Forward modeling method and system for scattering characteristics of metal-medium mixed dynamic group targets

Abstract

The present invention discloses a forward modeling method and system for the scattering characteristics of a metal-medium mixed dynamic group target. Specifically, the method comprises the following steps: geometrically modeling the target, decomposing the target into multiple components based on sudden changes in the target surface normal, performing triangulated facet subdivision on each component, and setting initial parameters; using the SBR method to perform occlusion judgment and ray tracing on all facets, classifying the rays, calculating the scattering field contribution of the classified rays, sorting the scattering fields of the classified rays from large to small, and retaining strong scattering centers whose scattering field contribution is greater than a threshold; reading the paths of the selected strong scattering centers to determine whether they are single-action rays or multiple-action rays, and obtaining equivalent points for multiple-action rays using the phase equivalence method; and determining the types of all equivalent points based on the obtained equivalent points and field values, thereby determining the parameters of the scattering centers. The present invention has the advantages of high accuracy, high modeling efficiency, accurate positioning, and concise description.

Description

Technical Field

[0001] The present invention relates to the field of target characteristic modeling and electromagnetic computing technology, in particular to a forward modeling method and system for scattering characteristics of a metal-medium mixed dynamic group target. Background Art

[0002] With the continuous development of radar systems, radar target recognition technology has become an important research direction. In recent years, the description of radar scattering centers has attracted widespread attention in the field of target recognition and characteristic analysis. Research on target characteristics has also become more in-depth. It is no longer limited to viewing the target as a fixed ideal point, but rather as a scattering center with different scattering characteristics, which exhibit different characteristics at different locations on the target.

[0003] There are two common approaches to parameterizing scattering centers: inverse and forward. The inverse approach analyzes and processes radar data to infer information such as the scattering center's location, intensity, and frequency characteristics, enabling target identification and analysis. The forward approach, on the other hand, considers the target's physical properties and scattering process, using theoretical analysis and approximate analytical derivations to isolate and describe the scattering centers and construct a parameterized model of the target's attributes. Compared to the inverse approach, the forward approach requires less computation and produces results with clear physical meaning, as it eliminates the need for an inversion process.

[0004] Patent CN110083915A discloses a forward automated modeling method for scattering centers of high-frequency radar targets. This method automatically outputs scattering center model parameters, is low-cost, and requires minimal computation, meeting the modeling requirements for online, near-real-time radar target identification. However, this method has limitations when processing mixed metal and dielectric targets, making it unsuitable for such targets.

[0005] The attribute scattering center model can not only be used to describe the characteristics of a single scattering center, but also to describe the characteristics of multiple scattering centers on a complex target through a series of parameters. In the attribute scattering center model, each scattering center is assigned a set of parameters that describe in detail the physical characteristics of the scattering center, such as size, shape, and relative position, and reflect the complex relationship between the scattering characteristics of the scattering structure and the radar operating frequency and observation angle. In recent years, a variety of methods for establishing attribute scattering center models have emerged. Reference 1 (Xing XY, Yan H, Yin HC, et al. A bistatic attributed scattering center model for SAR ATR [J]. IEEE Transactions on Antennas and Propagation, 2021, 69 (11): 7855-7866.) proposed a two-dimensional attribute scattering center model for bistatic SAR data feature extraction. However, the algorithm is an inverse method with a high processing time cost, and the performance of the scattering center model still has room for improvement. Reference 2 (Liu J, He S, Zhang L, et al. An automatic and forward method to establish 3-D parametric scattering center models of complex targets for target recognition [J]. IEEE Transactions on Geoscience and Remote Sensing, 2020, 58 (12): 8701-8716.) proposes a forward modeling method for a scattering center model of known complex radar target attributes. This method obtains the target attribute scattering center model parameters from the target's CAD model structure, extending the scattering mechanism of the distributed scattering center from typical structures to curved surfaces. However, this method cannot obtain target parameters when dealing with parametric modeling of non-cooperative targets, and for complex structures, more reflections need to be considered, resulting in a large amount of calculation and low modeling efficiency. Summary of the Invention

[0006] The object of the present invention is to provide a forward modeling method and system for the scattering characteristics of a metal-medium mixed dynamic group target with high precision, high efficiency, accurate position and concise description.

[0007] The technical solution for achieving the purpose of the present invention is: a forward modeling method for the scattering characteristics of a metal-medium mixed dynamic group target, comprising the following steps:

[0008] Step 1: geometrically model the target. Based on the sudden change of the target surface normal, decompose the target into multiple components, perform triangulation on each component, and set the initial parameters.

[0009] Step 2: Use the bouncing ray (SBR) method to perform occlusion judgment and ray tracing on all surface elements. The rays are classified according to the number of interactions and interaction mechanisms between the rays and the surface elements. The scattering field contribution of the classified rays is calculated by combining the reflection coefficient and the transmission coefficient. The scattering fields of the classified rays are sorted from large to small, and strong scattering centers with scattering field contributions greater than the set threshold are retained.

