously describes the relative distance and direction of adjacent monitoring points. The linear expressions corresponding to all monitoring point pairs are summarized to form a set of equations. Since the number of equations is greater than the number of relative spatial relationships between adjacent monitoring points that need to be solved, an overdetermined linear equation system is formed, in which each equation uses the relative distance and direction between adjacent monitoring points as unknowns to be solved. The total number of equations is consistent with the total number of double-difference travel time data obtained in the third step.

[0024] In the fifth step, the step of solving the above-mentioned overdetermined linear equations using numerical methods to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication optical fiber means: solving the above-mentioned overdetermined linear equations using the least squares method, and obtaining the solution that minimizes the overall error by minimizing the sum of squared residuals of all equations in the equations; this solution corresponds to the numerical values ​​of the relative spatial relationships between each pair of adjacent monitoring points on the existing communication optical fiber, covering the relative distances or coordinate differences of all monitoring point pairs, forming a complete dataset of relative spatial relationships between adjacent monitoring points.

[0025] In the fifth step, when the least squares method is used to solve the above-mentioned overdetermined linear equation system, the overdetermined linear equation system is first preprocessed to remove abnormal equations whose residuals exceed a preset threshold. Then, the solution parameters are adjusted through iterative calculation until the sum of squared residuals converges to a stable value. Finally, the numerical values ​​of the relative spatial relationship between adjacent monitoring points that meet the accuracy requirements are output.

[0026] In the fifth step, the step of combining the absolute coordinates of one end of the existing communication optical fiber and deriving the absolute coordinates of all monitoring points on the existing communication optical fiber by vector superposition of the relative spatial relationships between adjacent monitoring points means: the absolute coordinates of the start and end of the existing communication optical fiber are known quantities; the start or end of the existing communication optical fiber is taken as the first monitoring point; the first monitoring point and the adjacent second monitoring point form a first pair of monitoring points; the absolute coordinates of the first monitoring point and the relative spatial relationship of this pair of monitoring points are vector superimposed to obtain the absolute coordinates of the second monitoring point; the second monitoring point and the adjacent third monitoring point form a second pair of monitoring points; the absolute coordinates of the second monitoring point and the relative spatial relationship of the second pair of monitoring points are vector superimposed to obtain the absolute coordinates of the third monitoring point; the relative spatial relationships of all monitoring point pairs are accumulated in this order until all monitoring points on the existing communication optical fiber are covered, and finally the absolute coordinates of all monitoring points are obtained.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. This invention discloses a positioning method for existing communication optical fibers based on earthquake arrival time difference (DOT). The method includes: First, deploying and connecting a DAS system at one end of an existing communication optical fiber; Second, uniformly setting multiple monitoring points along the fiber's length, selecting at least two earthquake sources in the vicinity, and collecting the arrival times of seismic waves at each monitoring point using the DAS system; Third, forming a monitoring point pair with every two adjacent monitoring points, calculating the time difference from the same earthquake source to the pair, and then calculating the DOT for different earthquake sources, covering all monitoring point pairs; Fourth, establishing linear relationships for each pair based on the DOT and the linear relationship with the relative positions of adjacent monitoring points, and summarizing them into an overdetermined linear equation system; Fifth, solving the equation system to obtain the relative spatial relationships between adjacent monitoring points, and combining the absolute coordinates at one end of the fiber, deriving the absolute coordinates of all monitoring points through vector superposition, thus completing the positioning. In application, first deploying a DAS system at one end of the existing communication optical fiber, connecting the DAS system to the fiber, and then uniformly setting multiple monitoring points along the fiber's length... At least two seismic sources are selected around the optical fiber at each monitoring point. The arrival time of seismic waves generated by each seismic source at each monitoring point is collected using a DAS system. Then, every two adjacent monitoring points form a monitoring point pair. Based on the collected arrival times of seismic waves at each monitoring point, for each monitoring point pair, the travel time difference from the same seismic source to the monitoring point pair is first calculated. Then, based on the travel time difference, the double-difference travel time corresponding to different seismic sources is calculated until the double-difference travel time of all monitoring point pairs is obtained. Then, based on the double-difference travel time of all monitoring point pairs and the linear relationship between their relative positions with adjacent monitoring points, a linear equation describing the relative spatial relationship (including distance and direction) is established for each monitoring point pair. This is summarized into an overdetermined linear equation system with the relative spatial relationship as the unknown. Finally, the equation system is solved numerically to obtain the relative spatial relationship between adjacent monitoring points. Combined with the absolute coordinates at one end of the optical fiber, the absolute coordinates of all monitoring points are derived by vector superposition, completing the optical fiber positioning. The advantages of this invention also include:

[0029] Firstly, by deploying a DAS system at one end of the existing communication fiber optic cable, setting up multiple monitoring points along the fiber optic cable length, and utilizing at least two surrounding seismic sources, the DAS system collects the arrival time of seismic waves at each monitoring point. Then, by calculating the travel time difference between adjacent monitoring point pairs and the double difference travel time of different seismic sources, an overdetermined linear equation system is established to solve for the relative spatial relationship between adjacent monitoring points. Combined with the absolute coordinates at one end of the fiber optic cable, the absolute coordinates of all monitoring points are derived to complete the positioning.

[0030] Secondly, this invention utilizes the propagation characteristics of seismic waves and the high-precision sensing capabilities of the DAS system to achieve positioning through time difference calculation and mathematical modeling. It eliminates the need for manual excavation and point-by-point operations, and the data acquisition and calculation process can be automated and processed in batches, significantly improving the positioning speed.

[0031] Thirdly, double-difference travel time calculation can offset common errors in seismic wave propagation. The overdetermined equations reduce random errors through multiple sets of data constraints and reduce cumulative deviations by combining endpoint coordinate calibration. Compared with the traditional method of inferring position by relying on vibration differences, it effectively improves positioning accuracy and solves the problem of insufficient positioning speed and accuracy in existing technologies.

