A ship state estimation method based on submarine optical cable sensing

Abstract

The present application relates to the field of optical fiber sensing and the field of navigation technology, and more particularly to a ship state estimation method based on submarine optical cable sensing. By multiplexing the submarine optical cable into a distributed acoustic sensor, the position, speed and azimuth angle of the ship can be estimated by analyzing the ship wave in the sensing signal. By using this method, the low-cost passive real-time monitoring and positioning of ships in the vast ocean can be effectively realized, and the limitations of the mainstream ship identification system relying on wireless communication networks are overcome. The technical scheme of the present application has wide application prospects in the fields of navigation safety and ship operation management.

Description

Technical Field

[0001] This invention relates to the fields of fiber optic sensing and marine technology, and more specifically, to a method for ship state estimation based on submarine optical cable sensing. Background Technology

[0002] Ship monitoring has broad application prospects in the fields of fiber optic sensing and navigation. Applying fiber optic sensing to navigation can provide strong technical support for maritime safety and marine environmental protection. In fiber optic sensing, this technology can monitor ocean acoustic signals in real time, leading to a better understanding of changes in the marine environment. Fiber optic sensing can also detect vibration responses caused by ships navigating at sea. In navigation, ship monitoring can be used for ship navigation and safety monitoring. For example, passive ship monitoring technology can be used to facilitate navigation at sea, reduce ship accidents and collisions, and improve navigation safety and efficiency.

[0003] Currently, the mainstream solution for ship detection is the Automatic Identification System (AIS). AIS is a technology used for the automatic exchange of information between ships, between ships and near-shore base stations, and satellites, and it has been widely used and promoted in the international shipping industry. Ships equipped with AIS synchronize their ship status information via wireless communication. However, AIS cannot be used outside the coverage area of ​​wireless communication networks, is greatly affected by severe weather at sea, and installing AIS is an additional operational burden for ships; to date, there are no unified and comprehensive standards and specifications. Other ship detection solutions include Synthetic Aperture Radar (SAR), satellite imagery, and hydrophone monitoring. SAR has high resolution and is resistant to severe weather, satellite imagery has a large coverage area, and hydrophones have high sensitivity. However, SAR imaging speed is slow, and it is difficult to balance resolution and coverage. Satellite imagery has low resolution, and hydrophones have a small sensing coverage area and are difficult to deploy and maintain. All three have high operating costs, which is not conducive to the application of real-time monitoring of a large number of ships. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention provides a ship state estimation method based on submarine optical cable sensing, which overcomes the limitation of mainstream ship identification systems relying on wireless communication networks.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a ship state estimation method based on submarine optical cable sensing, comprising the following steps:

[0006] S1. Acquire sensing data from submarine optical cables using a Distributed Acoustic Sensing (DAS) device;

[0007] S2. Locate data containing ship waves;

[0008] S3. Estimate the position and time when the ship passes the fiber optic cable based on the fiber optic cable deployment location;

[0009] S4. Obtain the slope of the two-sided scattering crest line and the slope of the scattering crest envelope line from the ship's traveling wave data;

[0010] S5. Combining the water depth estimation data, the slopes of the two-sided scattering crest lines and the slope of the scattering crest envelope line are substituted into the geometric model to estimate the magnitude of the ship speed and the angle with the optical fiber.

[0011] S6. Based on the fiber optic deployment, convert the estimated ship speed and the angle between the fiber optic cable into an azimuth angle.

[0012] Furthermore, the submarine optical cable is any optical cable that can be reused as a distributed acoustic sensor, and the data it acquires includes a spatiotemporal grid of vibration data composed of multi-channel one-dimensional space and one-dimensional data.

[0013] Furthermore, the ship's status includes its position, speed, and bearing.

[0014] Furthermore, the DAS device refers to a device that uses optical fiber for distributed acoustic signal sensing, and its implementation technology includes optical time domain reflection (OTDR) and optical frequency domain reflection (OFDR) technology.

[0015] Furthermore, in step S2, the determination of whether the data contains ship waves is based on ship wave theory and DAS sensing characteristics, which is achieved through manual identification or automatic extraction using target detection.

[0016] Furthermore, in step S3, the geographical coordinates and time are estimated by aligning the channel location and time of the ship wave disturbance origin in the distributed acoustic sensing data with the fiber optic deployment location information.

[0017] Further, in step S4, the slopes K1 and K2 of the bilateral astigmatic wave crest lines are extracted by Radon transform after time-domain data preprocessing and slicing the astigmatic waves on both sides. The slope K of the astigmatic wave crest envelope is obtained by linear regression of the slicing data on one side after time-domain data preprocessing. Env or K′Env .

