Submarine cable full-routing automatic positioning method based on distributed optical fiber acoustic wave sensing

Abstract

The invention relates to the technical field of submarine cable positioning, in particular to a submarine cable full-route automatic positioning method based on distributed optical fiber sound wave sensing, which comprises the following steps of: connecting a DAS demodulator with submarine cable optical fibers to form a sensing array, collecting passive acoustic noise generated by ship navigation and demodulating the passive acoustic noise into a vibration signal; acquiring position coordinates of the corresponding ship from the public AIS database; calculating a pseudo azimuth angle of each ship noise by adopting a beam forming algorithm based on the vibration signal; constructing a geometric model among the pseudo azimuth angle, the ship coordinates and submarine cable point position parameters; for a submarine cable point, multiple groups of pseudo azimuth angle data are accumulated to form a data vector, iterative inversion is carried out by adopting a damping least square method, and the coordinate and the azimuth angle of the point are solved; and repeating the process to determine parameters of each key position point of the submarine cable, and obtaining a complete route through linear interpolation. According to the invention, the passive sound source and the public AIS data are utilized, active emission, precise time service and complex marine work are avoided, and efficient and low-cost submarine cable full-route positioning is realized.

Description

Technical Field

[0001] This invention relates to the field of submarine cable positioning technology, and in particular to an automatic positioning method for the entire route of submarine cables based on distributed optical fiber acoustic wave sensing. Background Technology

[0002] As the backbone of global communication networks, submarine optical cables rely heavily on precise spatial location information for communication assurance, fault repair, marine engineering safety, and scientific research. However, due to factors such as sag, ocean current impact, and seabed topography changes during the laying process, the actual landing position of submarine cables often deviates from the designed route, and historical laying data may be missing or inaccurate. Therefore, developing efficient and reliable submarine cable routing and positioning technology has become an urgent need in the operation and maintenance field.

[0003] In existing technologies, positioning methods based on distributed acoustic sensing (DAS) have attracted attention due to their ability to utilize existing optical fibers in submarine cables for long-distance, distributed monitoring. Typical solutions all rely on actively transmitted acoustic signals. For example, Chinese Patent Publication No. CN114924317A discloses a method that uses a ship equipped with an acoustic transducer to transmit a swept-frequency acoustic signal, receives the signal through a DAS system, calculates the propagation time, and uses this information in conjunction with the sound source location for positioning. Similarly, Chinese Patent Publication No. CN114280543A discloses another method that controls multiple acoustic signal generators to send test signals of specific frequencies, records the transmission time and the signal arrival time monitored by the DAS system, and calculates the submarine cable coordinates based on the time difference and the sound source location.

[0004] However, the aforementioned positioning technologies relying on active sound sources face a series of engineering challenges and inherent limitations in practical applications: First, to obtain a signal with a sufficient signal-to-noise ratio, the active sound source needs to be sufficiently close to the submarine cable, which is difficult to achieve in vast sea areas where the precise location of the cable is unknown. Furthermore, high-frequency sound waves attenuate significantly over long distances, limiting the effective detection range. Second, the accuracy of both absolute travel time and relative time difference measurements heavily depends on high-precision time synchronization between the transmitting device and the DAS receiving system. Achieving and maintaining such synchronization in actual marine engineering environments is extremely difficult; even small synchronization errors can directly lead to significant positioning errors. Third, the DAS response to vibration signals is directionally sensitive. When the direction of sound wave propagation is nearly perpendicular to the cable axis, the signal-to-noise ratio of the received signal deteriorates significantly, further affecting the reliability of travel time extraction. Finally, these methods typically require coordinating multiple vessels carrying sound sources to transmit from different locations and calculating the signal for each location point individually. For submarine cables hundreds of kilometers long, this operation is complex, time-consuming, and costly, making it difficult to achieve regular, automated route review and monitoring.

[0005] Therefore, the industry urgently needs a submarine cable full-route positioning method that can overcome the above-mentioned defects, eliminate the need for active sound sources, avoid the requirement for precise time synchronization, and achieve efficient, low-cost, and automated operation. Summary of the Invention

[0006] The purpose of this invention is to provide an automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic wave sensing, which solves the problems of existing DAS submarine cable positioning technology based on active sound sources, such as strong dependence on sound source distance, difficulty in achieving high-precision time synchronization, low operation efficiency, high cost, and inability to achieve automated periodic positioning.