[0032] Therefore, this invention can not only locate existing communication optical fibers, but also achieve fast positioning speed and guaranteed accuracy.

[0033] 2. In this invention, a positioning method for existing communication optical fibers based on earthquake arrival time difference involves selecting the starting or ending end of the existing communication optical fiber as the installation point. The optical fiber at this installation point is physically connected to the optical interface of the DAS system, and the DAS system is fixed at the installation point, forming a path for optical signal transmission. In application, only the DAS system needs to be deployed at the starting or ending end of the existing communication optical fiber. By physically connecting the optical fiber to the DAS system's optical interface and fixing the DAS system, an optical signal transmission path can be formed without modifying or excavating the entire optical fiber. Compared to the cumbersome operation and interference with the normal operation of existing communication optical fibers caused by artificial vibration positioning in the prior art, the deployment method of this invention is simple to operate, reduces interference with the normal operation of existing communication optical fibers, and ensures positioning speed and accuracy while also being convenient to operate and compatible with the system. Therefore, this invention not only offers fast positioning speed and guaranteed accuracy but also combines convenient operation and system compatibility.

[0034] 3. In this invention, a positioning method for existing communication optical fibers based on earthquake time difference (DTD) involves setting multiple monitoring points along the length of the existing communication optical fiber. The spacing between adjacent monitoring points is equal, ranging from 1 to 100 meters. During application, the spacing between adjacent monitoring points is flexibly selected within the 1-100 meter range based on the total length of the existing communication optical fiber, the complexity of the geographical environment, and the required positioning accuracy. If the fiber traverses complex terrain (such as mountainous areas or areas with multiple pipelines), a smaller spacing is used; if it is a simple terrain environment with a long fiber distance, a larger spacing is used. After determining the spacing, monitoring points are evenly divided along the fiber length. The distributed monitoring function of the DAS system ensures stable data collection at each monitoring point. Compared to existing technologies that lack flexible adjustment mechanisms for different scenarios and struggle to balance positioning accuracy and data volume, this invention, by flexibly adjusting the spacing between adjacent monitoring points, can adapt to different application scenarios, providing uniformly distributed basic data support for subsequent time difference and DTD calculations. Therefore, this invention not only combines ease of operation and system compatibility but also improves the reliability and applicability of the positioning results. Attached Figure Description

[0035] Figure 1 This is a flowchart of the present invention.

[0036] Figure 2 This is a schematic diagram of the dual-difference positioning principle of the seismic source monitoring point in this invention.

[0037] Figure 3 This is a schematic diagram illustrating the positioning of each monitoring point in the existing communication optical fiber in this invention.

[0038] Figure 4 In this invention Figure 3 A magnified view of a portion of the image. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] See Figure 1 — Figure 4 A method for positioning existing optical fiber communication based on earthquake arrival time difference, the method comprising the following steps:

[0041] Step 1: Deploy a DAS system at one end of the existing communication fiber optic cable and connect the DAS system to the existing communication fiber optic cable;

[0042] Step 2: First, set up multiple monitoring points evenly along the length of the existing communication fiber optic cable. Then, select at least two seismic sources around the existing communication fiber optic cable and collect the time when the seismic waves generated by each seismic source arrive at each monitoring point through the DAS system.

[0043] Step 3: Each pair of adjacent monitoring points forms a monitoring point pair. Based on the arrival time of the collected seismic waves at each monitoring point, for each monitoring point pair, first calculate the travel time difference from the same seismic source to the monitoring point pair, and then calculate the double difference travel time corresponding to different seismic sources based on the travel time difference. Repeat the calculation of travel time difference and double difference travel time for all monitoring point pairs to finally obtain the double difference travel time of all monitoring point pairs.

[0044] Step 4: Based on the double-difference travel time of all the monitoring point pairs mentioned above, and combined with the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber, establish a linear relationship describing the relative spatial relationship of the monitoring point pair. The relative spatial relationship of the monitoring point pair includes the relative distance and direction of adjacent monitoring points. Then, summarize all the linear relationships corresponding to all monitoring point pairs to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as the unknown.

[0045] Step 5: First, use numerical methods to solve the above overdetermined linear equations to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication fiber; then, combine the absolute coordinates of one end of the existing communication fiber, and derive the absolute coordinates of all monitoring points on the existing communication fiber by vector superposition of the relative spatial relationships between adjacent monitoring points, thereby completing the positioning of the existing communication fiber.

[0046] In the first step, deploying a DAS system at one end of an existing communication optical fiber and connecting the DAS system with the existing communication optical fiber means: selecting the start or end of the existing communication optical fiber as the installation point, physically connecting the optical fiber at the installation point to the optical interface of the DAS system, and fixing the DAS system at the installation point to form a path for optical signal transmission.

[0047] In the second step, the earthquake source includes natural earthquake sources and artificial earthquake sources.

[0048] In the second step, the phrase "uniformly setting up multiple monitoring points along the length of the existing communication optical fiber" means: setting up multiple monitoring points along the length of the existing communication optical fiber, with equal spacing between adjacent monitoring points;

[0049] In the second step, selecting at least two seismic sources around the existing communication fiber means selecting two or more seismic sources that meet the propagation path conditions, wherein the propagation path of the seismic waves generated by the seismic sources to each monitoring point on the existing communication fiber is consistent, and the location of the seismic sources ensures that the seismic waves cover all monitoring points on the existing communication fiber.

[0050] In the second step, the acquisition of the arrival time of seismic waves generated by each earthquake source at each monitoring point by the DAS system mentioned above refers to the following: the DAS system transmits optical signals and receives backscattered light generated by the vibration of seismic waves in the existing communication optical fiber, demodulates the changes in the scattered light signals, identifies the time when the seismic waves arrive at multiple monitoring points on the existing communication optical fiber, and records and stores the seismic wave arrival time data corresponding to each monitoring point.