[0010] Step 3: Read the path of the screened strong scattering center to determine whether it is a single-action ray or a multiple-action ray. For the multiple-action ray, find the equivalent point using the phase equivalence method;

[0011] Step 4: Use the obtained equivalent points and field values ​​to determine the types of all equivalent points and determine the parameters of the scattering center.

[0012] A forward modeling system for scattering characteristics of a metal-medium mixed dynamic group target, the system is used to implement the forward modeling method for scattering characteristics of a metal-medium mixed dynamic group target, the system includes a geometric modeling module, a ray classification module, an equivalent point determination module and a scattering center determination module, wherein:

[0013] The geometric modeling module performs geometric modeling on the target, decomposes the target into multiple components based on the sudden change of the target surface normal, and performs triangulation on each component to set initial parameters;

[0014] The ray classification module uses the bouncing ray (SBR) method to perform occlusion judgment and ray tracing on all surface elements, and classifies the rays according to the number of interactions and interaction mechanisms between the rays and the surface elements. It calculates the scattering field contribution of the classified rays by combining the reflection coefficient and the transmission coefficient, sorts the scattering fields of the classified rays in descending order, and retains strong scattering centers whose scattering field contributions are greater than a set threshold.

[0015] The equivalent point obtaining module reads the path of the screened strong scattering center, determines whether it is a single-action ray or a multiple-action ray, and obtains the equivalent point for the multiple-action ray using the phase equivalence method;

[0016] The scattering center determination module determines the types of all equivalent points through the obtained equivalent points and field values, and determines the parameters of the scattering center.

[0017] A mobile terminal comprises a memory, a processor and a computer program stored in the memory and operable on the processor. When the processor executes the program, the forward modeling method of the metal-medium mixed dynamic group target scattering characteristics is realized.

[0018] Compared with the prior art, the present invention has the following significant advantages: (1) the scattered field solved by using the improved reflection coefficient and transmission coefficient formula is highly accurate; (2) by applying the phase equivalence method, the position of the equivalent point can be solved more accurately, the time required is short, and the calculation efficiency is high; (3) through a more comprehensive and accurate model description, the content of the scattering center forward modeling method is enriched, and an economical and efficient solution is provided for the identification of target characteristics of metal medium mixed groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the forward modeling method of the metal-medium mixed dynamic group target scattering characteristics of the present invention.

[0020] Figure 2 Schematic diagram of the geometric structure of the spherical-conical target model in an embodiment of the present invention.

[0021] Figure 3 Schematic diagram of the geometric component decomposition of the metal-medium mixed group target model in an embodiment of the present invention.

[0022] Figure 4 3 is a schematic diagram of the geometric component decomposition of the model of the metal-medium mixed group target at time t=0 in the embodiment.

[0023] Figure 5 1 is a schematic diagram of the geometric component decomposition of the model of the metal-medium mixed group target at time t=1 in the embodiment.

[0024] Figure 6 3 is a comparison diagram of the two-dimensional image results of the metal-medium mixed group target at time t=0 in the embodiment.

[0025] Figure 7 3 is a comparison diagram of the two-dimensional image results of the metal-medium mixed group target at time t=1 in the embodiment. DETAILED DESCRIPTION

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Combine Figure 1 The present invention provides a forward modeling method for scattering characteristics of a metal-medium mixed dynamic group target, comprising the following steps:

[0028] Step 1: geometrically model the target. Based on the sudden change of the target surface normal, decompose the target into multiple components, perform triangulation on each component, and set the initial parameters.

[0029] Step 2: Use the bouncing ray (SBR) method to perform occlusion judgment and ray tracing on all surface elements. The rays are classified according to the number of interactions and interaction mechanisms between the rays and the surface elements. The scattering field contribution of the classified rays is calculated by combining the reflection coefficient and the transmission coefficient. The scattering fields of the classified rays are sorted from large to small, and strong scattering centers with scattering field contributions greater than the set threshold are retained.

[0030] Step 3: Read the path of the screened strong scattering center to determine whether it is a single-action ray or a multiple-action ray. For the multiple-action ray, find the equivalent point using the phase equivalence method;

[0031] Step 4: Use the obtained equivalent points and field values ​​to determine the types of all equivalent points and determine the parameters of the scattering center.

[0032] As a specific example, in step 1, the target is geometrically modeled. Based on the sudden change of the target surface normal, the target is decomposed into multiple components, and each component is triangulated. The initial parameters are set as follows:

[0033] Step 1.1, divide the target into metal parts and dielectric parts, perform geometric modeling on the target, and decompose the target into M parts based on the sudden change of the target surface normal. The M parts are numbered and marked as I1, I2, I3, ..., I M ;

[0034] The present invention uses a spherical cone target model as an example for illustration. The spherical cone target size structure is as follows: Figure 2 First, all targets are geometrically modeled, and the targets are decomposed into multiple parts according to the sudden change of the target surface normal, and each part is numbered, as shown in Figure 3 As shown, the dielectric-metal mixed targets are numbered 1 to 15, where the target color of yellow represents metal, and the target color of sky blue represents dielectric.