[0018] Further, in the described step S5, the water depth estimation data is acquired by means of static hydrological information, buoy data, or DAS data analysis.

[0019] Further, in the described step S5, the geometric model describes the spatiotemporal relationship between the simplified supercritical ship-generated waves, the ship traveling at a constant speed in a straight line, and the straight optical fiber. Specifically, let the included angle between the ship speed and the optical fiber be The included angles between the ship speed and the wave crest line and the wave crest envelope line are α and γ respectively, the water depth is H, and the gravitational acceleration is g; traverse in the range of 0°<α<60° and α, all satisfying the constraint condition: of are all feasible solutions for estimation; where ε is a sufficiently small constraint threshold, set as required; according to the classic ship-generated wave theory, the linear approximation relationship between α and γ related to F is obtained: r r γ=f(F)·+O(α), where This relationship can be obtained by substituting the empirical value of F into the classic ship-generated wave crest formula to calculate the specific relational expression; combining the relationship between α and γ, the r feasible solutions are converted into the estimated range of , then the ship speed V can be calculated by the following formula: Where K Env and K' Env only one is taken, specifically depending on which side of the wave crest line is clearer and easier to extract.

[0020] Further, if the water depth data is unknown, the scattered wave velocity U can be used to estimate the water depth H=U 2 / g; the scattered wave velocity U satisfies: Where d is the spatial resolution of the acquisition device, that is, the channel interval, and fs is the sampling rate of the acquisition device. If the water depth data is known, the above relational expression can be used to further narrow the feasible solution range.

[0021] Compared with the prior art, the beneficial effects are as follows: The ship state estimation method based on submarine optical fiber sensing provided by the present invention can fully reuse the existing submarine optical fibers, realize large-scale and low-cost passive ship monitoring, and specifically can estimate the position, speed and direction of the ship passing through the optical fiber, making up for the limitation that mainstream ship identification systems rely on wireless communication networks. Brief Description of the Drawings

[0022] Figure 1 is a schematic flow diagram of the method of the present invention.​​

[0023] Figure 2 This is a geometric model diagram showing the relationship between the two-sided diffuse wave crest line and a straight optical fiber, and a ship traveling at a constant speed in a straight line.

[0024] Figure 3 This is a schematic diagram of the submarine optical cable deployment used for data collection in an embodiment of the present invention.

[0025] Figure 4 The data refers to ship wave data collected by the distributed acoustic sensing device in this embodiment of the invention.

[0026] Figure 5 This is a flowchart of an algorithm for processing and analyzing collected data to estimate ship speed and direction.

[0027] Figure 6 This is the data obtained from ship wave data collected in an embodiment of the present invention after time-domain preprocessing.

[0028] Figure 7 The ship wave data collected in this embodiment of the invention is preprocessed in the time domain, and then sliced ​​for Radon domain preprocessing to extract the data of the slope of the scattered wave crest line.

[0029] Figure 8 The ship wave data collected in this embodiment of the invention is preprocessed in the time domain, and then sliced ​​for linear regression to extract the slope of the envelope of the scattered wave peak.

[0030] Figure 9 The curve represents the relationship between α and γ.

[0031] Figure 10 This is a comparison chart of ship state estimated using the method of this patent in an embodiment of the present invention and AIS data. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The present invention will be described in one embodiment below with reference to specific embodiments. The accompanying drawings are for illustrative purposes only and represent schematic diagrams, not actual pictures, and should not be construed as limiting the present patent. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the actual product size. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0033] In the description of this invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, they are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms describing positional relationships in the accompanying drawings are only for illustrative purposes and should not be construed as limiting this patent. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances. In addition, if the embodiments of this invention involve descriptions of "first," "second," etc., such descriptions are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of those features. Furthermore, the meaning of "and / or" throughout the text is to include three parallel solutions. Taking "A and / or B" as an example, it includes solution A, or solution B, or a solution that simultaneously satisfies A and B.

[0034] Example 1:

[0035] like Figure 1 As shown, a ship state estimation method based on submarine optical cable sensing includes the following steps:

[0036] S1. Acquire sensing data from submarine optical cables using a Distributed Acoustic Sensing (DAS) device;

[0037] S2. Locate data containing ship waves;

[0038] S3. Estimate the position and time when the ship passes the fiber optic cable based on the fiber optic cable deployment location;

[0039] S4. Obtain the slope of the two-sided scattering crest line and the slope of the scattering crest envelope line from the ship's traveling wave data;

[0040] S5. Combining the water depth estimation data, the slopes of the two-sided scattering crest lines and the slope of the scattering crest envelope line are substituted into the geometric model to estimate the magnitude of the ship speed and the angle with the optical fiber.