[0051] The distance between adjacent monitoring points is 1-100 meters.

[0052] In the third step, based on the arrival time of the acquired seismic waves at each monitoring point, for each pair of monitoring points, the travel time difference from the same seismic source to the pair is first calculated, and then the double-difference travel time corresponding to different seismic sources is calculated based on the travel time difference. The calculation of travel time difference and double-difference travel time is repeated for all monitoring point pairs. Finally, the double-difference travel time of all monitoring point pairs is obtained as follows: for any pair of monitoring points on the existing communication optical fiber, namely monitoring point k and monitoring point l, and any two different seismic sources, namely seismic source i and seismic source j, based on the DAS system... The arrival times of the collected seismic waves at each monitoring point are calculated by first determining the travel time difference Δtikl = tkl - tki from seismic source i to monitoring point k and monitoring point l in the same group, where tki is the arrival time from seismic source i to monitoring point k and tkl is the arrival time from seismic source i to monitoring point l. Simultaneously, the travel time difference Δtjkl = tkl' - tki' from seismic source j to monitoring point k and monitoring point l in the same group is also calculated, where tki' is the arrival time from seismic source j to monitoring point k and tkl' is the arrival time from seismic source j to monitoring point l.

[0053] Then, the difference between the two travel times is used to calculate the corresponding double-difference travel time ΔΔtklij=Δtjkl-Δtikl for this group of monitoring points, so as to eliminate the systematic deviation in the process of seismic wave propagation;

[0054] Then, the above calculations are performed on all monitoring point pairs on the existing communication optical fiber one by one, and finally the double difference travel time corresponding to each monitoring point pair is obtained.

[0055] In the fourth step, based on the double-difference travel time of all the aforementioned monitoring point pairs, and combining the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, a linear relationship describing the relative spatial relationship of each monitoring point pair is established for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber. The relative spatial relationship of the monitoring point pairs includes the relative distance and direction of adjacent monitoring points. Then, all the linear relationships corresponding to all monitoring point pairs are summarized to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as unknowns. This means that for the double-difference travel time corresponding to each monitoring point pair obtained in the third step, based on the assumption that the propagation speed of seismic waves in the medium of this region remains constant, and combined with the absolute coordinates of the seismic source, the propagation speed of seismic waves to the set of monitoring point pairs is calculated. The direction components of the monitoring point pairs are identified. Based on this, it is determined that there is a direct proportional relationship between the relative spatial distance between adjacent monitoring points and the double-difference travel time, and the relative direction of adjacent monitoring points is reflected by the direction parameter determined based on the direction components in the linear expression. Subsequently, according to the direct proportional relationship and the direction parameter, the double-difference travel time of this set of monitoring point pairs is transformed into a linear expression that simultaneously describes the relative distance and direction of adjacent monitoring points. The linear expressions corresponding to all monitoring point pairs are summarized to form a set of equations. Since the number of equations is greater than the number of relative spatial relationships between adjacent monitoring points that need to be solved, an overdetermined linear equation system is formed, in which each equation uses the relative distance and direction between adjacent monitoring points as unknowns to be solved. The total number of equations is consistent with the total number of double-difference travel time data obtained in the third step.

[0056] In the fifth step, the step of solving the above-mentioned overdetermined linear equations using numerical methods to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication optical fiber means: solving the above-mentioned overdetermined linear equations using the least squares method, and obtaining the solution that minimizes the overall error by minimizing the sum of squared residuals of all equations in the equations; this solution corresponds to the numerical values ​​of the relative spatial relationships between each pair of adjacent monitoring points on the existing communication optical fiber, covering the relative distances or coordinate differences of all monitoring point pairs, forming a complete dataset of relative spatial relationships between adjacent monitoring points.

[0057] In the fifth step, when the least squares method is used to solve the above-mentioned overdetermined linear equation system, the overdetermined linear equation system is first preprocessed to remove abnormal equations whose residuals exceed a preset threshold. Then, the solution parameters are adjusted through iterative calculation until the sum of squared residuals converges to a stable value. Finally, the numerical values ​​of the relative spatial relationship between adjacent monitoring points that meet the accuracy requirements are output.

[0058] In the fifth step, the step of combining the absolute coordinates of one end of the existing communication optical fiber and deriving the absolute coordinates of all monitoring points on the existing communication optical fiber by vector superposition of the relative spatial relationships between adjacent monitoring points means: the absolute coordinates of the start and end of the existing communication optical fiber are known quantities; the start or end of the existing communication optical fiber is taken as the first monitoring point; the first monitoring point and the adjacent second monitoring point form a first pair of monitoring points; the absolute coordinates of the first monitoring point and the relative spatial relationship of this pair of monitoring points are vector superimposed to obtain the absolute coordinates of the second monitoring point; the second monitoring point and the adjacent third monitoring point form a second pair of monitoring points; the absolute coordinates of the second monitoring point and the relative spatial relationship of the second pair of monitoring points are vector superimposed to obtain the absolute coordinates of the third monitoring point; the relative spatial relationships of all monitoring point pairs are accumulated in this order until all monitoring points on the existing communication optical fiber are covered, and finally the absolute coordinates of all monitoring points are obtained.

[0059] The following are supplementary descriptions of the present invention:

[0060] The present invention preferably obtains the absolute coordinates of the starting end A and the ending end Z of the existing communication optical fiber by combining the query of existing engineering data with on-site measurement and calibration.

[0061] The DAS system of the present invention is preferably a distributed fiber acoustic demodulation host module.

[0062] Example 1:

[0063] See Figure 1 — Figure 4 A method for positioning existing optical fiber communication based on earthquake arrival time difference, the method comprising the following steps:

[0064] Step 1: Deploy a DAS system at one end of the existing communication fiber optic cable and connect the DAS system to the existing communication fiber optic cable;

[0065] Step 2: First, set up multiple monitoring points evenly along the length of the existing communication fiber optic cable. Then, select at least two seismic sources around the existing communication fiber optic cable and collect the time when the seismic waves generated by each seismic source arrive at each monitoring point through the DAS system.

