Method for calculating the relative dynamic lrcs of two aircrafts

Abstract

The application discloses a method for calculating double-aircraft relative dynamic LRCS and a control method thereof, and combines rough surface scattering theory and computer graphics, and establishes an LRCS calculation model by using the Kirchhoff method; geometric modeling is carried out on the aircraft target, the model target surface is meshed, is decomposed into a plurality of triangular surface elements, and is coded; the triangular surface elements are subdivided, a conversion relationship between a target coordinate system and a local coordinate system is established, and coordinates are determined; a coordinate system of an observation point and a target to be observed is established, the target aircraft is blanked, effective surface element data is acquired, the value of the LRCS of each surface element is obtained, and the value of the total target LRCS at the current time is obtained through algebraic summation. According to the working principle of the laser radar, the 3D modeling and simulation are combined with the laser radar target scattering theory, and the dynamic laser scattering cross section of the other party under the mutual visual angle between two high-speed flying carriers can be researched.

Description

Technical Field

[0001] This invention belongs to the field of aerospace and lidar technology, specifically relating to a method for calculating the relative dynamic LRCS of two aircraft. Background Technology

[0002] With the continuous development of aerospace technology, high-speed aircraft are becoming increasingly common, leading to increasingly fierce information warfare between nations. To adapt to the characteristics of modern electronic warfare, countries have invested significant human and material resources in the research and development of electronic countermeasures equipment. In recent years, research on laser detection technology for high-speed aerial targets has been a focus of attention both domestically and internationally. It differs significantly from traditional radar target detection in terms of performance indicators, and research on laser detection technology can provide a valuable supplement to radar target detection. Research on the detection of high-speed dynamic aerial targets (such as aircraft, artillery shells, and missiles) is of great significance in the development of laser detection technology. In range measurements, the trajectory measurement of guided or unguided flying targets is of great importance.

[0003] Radar target identification technology has a wide range of applications, including effective detection and reconnaissance of unidentified targets, precise countermeasures, high-precision target acquisition, and countermeasures. Radar target identification technology can effectively improve early warning capabilities, thereby enhancing safety. Target characteristics are information generated by the scattering of electromagnetic waves emitted by radar across the target surface. These characteristics describe certain aspects of the target and are a key and primary condition for radar target identification. The lidar cross section (LRCS), as part of the target characteristic attributes, is an important parameter for radar system design, optoelectronic countermeasures, target identification, and optoelectronic early warning applications. Currently, the calculation of the LRCS of flying targets is limited to the calculation of the LRCS of a single flying target, lacking methods for calculating the relative dynamic LRCS of two flying targets. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating the relative dynamic LRCS of two aircraft, which solves the problem that the calculation of the LRCS (Laser Radar Cross Section of Complex Bodies with Rough Surfaces) of flying targets in the prior art is limited to the calculation of the LRCS of a single flying target.

[0005] The technical solution adopted in this invention is:

[0006] The calculation method for the relative dynamic LRCS of two aircraft is carried out according to the following steps:

[0007] Step 1: Combining rough surface scattering theory and computational graphics, and using Kirchhoff's method, establish a computational model of the scattering cross section of a complex rough surface lidar.

[0008] Step 2: Using 3ds Max software, create a triangular facet model of the aircraft that needs to be calculated;

[0009] Step 3: Subdivide each triangular element and establish the transformation relationship between the target coordinate system and the local coordinate system to determine the coordinates of each point, thereby obtaining the center point, normal, and area of ​​the element;

[0010] Step 4: Establish the coordinate system between the observation point and the observed target, perform hidden surface removal processing on the observed target aircraft in the visual direction, obtain the effective surface data of the target in the detection view, calculate the LRCS value of each surface element, and obtain the total LRCS value of the target at the current time by algebraic summation.