[0041] S6. Based on the fiber optic deployment, convert the estimated ship speed and the angle between the fiber optic cable into an azimuth angle.

[0042] Herein, the submarine optical cable is any optical cable that can be multiplexed as a distributed acoustic sensor, and the data acquired thereby includes a spatiotemporal grid of vibration data composed of multi-channel one-dimensional space and one-dimensional data. The ship state includes the position, speed and azimuth of the ship. The DAS device refers to a device that uses optical fibers for distributed acoustic signal sensing, and its implementation technologies include Optical Time Domain Reflectometry (OTDR) and Optical Frequency Domain Reflectometry (OFDR) technologies.

[0043] In the described step S2, it is determined whether the data contains ship-generated waves based on the ship-generated wave theory and the DAS sensing characteristics, which is realized by manual identification or automatic extraction using target detection.

[0044] In the described step S3, the geographic coordinates and time are estimated by combining the optical fiber deployment position information through the channel positioning and time alignment of the starting point of the ship-generated wave disturbance in the distributed acoustic sensing data.

[0045] In the described step S4, the bilateral scattered wave peak lines are extracted to obtain the slopes K1 and K2 of the bilateral scattered wave peak lines by performing Radon transform after preprocessing the time-domain data and slicing the scattered waves on both sides respectively, and the scattered wave peak envelope line obtains the slope K through linear regression of the single-sided sliced data after preprocessing the time-domain data. Env or K′ Env .

[0046] In the described step S5, the water depth estimation data is acquired through static hydrological information, buoy data, or DAS data analysis.

[0047] In the described step S5, the geometric model describes the spatiotemporal relationship between the simplified supercritical ship-generated wave, the ship traveling at a constant speed in a straight line, and the straight optical fiber. Specifically, the included angle between the ship speed and the optical fiber is denoted as the included angles between the ship speed and the wave peak line and the wave peak envelope line are respectively α and γ, the water depth is H, and the gravitational acceleration is g; traverse in the range of 0°<α<60° and α, all those that satisfy the constraint condition: are all feasible solutions for estimation; wherein ε is a sufficiently small constraint threshold, which is set as required; according to the classic ship-generated wave theory, it is obtained that there is a linear approximation relationship between α and γ related to F r : γ=f(F r )·+O(α), wherein This relationship can be based on F rSubstituting empirical values ​​into the classic ship wave crest formula, a specific relationship is obtained; combining the relationship between α and γ, The feasible solution is transformed into If the estimated range is known, then the ship speed V can be calculated using the following formula:

[0048] Where K Env and K′ Env You can choose one; the choice depends on which side has a clearer and easier-to-extract peak line.

[0049] Example 2

[0050] The other steps in this embodiment are the same as in Embodiment 1. In this embodiment, they can be used to check the reasonableness of the estimation results or to further narrow down the possibilities in Embodiment 1. The feasible solution range. Specifically, if the water depth data is unknown, the water depth H = U can be estimated using the scattering wave velocity U. 2 / g; the dispersion wave velocity U satisfies: Where d is the spatial resolution of the acquisition device, i.e., the channel spacing, and fs is the sampling rate of the acquisition device. If the water depth data is known, the above relationship can be used to further reduce the resolution. The range of feasible solutions.

[0051] Example 3

[0052] According to classical ship wave theory, the state of a ship wave can be represented by the Froude number: Where V is the boat speed, H is the water depth, and g is the acceleration due to gravity. When F r When the value is greater than 1, the ship's traveling wave is in a supercritical state and consists of bilateral divergent waves.

[0053] Figure 2 This is a schematic diagram of the geometric model used in this paper. It simplifies the scenario of a ship passing through an optical fiber to a ship traveling straight along the route at a constant speed V at an angle. The ship's traveling wave generated above the optical fiber is in a supercritical state, consisting of bilateral scattered waves. This model simplifies the bilateral scattered waves to parallel wave crests propagating at wave speed U, with the wave crests making an angle α with the course. The starting points of a set of scattered wave crests on one side constitute the scattered wave envelope, which makes an angle γ with the course. After time Δt, the ship travels a distance VΔt, the scattered wave crests travel a distance UΔt, and the intersections of the left and right scattered wave crests with the optical fiber travel distances L1 and L2, respectively. The intersections of the bilateral scattered wave envelopes with the optical fiber travel distances L and L', respectively. The following relationships hold:

[0054]

[0055]

[0056]

[0057]

[0058] Due to symmetry,

[0059] According to the classical ship wave theory, when F r When the value of α is between 1 and 5 (most high-speed ships fall within this range), then: 0° < α < 60°.