[0066] Step 3: Each pair of adjacent monitoring points forms a monitoring point pair. Based on the arrival time of the collected seismic waves at each monitoring point, for each monitoring point pair, first calculate the travel time difference from the same seismic source to the monitoring point pair, and then calculate the double difference travel time corresponding to different seismic sources based on the travel time difference. Repeat the calculation of travel time difference and double difference travel time for all monitoring point pairs to finally obtain the double difference travel time of all monitoring point pairs.

[0067] Step 4: Based on the double-difference travel time of all the monitoring point pairs mentioned above, and combined with the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber, establish a linear relationship describing the relative spatial relationship of the monitoring point pair. The relative spatial relationship of the monitoring point pair includes the relative distance and direction of adjacent monitoring points. Then, summarize all the linear relationships corresponding to all monitoring point pairs to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as the unknown.

[0068] Step 5: First, use numerical methods to solve the above overdetermined linear equations to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication fiber; then, combine the absolute coordinates of one end of the existing communication fiber, and derive the absolute coordinates of all monitoring points on the existing communication fiber by vector superposition of the relative spatial relationships between adjacent monitoring points, thereby completing the positioning of the existing communication fiber.

[0069] Example 2:

[0070] The basic content is the same as in Example 1, except that: in the first step, deploying the DAS system at one end of the existing communication optical fiber and connecting the DAS system with the existing communication optical fiber means: selecting the start or end of the existing communication optical fiber as the installation point, physically connecting the optical fiber at the installation point to the optical interface of the DAS system, and fixing the DAS system at the installation point to form a path for optical signal transmission.

[0071] When applying the system, select the start or end of the existing communication fiber optic cable as the installation point. Physically connect the fiber optic cable at this location to the optical interface of the DAS system, and ensure a stable optical signal transmission path through the appropriate connector. Then, fix the DAS system at the installation point, ensuring that the DAS system equipment and the fiber optic interface are secure and form a reliable optical signal transmission and reception link. After deployment, start the DAS system to verify the connectivity between the existing communication fiber optic cable and the DAS system, and confirm that the optical signal transmission is normal.

[0072] Example 3:

[0073] The basic content is the same as in Example 1, except that in the second step, the earthquake source includes natural earthquake sources and artificial earthquake sources.

[0074] When applying this method, the type of seismic source should be selected based on the geological environment and monitoring needs of the area where the existing communication fiber optic cable is located. If natural seismic activity is frequent in the surrounding area, a suitable natural seismic source can be waited for, and monitoring can be carried out using the absolute coordinates of the seismic source already determined by the traditional seismic network. If active data acquisition is required or there are insufficient natural seismic sources, artificial seismic sources can be deployed in a reasonable area around the fiber optic cable, such as by generating seismic waves through controlled blasting, to ensure that the location of the seismic source is known and that the seismic waves can cover all monitoring points of the fiber optic cable. Regardless of whether a natural or artificial seismic source is selected, it is necessary to ensure that the distance between the seismic source and the fiber optic cable meets the condition of approximately consistent propagation paths, so that the path difference of the seismic waves reaching each monitoring point of the fiber optic cable can be ignored. Subsequently, the DAS system is used to collect the time data of the seismic waves arriving at each monitoring point in real time, providing reliable raw data for subsequent calculations of travel time difference and double-difference travel time.

[0075] Example 4:

[0076] The basic content is the same as in Example 3, except that: in the second step, the phrase "uniformly setting multiple monitoring points along the length of the existing communication optical fiber" means setting multiple monitoring points along the length of the existing communication optical fiber, with equal spacing between adjacent monitoring points; in the second step, the phrase "selecting at least two seismic sources around the existing communication optical fiber" means selecting two or more seismic sources that meet the propagation path conditions, where the propagation path of the seismic waves generated by the seismic sources to each monitoring point on the existing communication optical fiber is consistent, and the position of the seismic sources ensures that the seismic waves cover all monitoring points on the existing communication optical fiber; in the second step, the phrase "collecting the arrival time of the seismic waves generated by each seismic source at each monitoring point through the DAS system" means that the DAS system transmits optical signals and receives backscattered light generated by the vibration of seismic waves in the existing communication optical fiber, demodulates the changes in the scattered light signals, identifies the time when the seismic waves arrive at multiple monitoring points on the existing communication optical fiber, and records and stores the seismic wave arrival time data corresponding to each monitoring point; the spacing between adjacent monitoring points is 1-100 meters.

[0077] In application, firstly, based on the total length of the existing communication optical fiber and the positioning accuracy requirements, monitor points are uniformly marked along the fiber length at equal intervals. The distance between adjacent monitor points can be set to 1-100 meters to ensure a regular distribution of points and guarantee the accuracy of subsequent relative position calculations. When selecting earthquake sources, two or more natural or artificial earthquake sources that meet the propagation path conditions must be selected to ensure that the generated seismic waves can completely cover all monitor points on the optical fiber, and that the propagation paths of the seismic waves to each monitor point are approximately consistent. After the DAS system is started, it continuously transmits optical signals to the optical fiber. When the seismic wave is transmitted to the optical fiber through the soil or rock medium and causes vibration, the refractive index and length of the optical fiber will change slightly, resulting in a corresponding change in the intensity and phase of the backscattered light. The DAS system captures these changes in scattered light signals in real time, and accurately identifies the specific time when the seismic wave arrives at each monitor point through demodulation analysis. It then records and stores the corresponding arrival time data according to the monitor point number, providing complete and reliable original observation data for subsequent calculation of the travel time difference and double difference travel time of each pair of monitor points.

