A simulation method and system of sea surface ship kelvin wake radiance temperature image

Abstract

The application belongs to the technical field of electromagnetic simulation, and discloses a simulation method and system for a sea surface ship Kelvin wake radiation brightness temperature image, which comprises the following steps: three-dimensional shape models of a ship and a sea surface ship Kelvin wake are respectively established, and are divided into surface elements to obtain the numbering and node coordinates of each surface element in the entire integrated composite scene; the ship surface element is regarded as a smooth surface element, and the sea surface and the Kelvin wake surface element are regarded as rough surface elements; tracking rays are respectively emitted from observation directions to each position of the integrated composite scene; based on the incident coordinates, incident directions and node coordinates of each tracking ray, each surface element intersected by the tracking path and the integrated composite scene is obtained, and then the brightness temperature of each intersected surface element is determined in turn through reverse tracking, so that the radiation brightness temperature corresponding to each tracking ray is obtained, and the simulation of the sea surface ship Kelvin wake radiation brightness temperature image is realized. The application can improve the accuracy of the simulation of the sea surface ship Kelvin wake radiation brightness temperature image.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic simulation, and more particularly relates to a simulation method and system for a Kelvin wake radiation brightness temperature image of a ship on the sea. BACKGROUND

[0002] When a ship sails on the sea, the interaction between the moving ship and the sea will generate a wake. The ship wake, as a companion feature of the ship, has a wide coverage and a long duration, and its morphological characteristics are different from those of the sea background, so the geographical position of the ship can be determined by detecting the ship wake. Ship wake detection, as an auxiliary means for ship detection, is one of the research hotspots in the field of sea surveillance.

[0003] In the prior art, the radiation of the ship wake is mostly calculated by the traditional Kirchhoff approximation method. The sea surface and the ship wake scene are divided into a plurality of small facets, the emissivity of each small facet is calculated, and finally the radiation brightness temperature of the scene is calculated according to the physical temperature and the emissivity of the scene. This method does not consider the scattering and reflection of the coupling effect of the rough sea surface and the ship on the radiation signal transmission path, nor does it consider the influence of the radiation and attenuation on the received radiation signal on the transmission path. In addition, the Kirchhoff approximation method has low calculation accuracy at large incident angles, which leads to the inability to carry out radiation calculation of the wake at large incident angles. SUMMARY

[0004] In view of the above defects or improvement needs of the prior art, the application provides a simulation method and system for a Kelvin wake radiation brightness temperature image of a ship on the sea, which aims to improve the accuracy of the simulation of the Kelvin wake radiation brightness temperature image of the ship on the sea.

[0005] To achieve the above-mentioned purpose, the application provides a simulation method for a Kelvin wake radiation brightness temperature image of a ship on the sea, comprising: establishing a three-dimensional morphological model of the ship and the Kelvin wake of the ship on the sea respectively, and performing facet division on the three-dimensional morphological model to obtain the number and node coordinates of each facet in an integrated composite scene of the ship, the sea surface and the Kelvin wake of the ship on the sea;

[0006] The ship facets in the integrated composite scene are regarded as smooth facets, and the sea surface and the Kelvin wake of the ship facets are regarded as rough facets; a tracing ray is emitted from each position of the integrated composite scene to a preset observation direction;

[0007] For each tracking ray, based on the incident coordinates, incident direction of the tracking ray and the node coordinates, a line-surface intersection operation is adopted to obtain each surface element intersected by the tracking path of the tracking ray and the integrated composite scene, and then the brightness temperature of each intersected surface element is determined in sequence through backtracking, so that the corresponding radiance brightness temperature of each tracking ray is obtained, and the Kelvin wake radiance brightness temperature image simulation of the sea surface ship is realized.

[0008] The determination manner of the tracking path is as follows:

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

[0010] Further, the brightness temperature of each intersected surface element determined in sequence through backtracking comprises: the brightness temperature of the intersected surface element at the i-th level tracking direction on the current tracking path is determined according to the emissivity and reflectivity of the intersected surface element and the brightness temperature of the intersected surface element at the i+1-th level tracking direction.

[0011] The intersected surface element at the first level tracking direction is the first surface element intersected by the current tracking ray and the integrated composite scene, and the intersected surface element at the last level tracking direction is the last surface element intersected by the current tracking ray and 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.

