Submarine optical cable trajectory tracking system and method based on optical fiber distributed acoustic sensing

Abstract

The invention belongs to the technical field of submarine optical cable route detection and maintenance, and relates to a submarine optical cable trajectory tracking system and method based on optical fiber distributed acoustic sensing, and the system comprises a shipborne platform, an active sonar module, a high-precision positioning and navigation module, a shore-based DAS module, a high-precision time synchronization module, a matched filtering module, and a main control calculation module. The active sonar module is installed at the ship bottom of the shipborne platform, the high-precision positioning and navigation module is electrically connected with the master control calculation module and the shipborne platform, and the master control calculation module is electrically connected with the shipborne platform. The high-precision time synchronization module is electrically connected with the shore-based DAS module and the active sonar module, and the shore-based DAS module is in photoelectric connection with an idle fiber core in an optical cable; the matched filtering module is electrically connected with the shore-based DAS module and the active sonar module. The shore-based DAS module is electrically connected with the main control calculation module; according to the method, the optical fiber distributed acoustic sensing technology and the advanced trajectory tracking algorithm are combined, so that full-autonomous three-dimensional trajectory reconstruction of the submarine optical cable is realized.

Description

Technical Field

[0001] This invention belongs to the field of submarine optical cable route detection and maintenance technology, specifically relating to a submarine optical cable trajectory tracking system and method based on fiber optic distributed acoustic sensing. Background Technology

[0002] Submarine optical cables are communication lines laid on the seabed for transmitting optical signals. They are the cornerstone of modern global communication networks, undertaking more than 95% of international data transmission tasks. As a core infrastructure of the global communication network, the location of submarine optical cables is susceptible to displacement due to natural factors such as submarine landslides, geological activity, and ocean currents after their installation. Accurately monitoring the location changes of optical cables is crucial for ensuring their daily operation and maintenance and the stable operation of the communication network.

[0003] However, existing submarine fiber optic cable route detection technologies have the following limitations: Highly reliant on manual operation or prior information: Mainstream methods rely on highly human intervention methods such as visual inspection by divers and remotely operated underwater vehicles (ROVs), or require prior information such as the original route of the submarine optical cable and the coordinates of the calibration points. When historical data is lacking or optical cables in completely unknown areas are being probed, current technologies cannot achieve effective detection.

[0004] Low detection efficiency and poor continuity: Traditional detection technology requires repeated ship stops for fixed-point scanning. The detection process is highly dependent on the operator's experience and judgment, and cannot achieve continuous and dynamic optical cable detection, resulting in low operational efficiency.

[0005] Limited applicability: Some existing technologies rely on energized optical cables (such as magnetic field detection of power submarine cables), vibration transmission from buried marine mud, or external sound sources (such as noise from merchant ships). For exposed or suspended optical cables, such solutions cannot achieve effective detection due to the lack of necessary working conditions.

[0006] Insufficient positioning accuracy and trajectory rationality: Most existing methods estimate the optical cable position only by the point of strongest vibration or a rough Doppler frequency shift, lacking a quantitative detection mechanism; and discrete detection points are easily affected by noise interference or jump phenomena, resulting in the reconstructed optical cable trajectory appearing "zigzag", which violates the physical structural characteristics of the optical cable and has poor trajectory rationality.

[0007] Low system integration: Existing technologies often require complex underwater equipment such as ROVs and dipping sonar arrays, which are costly and have complicated deployment processes, making it difficult to meet the needs of large-scale, routine optical cable detection.

[0008] Therefore, there is an urgent need for a fully autonomous, continuous three-dimensional trajectory tracking technology for submarine optical cables that does not rely on prior routing information or external sound sources and whose trajectory conforms to physical constraints, in order to solve the above-mentioned technical problems. Summary of the Invention

[0009] This invention aims to construct a closed-loop submarine optical cable trajectory tracking architecture based on "active excitation—passive sensing—geometric calculation—state filtering—dynamic programming". This architecture includes the following: 1. Dual-mode initial point search strategy: It adopts two modes: "scanning at any starting position when the fiber optic cable endpoint is known" and "conical scanning of the initial position of the fiber optic cable with unknown prior information". Regardless of whether the original routing information of the fiber optic cable is available, the first effective vibration event can be captured, ensuring that the system can start detection under any initial conditions.

[0010] 2. Optical cable coordinate space calculation algorithm: By establishing the correspondence between the sonar transmission time and the shore-based DAS system response time, and combining the ship position, sonar depression angle, and azimuth angle, the three-dimensional coordinates of the optical cable point are calculated.

[0011] 3. Dynamic non-stop scanning mechanism: The shipborne platform continues to sail, and the sonar performs ±90° oscillation scanning with the bow as the center, which can realize the ship's autonomous continuous detection and greatly improve the efficiency of detection operations.

