Simulation method and system for Kelvin wake radiation brightness temperature image of sea surface ship

Abstract

The invention belongs to the technical field of electromagnetic simulation, and discloses a sea surface ship Kelvin wake radiation brightness temperature image simulation method and system, and the method comprises the steps: building three-dimensional morphological models of a ship and a sea surface ship Kelvin wake, and carrying out the surface element division of the three-dimensional morphological models, so as to obtain the serial number and node coordinates of each surface element in a whole integrated composite scene; the ship surface elements serve as smooth surface elements, and the sea surface and Kelvin wake surface elements serve as rough surface elements; tracking rays are emitted to all positions of the integrated composite scene from the observation azimuth; based on the incidence coordinate, the incidence direction and the node coordinate of each tracking ray, obtaining each surface element where the tracking path intersects with the integrated composite scene, and then determining the brightness temperature of each intersecting surface element in sequence through reverse tracking, thereby obtaining the radiation brightness temperature corresponding to each tracking ray, and realizing sea surface ship Kelvin wake radiation brightness temperature image simulation. According to the method, the accuracy of sea surface ship Kelvin wake radiation brightness temperature image simulation can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic simulation, and more specifically, relates to a simulation method and system for the radiation brightness temperature image of the Kelvin wake of a ship on the sea surface. Background Art

[0002] When a ship sails on the sea surface, the interaction between the moving ship and the sea surface will generate a wake. As an associated feature of the ship, the ship wake covers a wide area and has a long duration, and its morphological characteristics are different from those of the sea surface background. Therefore, the geographical location of the ship can be determined by detecting the ship wake. Ship wake detection, as an auxiliary means of ship detection, is one of the research hotspots in the field of maritime surveillance.

[0003] In the prior art, most of the radiation research on ship wakes calculates the emissivity of the wake through the traditional Kirchhoff approximation method. By dividing the sea surface and ship wake scenes into multiple small facets, the emissivity of each small facet is calculated respectively, and finally the radiation brightness temperature of the scene is calculated according to the physical temperature and emissivity of the scene. This method does not consider the scattering and reflection effects of the coupling between the rough sea surface and the ship on the radiation signal transmission path, nor does it consider the radiation and attenuation on the transmission path on the received radiation signal. In addition, the Kirchhoff approximation method has low calculation accuracy at large incident angles, resulting in the inability to carry out the radiation calculation of the wake at large incident angles. Summary of the Invention

[0004] Aiming at the above defects or improvement requirements of the prior art, the present invention provides a simulation method and system for the radiation brightness temperature image of the Kelvin wake of a ship on the sea surface, and its purpose is to improve the accuracy of the simulation of the radiation brightness temperature image of the Kelvin wake of a ship on the sea surface.

[0005] To achieve the above object, the present invention provides a simulation method for the radiation brightness temperature image of the Kelvin wake of a ship on the sea surface, including: respectively establishing three-dimensional morphological models of the ship and the Kelvin wake of the ship on the sea surface, and dividing them into facets to obtain the numbers and node coordinates of each facet in the integrated composite scene of the ship, the sea surface and the Kelvin wake of the ship;

[0006] Regarding the ship facets in the integrated composite scene as smooth facets, and the sea surface and Kelvin wake facets of the ship as rough facets; respectively emitting tracking rays from a preset observation azimuth to each position of the integrated composite scene;

[0007] For each tracking ray, based on the incident coordinates, incident direction of the tracking ray, and the node coordinates, line-plane intersection operations are used to obtain each surface element where the tracking path of the tracking ray intersects with the integrated composite scene. Then, by backtracking, the brightness temperatures of the intersecting surface elements are determined in sequence, thereby obtaining the radiation brightness temperature corresponding to each tracking ray, realizing the simulation of the radiation brightness temperature image of the Kelvin wake of ships on the sea surface;

[0008] Among them, the determination method of the tracking path is as follows:

[0009] If the currently intersecting surface element is a smooth surface element, the next-level tracking direction of the tracking ray after passing through the current intersecting surface element is the direction mirrored to the direction in which the tracking ray is incident on the current intersecting surface element; if the currently intersecting surface element is a rough surface element, the upper hemisphere 2π space of the current intersecting surface element is divided into N sub-regions, and the next-level tracking direction of the tracking ray after passing through the current intersecting surface element is the scattering ray direction of each sub-region; N≥1, and based on the number of the surface element, it is determined whether the currently intersecting surface element is a smooth surface element or a rough surface element.

[0010] Furthermore, the determination of the brightness temperatures of the intersecting surface elements by backtracking in sequence includes: the brightness temperature of the surface element intersecting in the i-th level tracking direction on the current tracking path is determined according to the emissivity, reflectivity of the intersecting surface element, and the brightness temperature of the surface element intersecting in the i + 1-th level tracking direction;

[0011] Among them, the surface element intersecting in the first-level tracking direction is the first surface element where the current tracking ray intersects with the integrated composite scene, and the surface element intersecting in the last-level tracking direction is the last surface element where the current tracking ray intersects with the integrated composite scene; the brightness temperature of the last surface element is determined by the emissivity, reflectivity of the last surface element, and the atmospheric brightness temperature.

