A method for directly establishing scattering center model based on geometric structure

Abstract

The invention discloses a method for directly establishing a scattering center model based on a geometric structure. The invention is a processing scheme for a grid file of an aerodynamic target or a ballistic missile target. The geometric information of a plane surface is extracted respectively, and the geometric information of the target of this type is directly calculated through the grid file. The construction of the scattering center model is completed according to the obtained geometric information of the aerodynamic target or the ballistic missile target and the scattering mechanism of the aerodynamic target or the ballistic missile target. The invention can directly establish the scattering center model, and has the effect of saving computing resources and reducing computing time.

Description

Technical Field

[0001] The invention belongs to the technical field of radar target characteristic modeling, and in particular relates to a method for directly establishing a scattering center model based on a geometric structure. Background Art

[0002] In the high frequency region, the total scattering field of radar targets can be expressed as the coherent superposition of contributions from several local scattering sources, which are usually called scattering centers. The study of scattering centers has been developed since the 1950s. With the improvement of radar system performance and the in-depth study of electromagnetic scattering mechanisms, a variety of typical models have been derived, including the point scattering center model, the attenuation exponential model, the scattering center model based on the geometric theory of diffraction (GTD), and the attribute scattering center model. As an early scattering center model, the point scattering center model is limited by the radar resolution at that time. The model expression contains the incident wave frequency, radar azimuth and scattering center position, but its amplitude is a constant and not accurate enough. The attenuation exponential model takes into account the frequency dependence factor and azimuth dependence factor of the scattering center amplitude, but the parameters of the electromagnetic scattering mechanism have not been added. In the scattering center model based on GTD, power function terms based on different scattering mechanisms are introduced, but it has great limitations because it cannot describe the change of the scattering center with the observation azimuth. The scattering center model widely used at present is the attribute scattering center model, which is based on the GTD scattering center model and adds the description of the scattering center amplitude based on the scattering center type and the relationship between the radar observation azimuth.

[0003] The unknown parameters contained in the scattering center model need to be determined before a complete scattering center model can be formed. There are two common methods for extracting scattering center parameters. One is to estimate the parameters in the scattering center model based on the target echo, that is, inverse modeling. The problem with this method is that when the image resolution is not high, aliasing is prone to occur, which limits the estimation of the scattering center parameters. When the frequency band and observation angle range are increased, the amount of calculation also increases accordingly. Another method is to calculate the local scattering contribution through the known geometric structure and radar parameters, and then estimate the corresponding scattering center parameters through the parameterization method, that is, forward modeling. The biggest limitation of this method is that it can only be used for cooperative targets. It cannot be used directly for non-cooperative targets and can only be used after estimating their appearance.

[0004] At present, the forward modeling method for radar target scattering center includes the forward automatic modeling method for high-frequency radar target scattering center, and its main steps include:

[0005] 1. Build the CAD file of the target model

[0006] 2. Partition and number the first-level components of the target model

[0007] 3. Number the target's secondary surface partitions based on the primary partition

[0008] 4. The radar incident plane wave is directed in parallel to the partitioned grid model in the form of rays, and the strong scattering center and its source are found through ray tracing and ray diversity.

[0009] 5. Forward calculation of the attribute parameters of the strong scattering center model

[0010] In the above scheme, since steps 4 and 5 involve ray diversity and tracing as well as physical optics methods, a large amount of calculation is required, which occupies a lot of computing resources and takes a long time. Summary of the invention

[0011] In view of this, the present invention provides a method for directly establishing a scattering center model based on a geometric structure, which can avoid a large amount of calculation and directly establish a scattering center model.

[0012] The technical solution for implementing the present invention is as follows:

[0013] A method for directly establishing a scattering center model based on a geometric structure comprises the following steps:

[0014] Step 1: read and input the grid file of the aerodynamic target (such as an aircraft, etc.) or ballistic missile target (such as a warhead target) model;

[0015] Step 2: distinguishing the plane area and the curved surface area in the target model according to the continuity of the external normal vectors of adjacent triangular face elements;

[0016] Step 3: for the plane area described in step 2, find the end point position and edge length information according to the contour information of the plane, as the geometric parameters of the plane area;

[0017] For the surface area described in step 2, by finding the contours existing in the surface area, the surface area is divided into independent local surfaces;

[0018] Step 4: for each local surface described in step 3, determine whether it is a single curved surface or a double curved surface according to the curvature information;