[0011] The invention is further characterized by;

[0012] Step 1 specifically involves the following: The laser scattering field of a rough target is a complex function of the target's geometry, optical constants, surface machining characteristics, or coating properties; according to the random field analysis method, its corresponding LRCS can be decomposed into coherent and incoherent parts, as shown in the following formula (1):

[0013] <σ>=<σ> i +<σ> c (1);

[0014] Kirchhoff's applicability is based on the condition that k0L > 6, L 2 >2.76δλ, where δ is the root mean square value of the height undulation of the target surface material, and L is the correlation length of the target surface material;

[0015] The incoherent components satisfy the superposition relationship of the illumination area as shown in formula (2):

[0016]

[0017] Where, σ 0 It is the scattering cross section per unit area of ​​the material, which can be obtained from characteristic parameters such as the surface undulation variance, correlation length, and reflection parameters, and then measured by experimental methods; u is the shielding function, indicating that the integration is carried out in the irradiated area. For a simple target, u satisfies the following formula (3):

[0018]

[0019] in, Let be the unit vector of the incident direction. It is the unit vector in the direction of the surface element's normal.

[0020] When the incident direction is close to the normal direction of the target surface, the effect of the RCS coherent component can no longer be ignored, especially for targets with small roughness, where <σ> cIt has always been dominant; it can be proven that the RCS coherent component <σ> c With the back RCSσ of an ideal conductor B The relationship is given by the following formula (4):

[0021] <σ> c =σ B |R P | 2 |χ(-2k0)| 2 (4);

[0022] Among them, R p Let χ be the Fresnel reflection coefficient, χ be the characteristic function of the rough surface undulation, and σ be the Fresnel reflection coefficient. B It can be obtained by the geometric optics method of the following formula (5):

[0023]

[0024] in, This is the position vector from the observation point to the target coordinate system.

[0025] Step 2 is as follows:

[0026] Step 2.1: Establish the geometric model of the aircraft;

[0027] Step 2.2: Mesh the surface of the aircraft model to generate several triangular facets;

[0028] Step 2.3: Number and store the face units.

[0029] Step 3 specifically involves:

[0030] Step 3.1: Extract the face elements that need to be subdivided and determine the points where the face elements are subdivided;

[0031] Step 3.2: Determine the base coordinates of each subdivision point;

[0032] Step 3.3: Store the index format and perform data conversion;

[0033] Step 3.4: Component assembly.

[0034] In step 4, establishing the coordinate system between the observation point and the observed target specifically involves setting the flight parameters and surface material information of aircraft model one and aircraft model two; assuming that the center position of aircraft model one is the observation point, then aircraft model two is the observed target, that is, the coordinate system where the center position of aircraft model one is located is the local coordinate system, and the coordinate system where aircraft model two is located is the target coordinate system.

[0035] The beneficial effects of this invention are that the calculation method and control method for the relative dynamic LRCS of two aircraft, based on laser scattering theory, lidar, rough surface scattering, 3D modeling of complex targets, calculation of target lidar scattering cross section, and tracking of target trajectory, systematically discuss the lidar scattering characteristics of high-speed flying targets. For two high-speed moving aircraft with different flight trajectories and attitudes, the dynamic laser scattering cross section characteristics of each other from their respective perspectives are studied. This provides certain assistance for fields such as lidar guidance, early warning, reconnaissance, target detection, feature extraction, identification, and air-to-air and ground-to-air laser monitoring in civilian industries, and has certain practical significance. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the triangular facet metadata storage format in the calculation method of the relative dynamic LRCS of two aircraft in this invention;

[0037] Figure 2 This is a schematic diagram of surface subdivision in the calculation method of relative dynamic LRCS of two aircraft in this invention;

[0038] Figure 3 This is a schematic diagram illustrating the transformation between the target coordinate system and the local coordinate system in the calculation method of the relative dynamic LRCS of two aircraft in this invention.

[0039] Figure 4 This is a schematic diagram of the dynamic LRCS of a straight-flying F16 in an embodiment of the method for calculating the relative dynamic LRCS of two aircraft in this invention. Detailed Implementation

[0040] The following detailed description of the calculation method and control method of the relative dynamic LRCS of two aircraft according to the present invention, with reference to the accompanying drawings and specific embodiments, is provided in detail.