[0012] Furthermore, if the intersecting surface element is a smooth surface element, the brightness temperature of the current intersecting surface element is:

[0013] TB i =T i e p (θ i )+TB i+1 (1 - e p (θ i ))

[0014] Among them, TB i 、T i and e p (θ i ) are respectively the brightness temperature, physical temperature, and emissivity of the smooth surface element intersecting in the i-th level tracking direction on the current tracking path, θ i is the incident angle of the tracking ray on the intersecting surface element in the i-th level tracking direction, p represents the polarization mode; TBi+1 is the brightness temperature of the intersecting surface element in the (i + 1)-th level tracking direction on the current tracking path;

[0015] If the intersecting surface element is a rough surface element, the brightness temperature TB of the current intersecting surface element i is:

[0016]

[0017] where r p (θ i ; θ s , φ s ; Δθ s , Δφ s ) is the reflectivity of the intersecting surface element in the i-th level tracking direction on the current tracking path; θ s (n), φ s (n) are respectively the scattering elevation angle and azimuth angle of the scattered ray in the n-th sub-region divided by the current intersecting surface element; Δθ s (n), Δφ s (n) are respectively the intervals of the N sub-regions divided by the current intersecting surface element in the directions of θ s (n), φ s (n); T is the physical temperature of the intersecting surface element; σ pp (θ i ; θ s , φ s ) and σ qp (θ i ; θ s , φ s ) represent the bistatic scattering coefficient σ pq (θ i ; θ s , φ s ) of the current intersecting surface element, where pp and qp respectively represent the co-polarization and cross-polarization polarization modes.

[0018] Furthermore, it also includes using a masking function to correct the above to obtain a corrected bistatic scattering coefficient

[0019]

[0020] where φ i is the azimuth angle between the current intersecting surface element and the intersecting surface element in the (i - 1)-th level tracking direction on the current tracking path, i > 1; when i = 1, φ i is the azimuth angle between the tracking ray and the radiometer of the first intersecting surface element of the integrated composite scene, and the radiometer is used to emit the tracking ray; s is the root mean square slope of the current intersecting surface element; μ takes μ i or μ s , and correspondingly θ takes θi or θ s ; erfc(·) is the complementary error function.

[0021] Furthermore, the radiance temperature T corresponding to the current tracking ray A is the brightness temperature T at the antenna aperture plane of the radiometer for the current tracking ray AP which is the antenna brightness temperature obtained after being weighted by the radiometer antenna pattern; wherein, the brightness temperature T of the current tracking ray at the antenna aperture plane of the radiometer AP is:

[0022]

[0023] wherein, T B is the brightness temperature of the first surface element where the current tracking ray intersects with the integrated composite scene, L a is the attenuation of the atmosphere on the tracking path, and T atmosphere is the atmospheric radiation on the tracking path.

[0024] Furthermore, the three-dimensional morphological model of the ship and the ship's Kelvin wake on the sea surface is divided into surface elements to obtain the numbers and node coordinates of each surface element in the integrated composite scene of the ship, the sea surface, and the ship's Kelvin wake, including:

[0025] The three-dimensional morphological model of the ship and the ship's Kelvin wake on the sea surface is divided into surface elements to obtain the numbers and node numbers of the ship surface elements and the ship's Kelvin wake surface elements on the sea surface;

[0026] The numbers and node numbers of the ship surface elements and the ship's Kelvin wake surface elements on the sea surface are merged to obtain the numbers and node numbers of each surface element in the integrated composite scene, and the node coordinates of each surface element in the integrated composite scene are determined using the node numbers of each surface element in the integrated composite scene.

[0027] Furthermore, the surface element is a triangular surface element, and the numbers and node numbers of the ship surface elements in the integrated composite scene are the same as those of the ship surface elements before merging; the number Num * and the node number Node * (v1, v2, v3) of the ship's Kelvin wake surface element on the sea surface in the integrated composite scene are respectively:

[0028] Num * = Num + P1

[0029] Node * (v1, v2, v3) = Node(v1, v2, v3) + P1

[0030] Among them, Num and Node(v1, v2, v3) respectively represent the number and node number of the sea surface ship Kelvin wake surface element before merging. v1, v2, and v3 represent the three vertex coordinates of the triangular surface element, and P1 is the total number of sea surface ship surface element nodes.

[0031] Furthermore, determining whether the currently intersecting surface element is a smooth surface element or a rough surface element based on the number of the surface element includes:

[0032] If the number Num* of the currently intersecting surface element ≤ P1, it is determined that the currently intersecting surface element is a smooth surface element; otherwise, it is a rough surface element.