[0019] Step 5: for the hyperbolic surface described in step 4, obtain the curvature radius of the points on the hyperbolic surface based on the curvature information, and use the external normal vector in step 2, the coordinates of the points on the hyperbolic surface and the curvature radius of each point as the geometric parameters of the hyperbolic surface;

[0020] For the single-curved surface described in step 4, by judging the range of curvature change, it is determined to be a cylindrical single-curved surface or a conical single-curved surface, and the curvature radius is solved based on the curvature information. After the coordinate transformation of the conical or cylindrical single-curved surface with the axial direction as the z direction, the geometric parameters of the single-curved surface are calculated;

[0021] Step 6: Use the geometric parameters of the plane area and the curved area and the scattering mechanism of the aerodynamic target or ballistic missile target to establish a scattering center model, without the need for parameter estimation. This method does not involve the electromagnetic calculation process (high frequency or full wave algorithm) or the parameter estimation process. The modeling process is direct and easy to achieve full automation of modeling.

[0022] Furthermore, the curvature information includes principal curvature 1, principal curvature 2, Gaussian curvature and mean curvature of each point.

[0023] Furthermore, the geometric parameters of the single-curved surface include bottom center coordinates, axial direction, generatrix length, and cone semi-cone angle information.

[0024] Beneficial effects:

[0025] 1. The method of the present invention is a processing scheme for the grid files of aerodynamic targets or ballistic missile targets. The geometric information of the plane and curved surfaces is extracted respectively, and the geometric information of the target of this type is directly calculated through the grid files, which has the effect of clearer physical meaning, intuitiveness and simplicity.

[0026] 2. The method of the present invention establishes a scattering center model without any calculation or parameter estimation process. The scattering center model is constructed directly based on the obtained geometric information of the aerodynamic target or ballistic missile target. This is an analysis at the structural level of the scattering center model. It improves the complex and cumbersome calculation process in previous models and has a direct, simple and automated effect.

[0027] 3. Compared with the existing technology, the method of the present invention can directly establish a scattering center model, which has the effect of saving computing resources and reducing computing time. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the overall framework diagram of the method for directly establishing a scattering center model based on geometric structure in the present invention.

[0029] Figure 2 This is a geometric model diagram of Example 1 of the present invention.

[0030] Figure 3 This is a result diagram of the midpoints of the plane partition edges in Example 1 of the present invention.

[0031] Figure 4 This is a result diagram of the center point of a single curved surface in Example 1 of the present invention.

[0032] Figure 5 This is a hyperbolic point result diagram of Example 1 of the present invention.

[0033] Figure 6 This is a comparison chart of radar cross section results of Example 1 of the present invention.

[0034] Figure 7 This is a geometric model diagram of embodiment 2 of the present invention.

[0035] Figure 8 This is a result diagram of the midpoints of the plane partition edges of Example 2 of the present invention.

[0036] Fig. 9 This is the result diagram of the center point of the single curved surface in Example 2 of the present invention.

[0037] Fig.10 This is a hyperbolic point result diagram of Example 2 of the present invention.

[0038] Fig.11 This is a comparison chart of radar cross section results of Example 2 of the present invention. DETAILED DESCRIPTION

[0039] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0040] A method to directly establish a scattering center model based on the geometric structure, such as Figure 1 As shown, the specific steps include:

[0041] Step 1: Input aerodynamic target or ballistic missile target grid file: Embodiment 1 of the present invention is an aircraft model, and the geometric model corresponding to the input target is as follows: Figure 2 As shown, the input grid file can obtain the target's subdivided triangles and point coordinate information;

[0042] Step 2: Distinguish the plane and curved surface areas contained in the aircraft model based on the continuity of the external normal vectors of adjacent triangles.

[0043] ① Since the mesh file is divided in such a way that each face is divided completely before the next face is divided, based on this, the external normal vectors of adjacent numbered triangles are subtracted. If the difference is less than the set threshold, the two triangles are considered to be on the same plane. If the difference is greater than the set threshold, they are considered to be distributed on the surface.

[0044] ② In the process, the external normal vectors of triangles on some small surfaces also meet the threshold conditions. Therefore, it is necessary to perform a second screening on the triangles after the first screening. The screening principle is to count the number of face elements of the plane screened out in the first screening. If the number of face elements is less than the threshold, it is considered to be a misjudgment of the face element on the surface.