[0007] To achieve the above objectives, this invention provides a method for automatic positioning of submarine cables along the entire route based on distributed fiber optic acoustic sensing, comprising the following steps: S1: Connect the distributed acoustic sensor demodulator to the communication optical fiber in the submarine cable to be located to form a linear distributed optical fiber sensor array. S2: The passive acoustic noise signal generated by ships sailing around the submarine cable is collected by the fiber optic sensing array and demodulated into an array vibration signal; S3: Obtain the position coordinates of one or more ships that match the array vibration signal in time from the public AIS database; S4: Based on the array vibration signal, a beamforming algorithm is used to calculate the pseudo azimuth angle of each ship noise signal relative to the fiber optic sensing array. S5: Construct a mathematical model to describe the geometric relationship between the ship's position coordinates, pseudo-azimuth, and the coordinates and azimuth of the submarine cable positioning point; S6: For a single submarine cable positioning point, repeat steps S3 to S5 to obtain a data vector d=[θ1 θ2 ... θ] consisting of multiple pseudo-azimuth angle observations. N ] T ; S7: Substitute multiple pseudo-azimuth observations and their corresponding ship position coordinates into the mathematical model, and use the damped least squares method for iterative inversion to solve for the coordinates and azimuth of a submarine cable positioning point; S8: For multiple key locations on the submarine cable route, repeat steps S3 to S7 to determine the coordinates and azimuth of each key location, and obtain the continuous spatial location information of the entire submarine cable route through interpolation calculation.

[0008] Specifically, step S4 includes: S41: Construct an array received data model based on the array vibration signal; S42: Calculate the sample covariance matrix of the array vibration signal and perform eigenvalue decomposition on the matrix; S43: Construct a noise subspace based on the eigenvalue decomposition results; S44: By searching for spectral peaks, the angle of the direction vector with the strongest orthogonality to the noise subspace is determined as the pseudo azimuth angle.

[0009] In step S44, the spectral peak search employs a multiple signal classification algorithm, which calculates the MUSIC pseudo-spectrum. The peak value is used to determine the pseudo azimuth angle.

[0010] In step S5, the mathematical model is as follows: , Where θ is the pseudo azimuth angle. The coordinates of the submarine cable positioning point. Let h be the angle between the direction of this section of the submarine cable and due north, and h be the water depth. The coordinates of the ship.

[0011] In step S7, the iterative inversion using the damped least squares method specifically involves: Construct the objective function , where S is the objective function, G is the system model, m is the model parameters, and d is the data vector; The model parameters are updated iteratively, starting from the initial guess value m0, using the following formula: ; Wherein, the parameter increment in the (k+1)th iteration By solving the normal equation We obtain J, where J is a Jacobian matrix of size Nx3 and λ is the damping coefficient.

[0012] In step S3, obtaining the location coordinates from the public AIS database specifically involves querying the geographical location information of ships that match the recording time of the array vibration signal and are located in the sea area surrounding the submarine cable.

[0013] In step S8, the key position is the turning point of the linear section of the submarine cable; the interpolation calculation refers to calculating the coordinates of other points on the cable segment between the two adjacent key positions by using linear interpolation after determining the coordinates of the two adjacent key positions.

[0014] This invention provides an automatic positioning method for the entire route of submarine cables based on distributed optical fiber acoustic sensing. Compared with existing technologies, this invention: 1. Most existing technologies rely on emitting active sound sources and then using the known locations and signal characteristics of these sources for localization. This invention proposes to effectively utilize the passive noise emitted by ships for localization, without imposing any restrictions on the excitation source signal itself.

[0015] 2. Existing technologies mostly calculate the coordinates of submarine cables by measuring the travel time of signals arriving at the cable, including absolute travel time or relative time difference, and assuming a constant underwater acoustic speed. This not only places extremely high demands on the precise time synchronization of the sound source and the demodulator (i.e., signal receiver), but also, due to the influence of the signal-to-noise ratio and the waveform of non-instantaneous signals, the travel time calculation may have significant errors, affecting the final practical application of these technologies. This invention, however, calculates the pseudo-azimuth angle of the passive source using noise data, effectively utilizing noise and avoiding the potential impacts of the aforementioned problems.