[0033] The present invention also provides a simulation system for the radiance temperature image of the sea surface ship Kelvin wake, including a computer-readable storage medium and a processor;

[0034] The computer-readable storage medium is used to store executable instructions;

[0035] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the simulation method of the radiance temperature image of the sea surface ship Kelvin wake described in any one of the above.

[0036] The present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the simulation method of the radiance temperature image of the sea surface ship Kelvin wake described in any one of the above.

[0037] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0038] (1) The present invention takes into account the scattering and reflection effects of the coupling between the rough sea surface and the ship on the radiation signal transmission path, which in turn affects the accuracy of the simulation of the radiance temperature image of the sea surface ship Kelvin wake. Based on this, the present invention divides the surface elements in the integrated composite scene into smooth surface elements and rough surface elements. The ship surface elements are regarded as smooth surface elements. On the tracking path of the ray, after passing through it, it can be regarded as specular reflection occurring, that is, the next-level tracking direction after passing through the smooth surface element is the direction mirror-image to its incident direction; while the sea surface and the sea surface ship Kelvin wake surface elements are regarded as rough surface elements. On the tracking path of the ray, after passing through it, the tracking ray will be scattered. Therefore, in the present invention, the upper hemisphere 2π space of the rough surface element is divided into N sub-regions, and the scattering ray direction of each sub-region is used as the next-level tracking direction after the tracking ray passes through the current rough surface element. In this way, the scattering and reflection effects of the coupling between the rough sea surface and the ship on the radiation signal transmission path are accurately simulated, and the accuracy of the simulation of the radiance temperature image of the sea surface ship Kelvin wake is improved.

[0039] (2) Preferably, for the sea surface and the ship Kelvin wake surface elements (rough surface elements), the method for calculating the brightness temperature of the surface elements provided by the present invention takes into account the influence of all scattered rays in N sub-regions divided in the upper hemisphere 2π space of the rough surface elements, further improving the accuracy of the simulation of the radiation brightness temperature image of the ship Kelvin wake on the sea surface.

[0040] (3) Further, considering that the Kirchhoff approximation method ignores the shielding effect and diffraction effect in the integrated composite scene, the present invention introduces a shielding function in the radar field to correct the bistatic scattering coefficient, realizing the accurate calculation of the radiation of the wake at large incident angles, and further improving the accuracy of the simulation of the radiation brightness temperature image of the ship Kelvin wake on the sea surface.

[0041] (4) Preferably, when calculating the brightness temperature T of the current tracking ray at the antenna aperture plane of the radiometer, the present invention AP simultaneously takes into account the attenuation and radiation of the atmosphere along the tracking path, further improving the accuracy of the simulation of the radiation brightness temperature image of the ship Kelvin wake on the sea surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic diagram of the simulation method of the radiation brightness temperature image of the ship Kelvin wake in the embodiment of the present invention.

[0043] Figure 2 is a flowchart of the simulation method of the radiation brightness temperature image of the ship Kelvin wake in the embodiment of the present invention.

[0044] Figure 3 are the three-dimensional model of the ship on the sea surface and the three-dimensional model of the ship wake in the embodiment of the present invention.

[0045] Figure 4 is a schematic diagram of calculating the zenith angle and azimuth angle of the emissivity of the surface element by the Kirchhoff approximation method in the embodiment of the present invention.

[0046] Figure 5 is a schematic diagram of a ray tracing in the embodiment of the present invention.

[0047] Figure 6 Millimeter-wave radiation apparent brightness temperature map and millimeter-wave radiation antenna brightness temperature map of the ship on the sea surface and the ship wake. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0049] Example 1

[0050] As Figure 1 - Figure 2 shown, the embodiment of the present invention provides a simulation method for the radiation brightness temperature image of the Kelvin wake of a sea vessel, mainly including:

[0051] S1. Respectively establish three-dimensional shape models of the sea vessel and the Kelvin wake of the sea vessel; and perform element division on the three-dimensional shape models of the sea vessel and the Kelvin wake of the sea vessel to obtain the numbers of each element and the node coordinates of each element in the integrated composite scene of the vessel, the sea surface, and the Kelvin wake of the sea vessel;

[0052] S2. Take the vessel elements in the integrated composite scene as smooth elements, and the sea surface and Kelvin wake elements of the vessel as rough elements; emit tracking rays from a preset observation azimuth to each position of the integrated composite scene;

[0053] S3. For each tracking ray, based on the incident coordinate, incident direction of the current tracking ray, and the node coordinates of all elements in the integrated composite scene, use the line-plane intersection operation to obtain the elements where the tracking path of the current tracking ray intersects with the integrated composite scene, and then sequentially determine the brightness temperature of each element intersecting with the tracking path of the current tracking ray through reverse tracking, so as to obtain the radiation brightness temperature corresponding to each tracking ray, and realize the simulation of the radiation brightness temperature image of the integrated composite scene.