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

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

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

[0015] If the intersecting surface elements are rough surface elements, then the brightness temperature TB of the current intersecting surface elements is... i for:

[0016]

[0017] Where, r p (θ i ;θ s ,φ s ;Δθ s ,Δφ s θ represents the reflectivity of the intersecting surface element along the i-th level tracking direction on the current tracking path; s (n), φ s (n) represents the elevation and azimuth angles of the scattered ray from the nth sub-region divided by the current intersecting surface element; Δθ s (n), Δφ s (n) represent the N sub-regions divided by the currently intersecting surface element at θ. s (n), φ s (n) represents the spacing in the direction, where 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 currently intersecting surface element. pq (θ i ;θ s ,φ s ), where pp and qp represent the same polarization and cross-polarization modes, respectively.

[0018] Furthermore, the method also includes correcting the bistatic scattering coefficient using a masking function to obtain a corrected bistatic scattering coefficient.

[0019]

[0020] Where, φ i φ 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, where i > 1; when i = 1, φ i To determine the azimuth angle between the tracking ray and the first intersecting surface element of the integrated composite scene and the radiometer, the radiometer is used to emit the tracking ray; s is the root mean square slope of the current intersecting surface element; μ is taken as μ i or μ s , corresponding to θ take θi or θ s ; erfc(·) is the complementary error function.

[0021] Further, the radiation brightness temperature T A is the brightness temperature T AP of the current tracing ray at the port surface of the radiometer antenna; wherein the brightness temperature T AP of the current tracing ray at the port surface of the radiometer antenna is:

[0022]

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

[0024] Further, the established three-dimensional model of the ship and the sea surface ship Kelvin wake is divided into surface elements to obtain the numbering and node coordinates of each surface element in the integrated composite scene of the ship, the sea surface and the ship Kelvin wake, including:

[0025] The established three-dimensional model of the ship and the sea surface ship Kelvin wake is divided into surface elements to obtain the numbering and node numbering of the ship surface elements and the sea surface ship Kelvin wake surface elements;

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

[0027] Further, the surface element is a triangular surface element, the numbering and node numbering of the ship surface element in the integrated composite scene are consistent with the numbering and node numbering of the ship surface element before merging; the numbering Num * and node numbering Node * (v1, v2, v3) of the sea surface ship Kelvin wake surface element in the integrated composite scene are:

[0028] Num * = Num + P1

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

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

[0031] Further, based on the number of the surface element, it is determined whether the current intersecting surface element is a smooth surface element or a rough surface element, comprising:

[0032] If the number of the current intersecting surface element Num* is less than or equal to P1, it is judged that the current intersecting surface element is a smooth surface element, otherwise, it is a rough surface element.

[0033] The application further provides a simulation system of a sea surface ship Kelvin wake radiance temperature image, comprising a computer readable storage medium and a processor.

[0034] The computer readable storage medium is used for storing executable instructions.

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

[0036] The application further provides a computer readable storage medium having a computer program stored thereon, wherein the program is executed by a processor to realize the simulation method of the sea surface ship Kelvin wake radiance temperature image according to any one of the above.

[0037] Overall, the above technical solutions conceived by the application can achieve the following beneficial effects:

[0038] (1) The application considers the scattering and reflection of the coupling effect of the rough sea surface and the ship on the radiative signal transmission path, and further affects the accuracy of the simulation of the sea surface ship Kelvin wake radiance temperature image. Based on this, in the application, the surface element in the integrated composite scene is divided into a smooth surface element and a rough surface element, the ship surface element is regarded as a smooth surface element, and after passing through the smooth surface element, the next level of tracking direction of the tracking ray is the direction mirror image of the incident direction. The sea surface and the ship Kelvin wake surface element are regarded as a rough surface element, and after passing through the rough surface element, the tracking ray will be scattered. Therefore, in the application, the upper hemisphere 2pi space of the rough surface element is divided into N sub-regions, and the scattering ray direction of each sub-region is regarded as the next level of tracking direction of the tracking ray after passing through the current rough surface element. In this way, the scattering and reflection of the coupling effect of the rough sea surface and the ship on the radiative signal transmission path are accurately simulated, and the accuracy of the simulation of the sea surface ship Kelvin wake radiance temperature image is improved.