[0041] The present invention provides a method for calculating the relative dynamic LRCS of two aircraft, as follows: Figure 1 As shown, step 1 is implemented in the following steps:

[0042] The laser scattering field of a rough target is a complex function of the target's geometry, optical constants, and surface machining or coating properties. According to random field analysis, its corresponding LRCS can be decomposed into coherent and incoherent components, as shown in the following formula (1):

[0043] <σ>=<σ> i +<σ> c (1);

[0044] Kirchhoff's applicability is based on the condition that k0L > 6, L 2>2.76δλ, where δ is the root mean square value of the height undulation of the target surface material, and L is the correlation length of the target surface material. The incoherent components satisfy the superposition relationship of the illumination area as follows: Equation (2):

[0045]

[0046] Where, σ 0 It is the scattering cross section per unit area of ​​the material, which can be obtained from characteristic parameters such as the surface undulation variance, correlation length, and reflection parameters, and then measured experimentally. u is the shielding function, indicating that the integration is performed in the irradiated area. For simple targets:

[0047]

[0048] When the incident direction is close to the normal direction of the target surface, the effect of the RCS coherent component can no longer be ignored, especially for targets with small roughness, where <σ> c It has always been dominant. It can be proven that the RCS coherent component <σ> c With the back RCSσ of an ideal conductor B The relationship is:

[0049] <σ> c =σ B |R P | 2 |χ(-2k0)| 2 (4);

[0050] Among them, R p Fresnel reflection coefficient (θ) i =0), χ is the characteristic function of the rough surface undulation, σ B It can be obtained by geometrical optics methods:

[0051]

[0052] Step 2 is implemented in the following steps:

[0053] For different types of aircraft models, the element-based method is used, employing 3ds Max modeling to generate triangular mesh models. This method primarily uses planar and curved elements, dividing the surface of complex targets into numerous small elements for calculation. The advantage of this approach is the ability to perform occlusion detection and phase calculation between elements. Modeling the target using triangles first involves meshing the target surface. Each element requires its own identifier, and each element consists of three points, each also requiring an identifier. Figure 1As shown: m1 and m2 are the numbers of the face elements, and 1 to 9 are the numbers of the points. In the storage format, the three points of each face element are read in a counterclockwise direction. For example, the points corresponding to m1 are arranged as 1, 2, 4; and m2 is 2, 5, 4. The origin of the coordinate system where the vertex coordinates of the face element are located is the geometric center of the model, and the coordinate axes are the feature axes. The coordinate system used is unified, and the established coordinate system must satisfy the description of the projectile or target coordinate system, thereby determining the position coordinates (x, y, z) of each vertex in the coordinate system. When reading the file, the vertex numbers of the triangular face elements are read first, and then the position coordinates of the vertices are obtained according to the vertex numbers. According to the vertex coordinates, the normal vector of the face element, the coordinates of the midpoint of the face element, and the area of ​​the face element can be calculated. For a triangular face element, there are two normal vectors with opposite directions. In this paper, we select the vector direction pointing from the surface of the target entity outward as the normal vector of the face element.

[0054] Step 3 is implemented in the following steps:

[0055] When using the surface element method to calculate the scattering cross section and echo characteristics of complex target lidar, if the area of ​​the curved surface element is too large or only part of the surface element is illuminated by the laser in the near field, the accuracy of the calculation will be affected. In order to improve the accuracy, the surface element needs to be subdivided.

[0056] Extract the face elements that need to be subdivided and determine the points where the face elements are subdivided.

[0057] like Figure 2 As shown, let the three points of the triangular element be b(x). B ,y B ,z B )a(x A ,y A ,z A ), c(x) C ,y C ,z C Let the quadrilateral have a height of h and a base of l. Divide the triangular element horizontally into m equal parts, with a spacing of h / m. Take n points evenly at the base and connect them to point a, with a distance of l / n between any two base points. Then further divide the quadrilateral into triangles.

[0058] Determine the base coordinates of each subdivided point.