[0054] Among them, for each tracking ray, the determination method of the tracking path is:

[0055] If the element where the tracking ray currently intersects with the integrated composite scene is a smooth element, the next-level tracking direction after the tracking ray passes through the currently intersecting smooth element is the direction that is the mirror image of the direction in which the tracking ray enters the currently intersecting smooth element;

[0056] If the element where the tracking ray currently intersects with the integrated composite scene is a rough element, divide the upper hemisphere 2π space of the currently intersecting rough element into N sub-regions, and the next-level tracking direction after the tracking ray passes through the currently intersecting rough element is the scattering ray direction of each sub-region; N≥1, and determine whether the current element is a smooth element or a rough element based on the numbers of each element in the integrated composite scene.

[0057] When the tracking ray no longer intersects with each element in the integrated composite scene, at this time, it has been tracked to the atmosphere, and the tracking of the current tracking ray ends, and the numbers of all intersecting elements under the current tracking path are obtained.

[0058] Preferably, in S1, the three-dimensional morphological model ζ(x, y) of the Kelvin wake of a sea vessel is as follows:

[0059] ζ(x,y) = ζ kelvin (x,y) + ζ sea (x,y)

[0060]

[0061] ζ sea (x,y) = ∑∑A(k x , k y ) exp[i(k x x + k y y)]

[0062]

[0063] Among them, ζ kelvin (x,y) represents the wave height distribution of the Kelvin wake of the vessel, ζ sea (x,y) represents the wave height distribution of the sea surface, (x, y) is the coordinate of any point on the model, b represents the half ship width, l represents the half ship length, d represents the draft depth, k = g / V 2 , V represents the ship speed, g represents the acceleration due to gravity, β is the integration variable, γ n is a Gaussian random variable, represents the conjugate of γ n , W(k x , k y ) represents the two-dimensional sea spectrum, k x and k y are the wave numbers of the sea waves in the x and y directions respectively, L x and L y are the sizes of the simulated sea surface in the x and y directions respectively.

[0064] In S1, the three-dimensional morphological model of the sea vessel and the three-dimensional morphological model of the Kelvin wake of the sea vessel are divided into surface elements to obtain the numbers of each surface element and the node coordinates of each surface element in the integrated composite scene of the vessel, the sea surface and the Kelvin wake of the vessel, including:

[0065] Perform surface element division on the three-dimensional shape model of the sea vessel and the three-dimensional shape model of the Kelvin wake of the sea vessel to obtain the numbers of the surface elements of the sea vessel after division and the numbers of the nodes of the surface elements, as well as the numbers of the nodes of the surface elements of the Kelvin wake of the sea vessel and the numbers of the nodes of the surface elements. Determine the node coordinates of each surface element using the numbers of the nodes of each surface element; and merge the numbers of the surface elements of the sea vessel and the numbers of the nodes of the surface elements of the Kelvin wake of the sea vessel to obtain the numbers of the surface elements of each surface element in the integrated composite scene of the sea, the vessel, and the Kelvin wake of the vessel and the numbers of the nodes of the surface elements. Determine the node coordinates of each merged surface element using the numbers of the nodes of the merged surface elements.

[0066] Preferably, in the embodiment of the present invention, the surface elements of the Kelvin wake of the sea vessel are divided into triangular surface elements.

[0067] In the embodiment of the present invention, if the row m of the surface element of the Kelvin wake of the sea vessel in the simulation scene matrix is an even number, the numbers of the nodes of the three vertices of the triangular surface element of the Kelvin wake of the sea vessel are expressed as:

[0068]

[0069] If the row m of the surface element of the Kelvin wake of the sea vessel in the simulation scene matrix is an odd number, the numbers of the nodes of the three vertices of the triangular surface element of the Kelvin wake of the sea vessel are expressed as:

[0070]

[0071] where m' represents the column number of the surface element of the Kelvin wake of the sea vessel in the simulation scene matrix, and the value starts from 1; B x is the number of columns of the simulation scene matrix, and the simulation scene matrix is used for the wave height distribution information of the Kelvin wake of the sea vessel; represents the floor operator, represents the ceiling operator.

[0072] Based on the node number representation method in the embodiment of the present invention, the node coordinates of each surface element can be quickly determined.

[0073] In the embodiment of the present invention, the three-dimensional shape model of the sea vessel is obtained using common three-dimensional modeling software. The obtained three-dimensional shape model of the sea vessel includes the numbers, node numbers, and node coordinates of the surface elements of the divided vessel. As Figure 3 shown, it is the three-dimensional model of the sea vessel and the three-dimensional model of the vessel wake in the embodiment of the present invention.

[0074] In the embodiment of the present invention, the numbers of the surface elements of the merged sea vessel and the numbers of the nodes of the surface elements remain unchanged. The number Num of the surface elements of the Kelvin wake of the sea vessel after merging *Node numbers of the dough-making element * (v1, v2, v3) is:

[0075] Num * = Num + P1

[0076] Node * (v1, v2, v3) = Node(v1, v2, v3) + P1

[0077] Wherein, Num and Node(v1, v2, v3) respectively represent the number of the Kelvin wake elements of the sea surface ship before merging and the node numbers of the elements, and P1 is the total number of the node elements of the sea surface ship elements.