[0039] (2) As preferred, for the sea surface and the ship Kelvin wake surface element (rough surface element), the surface element brightness temperature calculation method provided by the present application considers the influence of all scattering rays in the N sub-regions divided in the upper hemisphere 2pi space of the rough surface element, further improving the accuracy of the sea surface ship Kelvin wake radiation brightness temperature image simulation.

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

[0041] (4) As preferred, the present application considers the attenuation and atmospheric radiation of the tracking path when calculating the brightness temperature T AP of the current tracking ray at the radiometer antenna aperture, further improving the accuracy of the sea surface ship Kelvin wake radiation brightness temperature image simulation. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The simulation method of the sea surface ship Kelvin wake radiation brightness temperature image in the embodiment of the present application.

[0043] Figure 2 The simulation method flow chart of the sea surface ship Kelvin wake radiation brightness temperature image in the embodiment of the present application.

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

[0045] Figure 4 The Kirchhoff approximation method calculation surface element emissivity zenith angle and azimuth angle schematic diagram in the embodiment of the present application.

[0046] Figure 5 The ray tracing schematic diagram in the embodiment of the present application.

[0047] Figure 6 The millimeter wave radiation apparent brightness temperature image and the millimeter wave radiation antenna brightness temperature image of the sea surface ship and the ship wake. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0049] Embodiment 1

[0050] As Figures 1-2 shown, the embodiment of the present application provides a simulation method of sea surface ship Kelvin wake radiance brightness temperature image, mainly comprising:

[0051] S1, respectively establish a sea surface ship and a sea surface ship Kelvin wake three-dimensional shape model; and the sea surface ship three-dimensional shape model and the sea surface ship Kelvin wake three-dimensional shape model are divided into face elements, to obtain the number of each face element and the node coordinates of each face element in the integrated composite scene of the ship, sea surface and ship Kelvin wake;

[0052] S2, the ship face element in the integrated composite scene is taken as a smooth face element, and the sea surface and ship Kelvin wake face element is taken as a rough face element; from a preset observation direction, a tracking ray is respectively emitted to each position of the integrated composite scene;

[0053] S3, for each tracking ray, based on the incident coordinates, incident direction of the current tracking ray and the node coordinates of all face elements in the integrated composite scene, the line-surface intersection operation is adopted to obtain the tracking path of the current tracking ray and each face element intersected with the integrated composite scene, and then the brightness temperature of each face element intersected with the tracking path of the current tracking ray is determined in turn through the reverse tracking, so as to obtain the corresponding radiance brightness temperature of each tracking ray, and realize the radiance brightness temperature image simulation of the integrated composite scene.

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

[0055] If the face element currently intersected with the tracking ray and the integrated composite scene is a smooth face element, then the next level tracking direction of the tracking ray after passing through the current intersected smooth face element is the direction mirrored with the direction of the tracking ray incident to the current intersected smooth face element.

[0056] If the face element currently intersected with the tracking ray and the integrated composite scene is a rough face element, then the upper hemisphere 2pi space of the current intersected rough face element is divided into N sub-regions, and the next level tracking direction of the tracking ray after passing through the current intersected rough face element is the scattering ray direction of each sub-region; N≥1, and whether the current face element is a smooth face element or a rough face element is determined based on the number of each face element in the integrated composite scene.

[0057] When the tracking ray is no longer intersected with each face element in the integrated composite scene, at this time, it has been tracked to the atmosphere, the tracking of the current tracking ray is ended, and the number of all intersected face elements under the current tracking path is obtained.

[0058] As preferred, in S1, the three-dimensional shape model ζ(x, y) of the Kelvin wake of the sea surface ship is:

[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] wherein ζ kelvin (x, y) represents the wave height distribution of the Kelvin wake of the ship, 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, k = g / V 2 , V represents the ship speed, g represents the gravity acceleration, β is an integral 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 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 shape model of the sea surface ship and the three-dimensional shape model of the Kelvin wake of the sea surface ship are divided into panels to obtain the numbering of each panel and the node coordinates of each panel in the integrated composite scene of the ship, the sea surface and the Kelvin wake of the ship, including:

[0065] The three-dimensional model of the sea surface ship and the three-dimensional model of the Kelvin wake of the sea surface ship are divided into panels, to obtain the number of the divided sea surface ship panel and the node number of the panel, and the node number of the Kelvin wake panel of the sea surface ship and the node number of the panel, and the node coordinates of each panel are determined by the node number of each panel; and the number of the sea surface ship and the Kelvin wake panel of the sea surface ship and the node number of the panel are merged to obtain the number of each panel and the node number of the panel in the integrated composite scene of the sea surface, the ship and the Kelvin wake of the ship, and the node coordinates of each merged panel are determined by the node number of the merged panel.