[0012] 4. Arc length-based optical cable trajectory filtering algorithm: Custom-developed for submarine optical cable trajectory reconstruction scenarios, it constructs a state vector with optical fiber arc length as the independent variable, and embeds the physical constraint of the minimum bending radius of the optical cable into the process noise covariance matrix, so that the filtered trajectory is smooth and continuous, which conforms to the physical flexibility characteristics of the optical cable.

[0013] This invention is applicable to submarine optical cables in various laying states such as buried, exposed, and suspended, and does not rely on external sound sources or power supply to the optical cable, thus having a wide range of environmental adaptability.

[0014] The specific technical solution of this invention is: a submarine optical cable trajectory tracking system based on fiber optic distributed acoustic sensing, comprising: Shipborne platform: used to carry sonar, positioning equipment and main control computing module, and also used to achieve autonomous navigation and dynamic course adjustment.

[0015] Active sonar module: used to continuously emit short pulse sound waves, which excite the submarine optical cable to vibrate, providing a signal source for subsequent detection.

[0016] High-precision positioning and navigation module: used to acquire the position, heading, speed and timestamp information of the shipborne platform in real time, and send the data to the main control computing module.

[0017] Shore-based DAS module: Used to receive and demodulate optical cable vibration signals induced by the active sonar module in real time, and output the optical fiber arc length position and response timestamp corresponding to the vibration event.

[0018] High-precision time synchronization module: used to achieve time alignment between the active sonar module and the shore-based DAS module, providing a time reference for spatiotemporal matching positioning.

[0019] Matched filtering module: used to accurately match the active sonar emission time sequence with the response time of the shore-based DAS module to determine the sonar emission time corresponding to each vibration event.

[0020] Main control computing module: used to calculate the three-dimensional coordinates of cable points, filter the optical cable trajectory status, and generate heading planning and sonar scanning strategies.

[0021] The active sonar module is installed on the bottom of the shipborne platform. The high-precision positioning and navigation module is electrically connected to the main control computing module and the shipborne platform, respectively. The main control computing module is electrically connected to the shipborne platform.

[0022] The high-precision time synchronization module is electrically connected to the shore-based DAS module and the active sonar module respectively. The shore-based DAS module is opto-connected to the idle fiber core in the optical cable. The matched filter module is electrically connected to the shore-based DAS module and the active sonar module respectively. The shore-based DAS module is electrically connected to the main control computing module.

[0023] Preferably, the shipborne platform is a work vessel equipped with an automatic steering control system; the depression angle and azimuth angle of the short pulse acoustic wave emitting device of the active sonar module are adjustable.

[0024] Preferably, the high-precision positioning and navigation module integrates a Global Navigation Satellite System (GNSS) and an Automatic Identification System (AIS). The GNSS includes: the US Global Positioning System (GPS), the Chinese BeiDou Navigation Satellite System (BDS), the Russian GLONASS, and the European Galileo. The high-precision time synchronization module uses the PTP protocol or GPS timing method. The matched filtering module is equipped with a time calculation algorithm.

[0025] This invention also discloses a method for tracking submarine optical cables based on fiber optic distributed acoustic sensing. This tracking method employs the aforementioned submarine optical cable tracking system and includes the following steps: Step 1: Initial position search; After the active sonar module scans and the shore-based DAS module detects a vibration event, the shipborne platform moves forward to the initial position.

[0026] Step 2: Initial point coordinate calculation and initial heading adjustment; establish a spatial rectangular coordinate system with the location of the shore-based DAS module as the origin, and calculate the three-dimensional coordinates of the initial optical cable point. x c , y c , z cAfter that, the shipborne platform moves directly above the initial point and enters trajectory tracking mode.

[0027] Step 3: Trajectory Tracking Mode and 3D Coordinate Calculation of Optical Cable; After the shipborne platform enters the trajectory tracking stage, the 3D coordinates of the optical cable points are calculated. x , y , z ).

[0028] Step 4: Platform movement and heading adjustment.

[0029] Step 5: State filtering; construct a state vector with the fiber arc length s as the independent variable, predict the optical cable position based on the arc length increment, model the process noise covariance Q, use the geometric solution coordinates as observations for updates, and normalize the tangent vector.

[0030] Step 6: Repeat steps 2 through 5 until the entire optical cable trajectory is traced.

[0031] Preferably, in step 1, if the coordinates of the beginning and end of the optical cable are known, then step A is used; if there is no prior information or step A fails, then step B is used.

[0032] Step A includes: A1. Closest point matching: Calculate the perpendicular from the current ship position to the line connecting the beginning and end of the optical cable.

