Ship speed inversion method based on wake infrared polarization characteristics

Abstract

The invention discloses a ship speed inversion method based on wake infrared polarization characteristics. The method belongs to the technical field of navigational speed evaluation based on optical technology. The problem that an existing detection method is only suitable for wake infrared intensity detection under the condition that a large temperature difference exists between the wake and the sea surface and cannot be suitable for wake detection under complex conditions so as to analyze the ship speed is solved. The infrared polarization characteristics of the wake are detected and analyzed by using the difference between the infrared polarization characteristics of the ship wake and the infrared polarization characteristics of the surrounding sea surface, so that the visibility and identification degree of the ship wake are improved. A sea surface ship wake infrared polarization transmission model based on the ship wake infrared polarization degree is constructed, the correlation mechanism between the ship navigation speed and the infrared polarization characteristic is explained through theoretical analysis, and the navigation speed inversion result corresponding to any sea surface ship wake infrared polarization original image is further solved through inversion.

Description

Technical Field

[0001] The present invention belongs to the technical field of ship speed assessment based on optical technology, and in particular relates to a ship speed inversion method based on the infrared polarization characteristics of wakes. Background Art

[0002] Ships are important carriers of the maritime transport system, and the classification of their types and real-time monitoring of their navigation postures are key links in international maritime regulation. The wake characteristics formed during the navigation of ships are an important basis for marine remote sensing technology to identify ship targets, and are also regarded as an effective way to invert the dynamic parameters of ships. In the field of military reconnaissance, detection methods based on infrared radiation have long been used in ship identification. This technology achieves detection and positioning by capturing the difference in thermal radiation between the target and the sea surface. However, when the thermal radiation of the ship's wake is close to the ocean background radiation, or the target is in an area of ​​solar flare reflection interference, the traditional thermal contrast detection method is prone to technical bottlenecks such as reduced signal-to-noise ratio and blurred target features, which restricts the environmental adaptability of the detection system. When a ship is sailing at a constant speed in the ocean, the interaction between the ship and the seawater will cause a stable V-shaped Kelvin wake to form on the sea surface. The existence time and coverage of this wake have obvious advantages over the ship itself. The wake itself has distinct characteristics, making it easier to detect than the ship itself. Furthermore, the turbulence of the ship's hull causes the water at the bottom to surge to the surface. The temperature stratification of the seawater makes the bottom water cooler than the surface, so the infrared characteristics of the wake are significantly different from those of the surrounding sea surface.

[0003] At the same time, polarization occurs in the wake's own infrared radiation and the reflection of ambient radiation, making the wake's infrared polarization characteristics different from those of the surrounding seawater. Therefore, infrared polarization detection can fully utilize information such as the roughness and refractive index of the wake's surface, effectively suppressing background light and improving the wake's detection rate.

[0004] However, current ocean detection is primarily based on infrared detection using radiation intensity, which primarily utilizes the temperature difference between the target and the background for identification. This approach is only suitable for situations where there is a large temperature difference between the wake and the sea surface. When the temperature difference between the target and the background is small, infrared detection based on radiation intensity exhibits significant limitations and cannot guarantee the accuracy and efficiency of sea surface wake identification. Summary of the Invention

[0005] In order to solve the problem that the existing detection method is only applicable to the infrared intensity detection of the wake when there is a large temperature difference between the wake and the sea surface, but cannot be applied to the wake detection under complex conditions to analyze the ship speed, the present invention provides a ship speed inversion method based on the infrared polarization characteristics of the wake, which includes the following steps: S1. Use 3D modeling software to build a 3D model of the fluid domain of the ship wake on the sea surface; S2. Establish a height field model of the wake of a ship on the sea surface, use a three-dimensional model of the fluid domain of the wake of a ship on the sea surface to simulate the navigation of the ship, and use CFD simulation to obtain the numerical simulation results of the height field of the wake of the ship at different speeds; S3. Combining the sea surface ship wake height field model with the micro-facet polarization bidirectional reflectance distribution function PG model, an infrared polarization transmission model of the sea surface ship wake is established; S4. Substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the sea surface ship wake to obtain a simulation database of the infrared polarization characteristics of the sea surface ship wake; S5. Determine the original infrared polarization image of the sea surface ship wake to be inverted, and solve the sea surface ship velocity inversion result based on the sea surface ship wake infrared polarization characteristic simulation database.