[0060] Figure 3 This is a schematic diagram of the submarine optical cable deployment used for data acquisition in an embodiment of the present invention. The optical fiber is laid from the island on the left along the ground to the island on the right, with a 2km-13km section laid on the seabed. This section is approximately a straight line and its coordinates are known. Distributed acoustic sensing devices located on the shore collect distributed vibration data on the optical fiber in real time, i.e., spatiotemporal grid data of strain rate.

[0061] Figure 4 This is a typical ship traveling wave data collected by the distributed acoustic sensing device in this embodiment of the invention. The horizontal axis represents time, the vertical axis represents the spatial distance corresponding to the fiber optic sensing channel, and the color represents the strain rate measured by the device after Z-score normalization. The supercritical ship traveling wave appears in the collected data as two sets of asymmetrical wavelines, with their tails approximately parallel. Because fiber optic strain sensing is directionally sensitive, the symmetrical bilateral ship traveling wave dispersions in two-dimensional space exhibit intensity differences in the collected spatiotemporal data. Therefore, temporal data preprocessing is required to denoise and enhance the data before analysis. For ease of understanding, Figure 3 The slopes K1, K2, and K are marked in the figure. Env .

[0062] Figure 5 This is a flowchart of the algorithm for processing and analyzing the collected data to estimate the ship's speed and direction. First, the raw data is preprocessed in the time domain. Then, the scattering waves on both sides are sliced ​​and processed in the Radon domain to obtain the slopes K1 and K2 of the scattering wave crests. Finally, the slope K of the scattering wave crest envelope is obtained in the time domain through linear regression. Env or K′ Env Finally, combining the relationship between α and γ with water depth information, the slope is substituted into the geometric model to calculate the estimated ship speed and direction.

[0063] The collected ship wave data is preprocessed in the time domain as follows: Figure 6 As shown, the effects of sea clutter are effectively eliminated. The position and time of the ship passing the optical fiber can then be determined by locating the starting point of the ship's traveling wave. The position in the figure is 9.24 km from the optical fiber marker, and the time is 09:54:42.

[0064] Figure 6 The solid-line box in the image shows one of the slices selected in this embodiment, whose data on the slope of the scattering wave crest is preprocessed in the Radon domain and extracted as follows: Figure 7 As shown. Figure 7 The intermediate data consists of sliced ​​data that has undergone Radon transform and then Z-score data (denoted as RD). This data is then thresholded to remove the portion where |RD < 1.5σ| (σ is the standard deviation of RD). The resulting denoised result is shown below. Figure 7 As shown in the rightmost box, the denoised result is a clear and distinct bright spot, which facilitates slope extraction. The denoised data is sorted by maximum and minimum values, and the average of the top-5 maximum values ​​is used as an estimate of K1, calculated here to be 8.48 m / s. Similarly, for the slice of the upper half-wave (… Figure 6 The estimated value of K2 can be obtained by performing Radon domain data processing (within the dashed box). In this example, it is calculated to be 19.2 m / s.

[0065] Because the lower half-wave slice has a higher signal-to-noise ratio, it is also used for the extraction of the time-domain envelope, such as... Figure 8 As shown. Extracting all data points from the upper boundary of the slice (the dotted lines in the figure) and performing linear regression yields the scattering envelope (…). Figure 8 The estimated value K of the fitted solid line. Env = 4.6 m / s. At the same time, it can also be achieved through... Figure 8 As seen in the dashed line, K1 extracted in the Radon domain in the previous step matches the time-domain peak line.

[0066] exist Traversal within the range 0° < α < 60° And α, all satisfying the constraints of These are all estimated feasible solutions. Here, ε is a sufficiently small constraint threshold, set to 0.01.

[0067] And α and γ have a linear approximation relationship: = f(F r )·+O(α).

[0068] To obtain a specific value for this approximate relationship, we let F be an empirical value here. r =1.5, then the relationship between α and γ is as follows: Figure 9 As shown.

[0069] Combining the relationship between α and γ, The feasible solution is transformed into If the estimated range is known, then the ship speed V can be calculated using the following formula:

[0070]

[0071] Furthermore, the water depth H = U can be estimated using the scattering wave velocity U. 2 / g. The dispersion wave velocity U satisfies:

[0072] Where d is the spatial resolution of the acquisition device, i.e., the channel spacing, and fs is the sampling rate of the acquisition device.