[0033] A2. Set search route: Plan a straight search path from the current position to the vertical foot.

[0034] A3. Start scanning: Perform a directional scan vertically underwater along the straight search path.

[0035] A4. Event Trigger: When the shore-based DAS module detects a vibration event, the shipborne platform moves towards the initial point.

[0036] A5. Scheme Switching: If the shore-based DAS module does not detect any valid vibration events, expand the search range; if no valid vibration events are detected after expanding the range, switch to step B.

[0037] Step B includes: B1. Initial position setting: The shipborne platform starts from the origin point (0, 0, 0) on the shore where the shore-based DAS module is located.

[0038] B2, 360° cone scan: sonar fixed depression angle azimuth With angular velocity Perform a 360° cone scan.

[0039] B3. Depression Adjustment and Repeat Scan: If the initial point is not detected, gradually increase the angle. The scanning continues until the shore-based DAS module captures a valid vibration event, at which point the shipboard platform moves toward that initial position.

[0040] Preferably, step 2 specifically includes the following sub-steps: Step 2-1. Key Parameter Acquisition: When the shore-based DAS module first detects a vibration event caused by sonar excitation, record its fiber arc length s and response timestamp. t 2 .

[0041] Step 2-2. Use the matched filter module to reverse-engineer the sonar transmission time. t 1 .

[0042] Steps 2-3. Calculation of sound wave propagation distance: based on the speed of sound c w The distance the sound wave travels from the sonar to the optical cable is calculated as follows: .

[0043] Steps 2-4. Initial 3D coordinates of the optical cable point ( x c , y c , z c The solution is as follows:

[0044] in, x 1 、y 1 for t 1 The ship's position coordinates at that moment. , These are the depression angle and azimuth angle of the sonar scan, respectively.

[0045] Steps 2-5. Course Adjustment: The shipboard platform is oriented towards the initial optical cable point ( x c , y c , z c Move directly upwards to enter trajectory tracking mode.

[0046] Preferably, step 3 specifically includes the following sub-steps: Step 3-1. Setting Operating Parameters: Set the sailing speed of the shipborne platform. 、 Sonar depression angle, relative azimuth angle, and scanning angular velocity.

[0047] Step 3-2. Key Parameter Acquisition: Select the point closest in space to the previous detection point from the valid points and denote it as the valid detection point for this time.s k Obtain the cumulative relative azimuth and ship position coordinates from the start of the scan to the effective detection time. x 2 , y 2 ).

[0048] Step 3-3. Reverse estimation of ship position at the time of sonar launch: Obtain the ship's position at the time of sonar launch ( x 1 , y 1 ).

[0049] Steps 3-4. Calculate the straight-line distance from the ship to the fiber optic cable point. d .

[0050] Steps 3-5. Sonar azimuth calculation: (The following is a partial translation of the original text, which is not possible without further context.) t 1 relative azimuth and absolute azimuth at any time .

[0051] Step 3-6. Calculation of 3D coordinates of optical cable points: Calculate the 3D coordinates of optical cable points ( x , y , z ):

[0052] in, The angle of depression when the sonar is launched.

[0053] Preferably, step 4 specifically includes: Once the shore-based DAS module receives the vibration signal and completes the screening of effective detection points, the shipborne platform travels directly above the effective optical cable point, maintaining alignment with the local orientation of the optical cable. Simultaneously, the active sonar module continuously performs ±90° arc scanning with the bow as the center, ensuring full coverage detection of the sea area ahead.

[0054] Preferably, step 5 specifically includes the following sub-steps: Construct a state vector with the fiber arc length s as the independent variable:

[0056] in Location of the optical cable point. The unit tangent vector; Prediction steps: Based on arc length increments Updated location The tangent vector remains unchanged.

[0057] The state transition equation is: .

[0058] The state transition matrix is: .

[0059] Process noise covariance Q modeling: .

[0060] q p For position process noise intensity, q t The noise intensity of the tangent vector process, R min This is the minimum bending radius of the optical cable.

[0061] The predicted covariance is: .

[0062] Measurement update: The three-dimensional coordinates of the optical cable points calculated in step 3 are used as the measured values. z k Covariance , The position standard deviation is the geometric solution of the sonar + shore-based DAS module.

[0063]

[0064] Tangent vector normalization: state update It is a linear operation. After the update, Tnew is no longer strictly normalized. After each update, tangent vector normalization is performed. .

[0065] Preferably, step 6 specifically includes: predicting the position of the next detection point based on the filtered state, dynamically adjusting the sonar scanning strategy and the heading of the shipborne platform, continuously executing steps 2 to 5 in a loop until the trajectory tracking of the entire optical cable is completed; and finally outputting the three-dimensional optical cable trajectory.