[0035] Step 1.2: Set the mesh size of metal components to λ10 and the mesh size of dielectric components to less than λ10, where λ is the wavelength of the incident electromagnetic wave. Perform triangular facet meshing on each component, number each triangular facet and the corresponding nodes, calculate the center point of each triangular facet, and associate each triangular facet with the part number of the component to which it belongs.

[0036] Step 1.3: Set the initial radar incident direction and receiving direction They are:

[0037]

[0038]

[0039] Where θ and Represent the pitch angle and azimuth angle of the radar incident direction in the spherical coordinate system respectively; set the dielectric parameters and magnetic permeability of different dielectric components to be ε ri =ε r ' i -jε r ″ i and μ ri =μ r ' i -jμ r ″ i , where i represents different dielectric components.

[0040] As a specific example, in step 2, the bouncing ray (SBR) method is used to perform occlusion judgment and ray tracing on all surface elements. The rays are classified according to the number of interactions and interaction mechanisms between the rays and the surface elements. The scattering field contribution of the classified rays is calculated by combining the reflection coefficient and the transmission coefficient. The scattering fields of the classified rays are sorted from large to small, and strong scattering centers whose scattering field contributions are greater than the set threshold are retained, as follows:

[0041] Step 2.1: Use the SBR method to trace all unobstructed pixels. Ray r j Acting on the center Q of the triangle j , we get ray r j The path is marked with part number I rj =[I Q1 ,I Q2 ,...,I Qm ]; at the same time, record whether the ray is reflected or transmitted at each ejection point, using [T1, T2, ..., T N ] indicates that when T = 1, it indicates reflection, and when T = 2, it indicates transmission, and the ray path r is obtained. j The corresponding action sequence

[0042] Step 2.2: For rays propagating inside the target, if the amplitude of the ray at the current bin is less than the set threshold (1e-4) during the ray propagation inside the dielectric body, it is considered that the ray cannot be transmitted inside the dielectric body and is discarded. Rays with amplitudes greater than the threshold (1e-4) at the current bin are retained.

[0043] Step 2.3: For the case where the ray propagates outside the target, first classify the ray to determine whether it is a single-action ray or a multiple-action ray:

[0044] For a primary action ray, if the angle between the reflection direction and the radar receiving direction is greater than 90°, the ray is discarded; the rays whose angle between the reflection direction and the radar receiving direction is less than or equal to 90° are retained;

[0045] For multiple-action rays, if the number of ray bounces exceeds the set maximum number of 8 times or the angle between the last reflection direction or transmission direction and the radar receiving direction is greater than 90°, the ray will be discarded; rays with less than or equal to 8 bounces and the angle between the last reflection direction or transmission direction and the radar receiving direction is less than or equal to 90° will be retained;

[0046] Step 2.4: record the media components that the incident rays pass through from the time of incident to the time of exit, count the rays that finally hit the outer surface of the target, and classify the rays according to the number of times they act and the mechanism of action to form a ray set V = {r j ,j=1,2,...,N}, where N is the total number of rays that meet the conditions;

[0047] Step 2.5, using the improved reflection coefficient and transmission coefficient formulas, calculate the scattered field contribution of the subset of the classified ray total set;

[0048] Step 2.6. Calculate the size of the scattering field of each ray subset, sort the scattering fields of the ray subsets from large to small, and screen them by comparing them with a preset threshold size. If the scattering field of a ray subset is smaller than the threshold, it is eliminated; if it is larger than the threshold, it is retained. Finally, the scattering fields of P strong scattering centers are obtained.

[0049] As a specific example, in step 2.5, the scattered field contribution of the subset of the total set of classified rays is calculated by combining the improved reflection coefficient and transmission coefficient formulas; specifically, as follows:

[0050] Step 2.5.1. For dielectric targets, the calculation of the scattered field is divided into two cases: one is when the ray is emitted from the outer surface of the dielectric target to the inner surface of the dielectric target; the other is when the ray is emitted from the inner surface of the dielectric target to the outer surface of the dielectric target;

[0051] For the first case, when the ray is emitted from the outer surface of the dielectric target to the inner surface of the dielectric target, there are only incident fields and reflected fields above the outer surface of the dielectric target, so the equivalent current on the surface of the dielectric target is and equivalent magnetic current They are:

[0052]

[0053]

[0054] For the second case, when the ray is emitted from the inner surface of the dielectric target to the outer surface of the dielectric target, there is only a transmission field above the outer surface of the dielectric target, so the equivalent current on the surface of the dielectric target is and equivalent magnetic current They are:

[0055]

[0056]

[0057] The contribution of the scattered field is calculated using triangular surface elements. The total scattered field contribution of the target is the equivalent current and equivalent magnetic current The sum of the scattered fields generated is expressed as:

[0058]

[0059] Step 2.5.2: For metal targets, since there is only equivalent current on the target surface but no equivalent magnetic current,

[0060] Because the reflected electric field satisfies:

[0061]

[0062] The transmitted electric field satisfies:

[0063]

[0064] Therefore, to calculate the reflection field and transmission field of the target, the corresponding reflection coefficient and transmission coefficient must be obtained;

[0065] For vertically polarized waves, the reflection coefficient R ⊥ and the transmission coefficient T ⊥ They are:

[0066]

[0067]