[0045] ③ The third screening is also to eliminate the errors caused by the face elements on the surface. The screening principle is to solve the variance of the external normal vector of the plane after the first two screenings. If the solved variance is greater than the set threshold, it is considered that the surface is misjudged as a plane, and if it is less than the set threshold, it is judged to be a plane. After three screenings, the continuous triangular face element numbers judged to be planes are considered to be on the same plane. Among all the triangular face element numbers, after the plane is screened out, the remaining continuous triangular face element numbers are considered to be in the same surface area;

[0046] Step 3: Process the triangular face elements on each plane to obtain the plane geometric information of the aircraft target.

[0047] ①Since on the same plane, in the segmentation information of all triangular face elements, the edge that appears only once is the edge on the contour. On the same plane, there may be an internal contour and an external contour. When judging, the contour with a larger area is taken as the external contour.

[0048] ② After obtaining the contour information, the edges on the contour are collinearly judged, and the middle points on the edges on the same straight line are discarded, in order to obtain the endpoint coordinates of the plane. Under this method, for a circular plane, it can be approximated as a polygon and multiple vertex coordinates can be obtained. After obtaining the vertex coordinates, it is easy to obtain the length of each side of the plane, and finally record the external normal vector corresponding to each plane, as well as the endpoint coordinates and the side length;

[0049] Refine the triangular face elements of each surface area in the aircraft target to obtain the surface local information. Since each surface area is not divided more finely, it may contain multiple surface locals, so it needs to be refined. The refinement principle is: find the contour contained in the surface area. If there is no contour, it proves that the surface area should be a completely closed local area and does not need to be refined again. If the surface area contains multiple contours, it proves that the surface area contains multiple surface locals. According to the surface contour and the adjacent edge relationship of the triangular face element, the number of the triangular face element contained in each surface local area is inferred.

[0050] Step 4. For each local surface area in the aircraft target, decompose it into a single curved surface or a hyperbolic surface type by curvature, and then process them separately. Since in the principal curvature of a single curved surface, the larger principal curvature is the inverse of the radius of curvature, and the smaller principal curvature is approximately 0; in a hyperbolic surface, the two principal curvature values ​​are equal, and both are the inverse of the radius of curvature. Based on this, after solving the curvature of each point on the surface, the surface on each local surface area can be determined as a single curved surface or a hyperbolic surface. In the present invention, when the difference in the principal curvature is greater than the set threshold, and the smaller principal curvature is less than the set threshold, it is determined that the point is on a single curved surface. The single curved surface and the hyperbolic surface contained in each local surface area are distinguished by the numbering continuity of the triangles.

[0051] Step 5: Process the facet information of single-curved surface and hyperbolic surface respectively to obtain the geometric parameters required for establishing the scattering center model.

[0052] ① For a hyperbolic surface, it is necessary to obtain the coordinates of the center point of each triangular face element on the hyperbolic surface, the external normal vector of the face element, and the average value of the curvature radius of the three points of the face element.

[0053] ② For single-curved surfaces, since the methods of extracting information from cylindrical single-curved surfaces and conical single-curved surfaces are not exactly the same, we first distinguish between cylindrical single-curved surfaces and conical single-curved surfaces.

[0054] ③ For a cylindrical single-curved surface, the curvature value on the surface is single. In the geometric information extraction of a cylindrical single-curved surface, first find the triangular face elements whose external normal vectors are approximately parallel. The straight line where the center point coordinates of these face elements are located is the axis direction. The radius value of the cylindrical single-curved surface is the reciprocal of the curvature. The axial direction of the cylindrical single-curved surface is used as the z-axis direction in the coordinate transformation. After the coordinate system is transformed, the coordinates of the center point of the bottom surface of the cylindrical single-curved surface can be found by finding the lowest level coordinates in the z direction.

[0055] ④ For conical single-curved surfaces, first find two layers of points with equal curvature, and calculate the coordinates of the center point of the layer through their coordinates and curvature radius. The straight line where the center point is located is the axial direction. Use the axial direction of the conical single-curved surface as the z-axis direction in the coordinate transformation to transform the coordinate system. For conical single-curved surfaces, the information that needs to be extracted includes its maximum radius, generatrix length, semi-cone angle, and bottom center coordinates. The bottom center coordinates are the coordinates of the center point of the lowest layer after the coordinate system is transformed. The maximum radius is the maximum value of the projection of all points in the z direction after the coordinate system is transformed. The height of the conical single-curved surface is the maximum distance in the z direction. Through the height, maximum radius and minimum radius, the Pythagorean theorem can be used to calculate the generatrix length and semi-cone angle of the conical single-curved surface. The specific comparison of single-curved surface geometric information is shown in Table 1;