[0066] The beneficial effects of this invention are: 1. This invention enables fully autonomous unmanned operation: This invention requires no divers, ROVs or external sound sources, and supports scanning from any area without prior information.

[0067] 2. This invention can achieve 3D reconstruction with an accuracy of ten meters: This invention integrates DAS arc length measurement, acoustic ranging and ship position navigation information. After optimization by trajectory filtering algorithm, the positioning error can reach the ten-meter level, which is reduced by 25% compared with the original.

[0068] 3. This invention has strong versatility and robustness: This invention is applicable to various types of optical cables, such as buried, exposed, and suspended ones, and is not limited by factors such as marine mud medium and optical cable power supply status, and has strong environmental adaptability.

[0069] 4. This invention can achieve physical compliance of the trajectory: This invention adopts a state filtering method specially customized for submarine optical cable trajectory tracking, which ensures that the trajectory conforms to the flexible characteristics of the optical cable from the algorithm level, ensuring that the output trajectory is continuous, smooth and without abrupt changes, while further reducing positioning deviation.

[0070] 5. This invention enables efficient dynamic inspection: This invention adopts a continuous scanning mechanism without stopping the ship, which improves operational efficiency. Attached Figure Description

[0071] Figure 1 This is a schematic diagram of the sonar-ship position-optical cable geometric relationship of the submarine optical cable trajectory tracking system and method based on fiber optic distributed acoustic sensing according to the present invention. Figure 2 This is a schematic diagram of the system structure of the present invention; Figure 3 This is a schematic diagram of the process of the present invention; Figure 4 This is a timing diagram of the present invention; Figure 5 This is a schematic diagram of the trajectory state filtering algorithm of the present invention; Figure 6 This is a comparison diagram of the original noise point versus the system estimated point cable-finding case trajectory of the present invention. Detailed Implementation

[0072] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0073] The submarine optical cable trajectory tracking system based on fiber optic distributed acoustic sensing in this embodiment includes the following components: Shipborne platform: The work vessel is equipped with an automatic steering control system and is used to carry sonar, positioning equipment and main control computing unit to support autonomous navigation and dynamic course adjustment; the speed can reach 30-50 m / s when not in operation, and the speed is controlled at 2-5 m / s when in operation.

[0074] Active sonar module: Installed on the bottom of the ship, it has adjustable depression and azimuth angles and can continuously emit short pulse sound waves. The sound waves excite the submarine optical cable to vibrate, providing a signal source for subsequent detection.

[0075] High-precision positioning and navigation module: Integrates Global Navigation Satellite System (GNSS) and Automatic Identification System (AIS) to acquire the ship's position, heading, speed and timestamp information in real time, and send the data to the main control computing module.

[0076] Shore-based DAS module: It receives and demodulates the optical cable vibration signal caused by active sonar excitation in real time through the idle fiber core in the submarine optical cable, and outputs the optical fiber arc length position and response timestamp corresponding to the vibration event.

[0077] High-precision time synchronization module: Using PTP protocol or GPS timing method, it realizes time alignment between shipborne system and shore-based DAS system, and provides time reference for spatiotemporal matching positioning.

[0078] Matched filtering module: Equipped with a time calculation algorithm, it accurately matches the active sonar transmission time sequence with the shore-based DAS response time to determine the sonar transmission time corresponding to each vibration event.

[0079] Main control computing module: The trajectory tracking algorithm software running on the shipborne industrial control computer or shore-based server is responsible for calculating the three-dimensional coordinates of the cable point, filtering the optical cable trajectory status, and generating course planning and sonar scanning strategies.

[0080] Through the coordinated work of the above modules, this system achieves the following functions: coordination of active sonar excitation and shore-based DAS passive sensing, dual-mode initial point search, optical cable coordinate calculation and dynamic non-stop ship trajectory tracking, optical cable trajectory state filtering based on arc length, and finally completes the autonomous three-dimensional trajectory reconstruction of submarine optical cables with unknown orientation.

[0081] The fully autonomous trajectory tracking method for submarine optical cables in this embodiment mainly includes the following steps: Step 1: Initial point search: If the coordinates of the beginning and end of the optical cable are known, proceed with step A: A1. Closest Point Matching: Calculate the perpendicular from the current ship position to the line connecting the beginning and end of the optical cable. P nearest .

[0082] A2. Set the search route: Plan the route from the current position to the vertical foot. P nearest The straight-line search path.

[0083] A3. Start scanning: Perform a directional scan vertically underwater along the above straight path.

[0084] A4. Event Trigger: When the shore-based DAS module detects a vibration event, the shipborne platform moves towards the initial point.