[0066] Preferably, in the embodiment of the present application, the panel of the Kelvin wake of the sea surface ship is divided into a triangular panel.

[0067] In the embodiment of the present application, if the row m of the Kelvin wake panel of the sea surface ship in the simulation scene matrix is even, the node number of the three vertices of the Kelvin wake triangular panel of the sea surface ship is represented as:

[0068]

[0069] If the row m of the Kelvin wake panel of the sea surface ship in the simulation scene matrix is odd, the node number of the three vertices of the Kelvin wake triangular panel of the sea surface ship is represented as:

[0070]

[0071] Wherein, m' represents the column number of the Kelvin wake panel of the sea surface ship in the simulation scene matrix, and the value starts from 1; B x The column number 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 surface ship; represents the floor operator, represents the ceiling operator.

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

[0073] In the embodiment of the present application, the three-dimensional model of the sea surface ship is obtained by using a commonly used three-dimensional modeling software, and the obtained three-dimensional model of the sea surface ship contains the number of the divided ship panel, the node number and the node coordinates. As shown in the following figure, Figure 3 The three-dimensional model of the sea surface ship and the three-dimensional model of the ship wake in the embodiment of the present application.

[0074] In the embodiment of the present application, the number of the merged sea surface ship panel and the node number of the panel are unchanged, and the number of the merged Kelvin wake panel of the sea surface ship Num *Node * (v1,v2,v3) is:

[0075] Num * =Num+P1

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

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

[0078] In S2, a radiometer emits a tracking ray from a preset observation direction to each position of the integrated composite scene. As a preferred, the tracking ray emitted by the radiometer is a millimeter wave. The brightness temperature image in the embodiment of the present application is a millimeter wave brightness temperature image.

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

[0080] If the total number of ship cells is P1, the number of sea surface and ship Kelvin wake cells is P2, when the number of the intersected cell Num* is less than or equal to P1, it is judged that the intersected cell is a smooth cell, when the number of the intersected cell Num* is greater than P1, it is judged that the intersected cell is a rough cell.

[0081] In S3, the brightness temperature of each cell intersected by the current tracking ray tracking path is determined in turn by backtracking, wherein the brightness temperature of the cell intersected in the i-th level tracking direction on the current tracking path is determined according to the emissivity, reflectivity or scattering coefficient of the intersected cell and the brightness temperature of the cell intersected in the i+1-th level tracking direction; wherein the brightness temperature of the cell intersected in the last level tracking direction is determined by the emissivity, reflectivity or scattering coefficient of the intersected cell and the atmospheric brightness temperature.

[0082] In the embodiment of the present application, the first cell intersected by the current tracking ray and the integrated composite scene is the cell intersected in the first level tracking direction on the current tracking path, the second cell intersected by the reflected ray or scattered ray of the tracking ray after passing through the first cell again and the integrated composite scene is the cell intersected in the second level tracking direction, and so on until the current tracking ray is incident to the atmosphere. Before being incident to the atmosphere, the last cell intersected by the current tracking ray and the integrated composite scene is the cell intersected in the last level tracking direction on the current tracking path.

[0083] If the intersecting surface elements are smooth, then the brightness temperature of the intersecting surface elements along 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] Among them, TB i T i and e p (θ i θ represents the brightness temperature, physical temperature, and emissivity of the smooth surface element intersecting along the i-th level tracking direction on the current tracking path, respectively. i Let p represent the polarization mode; TB is the angle between the tracking ray and the normal vector of the intersecting surface element under the i-th level tracking direction, i.e., the incident angle of the tracking ray on the intersecting surface element under the i-th level tracking direction. i+1 This is the brightness temperature of the next level intersecting surface element traced by the ray in the i-th level tracing direction on the current tracing path, which is also the brightness temperature of the intersecting surface element in the (i+1)-th level tracing direction on the current tracing path.