[0006] Further, step S2 is specifically as follows: S21. Establish a Kelvin wake height field model, establish a sea surface height field model, and superimpose the Kelvin wake height field model and the sea surface height field model to obtain a sea surface ship wake height field model; S22. Determine simulated navigation conditions, including wave height, navigation speed, draft, and physical properties of seawater; S23. Using CFD simulation method, the height field model of the ship wake on the sea surface is simulated to obtain the numerical simulation results of the height field of the ship wake at different speeds.

[0007] Furthermore, the Kelvin wake height field model is specifically: ;in, , Indicates the ship's speed. represents the acceleration due to gravity, Indicates the half-width of the hull, Indicates half the length of the hull, Indicates the draft depth, represents the angle between the wake wave and the direction of ship motion, The coordinates are The wake portion of the Kelvin wake corresponds to the height of the Kelvin wake.

[0008] Furthermore, the sea surface height field model is specifically: ;in, represents the number of frequency divisions, Indicates the number of directional divisions; , , , represents the first frequencies, It represents the average wind speed at a height of 19.5m above the sea surface. , , , , , is the frequency corresponding to the peak of the sea surface power spectrum curve, Indicates the The propagation direction of each component wave relative to the coordinate system of the sea surface height field model The angle between the axes, express The increment of express increment; represents the wave number; Indicates random phase, with values ​​between ; The coordinates are The height corresponding to the sea surface part.

[0009] Furthermore, the infrared polarization transmission model of the sea surface ship wake is specifically as follows: ;in: , , , ; in, represents the Stokes vector, For strength, is the ratio of vertical or horizontal polarization in polarized light, Indicates the proportion of polarized light that is 45° to the vertical or horizontal direction. Indicates the proportion of circular polarization in polarized light; represents the radiation intensity of the trail, represents the incident light intensity, represents the object surface shading function, and are the angles between the incident light direction, the reflected light direction and the normal line of the macroscopic object surface, and are the azimuths of the incident light and the reflected light respectively; ζ total represents the height field model of the ship wake on the sea surface, represents the partial derivative operation, represents the surface roughness constant of the object, 、 are the vertical and parallel components of Fresnel reflectivity, It represents the angle between the plane ROZ formed by the reflected light direction and the Z axis and the plane RON formed by the reflected light direction and the microfacet normal, where the Z axis is the normal direction of the macroscopic object surface.

[0010] Furthermore, step S4 is specifically as follows: substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the sea surface ship wake, determining the normal direction of the macroscopic object surface to establish a conversion matrix, and then performing calculations based on the infrared polarization transmission model of the sea surface ship wake to obtain the simulation results of the infrared polarization characteristics of the wake, performing multiple simulations for different ship speeds, zenith angles and azimuth angles, thereby establishing a sea surface wake infrared polarization database; wherein the zenith angle includes and , azimuth includes and .

[0011] Further, step S5 is specifically as follows: S51, solving the infrared polarization degree image of the sea surface ship wake by using the original infrared polarization image of the sea surface ship wake; S52, shielding the ship hull in the infrared polarization image of the sea surface ship wake to prevent it from affecting the inversion result; S53, extract the tail length and Kelvin arm angle, and extract the infrared polarization degree of the tail area; S54, performing ship speed inversion based on infrared polarization degree on the wake, querying the sea surface wake infrared polarization database based on the extracted wake features, and generating an initial population of 50 individuals based on the database query results; S55, calculating the residuals between the individuals in the initial population and the sea surface wake infrared polarization database query results, and setting the reciprocal of the residuals as the retention degree of each individual; S56. Retain the two individuals with the highest retention, sum the retention of the remaining individuals to get the total retention, and select 50% of the individuals with a probability based on the ratio of the individual's own retention to the total retention; S57. Randomly select a crossover point and exchange the crossover point of each individual with another individual; S58, set the individual mutation probability to 0.05, and generate random disturbance at a mutation point on the mutation individual; S59. Filter out individuals with speeds in the range of 2-40 knots, substitute the parameters of the filtered individuals into the infrared polarization transmission model of the wake of a sea ship for calculation, compare the calculation results with the polarization degree of the input image, calculate the error rate, and set the inverse of the error rate as the fitness. If the fitness is greater than or equal to 10, output the speed inversion result. If the fitness is less than 10, return to the retention calculation stage and re-iterate the population.

[0012] The beneficial effects of the method of the present invention are: (1) The present invention proposes an inversion method for analyzing the ship's navigation speed based on the infrared polarization characteristics of the ship's wake. The infrared polarization characteristics of the ship's wake are detected and analyzed by utilizing the difference between the infrared polarization characteristics of the ship's wake and the infrared polarization characteristics of the surrounding sea surface, thereby improving the visibility and recognition of the ship's wake.