[0085] A5. Scheme Switching: If the shore-based DAS module does not detect any valid vibration events, expand the search range; if no valid vibration events are detected after expanding the range, switch to step B.

[0086] If there is no prior information or step A fails, proceed to step B (starting from the origin): B1. Initial position setting: The shipborne platform starts from the origin point (0, 0, 0) on the shore where the shore-based DAS module is located.

[0087] B2, 360° cone scan: sonar fixed depression angle azimuth With angular velocity Perform a 360° cone scan.

[0088] B3. Depression Adjustment and Repeat Scan: If the initial point is not detected, gradually increase the angle. The scanning continues until the shore-based DAS module captures a valid vibration event, at which point the shipboard platform moves toward that initial position.

[0089] Step 2: Initial point coordinate calculation and initial heading adjustment: Establish a spatial rectangular coordinate system with the location of the shore-based DAS module as the origin (0, 0, 0). The specific operation is as follows: 2-1. Key Parameter Acquisition: When the shore-based DAS module first detects a vibration event caused by sonar excitation, it records the fiber arc length s and the response timestamp. t 2 .

[0090] refer to Figure 4 , t 1 Constantly transmitting sonar signals. t 3 The constant vibration of the optical cable causes the optical fiber to vibrate. t 2 Send pulse signals at all times t 4 It is constantly detected by the shore-based DAS module. Because... t 2 arrive t 4 , t 3 arrive t 4 The time differences between them are much smaller than the propagation time of sonar in water, which will t 2 , t 3 , t 4 merged into t 2 , which represents the sonar response time.

[0091] 2-2. Using a matched filter module to inversely calculate the sonar transmission time t 1 .

[0092] (2-2-1) Reference Figure 4Extracting data from DAS time series data t 2 A local waveform centered on a specific element and spanning a typical DAS response width (e.g., 40–100 ms) is used as the adaptive matching template r[n] (n = 0, 1, 2…N-1, where N is the template length). This template directly reflects the true response of the sonar excitation in the optical fiber, without relying on a priori waveform model. The discrete impulse response of the matched filter is: .

[0093] (2-2-2) The system acquires the sonar transmission time sequence s[n] (n=0, 1, 2…L-1) broadcast from the shipborne terminal, where L is the length of the sonar time sequence that may cause a DAS response, and the DAS echo arrival time is used as the basis for the acquisition. t 2 (Based on the baseline, push forward by 2 seconds).

[0094] (2-2-3) Perform sliding cross-correlation calculation on the template m[n] over the sonar emission time sequence: .

[0095] (2-2-4) System selects cross-correlation value The largest n The corresponding launch time was taken as the actual sonar launch time of this event. t 1 。

[0096] 2-3. Calculation of sound wave propagation distance: based on the speed of sound c w Calculate the distance the sound wave travels from the sonar to the optical fiber: .

[0097] 2-4. Initial 3D coordinate calculation of optical cable points: Combination t 1 Ship's position coordinates at that moment ( x 1 ， y 1 ), the depression angle of the sonar scan with absolute azimuth Distance from ship to fiber optic cable point d Solve the three-dimensional coordinates of the initial optical cable point. x c , y c , z c ).

[0098] .

[0099] 2-5. Course Adjustment: The shipboard platform adjusts its course, moving directly above the initial point and entering trajectory tracking mode.

[0100] Step 3: Tracking mode and optical cable 3D coordinate calculation: After the shipborne platform enters the dynamic trajectory tracking stage, the three-dimensional coordinates of the optical cable are calculated according to the following process.

[0101] 3-1. Operational Parameter Settings: The shipborne platform operates at a speed... v（ 2-5 m / s ） Uniform speed navigation; sonar at a fixed angle of depression The work, its relative azimuth angle heading by bow Centered on the target, the system continuously oscillates and scans within a range of ±90°, with an angular velocity of [value missing]. .

[0102] 3-2. Key Parameter Acquisition: If multiple DAS events are triggered in a single scan, only those satisfying the fiber optic cable arc length are retained. s > s k−1 + s min (like s min =0.1km); among the valid points, the one with the closest spatial distance to the previous detection point is selected as the valid detection point for this time, denoted as. s k This avoids jump points or reverse probing.

[0103] The cumulative relative azimuth angle from the start of the scan to the effective detection time is obtained as follows: and ship position coordinates ( x 2 , y 2 ).

[0104] 3-3. Ship position backwards at the time of sonar launch: (3-3-1) Using the matched filtering method in step two, the sonar launch time can be accurately deduced. t 1 .

[0105] (3-3-2) Combined with ship speed v The time difference between sonar transmission and DAS signal reception is used to calculate the shipborne platform's travel distance. s And reverse-engineer the ship's position at the time of sonar launch ( x 1 , y 1 ); .