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

[0087]

[0088] Where μ2 and ε2 are the magnetic permeability and dielectric constant of the ship material, respectively; 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 elements are rough surface elements, then the emissivity e of the rough surface elements is... p (θ) can be expressed as:

[0090]

[0091] Where, r p (θ i θ represents the reflectivity of a rough surface element. s and φ s These are the scattering elevation and azimuth angles of the currently intersecting rough surface element, respectively.

[0092] In this embodiment of the invention, the upper hemisphere 2π space of the rough surface element is divided into N sub-regions. Then, the reflectivity r of the surface elements intersecting in the i-th level tracking direction on the current tracking path is... p (θ i ;θ s ,φ s ;Δθs ,Δφ s ), emissivity e p (θ i ) and brightness temperature TB i It can be calculated using the discrete summation method:

[0093]

[0094] Where, θ s (n), φ s (n) represents the pitch and azimuth angles of the scattered rays from the nth sub-region of the intersecting rough surface element (current intersecting rough surface element) along the i-th level tracking direction on the current tracking path; Δθ s (n), Δφ s (n) represent the N sub-regions of the current rough surface element at θ. s (n), φ s (n) represents the interval in the direction, where N is the number of sub-regions divided in the upper hemisphere 2π space of the currently intersecting rough surface element, and 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 σ is the bistatic scattering coefficient of the currently intersecting rough surface element. pq (θ i ;θ s ,φ s ), pp and qp represent the same polarization mode and cross-polarization mode, respectively; TB i+1 [θ s (n),φ s (n) represents the current tracking direction as θ s (n), φ s The brightness temperature of the next level intersecting surface element traced by the ray tracing of (n).

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

[0096]

[0097] Among them, P pq The total power at the receiving antenna (radiometer) The scattering field of the currently intersecting rough surface elements. for The conjugate of the current intersection rough surface element center point to the observation point distance, The total incident power of the current tracking ray, A0 is the irradiation area.

[0098] In the embodiment of the present application, the scattering field of the current intersection rough surface element

[0099]

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

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

[0102]

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

[0104] In S3, the radiation brightness temperature T corresponding to the current tracking ray A The brightness temperature T of the current tracking ray at the radiometer antenna aperture. AP (θ,φ; p) Antenna brightness temperature after antenna pattern weighting:

[0105]

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

[0107]

[0108] Among them, T B (θ, φ; p) represents the brightness temperature of the surface element intersecting the first-level tracking direction on the current tracking path, i.e., the brightness temperature of the first surface element intersecting the current tracking ray with the integrated composite scene. θ and φ are the elevation and azimuth angles of the radiometer scan, respectively, i.e., θ and φ are the incident angles of the current tracking ray on the first surface element intersecting the integrated composite scene (θ when i = 1). i The azimuth angle between the first intersecting surface element of the current tracking ray and the integrated composite scene and the radiometer (φ when i=1). i ), p represents the polarization mode; L a To track atmospheric attenuation along the path, T atmosphere To track atmospheric radiation along the transmission path, this technique simultaneously considers atmospheric attenuation and radiation along the transmission path, further improving the accuracy of the simulation.

[0109] Using the above method, the radiation brightness temperature of each tracking ray is obtained, thereby obtaining a millimeter-wave radiation image of the entire integrated composite scene.

[0110] In the embodiment of the present application, aiming at the problem that the calculation precision of Kelvin wake radiation calculation is not high at large incidence angle, and the coupling effect of sea surface and ship is not considered, firstly, a three-dimensional physical model of sea surface and ship wake is established, and surface element division is carried out. Then, the tracking rays are emitted from the observation direction, the ray-surface intersection operation is carried out, the transmission path of the radiation signal is calculated, and the attenuation and radiation on the transmission path are considered. The surface element emissivity calculated by the Kirchhoff approximation method at large incidence angle is modified by introducing the shielding function, so that the wake brightness temperature is more accurately calculated. Finally, the apparent brightness temperature reaching the antenna aperture and the antenna brightness temperature weighted by the antenna pattern are calculated, and the millimeter wave radiation brightness temperature image of the sea surface ship Kelvin wake at large incidence angle is simulated, which provides a basis for the millimeter wave radiation characteristics of the wake and the detection of the ship.