[0068] For a flat polarized wave, the reflection coefficient R || and the transmission coefficient T || They are:

[0069]

[0070]

[0071] Among them, the relative dielectric parameters and magnetic permeability of medium i are εri =ε′ ri -jε″ ri and μ ri =μ′ ri -jμ″ ri ; is the wave vector in medium i; ξ i is the angle between the wave vector and the normal in medium i, which is taken as the acute angle;

[0072] As a specific example, in step 3, the path of the screened strong scattering center is read to determine whether it is a single-action ray or a multiple-action ray. For the multiple-action ray, the equivalent point is obtained by the phase equivalence method, as follows:

[0073] Step 3.1, read the path of the screened strong scattering center to determine whether it is a single action ray or a multiple action ray;

[0074] Step 3.2: For the ray that acts once, directly use the center point of the triangle element as the equivalent point. for:

[0075]

[0076] Among them, (x n ,y n ,z n ) represents the coordinates of the center point of the triangle surface element, and i represents the number of times the ray interacts with the triangle surface element;

[0077] Step 3.3: For multiple action rays, use phase equivalence to find the equivalent point. The formula is:

[0078]

[0079] in, represents the wave vector, i represents the number of interactions between the ray and the surface element, i≥2; j represents the ray action mechanism, j=1 represents the ray reflection, j=2 represents the ray transmission; Indicates the coordinates of the center point when the ray interacts with the triangle element for the i-th time, Indicates the equivalence point;

[0080] One equation cannot be solved by formula (1) There are three unknowns in the equation, so we can make the following approximation: let the pitch angle θ and the azimuth angle Each ray is deflected by the same small angle, which can be set to 0.0005°. At this time, it can be approximately considered that the contact point of the ray with the surface element and the direction of the wave vector do not change in the middle process of propagation, except for the direction of the last wave vector.

[0081] When θ-0.0005°, When , formula (1) can be rewritten as:

[0082]

[0083] in, Represents the wave vector when the ray is last reflected or transmitted; represents the wave vector, i represents the number of interactions between the ray and the surface element, i≥2; j represents the ray action mechanism, j=1 represents the ray reflection, j=2 represents the ray transmission; Indicates the coordinates of the center point when the ray interacts with the triangle element for the i-th time, Indicates the equivalence point;

[0084] When θ+0.0005°, When , formula (1) can be rewritten as:

[0085]

[0086] in, Represents the wave vector when the ray is last reflected or transmitted; represents the wave vector, i represents the number of interactions between the ray and the surface element, i≥2; j represents the ray action mechanism, j=1 represents the ray reflection, j=2 represents the ray transmission; Indicates the coordinates of the center point when the ray interacts with the triangle element for the i-th time, Indicates the equivalence point;

[0087] By combining equations (1), (2) and (3), we can obtain the equivalent point The only solution of .

[0088] As a specific example, in step 4, the types of all equivalent points are judged by the obtained equivalent points and field values, and the parameters of the scattering center are determined as follows:

[0089] Step 4.1: Although the ideal point scattering center model is simple, it cannot describe the relationship between frequency and orientation, nor can it accurately reflect the scattering characteristics of the target. According to the attribute scattering center model theory, the target scattering field is expressed as:

[0090]

[0091] Among them, A i is the amplitude of each scattering center; f represents the size of the step frequency, f c represents the size of the center frequency; c represents the speed of light; α i is the frequency dependence factor; γ i The factor that represents the dependence of the amplitude of the local scattering center on the azimuth; L irepresents the length of the i-th scattering center, when L i When it is 0, it represents the local scattering center. i ≠0 and γ i = 0 represents a distributed scattering center; according to the dependence of the scattering mechanism on the azimuth angle, the attenuation exponential function is used to describe the local scattering center, while the sinc function is used to describe the distributed scattering center; x i 、y i Indicates the size of the scattering center in the range and azimuth directions; Indicates the azimuth angle of the radar, Indicates the center azimuth of the radar;

[0092] Step 4.2, determine the frequency dependent parameters:

[0093] The frequency dependence factor α of the scattering structure and the length L of the scattering center are determined as follows: cylindrical surface, α = 0.5, L > 0; flat plate, α = 1.0, L > 0; sphere α = 0.0, L = 0; top hat structure: α = 0.5, L = 0; dihedral angle: α = 1.0, L > 0; trihedral angle: α = 1.0, L > 0; edge diffraction: α = -0.5, L > 0; angular diffraction: α = -1.0, L = 0;

[0094] For rays that are reflected only once, the α of the component corresponding to the strong scattering center is the α of the entire component. For rays that are reflected multiple times, each component has a corresponding α when the ray interacts with the component. The α of the coupled scattering center is obtained by multiplying the α corresponding to the component at each reflection of the ray.