[0106] 3-4. Calculate the straight-line distance from the ship to the optical cable point. d : .

[0107] 3-5. Sonar azimuth calculation: Based on the cumulative relative azimuth angle turned by the sonar at the DAS response time. ,calculate t 1 relative azimuth at any time and absolute azimuth .

[0108] .

[0109] 3-6. Calculation of three-dimensional coordinates of the optical cable point: based on the depression angle at which the sonar was emitted. Absolute azimuth and ship position ( x 1 , y 1 , 0), calculate the three-dimensional coordinates of the optical cable point: .

[0110] Step 4: Platform movement and heading adjustment: Once the shore-based DAS system receives the vibration signal and completes the screening of effective detection points, the shipborne platform immediately changes course and heads directly above the effective optical cable point, maintaining alignment with the local direction of the optical cable. At the same time, the active sonar continuously performs ±90° arc scans centered on the bow to ensure full coverage detection of the sea area in front of the ship.

[0111] Step 5: State filtering: refer to Figure 5 The overall process of the arc-length-based trajectory filtering algorithm, which is specifically developed for submarine optical cable trajectory tracking scenarios, is as follows: To eliminate the traditional time variable and adapt to the characteristics of optical cable extension, a state vector is constructed with the optical fiber arc length s as the independent variable: .

[0112] The first three dimensions represent the location of the optical cable points, and the last three dimensions represent the unit tangent vector, which is used to characterize the local direction of the optical cable and adapt to the need for continuous trajectory tracking.

[0113] Prediction steps: Based on arc length increments (Provided directly by DAS), update location is The tangent vector remains unchanged.

[0114] The state transition equation is: .

[0115] The state transition matrix is: .

[0116] Process noise covariance Q modeling: .

[0117] q p For position process noise intensity, q t The noise intensity of the tangent vector process, R min To determine the minimum bending radius of the optical cable, this method embeds the physical constraints of the optical cable into the filter core to avoid the trajectory violating the flexibility characteristics.

[0118] The predicted covariance is: .

[0119] Measurement update: The three-dimensional coordinates of the optical cable points calculated in step 3 are used as the measured values. z k Covariance , The standard deviation of the position calculated by the sonar + DAS geometry solution (20m);

[0120] Tangent vector normalization: State updates are linear operations: The updated T is no longer strictly normalized. Therefore, after each update, tangent vector normalization is performed:

[0121] Step 6: Execute repeatedly: Based on the filtered state, the position of the next detection point is predicted, and the sonar scanning strategy and the heading of the shipborne platform are dynamically adjusted. Steps 2 to 5 are continuously executed in a loop until the trajectory tracking of the entire optical cable is completed. Finally, a smooth, continuous three-dimensional optical cable trajectory that conforms to the physical constraint of the minimum bending radius of the optical cable is output.

[0122] Example

[0123] Figure 6 The image shows a trajectory comparison for two cable-tracking cases (original measurement points vs. system-estimated points), displaying results with average measurement errors of 17.3 meters and 34.1 meters, respectively. The top-down view shows that the vessel trajectory effectively tracks the underwater optical cable. The 3D reconstruction image shows that the system-estimated result (red dots) is smoother than the original green measurement points. When the average measurement error is 17.3 meters, the system estimation error is 12.9 meters, an effective reduction of 25.4%; when the average measurement error is 34.1 meters, the system estimation error is 25.1 meters, an effective reduction of 26.4%, indicating that the system can reduce measurement errors and improve the accuracy of underwater optical cable trajectory estimation.

[0124] In summary, this invention achieves fully autonomous 3D trajectory reconstruction of submarine optical cables by combining fiber optic distributed acoustic sensing technology with advanced trajectory tracking algorithms. This system not only boasts significant functional advantages, such as fully autonomous unmanned operation, 10-meter-level accuracy 3D reconstruction, strong versatility and robustness, trajectory physical compliance, and efficient dynamic inspection, but also demonstrates excellent performance in practical applications, effectively reducing measurement errors and improving the accuracy of underwater optical cable trajectory estimation.

[0125] This invention has broad application prospects in the future field of marine engineering. With the continuous development of the marine economy, submarine optical cables, as a crucial infrastructure for marine communication, are of paramount importance for their safe and stable operation. This invention can provide strong technical support for the laying, maintenance, and monitoring of submarine optical cables, helping to promptly detect potential faults and safety hazards, and ensuring uninterrupted marine communication.

[0126] Meanwhile, the technical concepts and methods of this invention also provide valuable insights for research in other related fields. For example, in the development of marine resources such as oil and natural gas, the technical solutions of this invention can be referenced to develop similar systems and methods for tracking and monitoring the trajectory of subsea pipelines, thereby improving the safety and efficiency of resource development.