[0013] (2) An infrared polarization transmission model of ship wakes on the sea surface is constructed based on the infrared polarization degree of ship wakes. The correlation mechanism between ship speed and infrared polarization characteristics is explained through theoretical analysis. The speed inversion result corresponding to the original infrared polarization image of any ship wake on the sea surface is further solved through inversion. This solves the problem that the ship wake is difficult to effectively identify the ship speed when the temperature difference between the wake and the sea surface is small.

[0014] The present invention can be applied in the practical field of ocean exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a flow chart of the method described in an embodiment of the present invention; Figure 2 This is a numerical simulation effect diagram of the height field of the wake of a ship on the sea surface according to an embodiment of the present invention; Figure 3 This is an effect diagram of the wake polarization degree in the simulation of infrared polarization characteristics of a sea surface ship wake in an embodiment of the present invention; Figure 4 This is a flow chart of solving the inversion result of sea surface ship velocity based on the simulation database of infrared polarization characteristics of sea surface ship wakes in an embodiment of the present invention. DETAILED DESCRIPTION

[0016] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0017] Example 1 like Figure 1 The flowchart of the ship speed inversion method based on the infrared polarization characteristics of the wake according to the present invention is shown. The method includes the following steps: S1. Use 3D modeling software to build a 3D model of the fluid domain of the ship wake on the sea surface; S2. Establish a height field model of the wake of a ship on the sea surface, use a three-dimensional model of the fluid domain of the wake of a ship on the sea surface to simulate the navigation of the ship, and use CFD simulation to obtain the numerical simulation results of the height field of the wake of the ship at different speeds; S3. Combining the sea surface ship wake height field model with the micro-facet polarization bidirectional reflectance distribution function PG model, an infrared polarization transmission model of the sea surface ship wake is established; S4. Substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the sea surface ship wake to obtain a simulation database of the infrared polarization characteristics of the sea surface ship wake; S5. Determine the original infrared polarization image of the sea surface ship wake to be inverted, and solve the sea surface ship velocity inversion result based on the sea surface ship wake infrared polarization characteristic simulation database.

[0018] Example 2 This embodiment further limits the embodiment 1 and further explains step S2. Step S2 is specifically as follows: S21. Establish a Kelvin wake height field model, establish a sea surface height field model, and superimpose the Kelvin wake height field model and the sea surface height field model to obtain a sea surface ship wake height field model; S22. Determine simulated navigation conditions, including wave height, navigation speed, draft, and physical properties of seawater; S23, using CFD simulation method, through the sea surface ship wake height field model simulation to obtain the height field numerical simulation results of the ship wake at different speeds, such as Figure 2 Shown is the numerical simulation effect of the height field of the wake of a ship on the sea surface.

[0019] The Kelvin wake height field model is specifically: ;in, , Indicates the ship's speed. represents the acceleration due to gravity, Indicates the half-width of the hull, Indicates half the length of the hull, Indicates the draft depth, represents the angle between the wake wave and the direction of ship motion, The coordinates are The wake portion of the Kelvin wake corresponds to the height of the Kelvin wake.

[0020] The sea surface height field model is specifically: ;in, represents the number of frequency divisions, Indicates the number of directional divisions; , , , represents the first frequencies, It represents the average wind speed at a height of 19.5m above the sea surface. , , , , , is the frequency corresponding to the peak of the sea surface power spectrum curve, Indicates the The propagation direction of each component wave relative to the coordinate system of the sea surface height field model The angle between the axes, express The increment of express increment; represents the wave number; Indicates random phase, with values ​​between ; The coordinates are The height corresponding to the sea surface part.

[0021] Example 3 This embodiment further limits the embodiment 1 and further explains step S3.

[0022] The infrared polarization transmission model of the wake of a ship on the sea surface is as follows: ;in: , , , ; in, represents the Stokes vector, For strength, is the ratio of vertical or horizontal polarization in polarized light, Indicates the proportion of polarized light that is 45° to the vertical or horizontal direction. Indicates the proportion of circular polarization in polarized light; represents the radiation intensity of the trail, represents the incident light intensity, represents the object surface shading function, and are the angles between the incident light direction, the reflected light direction and the normal line of the macroscopic object surface, and are the azimuths of the incident light and the reflected light respectively; ζ total represents the height field model of the ship wake on the sea surface, represents the partial derivative operation, represents the surface roughness constant of the object, 、 are the vertical and parallel components of Fresnel reflectivity, It represents the angle between the plane ROZ formed by the reflected light direction and the Z axis and the plane RON formed by the reflected light direction and the microfacet normal; the direction of the Z axis is the direction of the normal of the macroscopic object surface, and the macroscopic surface coordinate system is established with the macroscopic object surface normal as the Z axis.