[0095] Step 4.3, determine the length parameter:

[0096] Calculate the projection of the equivalent point in the distance direction and azimuth direction for all rays in the ray set, denoted as U m and V m , the maximum value of the upward projection is: maximum value U max =(U m ) max , minimum value U min =(U m ) min ; The maximum value of the projection in the azimuth direction is: maximum value V max =(V m ) max , minimum value V min =(V m ) min , then the upward projection length of the set is L U =U max -U min , the projection length in the azimuth direction is L V =V max-V min ;

[0097] Step 4.4: Determine the amplitude and position parameters:

[0098] (1) For a distributed scattering center, if the projection length in the distance direction of the ray set is less than the set threshold, its length in the azimuth direction is L V The amplitude parameter E is the sum of the amplitudes of the equivalent points that are not eliminated in the ray set, and the position parameter z is half of the sum of the maximum and minimum values ​​of the equivalent points in the ray set in the azimuth direction, expressed as follows:

[0099] E=E1+E2+···+E p

[0100]

[0101] Among them, E1, E2, ···, E p Represents the amplitude of the first p equivalent points in the ray set; z min and z max Respectively represent the positions of the equivalent point at the minimum and maximum values ​​of the azimuth upward projection;

[0102] (2) For a localized scattering center, if the azimuth projection length in the ray set is less than the set threshold, its azimuth length is 0, and the frequency dependence factor is also 0. The amplitude parameter E is the accumulation of the amplitudes of the equivalent points that are not eliminated in the ray set, and the position parameter z is the accumulation of the sum of all equivalent reflection points in the ray set divided by the total number of equivalent reflection points, expressed as follows:

[0103] E=E1+E2+···+E p

[0104]

[0105] Among them, E1, E2, ···, E p Represent the amplitudes of the first p equivalent points in the ray set; z1,z2,···,z p They represent the positions of the first p equivalent points in the set, and p represents the number of equivalent points;

[0106] (3) If the projection length in the distance direction of the ray set is greater than the set threshold, the scattering center is fixed at the two end points in the azimuth direction. At this time, the length and frequency dependence factor of the scattering center at the two end points are both 0, and the positions of the two end points are z l and z r , the amplitude parameters are E l and E r , which is expressed as follows:

[0107] zl =z1,z r =z p

[0108]

[0109] Among them, z1 and z p Represents the coordinates of the two endpoints in the azimuth direction; E1, E2, ···, E q Represent the amplitudes of the first q equivalent points in the ray set; E q+1 ,E q+2 ,···,E p-q Respectively represent the amplitudes of the last pq equivalent points in the ray set; E1, E2, ···, E p Represent the amplitudes of a total of p equivalent points in the ray set; It means rounding up half of the total number of p equivalent points. It means rounding down half of the total number of p equivalent points.

[0110] The present invention also provides a forward modeling system for the scattering characteristics of a metal-medium mixed dynamic group target, which is used to implement the forward modeling method for the scattering characteristics of a metal-medium mixed dynamic group target. The system includes a geometric modeling module, a ray classification module, an equivalent point determination module, and a scattering center determination module, wherein:

[0111] The geometric modeling module performs geometric modeling on the target, decomposes the target into multiple components based on the sudden change of the target surface normal, and performs triangulation on each component to set initial parameters;

[0112] The ray classification module uses the bouncing ray (SBR) method to perform occlusion judgment and ray tracing on all surface elements, and classifies the rays according to the number of interactions and interaction mechanisms between the rays and the surface elements. It calculates the scattering field contribution of the classified rays by combining the reflection coefficient and the transmission coefficient, sorts the scattering fields of the classified rays in descending order, and retains strong scattering centers whose scattering field contributions are greater than a set threshold.

[0113] The equivalent point obtaining module reads the path of the screened strong scattering center, determines whether it is a single-action ray or a multiple-action ray, and obtains the equivalent point for the multiple-action ray using the phase equivalence method;

[0114] The scattering center determination module determines the types of all equivalent points through the obtained equivalent points and field values, and determines the parameters of the scattering center.

[0115] The present invention also provides a mobile terminal, comprising a memory, a processor, and a computer program stored in the memory and runnable on the processor. When the processor executes the program, the forward modeling method of the metal-medium mixed dynamic group target scattering characteristics is implemented.

[0116] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0117] Example

[0118] This embodiment takes the metal-medium mixed cone group target model as an example to perform forward modeling on the target scattering characteristics of the metal-medium mixed dynamic group. The radar parameters are: radar center frequency f c =10GHz, bandwidth B = 2GHz, number of frequency points 201, radar pitch angle θ = 90°, azimuth angle Scanning is performed in the azimuth direction. The azimuth radar sweep width is 4°, the number of sweeps is 41, the polarization mode is VV polarization, and the dielectric parameter ε r1 =2.0-j4.0, μ r1 =1.0-j0.0.