[0078] In S2, a radiometer is used to emit tracking rays from a preset observation azimuth to each position of the integrated composite scene. Preferably, the tracking rays emitted by the radiometer are millimeter waves. The radiance temperature image in the embodiment of the present invention is a millimeter wave radiance temperature image.

[0079] In S3, based on the numbers of each element in the integrated composite scene, it is determined whether the current element is a smooth element or a rough element, including:

[0080] If the total number of ship elements is P1 and the number of sea surface and ship Kelvin wake elements is P2, when the number Num* of the intersecting elements traced is ≤ P1, it is determined that the traced intersecting element is a smooth element, and when the number Num* of the traced intersecting elements > P1, it is determined that the traced intersecting element is a rough element.

[0081] In S3, the radiance temperatures of the elements intersecting with the current tracking ray tracking path are determined in turn by backtracking. Among them, the radiance temperature of the element intersecting in the i-th level tracking direction on the current tracking path is determined according to the emissivity, reflectivity or scattering coefficient of the intersecting element and the radiance temperature of the element intersecting in the (i + 1)-th level tracking direction; among them, the radiance temperature of the element intersecting in the last level tracking direction is determined by the emissivity, reflectivity or scattering coefficient of the intersecting element and the atmospheric radiance temperature.

[0082] In the embodiment of the present invention, the first element where the current tracking ray intersects with the integrated composite scene is the element intersecting in the 1st level tracking direction on the current tracking path, and the reflected ray or scattered ray of the tracking ray passing through the first element again intersects with the integrated composite scene at the second element, which is the element intersecting in the 2nd level tracking direction, and so on, until the current tracking ray enters the atmosphere. Before entering the atmosphere, the last element where the current tracking ray intersects with the integrated composite scene is the element intersecting in the last level tracking direction on the current tracking path.

[0083] If the intersecting surface element is a smooth surface element, the brightness temperature of the surface element intersected in the i-th tracking direction on the current tracking path is:

[0084] TB i = T i e p (θ i ) + TB i+1 (1 - e p (θ i ))

[0085] Wherein, TB i , T i and e p (θ i ) are respectively the brightness temperature, physical temperature and emissivity of the smooth surface element intersected in the i-th tracking direction on the current tracking path, θ i is the angle between the tracking ray and the normal vector of the surface element intersected in the i-th tracking direction, that is, the incident angle of the tracking ray on the intersecting surface element in the i-th tracking direction, p represents the polarization mode; TB i+1 is the brightness temperature of the next-level intersecting surface element traced by the ray in the i-th tracking direction on the current tracking path, that is, the brightness temperature of the surface element intersected in the (i + 1)-th tracking direction on the current tracking path.

[0086] In the embodiment of the present invention, the emissivity of the ship surface element is:

[0087]

[0088] Wherein, μ2 and ε2 are respectively the magnetic permeability and dielectric constant of the ship material; p = h indicates that the polarization mode is horizontal polarization, and p = v indicates that the polarization mode is vertical polarization.

[0089] If the intersecting surface element is a rough surface element, the emissivity e p (θ) of the rough surface element can be expressed as:

[0090]

[0091] Wherein, r p (θ i ) represents the reflectivity of the rough surface element, and θ s and φ s are respectively the scattering elevation angle and azimuth angle of the current intersecting rough surface element.

[0092] In the embodiment of the present invention, the upper hemisphere 2π space of the rough surface element is divided into N sub-regions, then the reflectivity r p (θ i ; θ s , φ s ; Δθs , Δφ s ), emissivity e p (θ i ) and brightness temperature TB i can be calculated by the discrete summation method:

[0093]

[0094] where θ s (n), φ s (n) are the scattering elevation angle and azimuth angle of the scattering ray of the nth sub-region of the intersecting rough surface element (the current intersecting rough surface element) in the i-th tracking direction on the current tracking path respectively; Δθ s (n), Δφ s (n) are the intervals of the N sub-regions of the current rough surface element in the directions of θ s (n), φ s (n) respectively, N is the number of sub-regions divided in the 2π space of the upper hemisphere of the current intersecting rough surface element, T is the physical temperature of the rough surface element; σ pp (θ i ; θ s , φ s ) and σ qp (θ i ; θ s , φ s ) are the bistatic scattering coefficients σ pq (θ i ; θ s , φ s ) of the current intersecting rough surface element, pp and qp represent the polarization modes of co-polarization and cross-polarization respectively; TB i+1 [θ s (n), φ s (n) is the brightness temperature of the next-level intersecting surface element traced by the ray with the current tracking directions of θ s (n), φ s (n).