[0059] Based on geometric knowledge, the coordinates of each point after subdivision are linear combinations of the coordinates of points a, b, and c. The coordinates of the j-th point on the base bc are:

[0060] x j =(1-j / n)x B +(j / n)x C

[0061] y j =(1-j / n)yB +(j / n)y C

[0062] z l =(1-l / n)z B +(l / n)z C (6);

[0063] The coordinates of any point after subdivision can be written as:

[0064] x i,j =(1-i / m)x A +(i / m)x j

[0065] y i,j =(1-i / m)y A +(i / m)y j

[0066] z i,j =(1-i / m)z A +(i / m)z j (7);

[0067] The storage point index format is used for data transformation.

[0068] After determining the coordinates of each point, rearrange the coordinates and then transform the data into a cell index format for easier calculation.

[0069] Component assembly.

[0070] After all the triangular facets that need to be subdivided are subdivided, all the components are recombined to restore the original overall appearance of the target.

[0071] Coordinate transformation.

[0072] When calculating the scattering of complex targets, the target itself exists in a coordinate system, which we call the target coordinate system. The directions and angles of the incident and scattered waves are defined in this target coordinate system. When calculating the target's LRCS value, we need to calculate the LRCS value of each surface element. According to the scattering theory of rough surfaces, we know that all calculated parameters are defined in the coordinate system of the surface element, which we call the local coordinate system.

[0073] like Figure 3 As shown, the three coordinate vectors of the known target coordinate system are respectively The three coordinate axis vectors of the local coordinate system are respectively Assuming wave vector The coordinate vector in the target coordinate system is Now, find its coordinate vector value in the local coordinate system (target surface element coordinate system). And the outward normal components of the surface element are known to be used as the local coordinate system of the surface element. Axis vector.

[0074] Based on the process of establishing the target coordinate system, the right-handed coordinate system can be used to obtain... and In the plane of incidence, From this, the incident wave vector can be obtained. Transformation formulas for different coordinate systems:

[0075]

[0076] in,

[0077]

[0078] in, This is the transformation matrix.

[0079] Using the above formulas to determine the incident direction and scattering direction (target coordinate system) ) Convert to and (local coordinate system) ).

[0080] incident direction After coordinate transformation, it becomes:

[0081]

[0082] Scattering direction After coordinate transformation, it becomes:

[0083]

[0084] Step 4 is implemented in the following steps:

[0085] Set the flight parameters and surface material information for aircraft model one and aircraft model two. Assume that the center position of aircraft model one is the observation point, and aircraft model two is the observed target. That is, the coordinate system where the center position of aircraft model one is located is the local coordinate system, and the coordinate system where aircraft model two is located is the target coordinate system.

[0086] The target aircraft undergoes hidden surface removal processing in the visual direction to accurately obtain effective surface data of the target from the detection viewpoint. This involves calculating the outward normal of each surface element. and and The dot product, if or If a facet is obscured by the component itself, it is discarded immediately. Otherwise, it is added to the initial facet table for further evaluation. The facets in the initial facet table are sorted along the z′ and z″ axes to generate data on their order. In the projection plane, the projections of each facet are evaluated for overlay in front-to-back order. If a facet is completely obscured by the preceding facet, it is deleted; if the facet is fully visible, it is inserted into the visible facet table; otherwise, it is a partially obscured facet, which is divided into four sub-facets. The old facet is deleted, and the overlay evaluation is repeated for these four new facets.

[0087] The LRCS values ​​of each effective surface element are obtained, and the LRCS value of the total target at the current moment is obtained by algebraic summation. Finally, the dynamic lidar scattering cross section of the complex target is calculated.