[0119] Figure 4 and Figure 5 They are the spatial distribution of metal-medium mixed group targets at two different times, Figure 6 (a) and Figure 7 (a) in the equation are Figure 4 and Figure 5 Scattering center modeling results. Because the scattering center of the cone target contains length information, only the scattering center of the cone bottom is analyzed. Figure 6 The cone scattering center of (a) is: z1 = [1.98, 0.01, 0] T , L1=0.75; z2=[-1,-1,1.99] T , L2=0; z3=[0.9,2.49,2.1] T , L3=0; z4=[0.01,1.98,0] T , L4=0; z5=[-1.5,-2,-0.99] T , L5=0; for Figure 7 The cone scattering center of (a) is: z1 = [4, 0, 0] T , L1=0.75; z2=[0.01,-3,0.99] T , L2=0; z3=[2.97,2.99,3] T , L3=0; z4=[1.1,2.2,-1.01] T , L4=0; z5=[-1,-2.48,-1.53]T , L5=0. Figure 6 (b) and Figure 7 (b) in the figure are Figure 4 and Figure 5 The ISAR imaging results show that the scattering center model established using the proposed method for a mixed metal-medium target cluster closely matches the actual model structure. Compared to traditional methods, the scattering center modeling in this invention achieves higher accuracy and computational efficiency.

[0120] It is worth noting that the above content only represents the best implementation of the present invention. Without departing from the present invention, ordinary technicians may make some improvements and adjustments thereto, and these improvements and adjustments should also be considered within the scope of protection of the present invention.

Claims

1. A forward modeling method for the scattering characteristics of a metal-medium mixed dynamic group target, characterized in that: The following steps are involved: Step 1: geometrically model the target. Based on the sudden change of the target surface normal, decompose the target into multiple components, perform triangulation on each component, and set the initial parameters. Step 2: Use the bouncing ray (SBR) method to perform occlusion judgment and ray tracing on all surface elements. The rays are classified according to the number of interactions and interaction mechanisms between the rays and the surface elements. The scattering field contribution of the classified rays is calculated by combining the reflection coefficient and the transmission coefficient. The scattering fields of the classified rays are sorted from large to small, and strong scattering centers with scattering field contributions greater than the set threshold are retained. Step 3: Read the path of the screened strong scattering center to determine whether it is a single-action ray or a multiple-action ray. For the multiple-action ray, find the equivalent point using the phase equivalence method; Step 4: Using the obtained equivalent points and field values, determine the types of all equivalent points and determine the parameters of the scattering center; In step 2, the bouncing ray (SBR) method is used to perform occlusion judgment and ray tracing on all surface elements. The rays are classified according to the number of interactions and interaction mechanisms between the rays and the surface elements. The scattering field contribution of the classified rays is calculated by combining the reflection coefficient and the transmission coefficient. The scattering fields of the classified rays are sorted from large to small, and strong scattering centers whose scattering field contributions are greater than the set threshold are retained. The details are as follows: Step 2.1: Use the SBR method to trace all unobstructed pixels. Ray r j Acting on the center Q of the triangle j , we get ray r j The paths are marked with part numbers. At the same time, record whether the ray is reflected or transmitted at each ejection point, and use [T1, T2, ..., T N ] indicates that when T = 1, it indicates reflection, and when T = 2, it indicates transmission, and the ray path r is obtained. j The corresponding action sequence Step 2.2: For the case where the ray propagates inside the target, if the amplitude of the ray at the current bin is less than the set threshold 1e-4 during the ray propagation inside the dielectric body, the ray is considered to be unable to penetrate the dielectric body and is rejected. Retain the rays whose amplitude at the current pixel is greater than the threshold 1e-4; Step 2.3: For the case where the ray propagates outside the target, first classify the ray to determine whether it is a single-action ray or a multiple-action ray: For a primary action ray, if the angle between the reflection direction and the radar receiving direction is greater than 90°, the ray is discarded; the rays whose angle between the reflection direction and the radar receiving direction is less than or equal to 90° are retained; For multiple-action rays, if the number of ray bounces exceeds the set maximum number of 8 times, or the angle between the last reflection direction or transmission direction and the radar receiving direction is greater than 90°, the ray will be discarded; rays with less than or equal to 8 bounces and the angle between the last reflection direction or transmission direction and the radar receiving direction is less than or equal to 90° will be retained; Step 2.4: record the media components that the incident rays pass through from the time of incident to the time of exit, count the rays that finally hit the outer surface of the target, and classify the rays according to the number of times they act and the mechanism of action to form a ray set V = {r j ,j=1,2,...,N}, where N is the total number of rays that meet the conditions; Step 2.5, using the improved reflection coefficient and transmission coefficient formulas, calculate the scattered field contribution of the subset of the classified ray total set; Step 2.

6. Calculate the size of the scattering field of each ray subset, sort the scattering fields of the ray subsets from large to small, and screen them by comparing them with a preset threshold size. If the scattering field of a ray subset is smaller than the threshold, it is eliminated; if it is larger than the threshold, it is retained. Finally, the scattering fields of P strong scattering centers are obtained.

2. The forward modeling method for the scattering characteristics of metal-medium mixed dynamic group targets according to claim 1 is characterized in that: In step 1, the target is geometrically modeled. Based on the sudden change of the target surface normal, the target is decomposed into multiple components, and each component is triangulated. The initial parameters are set as follows: Step 1.1, divide the target into metal parts and dielectric parts, perform geometric modeling on the target, and decompose the target into M parts based on the sudden change of the target surface normal. The M parts are numbered and marked as I1, I2, I3, ..., I M ; Step 1.2: Set the mesh size of metal components to λ10 and the mesh size of dielectric components to less than λ10, where λ is the wavelength of the incident electromagnetic wave. Perform triangular facet meshing on each component, number each triangular facet and the corresponding nodes, calculate the center point of each triangular facet, and associate each triangular facet with the part number of the component to which it belongs. Step 1.3: Set the initial radar incident direction and receiving direction They are: Where θ and Represent the pitch angle and azimuth angle of the radar incident direction in the spherical coordinate system respectively; set the dielectric parameters and magnetic permeability of different dielectric components to be ε ri =ε′ ri -jε″ ri and μ ri =μ′ ri -jμ″ ri , where i represents different dielectric components.