[0023] Example 4 This embodiment is a further limitation of embodiment 1, and further explains step S4. Step S4 is specifically as follows: substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the sea surface ship wake, determining the normal direction of the macroscopic object surface to establish a conversion matrix, and then performing calculations based on the infrared polarization transmission model of the sea surface ship wake to obtain the simulation results of the infrared polarization characteristics of the wake, performing multiple simulations for different ship speeds, zenith angles, and azimuth angles, thereby establishing a sea surface wake infrared polarization database; wherein the zenith angle includes and , azimuth includes and .

[0024] The numerical simulation results of the sea surface ship wake height field model are brought into the established sea surface ship wake infrared polarization transmission model, normalized, and attached to the normal line of the sea surface ship wake height field three-dimensional model. Based on the numerical simulation results attached to the normal line, the sea surface ship wake height field three-dimensional model is rendered in grayscale value, and the sea surface ship wake infrared polarization effect diagram is output. The infrared polarization characteristics can be expressed by the degree of linear polarization (DOLP) and the angle of polarization (AOP), as expressed by: , .

[0025] like Figure 3 The figure shows the effect of the wake polarization degree in the simulation of the infrared polarization characteristics of the wake of a sea surface ship.

[0026] Example 5 This embodiment further limits the embodiment 1 and further explains step S5.

[0027] like Figure 4 As shown, step S5 is specifically as follows: S51, solving the infrared polarization degree image of the sea surface ship wake by using the original infrared polarization image of the sea surface ship wake; S52, shielding the ship hull in the infrared polarization image of the sea surface ship wake to prevent it from affecting the inversion result; S53, extract the tail length and Kelvin arm angle, and extract the infrared polarization degree of the tail area; S54, performing ship speed inversion based on infrared polarization degree on the wake, querying the sea surface wake infrared polarization database based on the extracted wake features, and generating an initial population of 50 individuals based on the database query results; S55, calculating the residuals between the individuals in the initial population and the sea surface wake infrared polarization database query results, and setting the reciprocal of the residuals as the retention degree of each individual; S56. Retain the two individuals with the highest retention, sum the retention of the remaining individuals to get the total retention, and select 50% of the individuals with a probability based on the ratio of the individual's own retention to the total retention; S57. Randomly select a crossover point and exchange the crossover point of each individual with another individual; S58, set the individual mutation probability to 0.05, and generate random disturbance at a mutation point on the mutation individual; S59. Filter out individuals with speeds in the range of 2-40 knots, substitute the parameters of the filtered individuals into the infrared polarization transmission model of the wake of a sea ship for calculation, compare the calculation results with the polarization degree of the input image, calculate the error rate, and set the inverse of the error rate as the fitness. If the fitness is greater than or equal to 10, output the speed inversion result. If the fitness is less than 10, return to the retention calculation stage and re-iterate the population.

Claims

1. A ship speed inversion method based on the infrared polarization characteristics of the wake, characterized by: The method comprises the following steps: S1. Use 3D modeling software to build a 3D model of the fluid domain of the ship wake on the sea surface; S2. Establish a height field model of the wake of a ship on the sea surface, use a three-dimensional model of the fluid domain of the wake of a ship on the sea surface to simulate the navigation of the ship, and use CFD simulation to obtain the numerical simulation results of the height field of the wake of the ship at different speeds; S3. Combining the sea surface ship wake height field model with the micro-facet polarization bidirectional reflectance distribution function PG model, an infrared polarization transmission model of the sea surface ship wake is established; S4. Substituting the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the sea surface ship wake to obtain a simulation database of the infrared polarization characteristics of the sea surface ship wake; S5. Determine the original infrared polarization image of the sea surface ship wake to be inverted, and solve the sea surface ship velocity inversion result based on the sea surface ship wake infrared polarization characteristic simulation database.

2. The ship speed inversion method based on wake infrared polarization characteristics according to claim 1 is characterized in that: Step S2 is specifically as follows: S21. Establish a Kelvin wake height field model, establish a sea surface height field model, and superimpose the Kelvin wake height field model and the sea surface height field model to obtain a sea surface ship wake height field model; S22. Determine simulated navigation conditions, including wave height, navigation speed, draft, and physical properties of seawater; S23. Using CFD simulation method, the height field model of the ship wake on the sea surface is simulated to obtain the numerical simulation results of the height field of the ship wake at different speeds.