[0073] Given that the water depth in this area ranges from 7m to 14m, the above formula can be used to further narrow down the possibilities. The range of feasible solutions.

[0074] Finally, based on the fiber optic cable deployment coordinates, the angle between the ship and the fiber optic cable is determined. Convert to geographical azimuth.

[0075] The above steps yield multiple feasible solutions, representing the estimated range of the ship's state. Plotting all feasible solutions as vectors, where the magnitude and direction of the vectors represent the estimated ship speed and azimuth, results are shown below. Figure 10 As shown, the interpolated data, after spatiotemporal alignment with the discrete ship state information of AIS and the ship's passage through the optical fiber, shows good agreement. The method of this invention can quickly determine the position, speed, and direction range of a ship, enabling real-time monitoring, and holds promise for applications in vast sea areas not covered by the wireless communication networks upon which AIS relies.

[0076] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for ship state estimation based on submarine optical cable sensing, characterized in that, Includes the following steps: S1. Acquire sensor data from submarine optical cables using a distributed acoustic sensing (DAS) device; S2. Find data containing ship waves; wherein, based on ship wave theory and DAS sensing characteristics, it is determined whether the data contains ship waves, which is achieved through manual identification or automatic extraction using target detection. S3. Estimate the position and time of the ship passing through the fiber optic cable based on the fiber optic cable deployment location; wherein, the geographical coordinates and time are estimated by aligning the channel location and time of the ship's traveling wave disturbance origin in the distributed acoustic sensor data with the fiber optic cable deployment location information. S4. Obtain the slopes of the bilateral scattering crest lines and the slopes of the scattering crest envelope lines from the ship's sailing wave data; wherein, the slopes of the bilateral scattering crest lines are extracted by performing Radon transform on the scattering waves on both sides after time-domain data preprocessing. and The slope of the diffuse wave crest envelope was obtained by linear regression of single-sided slice data after preprocessing the time-domain data. or ; S5. Combining water depth estimation data, the slopes of the scattering wave crests and the envelope of the scattering wave crests are substituted into the geometric model to estimate the magnitude of the ship speed and the angle between the ship and the optical fiber. The geometric model describes the spatiotemporal relationship between the simplified supercritical ship wave and the uniformly moving straight-line ship and optical fiber. Specifically, the angle between the ship speed and the optical fiber is denoted as... The angles between the ship's speed and the crest line and the crest envelope are respectively and The water depth is The acceleration due to gravity is ; Traversal Within range and All constraints are satisfied: of( ) are all estimated feasible solutions; among them It is a sufficiently small constraint threshold, set as needed; obtained according to classical ship wave theory. and Existence and Relevant linear approximation relationships: ,in The relationship is based on The empirical values ​​are substituted into the classic ship wave crest formula to obtain the specific relationship. Representing Froude numbers, For the ship's speed, Because of the water depth, It is the acceleration due to gravity; combined with and The relationship will ( The feasible solution of ) is transformed into ( The estimated range of the ship speed is then determined by the estimated range of the ship speed. The following formula can be used to calculate: ， in and You can choose one; it depends on which side's peak line is clearer and easier to extract. S6. Based on the fiber optic deployment, convert the estimated ship speed and the angle between the fiber optic cable into an azimuth angle.

2. The ship state estimation method based on submarine optical cable sensing according to claim 1, characterized in that, The submarine optical cable mentioned above is any optical cable that can be reused as a distributed acoustic sensor, and the data it acquires includes a spatiotemporal grid of vibration data composed of multi-channel one-dimensional space and one-dimensional data.

3. The ship state estimation method based on submarine optical cable sensing according to claim 1, characterized in that, Ship status includes the ship's position, speed, and bearing.

4. The ship state estimation method based on submarine optical cable sensing according to claim 1, characterized in that, The aforementioned DAS device refers to a device that uses optical fiber for distributed acoustic signal sensing, and its implementation technology includes optical time domain reflection and optical frequency domain reflection technology.

5. The ship state estimation method based on submarine optical cable sensing according to claim 1, characterized in that, In step S5, the water depth estimation data is obtained through static hydrological information, buoy data, or DAS data analysis.

6. The ship state estimation method based on submarine optical cable sensing according to claim 1, characterized in that, If the water depth data is unknown, the divergence wave velocity can be used. Estimate water depth ;Diffuse wave velocity satisfy: ,in This refers to the spatial resolution of the acquisition device, i.e., the channel spacing. This is the sampling rate of the data acquisition device; if the water depth data is known, the above relationship can be used to further reduce the value (…). The range of feasible solutions.

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