3. The forward modeling method for the scattering characteristics of metal-medium mixed dynamic group targets according to claim 2 is characterized in that: In step 2.5, the improved reflection coefficient and transmission coefficient formulas are combined to calculate the scattered field contribution of the subset of the total set of classified rays, as follows: Step 2.5.

1. For dielectric targets, the calculation of the scattered field is divided into two cases: one is when the ray is emitted from the outer surface of the dielectric target to the inner surface of the dielectric target; the other is when the ray is emitted from the inner surface of the dielectric target to the outer surface of the dielectric target; For the first case, when the ray is emitted from the outer surface of the dielectric target to the inner surface of the dielectric target, there are only incident fields and reflected fields above the outer surface of the dielectric target, so the equivalent current on the surface of the dielectric target is and equivalent magnetic current They are: For the second case, when the ray is emitted from the inner surface of the dielectric target to the outer surface of the dielectric target, there is only a transmission field above the outer surface of the dielectric target, so the equivalent current on the surface of the dielectric target is and equivalent magnetic current They are: The contribution of the scattered field is calculated using triangular surface elements. The total scattered field contribution of the target is the equivalent current and equivalent magnetic current The sum of the scattered fields generated is expressed as: Step 2.5.2: For metal targets, since there is only equivalent current on the target surface but no equivalent magnetic current, Because the reflected electric field satisfies: The transmitted electric field satisfies: Therefore, to calculate the reflection field and transmission field of the target, the corresponding reflection coefficient and transmission coefficient must be obtained; For vertically polarized waves, the reflection coefficient R ⊥ and the transmission coefficient T ⊥ They are: For a flat polarized wave, the reflection coefficient R || and the transmission coefficient T || They are: Among them, the relative dielectric parameters and magnetic permeability of medium i are ε ri =ε′ ri -jε″ ri and μ ri =μ′ ri -jμ″ ri ; is the wave vector in medium i; ξ i is the angle between the wave vector and the normal in medium i, which is an acute angle.

4. The forward modeling method for the scattering characteristics of metal-medium mixed dynamic group targets according to claim 3 is characterized in that: In step 3, the path of the screened strong scattering center is read to determine whether it is a single-action ray or a multiple-action ray. For multiple-action rays, the equivalent point is obtained by the phase equivalence method, as follows: Step 3.1, read the path of the screened strong scattering center to determine whether it is a single action ray or a multiple action ray; Step 3.2: For the ray that acts once, directly use the center point of the triangle element as the equivalent point. for: Among them, (x n ,y n ,z n ) represents the coordinates of the center point of the triangle surface element, and i represents the number of times the ray interacts with the triangle surface element; Step 3.3: For multiple action rays, use phase equivalence to find the equivalent point. The formula is: in, represents the wave vector, i represents the number of interactions between the ray and the surface element, i≥2; j represents the ray action mechanism, j=1 represents the ray reflection, j=2 represents the ray transmission; Indicates the coordinates of the center point when the ray interacts with the triangle element for the i-th time, Indicates the equivalence point; When θ-0.0005°, When , formula (1) is rewritten as: in, Represents the wave vector when the ray is last reflected or transmitted; represents the wave vector, i represents the number of interactions between the ray and the surface element, i≥2; j represents the ray action mechanism, j=1 represents the ray reflection, j=2 represents the ray transmission; Indicates the coordinates of the center point when the ray interacts with the triangle element for the i-th time, Indicates the equivalence point; When θ+0.0005°, When , formula (1) is rewritten as: in, Represents the wave vector when the ray is last reflected or transmitted; represents the wave vector, i represents the number of interactions between the ray and the surface element, i≥2; j represents the ray action mechanism, j=1 represents the ray reflection, j=2 represents the ray transmission; Indicates the coordinates of the center point when the ray interacts with the triangle element for the i-th time, Indicates the equivalence point; Combine equations (1), (2), and (3) to obtain the equivalent point The only solution of .