[0088] like Figure 4 As shown: Assume aircraft 1 is a J-20 and aircraft 2 is an F-16; both aircraft 1 and aircraft 2 are made of aluminum with a complex refractive index of 2.43 + 10.7i, an incident wavelength of 1.06 μm, an altitude fluctuation of 0.2 m, and a correlation length of 5.89 m; the J-20's flight trajectory is a straight flight with an initial coordinate point (0,0,0), a speed of 100 m / s, and a flight orientation point coordinate of (3,5,9); the F-16's flight trajectory is a hovering flight with a speed of 100 m / s, a hovering trajectory center coordinate of (3,15,20), a hovering radius of 50 m, a simulated flight time of 20 s, and a frame rate of 50 frames. The observed aircraft is an F-16, and the simulation results are as follows. Figure 4 As shown, it can be seen that when the F-16 flies in a straight line and the J-20 circles, the LRCS of the F-16 under the view of the J-20 generally exhibits periodic changes.

[0089] This invention presents a method for calculating and controlling the relative dynamic laser scattering cross section (LRCS) of two aircraft. Based on the working principle of lidar, it uses 3D modeling and simulation, combined with lidar target scattering theory, to study the dynamic laser scattering cross section of the other aircraft from their mutual perspectives. This method has certain practical significance.

Claims

1. A method for calculating the relative dynamic LRCS of two aircraft, characterized in that, The specific steps are as follows: Step 1: Combining rough surface scattering theory and computational graphics, and using Kirchhoff's method, establish a computational model of the scattering cross section of a complex rough surface lidar. Step 1 is as follows: The laser scattering field of a rough target is a complex function of the target's geometry, optical constants, and surface machining characteristics or coating properties. According to the random field analysis method, its corresponding LRCS can be decomposed into coherent and incoherent parts, as shown in the following formula (1): （1）； Among them, the conditions under which Kirchhoff applies are: , , δ The root mean square value of the height undulation of the target surface material. L The relevant length of the target surface material; The incoherent components satisfy the superposition relationship of the illumination area as shown in the following formula (2): （2）； in, It is the scattering cross section per unit area of ​​the material. Let be the masking function, indicating that the integration is performed in the illuminated area. For simple targets... Satisfy the following formula (3): （3）； in, Let be the unit vector of the incident direction. It is the unit vector in the direction of the surface element's normal. When the incident direction is close to the normal direction of the target surface, the RCS coherent component Backward RCS of an ideal conductor The relationship is as follows (4): （4）； in, For Fresnel reflection coefficient, The characteristic function of the rough surface undulation. It can be obtained by the geometric optics method of the following formula (5): （5）； in, The position vector from the observation point to the target coordinate system; Step 2: Using 3ds Max software, create a triangular facet model of the aircraft that needs to be calculated; Step 3: Subdivide each triangular element and establish the transformation relationship between the target coordinate system and the local coordinate system to determine the coordinates of each point, thereby obtaining the center point, normal, and area of ​​the element; Step 4: Establish the coordinate system between the observation point and the observed target, perform hidden surface removal processing on the observed target aircraft in the visual direction, obtain the effective surface data of the target in the detection view, calculate the LRCS value of each surface element, and obtain the total LRCS value of the target at the current time by algebraic summation.

2. The method for calculating the relative dynamic LRCS of two aircraft according to claim 1, characterized in that, Step 2 is as follows: Step 2.1: Establish the geometric model of the aircraft; Step 2.2: Mesh the surface of the aircraft model to generate several triangular facets; Step 2.3: Number and store the face units.

3. The method for calculating the relative dynamic LRCS of two aircraft according to claim 1, characterized in that, Step 3 specifically involves: Step 3.1: Extract the face elements that need to be subdivided and determine the points where the face elements are subdivided; Step 3.2: Determine the base coordinates of each subdivision point; Step 3.3: Store the index format and perform data conversion; Step 3.4: Component assembly.

4. The method for calculating the relative dynamic LRCS of two aircraft according to claim 1, characterized in that, In step 4, establishing the coordinate system between the observation point and the observed target specifically involves setting the flight parameters and surface material information of aircraft model one and aircraft model two; assuming that the center position of aircraft model one is the observation point, then aircraft model two is the observed target, that is, the coordinate system where the center position of aircraft model one is located is the local coordinate system, and the coordinate system where aircraft model two is located is the target coordinate system.

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