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

[0112] Figure 6 It is the millimeter wave radiation apparent brightness temperature image (left) and the millimeter wave radiation antenna brightness temperature image (right) of the sea surface ship and the ship wake simulated in the embodiment of the present application. Among them, the sea surface ship is a metal ship on the sea surface, the length is 75m, the width is 10m, the draft is 5m, the ship speed is 5m / s, the sea surface wind speed is 2.5m / s, and the observation pitch angle is-25°. As can be seen from Figure 6 , compared with the sea surface background, the Kelvin wake presents high brightness temperature, the ship body part of the sea surface ship presents high brightness temperature, the deck part of the sea surface ship presents low brightness temperature, and the sea surface ship can be seen when observed at large incidence angle (the embodiment of the coupling effect between the rough sea surface and the ship), at this time, the reflection presents low brightness temperature.

[0113] The present application can simulate the millimeter wave radiation image of the sea surface ship Kelvin wake under different observation parameters, and provides effective support for analyzing the radiation characteristics of the sea surface ship Kelvin wake.

[0114] Embodiment 2

[0115] The embodiment of the present application provides a simulation method of a sea surface ship Kelvin wake radiation brightness temperature image, including a memory and a processor, the memory stores a computer program, and the processor realizes the steps of the simulation method of the sea surface ship Kelvin wake radiation brightness temperature image in the above-mentioned embodiment 1 when executing the computer program.

[0116] The related technical solutions are the same as above, and details are not repeated here.

[0117] Embodiment 3

[0118] The embodiment of the present application provides a computer readable storage medium, which stores a computer program, and the computer program realizes the steps of the simulation method of the sea surface ship Kelvin wake radiation brightness temperature image in the above-mentioned embodiment 1 when executed by a processor.

[0119] Specifically, the memory can include a high-speed random access memory, and can also include a non-volatile memory, for example, 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 memory devices.

[0120] The related technical solutions are the same as above, and details are not repeated here.

[0121] Embodiment 4

[0122] The embodiment of the present application provides a computer program product, including a computer program, when the computer program runs on a computer, so that the computer executes the steps of the simulation method of the sea surface ship Kelvin wake radiation brightness temperature image in the above-mentioned embodiment 1.

[0123] The related technical solutions are the same as above, and details are not repeated here.

[0124] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A simulation method of sea surface ship Kelvin wake radiance brightness temperature image, characterized in that, The method comprises the following steps: Three-dimensional shape models of a ship and a ship Kelvin wake on the sea surface are respectively established, and are divided into surface elements to obtain the numbers and node coordinates of the surface elements in an integrated composite scene of the ship, the sea surface and the ship Kelvin wake; The ship surface elements in the integrated composite scene are taken as smooth surface elements, and the sea surface and the ship Kelvin wake surface elements are taken as rough surface elements; Tracking rays are respectively emitted from each position of the integrated composite scene to a preset observation direction; For each tracking ray, the node coordinates, the incident direction and the incident coordinates of the tracking ray are used to obtain the surface elements intersected by the tracking path of the tracking ray and the integrated composite scene by line-surface intersection operation, and the brightness temperatures of the intersected surface elements are sequentially determined by backtracking to obtain the corresponding radiative brightness temperature of each tracking ray, thereby realizing simulation of a radiative brightness temperature image of the ship Kelvin wake on the sea surface. The determination manner of the tracking path is as follows: If the current intersected facet is a smooth facet, the next tracking direction of the tracking ray after passing through the current intersected facet is a direction mirrored to the direction of the tracking ray incident to the current intersected facet; if the current intersected facet is a rough facet, the upper hemisphere 2π space of the current intersected facet is divided into N sub-regions, and the next tracking direction of the tracking ray after passing through the current intersected facet is a scattered ray direction of each sub-region; N ≥1, and whether the current intersected facet is a smooth facet or a rough facet is determined based on the number of the facet.