[0127] Furthermore, with continuous advancements in technology, this invention can be further optimized and improved. For example, more advanced sensor technologies and data processing algorithms can be introduced to improve the system's accuracy and reliability; the system's intelligence level can be enhanced to achieve more autonomous and efficient operations. It is believed that in the future, this invention will play a greater role in the field of marine engineering and make significant contributions to promoting the development of the marine economy.

[0128] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A submarine optical cable trajectory tracking system based on fiber optic distributed acoustic sensing, characterized in that, include: Shipborne platform: used to carry sonar, positioning equipment and main control computing module, and also used to achieve autonomous navigation and dynamic course adjustment; Active sonar module: used to continuously emit short pulse sound waves, which excite the submarine optical cable to vibrate, providing a signal source for subsequent detection; High-precision positioning and navigation module: used to acquire the position, heading, speed and timestamp information of the shipborne platform in real time, and send the data to the main control computing module; Shore-based DAS module: Used to receive and demodulate optical cable vibration signals induced by the active sonar module in real time, and output the optical fiber arc length position and response timestamp corresponding to the vibration event; High-precision time synchronization module: used to achieve time alignment between the active sonar module and the shore-based DAS module, providing a time reference for spatiotemporal matching positioning; Matched filtering module: used to accurately match the active sonar emission time sequence with the response time of the shore-based DAS module to determine the sonar emission time corresponding to each vibration event; Main control computing module: used to calculate the three-dimensional coordinates of cable points, filter the optical cable trajectory status, and generate heading planning and sonar scanning strategies; The active sonar module is installed on the bottom of the shipborne platform, and the high-precision positioning and navigation module is electrically connected to the main control computing module and the shipborne platform respectively. The main control computing module is electrically connected to the shipborne platform. The high-precision time synchronization module is electrically connected to the shore-based DAS module and the active sonar module respectively, and the shore-based DAS module is opto-connected to the idle fiber core in the optical cable; the matched filter module is electrically connected to the shore-based DAS module and the active sonar module respectively; the shore-based DAS module is electrically connected to the main control computing module.

2. The submarine optical cable trajectory tracking system based on fiber optic distributed acoustic sensing according to claim 1, characterized in that, The shipboard platform is a work vessel equipped with an automatic steering control system; the depression angle and azimuth angle of the short pulse acoustic wave emitting device of the active sonar module are adjustable.

3. The submarine optical cable trajectory tracking system based on fiber optic distributed acoustic sensing according to claim 1, characterized in that, The high-precision positioning and navigation module integrates the Global Navigation Satellite System (GNSS) and the Automatic Identification System (AIS); the high-precision time synchronization module adopts the PTP protocol or GPS timing method; and the matched filtering module is equipped with a time calculation algorithm.

4. A method for tracking submarine optical cable trajectories based on fiber optic distributed acoustic sensing, characterized in that, The tracking method employs the submarine optical cable trajectory tracking system as described in any one of claims 1 to 3, and the tracking method includes the following steps: Step 1: Initial position search; After the active sonar module scans and the shore-based DAS module detects a vibration event, the shipborne platform moves forward to the initial position; Step 2: Initial point coordinate calculation and initial heading adjustment; establish a spatial rectangular coordinate system with the location of the shore-based DAS module as the origin, and calculate the three-dimensional coordinates of the initial optical cable point. x c , y c , z c After that, the shipborne platform moves directly above the initial point and enters trajectory tracking mode; Step 3: Trajectory Tracking Mode and 3D Coordinate Calculation of Optical Cable; After the shipborne platform enters the trajectory tracking stage, the 3D coordinates of the optical cable points are calculated. x , y , z ); Step 4: Platform movement and heading adjustment; Step 5: State filtering; construct a state vector with fiber arc length s as the independent variable, predict the optical cable position based on the arc length increment, model the process noise covariance Q, use the geometric solution coordinates as the observation value for observation and update, and normalize the tangent vector. Step 6: Repeat steps 2 through 5 until the entire optical cable trajectory is traced.