[0078] Example 5:

[0079] The basic content is the same as in Example 1, except that in the third step, based on the arrival time of the acquired seismic waves at each monitoring point, for each pair of monitoring points, the travel time difference from the same seismic source to the pair is first calculated, and then the double-difference travel time corresponding to different seismic sources is calculated based on the travel time difference. The calculation of travel time difference and double-difference travel time is repeated for all monitoring point pairs. Finally, the double-difference travel time of all monitoring point pairs is obtained as follows: For any pair of monitoring points on the existing communication optical fiber, namely monitoring point k and monitoring point l, and any two different seismic sources, namely seismic source i and seismic source j, based on the arrival time of the seismic waves acquired by the DAS system at each monitoring point, the travel time difference Δtikl from seismic source i to the pair of monitoring points k and monitoring point l is first calculated respectively. =tkl-tki, where tki is the arrival time from earthquake source i to monitoring point k, and tkl is the arrival time from earthquake source i to monitoring point l; simultaneously, calculate the travel time difference Δtjkl = tkl'-tki' from earthquake source j to monitoring point k and monitoring point l respectively; where tki' is the arrival time from earthquake source j to monitoring point k, and tkl' is the arrival time from earthquake source j to monitoring point l; then calculate the double-difference travel time ΔΔtklij = Δtjkl-Δtikl corresponding to the monitoring point pair using the difference between the two travel time differences, in order to eliminate the systematic deviation in the seismic wave propagation process; then, perform the above calculations one by one for all monitoring point pairs on the existing communication optical fiber, and finally obtain the double-difference travel time corresponding to each of the monitoring point pairs.

[0080] In application, for monitoring points already evenly distributed on existing communication optical fibers, the DAS system is first used to accurately collect the arrival time data of seismic waves generated by each seismic source at each monitoring point, ensuring that the data records accurately correspond to the monitoring point number and the seismic source identifier. For any pair of adjacent monitoring points k and l, the arrival times of the seismic waves recorded by the DAS system are retrieved. The arrival time tki from seismic source i to monitoring point k and the arrival time tkl from seismic source i to monitoring point l are extracted. The travel time difference from the seismic source to this pair of monitoring points is calculated using the formula Δtikl = tkl - tki. Simultaneously, the arrival time from another seismic source j to monitoring point k is extracted. The travel time difference between tki' and the arrival time tkl' of monitoring point l is calculated using the formula Δtjkl=tkl'-tki'. Then, the double-difference travel time of the monitoring point pair is obtained by the difference calculation of ΔΔtklij=Δtjkl-Δtikl, thereby eliminating the interference of system deviations such as uneven formation velocity on positioning. Following the above process, the travel time difference and double-difference travel time are calculated for each monitoring point pair on the existing communication optical fiber, and finally a double-difference travel time dataset covering all monitoring point pairs is formed, laying the data foundation for subsequent construction of overdetermined linear equations and solving the relative spatial relationship between adjacent monitoring points.

[0081] Example 6:

[0082] The basic content is the same as in Example 1, except that in the fourth step, based on the double-difference travel time of all the above-mentioned monitoring point pairs, and combined with the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, a linear relationship describing the relative spatial relationship of each monitoring point pair is established for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber. The relative spatial relationship of the monitoring point pairs includes the relative distance and direction of adjacent monitoring points. Then, all the linear relationships corresponding to all monitoring point pairs are summarized to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as the unknown. This means that for the double-difference travel time corresponding to each monitoring point pair obtained in the third step, based on the assumption that the propagation speed of seismic waves in the medium of this region remains constant, and combined with the absolute coordinates of the seismic source... Calculate the directional components of seismic waves propagating to the monitoring point pair. Based on this, it is determined that there is a direct proportional relationship between the relative spatial distance between adjacent monitoring points and the double-difference travel time, and the relative direction of adjacent monitoring points is reflected by the direction parameter determined based on the directional components in the linear expression. Subsequently, according to the direct proportional relationship and the direction parameter, the double-difference travel time of the monitoring point pair is transformed into a linear expression that simultaneously describes the relative distance and direction of adjacent monitoring points. The linear expressions corresponding to all monitoring point pairs are summarized to form a set of equations. Since the number of equations is greater than the number of relative spatial relationships between adjacent monitoring points that need to be solved, an overdetermined linear equation system is formed, in which each equation uses the relative distance and direction between adjacent monitoring points as unknowns to be solved. The total number of equations is consistent with the total number of double-difference travel time data obtained in the third step.

[0083] When applying the data, first collect and organize the double-difference travel time data of all monitoring points obtained in the third step; then simultaneously retrieve the known parameters, including the absolute coordinates of the two earthquake sources, such as the coordinates of earthquake source i being (xi, yi, zi) and the coordinates of earthquake source j being (xj, yj, zj), as well as the average propagation velocity v of seismic waves in the area, to provide basic data for location calculation.

[0084] For any pair of monitoring points (k, l) on the optical fiber, the direction parameters of seismic wave propagation are calculated based on the absolute coordinates of the seismic source and the coordinates of the monitoring points. The spatial distance from the seismic source i to the monitoring point k is calculated using the geometric distance formula. (Where, xk, yk, zk are the absolute coordinates of monitoring point k);

[0085] Based on this spatial distance, the direction vector of the seismic wave propagating from the epicenter i to the monitoring point k is derived. Similarly, the propagation direction vector from the earthquake source i to the monitoring point l can be obtained. From the epicenter j to k and the epicenter from j to l Calculate the difference between the direction vectors to obtain the difference in direction components. Quantifying the relative changes in the direction of seismic wave propagation;

[0086] Based on the direct proportionality between relative spatial distance and double-difference travel time, a linear expression is constructed by combining the directional component difference: Let the displacement vector of monitoring point l relative to monitoring point k be... (i.e., the coordinate difference between the two monitoring points), then the double difference travel time ΔΔtklij of this set of monitoring point pairs satisfies (where · represents the vector dot product operation), this formula correlates the double-difference travel time (known quantity) with the relative displacement of the monitoring point (quantity to be determined), and 1 / v is the proportionality coefficient. Known parameters that reflect the characteristics of the propagation direction;

[0087] Repeat the above operation for all monitoring point pairs on the optical fiber (such as monitoring point l and m, monitoring point m and n, etc.) to establish them sequentially. The linear expressions are ultimately summarized to form an overdetermined system of linear equations Ax = b; where each row of the coefficient matrix A contains the following elements: The components (calculated from the direction vector difference and wave velocity, are known quantities), and the unknown vector x is the relative displacement vector x = (Δx) of all monitoring point pairs. kl Δy kl Δz kl Δx lm Δy lm Δz lm ,...) T , where is the parameter to be solved; the observation vector b is the double-difference travel time data ΔΔt for each monitoring point pair, which is a known quantity. The number of equations is consistent with the total amount of double-difference travel time data. The reliability of the solution is improved by using multiple sets of data constraints.