[0016] 3. Existing technologies all use multiple known sources to locate individual submarine cable points one by one. This invention proposes an extended method for simultaneously calculating multiple submarine cables. In addition to calculating the coordinate position of the submarine cable, it also proposes a method for calculating the azimuth angle of the submarine cable. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0018] Fig. 1 This is a schematic diagram of the reference coordinate system plane when the present invention measures the azimuth angle of the sound source.

[0019] Fig. 2 This is a schematic diagram of the pseudo azimuth angle result after beamforming of a noise source according to the present invention.

[0020] Fig. 3 This is a flowchart of the automatic positioning method for submarine cable full route based on distributed optical fiber acoustic wave sensing according to the present invention. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0022] Please see Figs. 1 to 3 This invention provides an automatic positioning method for submarine cables along their entire route based on distributed fiber optic acoustic sensing. This method utilizes intermittent sound sources, namely vessels navigating near the cable, and uses their Automatic Identification System (AIS) to obtain their positions as effective acoustic signal sources to reposition straight segments (or multiple connected segments) of the cable. This method can simultaneously determine the spatial coordinates and three-dimensional orientation of the center point of a selected cable segment. Specifically, it includes the following steps: S1: Connect the distributed acoustic sensor demodulator to the communication optical fiber in the submarine cable to be located to form a linear distributed optical fiber sensor array.

[0023] In this embodiment, the distributed acoustic sensing (DAS) demodulator is connected to the optical fiber unit in the submarine cable, so that the optical fiber is transformed into a linear sensor array, namely N-segment optical fiber sensing unit.

[0024] S2: The passive acoustic noise signal generated by ships sailing around the submarine cable is collected by the fiber optic sensing array and demodulated into an array vibration signal.

[0025] In this embodiment, the fiber optic sensing unit undergoes strain deformation under external vibration, resulting in a change in its length and the generation of a backscattered Rayleigh light signal. The strain of the fiber optic sensing unit is measured by detecting the phase change of the backscattered Rayleigh light signal. Each generated backscattered Rayleigh light signal is transmitted by the corresponding fiber optic sensing unit to a DAS demodulator for demodulation. The demodulation process converts the optical signal into an output array vibration signal.

[0026] S3: Obtain the position coordinates of one or more ships that match the array vibration signal in time from a public AIS database.

[0027] In this embodiment, the geographical location information of vessels near the submarine cable that coincide with the recording time of ship noise signals is selected from a public AIS database. .

[0028] S4: Based on the array vibration signal, a beamforming algorithm is used to calculate the pseudo azimuth angle of each ship noise signal relative to the fiber optic sensing array.

[0029] In this embodiment, beamforming is used to estimate the pseudo azimuth angle of the array vibration signal, which is the angle θ between the cable axis and the cable-source direction (called the pseudo azimuth angle) in three-dimensional space. Specifically, it is calculated using the Multiple Signal Classification (MUSIC) algorithm.

[0030] The MUSIC algorithm is based on a signal model for array-received data. Assume an M-element uniform linear array (ULA) receiving signals from K signal sources. At any time t, the received data vector x(t) can be expressed as: , Where: A is an M×K array manifold matrix, each column a(θ) is the "arrival vector" corresponding to the direction of arrival θ of the signal source, s(t) is a K×1 signal source vector, and n(t) is an M×1 noise vector. The expression for the arrival vector is: , Where k = 2π / λ is the wave number and d is the element spacing.

[0031] The core of the MUSIC algorithm lies in performing eigenvalue decomposition on the sensor covariance matrix Rx, that is: , Where Rs is the signal source covariance matrix. I is the noise power, and I is the identity matrix.

[0032] Next, the covariance matrix Rx (sample covariance matrix) is used for eigenvalue decomposition to obtain the noise subspace, and then the MUSIC pseudospectrum is calculated. The MUSIC pseudospectrum is defined as follows:

[0033] The arrival vector of the signal source is orthogonal to the noise subspace. Therefore, when the search angle θ is consistent with the direction of the real signal, the orthogonality between the arrival vector a(θ) and the noise subspace is strongest, and the MUSIC pseudospectrum will show a peak.