[0095] In the embodiment of the present invention, the bistatic scattering coefficient σ pp (θ i ; θ s , φ s ) of the current intersecting rough surface element is:

[0096]

[0097] where P pq is the total power at the receiving antenna (radiometer), is the scattering field of the current intersecting rough surface element, is Conjugate; R0 is the distance from the center point of the current intersecting rough surface element to the observation point. is the total incident power of the current tracking ray, and A0 is the illumination area.

[0098] In the embodiment of the present invention, the scattering field of the current intersecting rough surface element

[0099]

[0100] where k1 is the wave number of medium 1, and η1 is the intrinsic impedance of medium 1. is the unit vector of the scattering direction of all scattering rays on the current intersecting rough surface element. is the unit vector of the direction of the ray incident on the current rough surface element. is the unit normal vector of the surface of medium 2, and ks is the scattering wave number. is the position (x, y, z) of the point on the sea surface wake (current intersecting rough surface element), E is the incident electromagnetic wave field. is the magnetic field of the electromagnetic wave, j is the imaginary unit, and S represents the integral variable of the surface function; in the embodiment of the present invention, medium 1 is air and medium 2 is seawater, and the stationary phase method is used to solve the scattering field of the surface element. To simplify the calculation process, in the embodiment of the present invention, only the scattering in the mirror direction of the scattering field is considered, the diffraction effect is ignored, and the phase of the surface element is in a steady state. As Figure 4 shown in the embodiment of the present invention θ i 、θ s 、φ s The schematic diagram of the relationship among them.

[0101] As a further design of the present invention, considering that the Kirchhoff approximation method has low calculation accuracy for the scattering coefficient at large incident angles due to ignoring the shadowing effect and the diffraction effect, in the implementation of the present invention, a shadowing function in the radar field is introduced to correct the scattering coefficient of the rough surface element. The corrected bistatic scattering coefficient is:

[0102]

[0103] where φ i is the azimuth angle between the current intersecting rough surface element and the intersecting surface element at the (i - 1)-th level tracking direction on the current tracking path, i > 1; when i = 1, φ i is the azimuth angle between the current intersecting rough surface element (the first intersecting surface element of the tracking ray and the integrated composite scene) and the radiometer; s is the root mean square slope of the current intersecting rough surface element; μ takes μ i or μ s , corresponding to θ taking θ i or θ s, ; erfc(·) is the complementary error function.

[0104] In S3, the radiometric brightness temperature T corresponding to the current tracking ray A is the brightness temperature T at the antenna aperture plane of the radiometer for the current tracking ray AP The antenna brightness temperature after weighting by the antenna pattern:

[0105]

[0106] where is the normalized radiation pattern of the antenna, and Ω is the area integration variable. The brightness temperature T at the antenna aperture plane of the radiometer for the current tracking ray AP (θ, φ; p) is:

[0107]

[0108] where T B (θ, φ; p) is the brightness temperature of the surface element intersected by the current tracking ray at the first-level tracking direction on the current tracking path, that is, the brightness temperature of the first surface element intersected by the current tracking ray with the integrated composite scene. θ and φ are the elevation angle and azimuth angle of the radiometer scan respectively, that is, θ and φ are the incident angles of the current tracking ray on the first surface element intersected by the integrated composite scene (θ i ) when i = 1, and the azimuth angle between the first surface element intersected by the current tracking ray with the integrated composite scene and the radiometer (φ i ) when i = 1, and p is the polarization mode; L a is the attenuation of the atmosphere on the tracking path, and T atmosphere is the atmospheric radiation on the tracking path. This technical method simultaneously considers the atmospheric attenuation and radiation on the transmission path, further improving the accuracy of the simulation.

[0109] By the above method, the radiometric brightness temperature of each tracking ray is obtained, and then the millimeter-wave radiation image of the entire integrated composite scene is obtained.

[0110] In the embodiments of the present invention, aiming at the problems that the calculation accuracy of Kelvin wake radiation is not high under large incident angles and the coupling effect between sea surface ships and rough sea surfaces is not considered. First, a three-dimensional physical model of a sea surface ship and its wake is established, and the surface element division is carried out. Then, tracking rays are emitted from the observation azimuth, the ray-plane intersection operation is performed, the transmission path of the radiation signal is calculated, and the attenuation and radiation on the transmission path are considered. The masking function is introduced to correct the emissivity of the surface element under large incident angles calculated by the Kirchhoff approximation method, so as to more accurately calculate the wake brightness temperature. Finally, by calculating the apparent brightness temperature reaching the antenna aperture plane and the antenna brightness temperature weighted by the antenna pattern, the millimeter-wave radiation brightness temperature image of the Kelvin wake of the sea surface ship under large incident angles is simulated, providing a basis for the research on the millimeter-wave radiation characteristics of the wake and ship detection.