[0088] Example 7:

[0089] The basic content is the same as in Example 1, except that: in the fifth step, the numerical method is used to solve the above-mentioned overdetermined linear equations to obtain the relative spatial relationship between all adjacent monitoring points on the existing communication fiber. This means: the least squares method is used to solve the above-mentioned overdetermined linear equations, and the solution that minimizes the sum of squared residuals of all equations in the equations is obtained. This solution corresponds to the numerical value of the relative spatial relationship between each pair of adjacent monitoring points on the existing communication fiber, covering the relative distance or coordinate difference of all monitoring point pairs, forming a complete dataset of relative spatial relationships between adjacent monitoring points. In the fifth step, when the least squares method is used to solve the above-mentioned overdetermined linear equations, the overdetermined linear equations are first preprocessed to remove abnormal equations with residuals exceeding a preset threshold. Then, the solution parameters are adjusted through iterative calculation until the sum of squared residuals converges to a stable value, and finally, the numerical value of the relative spatial relationship between adjacent monitoring points that meets the accuracy requirements is output.

[0090] When applying the data, after obtaining the overdetermined linear equation system Ax=b, the data preprocessing process is initiated first: by initially calculating the residuals of the equation system ||Ax-b||2, abnormal equations with residuals exceeding a preset threshold (the preset threshold is set based on the regional seismic wave velocity error) are screened out and removed to reduce the interference of noise on the solution results.

[0091] After preprocessing, the core algorithm of least squares is used for iterative solution: using the sum of squared residuals... To optimize the objective, matrix operations are used: x = (A T A) -1 A T b. Obtain the initial solution, then adjust the weights of the coefficient matrix A according to the residual distribution (assign higher weights to equations with smaller residuals), and repeat the iterative calculation. After each iteration, check the rate of change of the sum of squared residuals. When the rate of change of two consecutive iterations is less than the preset accuracy threshold (e.g., 1e-6), the result is determined to be converged, the iteration is stopped, and the final solution is output. This solution contains the relative coordinate differences (Δxkl, Δykl, Δzkl, etc.) of all monitoring point pairs on the existing communication optical fiber, forming a complete relative spatial relationship dataset, which provides an accurate numerical basis for subsequent splicing of the overall optical fiber orientation by combining the absolute coordinates of the endpoints.

[0092] Example 8:

[0093] The basic content is the same as in Example 1, except that in the fifth step, the step of combining the absolute coordinates of one end of the existing communication optical fiber and deriving the absolute coordinates of all monitoring points on the existing communication optical fiber by vector superposition of the relative spatial relationships between adjacent monitoring points means that: the absolute coordinates of the start and end of the existing communication optical fiber are known quantities; the start or end of the existing communication optical fiber is taken as the first monitoring point; the first monitoring point and the adjacent second monitoring point form a first pair of monitoring points; the absolute coordinates of the first monitoring point and the relative spatial relationship of this pair of monitoring points are vector superimposed to obtain the absolute coordinates of the second monitoring point; the second monitoring point and the adjacent third monitoring point form a second pair of monitoring points; the absolute coordinates of the second monitoring point and the relative spatial relationship of the second pair of monitoring points are vector superimposed to obtain the absolute coordinates of the third monitoring point; the relative spatial relationships of all monitoring point pairs are accumulated in this order until all monitoring points on the existing communication optical fiber are covered, and finally the absolute coordinates of all monitoring points are obtained.

[0094] When applying this method, first determine the known coordinates of the starting end A of the existing communication optical fiber as (xA, yA, zA) and the ending end Z as (xZ, yZ, zZ), and use them as the positioning reference. Set the starting end A as the first monitoring point, and mark the monitoring points sequentially as P1 (i.e., A), P2, P3...Pn (i.e., Z) along the fiber length.

[0095] For the first pair of monitoring points (P1, P2), the relative coordinate differences (Δx12, Δy12, Δz12) obtained in step 5 are used to calculate the absolute coordinates of P2 through vector superposition:

[0096] xP2 = xA + Δx12,

[0097] yP2=yA+Δy12,

[0098] zP2 = zA + Δz12;

[0099] Next, the second set of monitoring point pairs (P2, P3) is processed. Using the previously obtained coordinates of P2 and the relative coordinate differences (Δx23, Δy23, Δz23), the coordinates of P3 are obtained by superimposing them:

[0100] xP3 = xP2 + Δx23,

[0101] yP3=yP2+Δy23,

[0102] zP3 = zP2 + Δz23;

[0103] Following this logic, the process iterates sequentially. For the k-th monitoring point pair (Pk, Pk+1), the absolute coordinates of Pk+1 are obtained by superimposing the absolute coordinates of Pk with the relative coordinate differences (Δxk(k+1), Δyk(k+1), Δzk(k+1)): xP(k+1) = xPk + Δxk(k+1).

[0104] yP(k+1)=yPk+Δyk(k+1),

[0105] zP(k+1)=zPk+Δzk(k+1);

[0106] When iterating to the last monitoring point pair (Pn-1, Pn), the calculated coordinates of Pn should be basically consistent with the coordinates of the known termination point Z (within the preset accuracy range) to verify the reliability of the superposition result; finally, the absolute coordinate dataset of all monitoring points is output to fully present the spatial direction of the optical fiber from the start end to the termination end.