3. The ship speed inversion method based on wake infrared polarization characteristics according to claim 2 is characterized in that: The Kelvin wake height field model is specifically: ;in, , Indicates the ship's speed. represents the acceleration due to gravity, Indicates the half-width of the hull, Indicates half the length of the hull, Indicates the draft depth, represents the angle between the wake wave and the direction of ship motion, The coordinates are The wake portion of the Kelvin wake corresponds to the height of the Kelvin wake.

4. The ship speed inversion method based on wake infrared polarization characteristics according to claim 3 is characterized in that: The sea surface height field model is specifically: ;in, represents the number of frequency divisions, Indicates the number of directional divisions; , , , represents the first frequencies, It represents the average wind speed at a height of 19.5m above the sea surface. , , , , , is the frequency corresponding to the peak of the sea surface power spectrum curve, Indicates the The propagation direction of each component wave relative to the coordinate system of the sea surface height field model The angle of the axis, express The increment of express increment; represents the wave number; Indicates random phase, with values ​​between ; The coordinates are The height corresponding to the sea surface part.

5. The ship speed inversion method based on wake infrared polarization characteristics according to claim 4 is characterized in that: The infrared polarization transmission model of the sea surface ship wake is specifically as follows: ;in: ， ， ， ； in, represents the Stokes vector, For strength, is the ratio of vertical or horizontal polarization in polarized light, Indicates the proportion of polarized light that is 45° to the vertical or horizontal direction. Indicates the proportion of circular polarization in polarized light; represents the radiation intensity of the wake, represents the incident light intensity, represents the object surface occlusion function, and are the angles between the incident light direction, the reflected light direction and the normal line of the macroscopic object surface, and are the azimuths of the incident light and the reflected light respectively; ζ total represents the height field model of the ship wake on the sea surface, represents the partial derivative operation, represents the surface roughness constant of the object, 、 are the vertical and parallel components of Fresnel reflectivity, It represents the angle between the plane ROZ formed by the reflected light direction and the Z axis and the plane RON formed by the reflected light direction and the microfacet normal, where the Z axis is the normal direction of the macroscopic object surface.

6. The ship speed inversion method based on wake infrared polarization characteristics according to claim 5 is characterized in that: Step S4 is specifically as follows: Substitute the numerical simulation results obtained in step S2 into the infrared polarization transmission model of the sea surface ship wake, determine the normal direction of the macroscopic object surface to establish a conversion matrix, and then perform calculations based on the infrared polarization transmission model of the sea surface ship wake to obtain the simulation results of the infrared polarization characteristics of the wake, perform multiple simulations for different ship speeds, zenith angles and azimuth angles, and thus establish a sea surface wake infrared polarization database; wherein the zenith angle includes and , azimuth includes and .

7. The ship speed inversion method based on wake infrared polarization characteristics according to claim 6 is characterized in that: Step S5 is specifically as follows: S51, solving the infrared polarization degree image of the sea surface ship wake by using the original infrared polarization image of the sea surface ship wake; S52, shielding the ship hull in the infrared polarization image of the sea surface ship wake to prevent it from affecting the inversion result; S53, extract the tail length and Kelvin arm angle, and extract the infrared polarization degree of the tail area; S54, performing ship speed inversion based on infrared polarization degree on the wake, querying the sea surface wake infrared polarization database based on the extracted wake features, and generating an initial population of 50 individuals based on the database query results; S55, calculating the residuals between the individuals in the initial population and the sea surface wake infrared polarization database query results, and setting the reciprocal of the residuals as the retention degree of each individual; S56. Retain the two individuals with the highest retention, sum the retention of the remaining individuals to get the total retention, and select 50% of the individuals with a probability based on the ratio of the individual's own retention to the total retention; S57. Randomly select a crossover point and exchange the crossover point of each individual with another individual; S58, set the individual mutation probability to 0.05, and generate random disturbance at a mutation point on the mutation individual; S59. Filter out individuals with speeds in the range of 2-40 knots, substitute the parameters of the filtered individuals into the infrared polarization transmission model of the wake of a sea ship for calculation, compare the calculation results with the polarization degree of the input image, calculate the error rate, and set the inverse of the error rate as the fitness. If the fitness is greater than or equal to 10, output the speed inversion result. If the fitness is less than 10, return to the retention calculation stage and re-iterate the population.

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