2. The method of simulating sea surface ship Kelvin wake radiance temperature images according to claim 1, wherein, The step of determining the brightness temperature of each intersecting surface element in turn by backtracking comprises: i determining the brightness temperature of the intersecting surface element in the first i +1 level tracking direction according to the emissivity and reflectivity of the intersecting surface element and the brightness temperature of the surface element in the first i +1 level tracking direction. The first intersected surface element is the first surface element intersected by the current tracking ray and the integrated composite scene in the first-level tracking direction, and the last intersected surface element is the last surface element intersected by the current tracking ray and the integrated composite scene in the last-level tracking direction; 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 of simulating sea surface ship Kelvin wake radiance temperature images according to claim 2, wherein, If the intersected surface element is a smooth surface element, the brightness temperature of the current intersected surface element is as follows: in, TB i , T i and These are the first two digits on the current tracking path. i Brightness temperature, physical temperature, and emissivity of intersecting smooth surface elements in the tracking direction. For the first i The incident angle of the tracking ray on the intersecting surface element in the tracking direction. p Indicates the polarization mode; TB i+1 For the first on the current tracking path i Brightness temperature of intersecting surface elements in the +1 level tracking direction; If the intersecting facet is a rough facet, the brightness temperature of the current intersecting facet is: ​ wherein, is the reflectivity of the intersecting cell in the current tracking direction on the current tracking path; i , are the scattering elevation and azimuth angles of the scattered rays of the i-th sub-region of the current intersecting cell, respectively; n , are the intervals of the i-th sub-region of the current intersecting cell in the and directions, respectively, N , T is the physical temperature of the intersecting cell; and denote the bistatic scattering coefficients of the current intersecting cell , pp and qp denote the co-polarized and cross-polarized, i.e. and denote the co-polarized and cross-polarized bistatic scattering coefficients of the current intersecting cell.​​​​ 4. The method of simulating sea surface ship Kelvin wake radiance temperature images according to claim 3, wherein, Also included is employing a masking function on the bistatic scattering coefficient to obtain a modified bistatic scattering coefficient : wherein is the azimuth angle between the current intersection patch and the first intersection patch on the current tracking path in the tracking direction of order 1, i- 1, and i > 1; i = 1, is the azimuth angle between the first intersection patch of the integrated composite scene and the radiometer used to emit the tracking ray; s is the root mean square slope of the current intersection patch; = 1, or , corresponding to = 1, or ; is the complementary error function.

5. The method of simulating a sea surface ship Kelvin wake radiance temperature image according to claim 3 or 4, characterized in that, the current tracked ray's corresponding radiance brightness temperature the current tracked ray's brightness temperature at the radiometer antenna aperture the current tracked ray's brightness temperature at the radiometer antenna aperture is: wherein, is the brightness temperature of the first facet that the current traced ray intersects with the integrated composite scene, L a is the attenuation of the atmosphere along the traced path, T atmosphere is the atmospheric emission along the traced path.

6. The method according to any one of claims 1 to 4, wherein The three-dimensional shape models of the ship and the ship Kelvin wake on the sea surface are divided into surface elements to obtain the numbers and node coordinates of the surface elements in an integrated composite scene of the ship, the sea surface and the ship Kelvin wake, which comprises the following steps: The three-dimensional shape models of the ship and the ship Kelvin wake on the sea surface are divided into surface elements to obtain the numbers and node coordinates of the surface elements in an integrated composite scene of the ship, the sea surface and the ship Kelvin wake, which comprises the following steps: The numbers and node numbers of the ship surface elements and the ship Kelvin wake surface elements are merged to obtain the numbers and node numbers of the surface elements in the integrated composite scene, and the node coordinates of the surface elements in the integrated composite scene are determined by the node numbers of the surface elements in the integrated composite scene.

7. The method of simulating a sea surface ship Kelvin wake radiance temperature image according to claim 6, wherein, The surface elements are triangular surface elements, the numbers and node numbers of the ship surface elements in the integrated composite scene are consistent with the numbers and node numbers of the ship surface elements before merging; The number of Kelvin wake surface elements of a sea surface ship in the integrated composite scene And node number Respectively: wherein, , denote the number of the Kelvin wake surface element and the node number of the sea surface ship before merging, respectively, denote the three vertex coordinates of the triangular surface element, is the total number of the sea surface ship surface element nodes.

8. The method of simulating a sea surface ship Kelvin wake radiance temperature image according to claim 7, wherein, The numbers of the surface elements are used to determine whether the current intersected surface element is a smooth surface element or a rough surface element, which comprises the following steps: If the current intersected facet number is smooth, otherwise, it is rough.

9. A simulation system of sea surface ship Kelvin wake radiance brightness temperature image, characterized in that, The computer readable storage medium and the processor are included; 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 radiative brightness temperature image of the ship Kelvin wake on the sea surface according to any one of claims 1-8.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to realize the simulation method of the radiative brightness temperature image of the ship Kelvin wake on the sea surface according to any one of claims 1-8.

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