[0107] Example 9:

[0108] The basic content is the same as in Example 8, except that: the absolute coordinates of the starting end A of the existing communication optical fiber are (xA, yA, zA) and the absolute coordinates of the ending end Z are (xZ, yZ, zZ). The monitoring points are evenly distributed along the optical fiber and spaced at intervals of 10 meters or 100 meters. Based on the coordinates of the two ends (starting end A and ending end Z), the positions of each intermediate monitoring point are derived by linear interpolation or piecewise interpolation.

[0109] In application, the absolute coordinates (xA, yA, zA) of the starting end A and the absolute coordinates (xZ, yZ, zZ) of the terminating end Z of the existing communication optical fiber are known, and the actual route of the optical fiber between the two ends is recorded (e.g., whether it passes through curved sections or areas of abrupt terrain change). Then, based on the complexity of the optical fiber route, a monitoring point interval of 10 meters (complex terrain) or 100 meters (flat areas) is selected. For straight sections, monitoring points are directly divided according to the interval. For complex areas such as curved sections and areas of abrupt terrain change, the absolute coordinates of feature points such as inflection points and slope change points are additionally located using double-difference positioning. Finally, a hybrid method of double-difference positioning feature points + linear interpolation completion is used to calculate the intermediate monitoring points. For point locations, in straight sections, the endpoints or feature points of double-difference positioning are used as references. The coordinate differences are distributed according to the proportion of the cumulative interval to the section length to derive the coordinates of intermediate points. In complex sections, the relative spatial relationship of feature points calculated by double-difference travel time is used, and interpolation is performed according to the principle of uniform distribution of relative coordinate differences to fit the actual route trend. After interpolation, the arrival time data of seismic waves collected by the DAS system are called to recalculate the double-difference travel time of intermediate points and adjacent points. The theoretical value is compared with the actual value. If the deviation is greater than the preset standard, the coordinate correction amount is back-derived using double-difference travel time and the interpolation parameters are adjusted. Finally, the coordinates of all monitoring points verified by double-difference travel time constraints are integrated to form a high-precision coordinate system covering the entire optical fiber.

[0110] The above description is only a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or changes made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A method for positioning existing optical fiber communication based on earthquake arrival time difference, characterized in that: The method includes the following steps: Step 1: Deploy a DAS system at one end of the existing communication fiber optic cable and connect the DAS system to the existing communication fiber optic cable; Step 2: First, set up multiple monitoring points evenly along the length of the existing communication fiber optic cable. Then, select at least two seismic sources around the existing communication fiber optic cable and collect the time when the seismic waves generated by each seismic source arrive at each monitoring point through the DAS system. Step 3: Each pair of adjacent monitoring points forms a monitoring point pair. Based on the arrival time of the collected seismic waves at each monitoring point, for each monitoring point pair, first calculate the travel time difference from the same seismic source to the monitoring point pair, and then calculate the double difference travel time corresponding to different seismic sources based on the travel time difference. Repeat the calculation of travel time difference and double difference travel time for all monitoring point pairs to finally obtain the double difference travel time of all monitoring point pairs. Step 4: Based on the double-difference travel time of all the monitoring point pairs mentioned above, and combined with the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber, establish a linear relationship describing the relative spatial relationship of the monitoring point pair. The relative spatial relationship of the monitoring point pair includes the relative distance and direction of adjacent monitoring points. Then, summarize all the linear relationships corresponding to all monitoring point pairs to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as the unknown. Step 5: First, use numerical methods to solve the above overdetermined linear equations to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication fiber; then, combine the absolute coordinates of one end of the existing communication fiber, and derive the absolute coordinates of all monitoring points on the existing communication fiber by vector superposition of the relative spatial relationships between adjacent monitoring points, thereby completing the positioning of the existing communication fiber.

2. The existing optical fiber positioning method based on earthquake arrival time difference as described in claim 1, characterized in that: In the first step, deploying a DAS system at one end of an existing communication optical fiber and connecting the DAS system with the existing communication optical fiber means: selecting the start or end of the existing communication optical fiber as the installation point, physically connecting the optical fiber at the installation point to the optical interface of the DAS system, and fixing the DAS system at the installation point to form a path for optical signal transmission.

3. A method for positioning existing optical fiber communication based on earthquake arrival time difference according to claim 1 or 2, characterized in that: In the second step, the earthquake source includes natural earthquake sources and artificial earthquake sources.

4. The existing optical fiber positioning method based on earthquake time difference as described in claim 3, characterized in that: In the second step, the phrase "uniformly setting up multiple monitoring points along the length of the existing communication optical fiber" means: setting up multiple monitoring points along the length of the existing communication optical fiber, with equal spacing between adjacent monitoring points; In the second step, selecting at least two seismic sources around the existing communication fiber means selecting two or more seismic sources that meet the propagation path conditions, wherein the propagation path of the seismic waves generated by the seismic sources to each monitoring point on the existing communication fiber is consistent, and the location of the seismic sources ensures that the seismic waves cover all monitoring points on the existing communication fiber. In the second step, the acquisition of the arrival time of seismic waves generated by each earthquake source at each monitoring point by the DAS system mentioned above refers to the following: the DAS system transmits optical signals and receives backscattered light generated by the vibration of seismic waves in the existing communication optical fiber, demodulates the changes in the scattered light signals, identifies the time when the seismic waves arrive at multiple monitoring points on the existing communication optical fiber, and records and stores the seismic wave arrival time data corresponding to each monitoring point.

5. The existing optical fiber positioning method based on earthquake arrival time difference as described in claim 4, characterized in that: The distance between adjacent monitoring points is 1-100 meters.