5. The submarine optical cable trajectory tracking method based on fiber optic distributed acoustic sensing according to claim 4, characterized in that, In step 1, if the coordinates of the beginning and end of the optical cable are known, then step A is used; if there is no prior information or step A fails, then step B is used. Step A includes: A1. Closest point matching: Calculate the perpendicular from the current ship position to the line connecting the beginning and end of the optical cable; A2. Set search route: Plan a straight search path from the current position to the vertical foot; A3. Start scanning: Perform a directional scan vertically underwater along the described straight search path; A4. Event Trigger: When the shore-based DAS module detects a vibration event, the shipborne platform moves towards the initial point. A5. Scheme Switching: If the shore-based DAS module does not detect any valid vibration events, expand the search range; if no valid vibration events are detected after expanding the range, switch to step B. Step B includes: B1. Initial position setting: The shipborne platform starts from the origin point (0, 0, 0) on the shore where the shore-based DAS module is located; B2, 360° cone scan: sonar fixed depression angle azimuth With angular velocity Perform a 360° cone scan; B3. Depression Adjustment and Repeat Scan: If the initial point is not detected, gradually increase the angle. The scanning continues until the shore-based DAS module captures a valid vibration event, at which point the shipboard platform moves toward that initial position.

6. The method for tracking submarine optical cable trajectories based on fiber optic distributed acoustic sensing according to claim 4, characterized in that, Step 2 specifically includes the following sub-steps: Step 2-1. Key Parameter Acquisition: When the shore-based DAS module first detects a vibration event caused by sonar excitation, record its fiber arc length s and response timestamp. t 2 ; Step 2-2. Use the matched filter module to reverse-engineer the sonar transmission time. t 1 ; Steps 2-3. Calculation of sound wave propagation distance: based on the speed of sound c w The distance the sound wave travels from the sonar to the optical cable is calculated as follows: ; Steps 2-4. Initial 3D coordinates of the optical cable point ( x c , y c , z c The solution is as follows: ; in, x 1 、y 1 for t 1 The ship's position coordinates at that moment. , These are the depression angle and azimuth angle of the sonar scan, respectively; Steps 2-5. Course Adjustment: The shipboard platform is oriented towards the initial optical cable point ( x c , y c , z c Move directly upwards to enter trajectory tracking mode.

7. The submarine optical cable trajectory tracking method based on fiber optic distributed acoustic sensing according to claim 4, characterized in that, Step 3 specifically includes the following sub-steps: Step 3-1. Setting Operating Parameters: Set the sailing speed of the shipborne platform. 、 Sonar depression angle, relative azimuth angle, scanning angular velocity; Step 3-2. Key Parameter Acquisition: Select the point closest in space to the previous detection point from the valid points and denote it as the valid detection point for this time. s k Obtain the cumulative relative azimuth and ship position coordinates from the start of the scan to the effective detection time. x 2 , y 2 ); Step 3-3. Reverse estimation of ship position at the time of sonar launch: Obtain the ship's position at the time of sonar launch ( x 1 , y 1 ); Steps 3-4. Calculate the straight-line distance from the ship to the fiber optic cable point. d : Steps 3-5. Sonar azimuth calculation: (The following is a partial translation of the original text, which is not possible without further context.) t 1 relative azimuth and absolute azimuth at any time ; Step 3-6. Calculation of 3D coordinates of optical cable points: Calculate the 3D coordinates of optical cable points ( x , y , z ): ; in, The angle of depression when the sonar is launched.

8. The submarine optical cable trajectory tracking method based on fiber optic distributed acoustic sensing according to claim 4, characterized in that, Step 4 specifically includes: Once the shore-based DAS module receives the vibration signal and completes the screening of effective detection points, the shipborne platform travels directly above the effective optical cable point, maintaining alignment with the local orientation of the optical cable. Simultaneously, the active sonar module continuously performs ±90° arc scanning with the bow as the center, ensuring full coverage detection of the sea area ahead.

9. The submarine optical cable trajectory tracking method based on fiber optic distributed acoustic sensing according to claim 4, characterized in that, Step 5 specifically includes the following sub-steps: Construct a state vector with the fiber arc length s as the independent variable: ; in Location of the optical cable point. The unit tangent vector; Prediction steps: Based on arc length increments Updated location The tangent vector remains unchanged; The state transition equation is: ; The state transition matrix is: ; Process noise covariance Q modeling: ; q p For position process noise intensity, q t The noise intensity of the tangent vector process, R min This is the minimum bending radius of the optical cable; The predicted covariance is: ; Measurement update: The three-dimensional coordinates of the optical cable points calculated in step 3 are used as the measured values. z k Covariance , The position standard deviation for the geometric solution of the sonar + shore-based DAS module; ; Tangent vector normalization: state update It is a linear operation. After the update, Tnew is no longer strictly normalized. After each update, tangent vector normalization is performed. .

10. The method for tracking submarine optical cable trajectories based on fiber optic distributed acoustic sensing according to claim 4, characterized in that, Step 6 specifically includes: Based on the filtered state, the position of the next detection point is predicted, the sonar scanning strategy and the heading of the shipborne platform are dynamically adjusted, and steps 2 to 5 are continuously executed in a loop until the trajectory tracking of the entire optical cable is completed; finally, the three-dimensional optical cable trajectory is output.

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