[0034] S5: Construct a mathematical model to describe the geometric relationship between the ship's position coordinates, pseudo-azimuth, and the coordinates and azimuth of the submarine cable positioning point.

[0035] In this embodiment, for the selected submarine cable positioning point (This refers to a specific location on the submarine cable that needs to be determined), where... The coordinates of the submarine cable positioning point. Let this be the angle between the cable's direction and true north. The relationship between the ship's known position and the unknown cable location point is obtained using the following formula: , Where θ is the pseudo azimuth angle. The coordinates of the submarine cable positioning point are unknown. The angle between the direction of this section of the submarine cable and due north is also unknown, and h is the water depth, while the water depth where this section of the submarine cable is located is known. The coordinates of the ship are also known and are obtained through step S3.

[0036] S6: For a single submarine cable positioning point, repeat steps S3 to S5 to obtain a data vector d=[θ1 θ2 ... θ] consisting of multiple pseudo-azimuth angle observations. N ] T .

[0037] S7: Substitute multiple pseudo-azimuth observations and their corresponding ship position coordinates into the mathematical model, and use the damped least squares method for iterative inversion to solve for the coordinates and azimuth of a submarine cable positioning point.

[0038] In this embodiment, the data vector d obtained in step S6 contains N pseudo-azimuth angle observations for the same submarine cable positioning point. To calculate the position parameters of this point from these observation data, an inversion system needs to be established and solved.

[0039] First, a system model G is established, and the predicted value G(m) is the matrix product of the state vectors m, where m is the location point to be determined. and azimuth The system model consists of a three-dimensional model parameter vector. The system model is the model parameter expressed by formula (1), i.e., the unknown submarine cable coordinates. .

[0040] Construct the objective function Using the damped least squares method, the objective function is minimized by iteratively solving for m: , in Let G be the objective function, G be the system model, m be the model parameters, and d be the data vector.

[0041] The model parameters are updated iteratively, starting from the initial guess value m0, using the following formula: , in, These are the model parameters for the (k+1)th iteration. For the model parameters of the kth iteration, For the parameter increment of the (k+1)th iteration, the following normal equation is satisfied: , Where J is a Jacobian matrix of size Nx3, and λ is the damping coefficient.

[0042] By continuously iterating and updating the model parameters, when the objective function is minimized, the obtained m is the coordinates and azimuth of the submarine cable positioning point to be determined.

[0043] S8: For multiple key locations on the submarine cable route, repeat steps S3 to S7 to determine the coordinates and azimuth of each key location, and obtain the continuous spatial location information of the entire submarine cable route through interpolation calculation.

[0044] In this embodiment, steps S3 to S7 are repeated until all critical locations of the submarine cable are covered. The critical locations refer to the turning points of the linear sections of the submarine cable. The coordinates of the intermediate linear sections at the turning points are calculated using basic linear interpolation.

[0045] Furthermore, this method can be extended to jointly estimate the parameters of all cable segments, which requires corresponding modifications to the definitions of the model vector, data vector, and forward operators in the inversion scheme. The complete model vector m ∈ R 3Nseg Now includes all N seg The series parameters of each fiber segment j. Each segment j is determined by its horizontal and vertical coordinates (x, y, z). j, y j ) and its azimuth angle γj Description. Observation data vector d ∈ R NobsxNseg All cable segments j at time t i The measured pseudo azimuth angle θ i Composition. The current dimension of the Jacobian matrix is ​​J ∈ R. NobsxNsegx3Nseg This can be represented as a block diagonal matrix. Each sub-block J j ∈ R Nobs × 3 This corresponds to the contribution of cable segment j. The global Jacobian matrix J has a block diagonal structure: , Each sub-block contains the partial derivative of the observation angle with respect to the parameters (xj, yj, γj) of the j-th segment. Using this extended model vector, data vector, and block diagonal Jacobian matrix, the damped least squares inversion process, which is based on the same principle as described in step S7, is repeated to simultaneously calculate the position and azimuth parameters of multiple submarine cable segments.