6. A method for positioning existing optical fiber communication based on earthquake arrival time difference according to claim 1 or 2, characterized in that: In the third step, based on the arrival time of the acquired seismic waves at each monitoring point, for each pair of monitoring points, the travel time difference from the same seismic source to the pair of monitoring points is first calculated, and then the double-difference travel time corresponding to different seismic sources is calculated based on the travel time difference. The calculation of travel time difference and double-difference travel time is repeated for all monitoring point pairs. Finally, the double-difference travel time of all monitoring point pairs is obtained as follows: For any pair of monitoring points on the existing communication optical fiber, namely monitoring point k and monitoring point l, and any two different seismic sources, namely seismic source i and seismic source j, based on the arrival time of the seismic waves acquired by the DAS system at each monitoring point, the travel time difference Δtikl = tkl - tki from seismic source i to the pair of monitoring points k and monitoring point l is calculated respectively, where tki is the arrival time from seismic source i to monitoring point k, and tkl is the arrival time from seismic source i to monitoring point l. Simultaneously, the travel time difference Δtjkl = tkl' - tki' from earthquake source j to monitoring point k and monitoring point l in this group is calculated respectively; where tki' is the arrival time from earthquake source j to monitoring point k, and tkl' is the arrival time from earthquake source j to monitoring point l. Then, the difference between the two travel times is used to calculate the corresponding double-difference travel time ΔΔtklij=Δtjkl-Δtikl for this group of monitoring points, so as to eliminate the systematic deviation in the process of seismic wave propagation; Then, the above calculations are performed on all monitoring point pairs on the existing communication optical fiber one by one, and finally the double difference travel time corresponding to each monitoring point pair is obtained.

7. A method for positioning existing optical fiber communication based on earthquake arrival time difference according to claim 1 or 2, characterized in that: In the fourth step, based on the double-difference travel time of all the aforementioned monitoring point pairs, and combining the linear relationship between the double-difference travel time and the relative positions of adjacent monitoring points on the existing communication optical fiber, a linear relationship describing the relative spatial relationship of each monitoring point pair is established for each double-difference travel time data corresponding to each monitoring point pair on the existing communication optical fiber. The relative spatial relationship of the monitoring point pairs includes the relative distance and direction of adjacent monitoring points. Then, all the linear relationships corresponding to all monitoring point pairs are summarized to form an overdetermined linear equation system with the relative spatial relationship of all monitoring point pairs on the existing communication optical fiber as unknowns. This means that for the double-difference travel time corresponding to each monitoring point pair obtained in the third step, based on the assumption that the propagation speed of seismic waves in the medium of this region remains constant, and combined with the absolute coordinates of the seismic source, the propagation speed of seismic waves to the set of monitoring point pairs is calculated. The direction components of the monitoring point pairs are identified. Based on this, it is determined that there is a direct proportional relationship between the relative spatial distance between adjacent monitoring points and the double-difference travel time, and the relative direction of adjacent monitoring points is reflected by the direction parameter determined based on the direction components in the linear expression. Subsequently, according to the direct proportional relationship and the direction parameter, the double-difference travel time of this set of monitoring point pairs is transformed into a linear expression that simultaneously describes the relative distance and direction of adjacent monitoring points. The linear expressions corresponding to all monitoring point pairs are summarized to form a set of equations. Since the number of equations is greater than the number of relative spatial relationships between adjacent monitoring points that need to be solved, an overdetermined linear equation system is formed, in which each equation uses the relative distance and direction between adjacent monitoring points as unknowns to be solved. The total number of equations is consistent with the total number of double-difference travel time data obtained in the third step.

8. A method for positioning existing optical fiber communication based on earthquake arrival time difference according to claim 1 or 2, characterized in that: In the fifth step, the step of solving the above-mentioned overdetermined linear equations using numerical methods to obtain the relative spatial relationships between all adjacent monitoring points on the existing communication optical fiber means: solving the above-mentioned overdetermined linear equations using the least squares method, and obtaining the solution that minimizes the overall error by minimizing the sum of squared residuals of all equations in the equations; this solution corresponds to the numerical values ​​of the relative spatial relationships between each pair of adjacent monitoring points on the existing communication optical fiber, covering the relative distances or coordinate differences of all monitoring point pairs, forming a complete dataset of relative spatial relationships between adjacent monitoring points.

9. The existing optical fiber positioning method based on earthquake arrival time difference as described in claim 8, characterized in that: In the fifth step, when solving the above-mentioned overdetermined linear equation system using the least squares method, the overdetermined linear equation system is first preprocessed to remove abnormal equations whose residuals exceed a preset threshold. Then, the solution parameters are adjusted through iterative calculation until the sum of squared residuals converges to a stable value. Finally, the numerical values ​​of the relative spatial relationship between adjacent monitoring points that meet the accuracy requirements are output.

10. A method for positioning existing optical fiber communication based on earthquake arrival time difference according to claim 8, characterized in that: In the fifth step, the step of combining the absolute coordinates of one end of the existing communication optical fiber and deriving the absolute coordinates of all monitoring points on the existing communication optical fiber by vector superposition of the relative spatial relationships between adjacent monitoring points means: the absolute coordinates of the start and end of the existing communication optical fiber are known quantities; the start or end of the existing communication optical fiber is taken as the first monitoring point; the first monitoring point and the adjacent second monitoring point form a first pair of monitoring points; the absolute coordinates of the first monitoring point and the relative spatial relationship of this pair of monitoring points are vector superimposed to obtain the absolute coordinates of the second monitoring point; the second monitoring point and the adjacent third monitoring point form a second pair of monitoring points; the absolute coordinates of the second monitoring point and the relative spatial relationship of the second pair of monitoring points are vector superimposed to obtain the absolute coordinates of the third monitoring point; the relative spatial relationships of all monitoring point pairs are accumulated in this order until all monitoring points on the existing communication optical fiber are covered, and finally the absolute coordinates of all monitoring points are obtained.

Images