[0056] Table 1

[0057]

[0058] Step 6: After obtaining the geometric information of the aircraft target, construct a scattering center model. The attribute scattering center model is used, and its expression is:

[0059]

[0060] Where: i = 1...N is the scattering center number, A i is the scattering amplitude of the scattering center corresponding to the i-th scattering center. For the hyperbolic surface, Where r is the radius of curvature of the hyperbolic surface; for a single curved surface, Where λ is the wavelength of the incident wave, r is the radius of curvature of the single curved surface; for a plane, Where k is the wave number, A is the area of ​​the plane, f is the incident wave frequency, f c is the center frequency, α i is the frequency dependence factor corresponding to the i-th scattering center, γ i is the amplitude attenuation factor of the local scattering center, is the spatial angle of the radar line of sight, which is a function of the radar's elevation and azimuth angles. c is the speed of light, L i represents the length of the distributed scattering center, is the observable angle of the scattering center, is the scattering center position vector, Represents the radar line of sight direction vector in the local coordinate system.

[0061] For the scattering center location parameter in the model, each edge of the plane can be considered as a separate scattering center located at the midpoint. Figure 3 The coordinates of the edge center point of the plane of the embodiment of the present invention are marked. For a single curved surface, the scattering center position is at the midpoint of the generatrix of the effective reflection area, such as Figure 4 As shown. For a hyperbolic surface, the scattering center is the center point of the effective reflection area. Figure 5 The positions of all the points on the hyperbolic surface in the model are marked, and the center point position of the effective reflection area can be calculated according to the radar incident wave parameters; finally, the radar scattering cross section (RCS) results of the scattering center modeling results of the embodiment are compared by the present invention. The Matlab result is the RCS result calculated according to the present invention, and the FEKO result is the actual RCS result of the aircraft target calculated by the optical physics method. The result comparison diagram is shown in FIG. Figure 6 Based on the above process, the Fiery Warhead target was simulated. The geometric model of the Fiery Warhead target is shown in Figure 7 The comparison of its geometric parameters and measured parameters is shown in Table 2.

[0062] Table 2

[0063]

[0064] Figure 8 – Fig.10 The equivalent point markings of the plane, single curved surface and hyperbolic surface of the inferno warhead target obtained based on this method are shown. Fig.11 This is the RCS result comparison of the warhead target according to the present invention. The Matlab result is the RCS result calculated according to the present invention, and FEKO is the actual RCS result of the aircraft target calculated by the optical physics method.

[0065] From this point on, the entire process of directly modeling scattering centers based on the geometric structure is completed.

[0066] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for directly establishing a scattering center model based on a geometric structure, characterized in that: The following steps are involved: Step 1, reading and inputting the grid file of the aerodynamic target or ballistic missile target model; Step 2: distinguishing the plane area and the curved surface area in the target model according to the continuity of the external normal vectors of adjacent triangular face elements; Step 3: for the plane area described in step 2, find the end point position and edge length information according to the contour information of the plane, as the geometric parameters of the plane area; For the surface area described in step 2, the surface area is divided into independent local surfaces by finding the contours existing in the surface area; Step 4: for each local surface described in step 3, determine whether it is a single curved surface or a double curved surface according to the curvature information; Step 5: for the hyperbolic surface described in step 4, obtain the curvature radius of the points on the hyperbolic surface based on the curvature information, and use the external normal vector in step 2, the coordinates of the points on the hyperbolic surface and the curvature radius of each point as the geometric parameters of the hyperbolic surface; For the single-curved surface described in step 4, by judging the range of curvature change, it is determined to be a cylindrical single-curved surface or a conical single-curved surface, and the curvature radius is solved based on the curvature information. After the coordinate transformation of the conical or cylindrical single-curved surface with the axial direction as the z direction, the geometric parameters of the single-curved surface are calculated; Step 6: Establish a scattering center model using the geometric parameters of the plane area and the curved surface area and the scattering mechanism of the aerodynamic target or ballistic missile target.

2. A method for directly establishing a scattering center model based on a geometric structure as claimed in claim 1, characterized in that: The curvature information includes the principal curvature 1, principal curvature 2, Gaussian curvature and mean curvature of each point.

3. The method for directly establishing a scattering center model based on a geometric structure according to claim 1, characterized in that: The geometric parameters of the single-curved surface include the coordinates of the center of the bottom surface, the axial direction, the generatrix length, and the semi-cone angle information of the cone.

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