5. The forward modeling method for the scattering characteristics of metal-medium mixed dynamic group targets according to claim 4 is characterized in that: In step 4, the types of all equivalent points are judged by the obtained equivalent points and field values, and the parameters of the scattering center are determined as follows: Step 4.1: According to the attribute scattering center model theory, the expression of the target scattering field is: Among them, A i is the amplitude of each scattering center; f represents the size of the step frequency, f c represents the size of the center frequency; c represents the speed of light; α i is the frequency dependence factor; γ i The factor that represents the dependence of the amplitude of the local scattering center on the azimuth; L i represents the length of the i-th scattering center, when L i When it is 0, it represents the local scattering center. i ≠0 and γ i = 0 represents a distributed scattering center; according to the dependence of the scattering mechanism on the azimuth angle, the attenuation exponential function is used to describe the local scattering center, while the sinc function is used to describe the distributed scattering center; x i 、y i Indicates the size of the scattering center in the range and azimuth directions; Indicates the azimuth angle of the radar, Indicates the center azimuth of the radar; Step 4.2, determine the frequency dependent parameters: The frequency dependence factor α of the scattering structure and the length L of the scattering center are determined as follows: cylindrical surface, α = 0.5, L > 0; flat plate, α = 1.0, L > 0; sphere α = 0.0, L = 0; top hat structure: α = 0.5, L = 0; dihedral angle: α = 1.0, L > 0; trihedral angle: α = 1.0, L > 0; edge diffraction: α = -0.5, L > 0; angular diffraction: α = -1.0, L = 0; For rays that are reflected only once, the α of the component corresponding to the strong scattering center is the α of the entire component. For rays that are reflected multiple times, each component has a corresponding α when the ray interacts with the component. The α of the coupled scattering center is obtained by multiplying the α corresponding to the component at each reflection of the ray. Step 4.3, determine the length parameter: Calculate the projection of the equivalent point in the distance direction and azimuth direction for all rays in the ray set, denoted as U m and V m , the maximum value of the upward projection is: maximum value U max =(U m ) max , minimum value U min =(U m ) min ; The maximum value of the upward projection is: maximum value V max =(V m ) max , minimum value V min =(V m ) min , then the upward projection length of the set is L U =U max -U min , the projection length in the azimuth direction is L V =V max -V min ; Step 4.4: Determine the amplitude and position parameters: (1) For a distributed scattering center, if the projection length in the distance direction of the ray set is less than the set threshold, its length in the azimuth direction is L V The amplitude parameter E is the sum of the amplitudes of the equivalent points that are not eliminated in the ray set, and the position parameter z is half of the sum of the maximum and minimum values ​​of the equivalent points in the ray set in the azimuth direction, expressed as follows: E1+E2+···+E p Among them, E1, E2, ···, E p Represents the amplitude of the first p equivalent points in the ray set; z min and z max Respectively represent the positions of the equivalent point at the minimum and maximum values ​​of the azimuth upward projection; (2) For a localized scattering center, if the azimuth projection length in the ray set is less than the set threshold, its azimuth length is 0, and the frequency dependence factor is also 0. The amplitude parameter E is the accumulation of the amplitudes of the equivalent points that are not eliminated in the ray set, and the position parameter z is the accumulation of the sum of all equivalent reflection points in the ray set divided by the total number of equivalent reflection points, expressed as follows: E1+E2+···+E p Among them, E1, E2, ···, E p Represent the amplitudes of the first p equivalent points in the ray set; z1,z2,···,z p They represent the positions of the first p equivalent points in the set, and p represents the number of equivalent points; (3) If the projection length in the distance direction of the ray set is greater than the set threshold, the scattering center is fixed at the two end points in the azimuth direction. At this time, the length and frequency dependence factor of the scattering center at the two end points are both 0, and the positions of the two end points are z l and z r , the amplitude parameters are E l and E r , which is expressed as follows: With l =z1,z r =z p Among them, z1 and z p Represents the coordinates of the two endpoints in the azimuth direction; E1, E2, ···, E q Represent the amplitudes of the first q equivalent points in the ray set; E q+1 ,E q+2 ,···,E p-q Respectively represent the amplitudes of the last pq equivalent points in the ray set; E1, E2, ···, E p Represent the amplitudes of a total of p equivalent points in the ray set; It means rounding up half of the total number of p equivalent points. It means rounding down half of the total number of p equivalent points.

6. A forward modeling system for the scattering characteristics of metal-medium mixed dynamic group targets, characterized by: The system is used to implement the forward modeling method for the scattering characteristics of a metal-medium mixed dynamic group target according to any one of claims 1 to 5, and the system includes a geometric modeling module, a ray classification module, an equivalent point determination module, and a scattering center determination module, wherein: The geometric modeling module performs geometric modeling on the target, decomposes the target into multiple components based on the sudden change of the target surface normal, and performs triangulation on each component to set initial parameters; The ray classification module uses the bouncing ray (SBR) method to perform occlusion judgment and ray tracing on all surface elements, and classifies the rays according to the number of interactions and interaction mechanisms between the rays and the surface elements. It calculates the scattering field contribution of the classified rays by combining the reflection coefficient and the transmission coefficient, sorts the scattering fields of the classified rays in descending order, and retains strong scattering centers whose scattering field contributions are greater than a set threshold. The equivalent point obtaining module reads the path of the screened strong scattering center, determines whether it is a single-action ray or a multiple-action ray, and obtains the equivalent point for the multiple-action ray using the phase equivalence method; The scattering center determination module determines the types of all equivalent points through the obtained equivalent points and field values, and determines the parameters of the scattering center.

7. A mobile terminal comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the forward modeling method for the scattering characteristics of a metal-medium mixed dynamic group target according to any one of claims 1 to 5 is implemented.

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