[0046] This invention utilizes the passive noise signal of a ship, without specific restrictions on the frequency and waveform of the signal source, greatly improving the practicality and economy of the method. Because this invention calculates the pseudo-azimuth angle of the sound source through beamforming, rather than relying on existing travel-time-based positioning techniques, it avoids problems such as equipment timing synchronization issues, uncertainties in non-instantaneous signal travel-time estimation, signal noise, and inconsistent signal-to-noise ratios across different channels. Furthermore, the positioning calculation in this invention includes not only coordinates but also the azimuth angle γ. j Compared with existing technologies, this invention provides richer information on submarine cables. Based on the inversion scheme for a single location point, this invention further extends to provide a general method that can simultaneously invert the location parameters of multiple submarine cable segments.

[0047] The above-disclosed embodiments are merely one or more preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art can understand that all or part of the processes for implementing the above embodiments and equivalent changes made in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A method for automatic positioning of submarine cables along their entire route based on distributed fiber optic acoustic sensing, characterized in that, Includes the following steps: S1: Connect the distributed acoustic sensor demodulator to the communication optical fiber in the submarine cable to be located to form a linear distributed optical fiber sensor array. S2: The passive acoustic noise signal generated by ships sailing around the submarine cable is collected by the fiber optic sensing array and demodulated into an array vibration signal; S3: Obtain the position coordinates of one or more ships that match the array vibration signal in time from the public AIS database; S4: Based on the array vibration signal, a beamforming algorithm is used to calculate the pseudo azimuth angle of each ship noise signal relative to the fiber optic sensing array. S5: Construct a mathematical model to describe the geometric relationship between the ship's position coordinates, pseudo-azimuth, and the coordinates and azimuth of the submarine cable positioning point; S6: For a single submarine cable positioning point, repeat steps S3 to S5 to obtain a data vector d=[θ1 θ2 ... θ] consisting of multiple pseudo-azimuth angle observations. N ] T ; S7: Substitute multiple pseudo-azimuth observations and their corresponding ship position coordinates into the mathematical model, and use the damped least squares method for iterative inversion to solve for the coordinates and azimuth of a submarine cable positioning point; S8: For multiple key locations on the submarine cable route, repeat steps S3 to S7 to determine the coordinates and azimuth of each key location, and obtain the continuous spatial location information of the entire submarine cable route through interpolation calculation.

2. The automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic sensing as described in claim 1, characterized in that, Step S4 specifically includes: S41: Construct an array received data model based on the array vibration signal; S42: Calculate the sample covariance matrix of the array vibration signal and perform eigenvalue decomposition on the matrix; S43: Construct a noise subspace based on the eigenvalue decomposition results; S44: By searching for spectral peaks, the angle of the direction vector with the strongest orthogonality to the noise subspace is determined as the pseudo azimuth angle.

3. The automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic sensing as described in claim 2, characterized in that, In step S44, the spectral peak search employs a multiple signal classification algorithm, which calculates the MUSIC pseudo-spectrum. The peak value is used to determine the pseudo azimuth angle.

4. The automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic sensing as described in claim 1, characterized in that, In step S5, the mathematical model is: ， Where θ is the pseudo azimuth angle. The coordinates of the submarine cable positioning point. Let h be the angle between the direction of this section of the submarine cable and due north, and h be the water depth. The coordinates of the ship.

5. The automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic sensing as described in claim 1, characterized in that, In step S7, the iterative inversion using the damped least squares method specifically involves: Construct the objective function , where S is the objective function, G is the system model, m is the model parameters, and d is the data vector; The model parameters are updated iteratively, starting from the initial guess value m0, using the following formula: ; Wherein, the parameter increment in the (k+1)th iteration By solving the normal equation We obtain J, where J is a Jacobian matrix of size Nx3 and λ is the damping coefficient.

6. The automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic sensing as described in claim 1, characterized in that, In step S3, obtaining the location coordinates from the public AIS database specifically involves querying the geographical location information of ships that match the recording time of the array vibration signal and are located in the sea area surrounding the submarine cable.

7. The automatic positioning method for submarine cables along the entire route based on distributed optical fiber acoustic sensing as described in claim 1, characterized in that, In step S8, the key position is the turning point of the linear section of the submarine cable; the interpolation calculation refers to calculating the coordinates of other points on the cable segment between the two adjacent key positions by using linear interpolation after determining the coordinates of the two adjacent key positions.

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