[0111] As Figure 5 shown, it is a schematic diagram of ray tracing in the embodiments of the present invention. In Figure 5 , the tracking ray emitted by the radiometer serves as the first-level radiation source and intersects with the target surface element (smooth surface element). The ray after reflection serves as the second-level radiation source and is incident on the wake surface element (rough surface element), and is scattered on N sub-regions of the current wake surface element respectively. In Figure 5 , T B0 represents the brightness temperature T AP (θ, φ; p) of the current tracking ray at the antenna aperture plane of the radiometer, and T B1 represents the brightness temperature T B (θ, φ; p) of the surface element intersected in the first-level tracking direction on the current tracking path, and T B21 -T B2N respectively represent the brightness temperatures corresponding to the N sub-regions of the rough surface element intersected in the second-level tracking direction on the current tracking path.

[0112] Figure 6 This is the millimeter-wave radiation apparent brightness temperature map (left) and millimeter-wave radiation antenna brightness temperature map (right) of the sea surface ship and its wake simulated in the embodiments of the present invention. Among them, the sea surface ship is a metal ship on the sea surface, with a length of 75 m, a width of 10 m, a draft of 5 m, a ship speed of 5 m / s, a sea surface wind speed of 2.5 m / s, and an observation elevation angle of -25°. From Figure 6 it can be seen that compared with the sea surface background, the Kelvin wake shows a high brightness temperature, the hull part of the sea surface ship shows a high brightness temperature, the deck part of the sea surface ship shows a low brightness temperature. When the sea surface ship is observed at a large incident angle, an image reflection (an embodiment of the coupling effect between the rough sea surface and the ship) can be seen, and at this time the image reflection shows a low brightness temperature.

[0113] The present invention can simulate the millimeter-wave radiation images of the Kelvin wake of sea surface ships under different observation parameters, providing effective support for analyzing the radiation characteristics of the Kelvin wake of sea surface ships.

[0114] Example 2

[0115] An embodiment of the present invention provides a simulation method and system for the radiometric brightness temperature image of the Kelvin wake of a sea vessel, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the steps of the simulation method for the radiometric brightness temperature image of the Kelvin wake of a sea vessel in the above-mentioned Embodiment 1 are implemented.

[0116] The related technical solutions are the same as above and will not be elaborated here.

[0117] Example 3

[0118] An embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the simulation method for the radiometric brightness temperature image of the Kelvin wake of a sea vessel in the above-mentioned Embodiment 1 are implemented.

[0119] Specifically, the memory may include a high-speed random access memory, and may also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) card, a Flash Card, at least one magnetic disk storage device, a flash memory device, or other volatile solid-state storage devices.

[0120] The related technical solutions are the same as above and will not be elaborated here.

[0121] Example 4

[0122] An embodiment of the present application provides a computer program product, including a computer program. When the computer program runs on a computer, the computer is caused to execute the steps of the simulation method for the radiometric brightness temperature image of the Kelvin wake of a sea vessel in the above-mentioned Embodiment 1.

[0123] The related technical solutions are the same as above and will not be elaborated here.

[0124] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship, characterized in that: include: The three-dimensional morphological models of the ship and the Kelvin wake of the ship on the sea surface are established respectively, and the surface elements are divided into them to obtain the number and node coordinates of each surface element in the integrated composite scene of the ship, the sea surface and the Kelvin wake of the ship; The ship surface element in the integrated composite scene is used as a smooth surface element, and the sea surface and the ship Kelvin wake surface element are used as a rough surface element; emitting tracing rays from a preset observation position to each position of the integrated composite scene; For each tracing ray, based on the incident coordinates, incident direction and node coordinates of the tracing ray, a line-surface intersection operation is used to obtain each facet where the tracing path of the tracing ray intersects with the integrated composite scene, and then the brightness temperature of each intersecting facet is determined in turn by reverse tracing, thereby obtaining the radiation brightness temperature corresponding to each tracing ray, and realizing the radiation brightness temperature image simulation of the Kelvin wake of a sea surface ship; The tracking path is determined as follows: If the currently intersecting surface element is a smooth surface element, the next level of tracing direction after the tracing ray passes through the currently intersecting surface element is the direction mirrored to the direction of the tracing ray incident on the currently intersecting surface element; if the currently intersecting surface element is a rough surface element, the 2π space in the upper hemisphere of the currently intersecting surface element is divided into N sub-areas, and the next level of tracing direction after the tracing ray passes through the currently intersecting surface element is the direction of the scattered ray in each sub-area; N≥1, and based on the number of the surface element, it is determined whether the currently intersecting surface element is a smooth surface element or a rough surface element.

2. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to claim 1, characterized in that: The method of sequentially determining the brightness temperature of each intersecting surface element by reverse tracking includes: determining the brightness temperature of the intersecting surface element in the i-th level tracking direction on the current tracking path according to the emissivity and reflectivity of the intersecting surface element and the brightness temperature of the intersecting surface element in the i+1-th level tracking direction; Among them, the intersecting surface element under the first level tracing direction is the first surface element where the current tracing ray intersects with the integrated composite scene, and the intersecting surface element under the last level tracing direction is the last surface element where the current tracing ray intersects with the integrated composite scene; the brightness temperature of the last surface element is determined by the emissivity, reflectivity and atmospheric brightness temperature of the last surface element.

3. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to claim 2, characterized in that: If the intersecting surface element is a smooth surface element, the brightness temperature of the current intersecting surface element is: TB i =T i And p (θ i )+TB i+1 (1-e p (θ i )) Among them, TB i , T i and e p (θ i ) are the brightness temperature, physical temperature and emissivity of the smooth surface element intersecting under the i-th level tracking direction on the current tracking path, θ i is the incident angle of the tracking ray on the intersection plane in the i-th level tracking direction, p represents the polarization mode; TB i+1 is the brightness temperature of the intersecting surface element in the i+1th level tracking direction on the current tracking path; If the intersecting surface element is a rough surface element, the brightness temperature TB of the current intersecting surface element is i for: Among them, r p (θ i θ s ,φ s ; Δθ s ,Δφ s ) is the reflectivity of the intersecting surface element in the i-th level tracking direction on the current tracking path; θ s (n),φ s (n) are the scattering pitch angle and azimuth angle of the scattered rays of the nth sub-region divided by the current intersection surface element; Δθ s (n), Δφ s (n) are the N sub-regions divided by the current intersection surface element in θ s (n),φ s (n) The interval in the direction, T is the physical temperature of the intersecting surface element; σ pp (θ i θ s ,φ s ) and σ qp (θ i θ s ,φ s ) represents the bistatic scattering coefficient σ of the current intersection surface element pq (θ i θ s ,φ s ), pp and qp represent the polarization modes as co-polarization and cross-polarization, respectively.

4. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to claim 3, characterized in that: The invention also includes using a masking function to correct the above-mentioned, and obtaining a corrected bistatic scattering coefficient. Among them, φ i is the azimuth between the current intersecting surface element and the intersecting surface element in the i-1th level tracking direction on the current tracking path, i>1; when i=1, φ i is the azimuth between the first intersecting face element of the tracing ray and the integrated composite scene and the radiometer, the radiometer is used to emit the tracing ray; s is the root mean square slope of the current intersecting face element; μ is μ i or μ s , corresponding to θ, take θ i or θ s ; erfc(·) is the complementary error function.

5. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to claim 3 or 4, characterized in that: The radiation brightness temperature T corresponding to the current tracing ray A is the brightness temperature T of the current tracing ray at the radiometer antenna aperture AP The antenna brightness temperature obtained after weighting the radiometer antenna pattern; wherein the brightness temperature T of the current tracking ray at the radiometer antenna aperture AP for: Among them, T B is the brightness temperature of the first surface element where the current tracing ray intersects the integrated composite scene, L a To track the atmospheric attenuation along the path, T atmosphere To track atmospheric radiation along the path.

6. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to any one of claims 1 to 4, characterized in that: The established three-dimensional morphological model of the ship and the Kelvin wake of the sea surface is divided into facets to obtain the number and node coordinates of each facet in the integrated composite scene of the ship, the sea surface and the Kelvin wake of the ship, including: Divide the established three-dimensional morphological model of the ship and the Kelvin wake of the sea surface ship into surface elements, and obtain the numbers and node numbers of the ship surface elements and the Kelvin wake surface elements of the sea surface ship; The numbers and node numbers of the ship face element and the Kelvin wake face element of the sea surface ship are merged to obtain the number and node number of each face element in the integrated composite scene, and the node coordinates of each face element in the integrated composite scene are determined using the node number of each face element in the integrated composite scene.

7. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to claim 6, characterized in that: The face element is a triangular face element, and the number and node number of the ship face element in the integrated composite scene are consistent with the number and node number of the ship face element before merging; The number of the Kelvin wake surface element of the sea ship in the integrated composite scene is * and node number Node * (v1,v2,v3) are: Is it? * =Num+P1 Node * (v1,v2,v3)=Node(v1,v2,v3)+P1 Among them, Num and Node (v1, v2, v3) represent the number and node number of the Kelvin wake surface element of the sea surface ship before merging, v1, v2, v3 represent the coordinates of the three vertices of the triangular surface element, and P1 is the total number of the sea surface ship surface element nodes.

8. The method for simulating the Kelvin wake radiation brightness temperature image of a sea surface ship according to claim 7, characterized in that: Determining whether the currently intersecting surface element is a smooth surface element or a rough surface element based on the number of the surface element includes: If the current intersecting surface element number Num*≤P1, the current intersecting surface element is judged to be a smooth surface element, otherwise, it is a rough surface element.

9. A simulation system for the Kelvin wake radiation brightness temperature image of a sea surface ship, characterized in that: comprising a computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium to execute the simulation method of the Kelvin wake radiation brightness temperature image of a surface ship according to any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, a simulation method for a Kelvin wake radiation brightness temperature image of a surface ship as described in any one of claims 1 to 8 is implemented.

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