Calculation method for equivalent model of radar cross-sectional area of large ship target

Abstract

The invention discloses a method for calculating an equivalent model of a radar cross-sectional area of a large ship target. The method comprises the following steps: establishing a three-dimensional geometric model of the large ship target; according to the target geometrical shape, establishing a virtual electromagnetic wave incident aperture surface at a position tending to infinity, and discretizing the aperture surface to obtain a single ray tube; tracking the reflection direction of each ray tube on the surface of the target until the rays leave the surface of the target; the scattered field of each ray tube in the receiving direction is calculated, and the scattered fields of all the ray tubes are superposed to obtain the total scattered field of the target; drawing a ship target horizontal section and a vertical gain graph according to the calculated target radar scattering gains of the typical horizontal azimuth angle and the vertical elevation angle; and based on the target radar scattering gain graph, calculating the ship target radar scattering sectional area when the radar equipment detects in different directions by adopting an interpolation formula. According to the method, the calculation precision and speed of large-scale ship target scattering are improved, and stealth evaluation of the large-scale ship target is facilitated.

Description

Technical Field

[0001] The invention relates to the field of radar and electronic countermeasures, and in particular to a method for calculating an equivalent model of a large ship target radar scattering cross-sectional area. Background Art

[0002] The target radar cross-section is a physical quantity that characterizes the target's ability to scatter electromagnetic waves. It is closely related to the target's structure, orientation, transmitter and receiver positions, attitude, polarization mode, and frequency of incident electromagnetic waves. Large surface ships are mostly 100m-300m long, with extremely large electrical dimensions. A large number of weapons, equipment, electronic equipment, and buildings on the deck are compactly arranged and have complex and varied styles. This makes large surface ships a dense combination of a large number of geometric shapes, and their radar wave scattering mechanisms are diverse and complex. Traditional geometric optics, physical optics, geometric diffraction theory, and physical diffraction theory only analyze and calculate the target radar cross-section from a single perspective, which is difficult to apply to the calculation of radar cross-sections for large ship targets. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for calculating an equivalent model of radar scattering cross-sectional area of ​​a large ship target, which provides target characteristic parameters for radar reconnaissance detection by establishing a radar scattering characteristic model of the target.

[0004] The objective of the present invention is achieved through the following technical scheme: a method for calculating an equivalent model of a large ship target radar cross-sectional area, comprising the following steps:

[0005] Step 1: Establish a three-dimensional geometric model of a large ship target;

[0006] Step 2: According to the target geometry, a virtual electromagnetic wave incident aperture plane is established at an infinite distance, and the aperture plane is discretized to obtain a single ray tube;

[0007] Step 3, tracking the reflection direction of each ray tube on the target surface until the ray leaves the target surface;

[0008] Step 4, calculate the scattered field of each ray tube in the receiving direction, and superimpose the scattered fields of all ray tubes to obtain the total scattered field of the target;

[0009] Step 5: Draw the ship target horizontal cross section and vertical gain diagram according to the calculated target radar scattering gain at typical horizontal azimuth angles and vertical elevation angles;

[0010] Step 6: Based on the target radar scattering gain map, use the interpolation formula to calculate the radar scattering cross-sectional area of ​​the ship target when the radar equipment detects in different directions.

[0011] Preferably, step 2 at least includes the following steps:

[0012] Step 2.1: Project the three-dimensional point information (X, Y, Z) on the target onto a virtual aperture plane at a certain distance from the target and perpendicular to the incident direction of the plane wave through coordinate transformation. The transformed coordinates are Where θ is X r The angle between the Z axis and Yes X r The angle between the projection in the xoy plane and the positive x-axis;

[0013] The conversion relationship is:

[0014]

[0015] Step 2.2: Traverse all two-dimensional points and obtain the maximum and minimum values ​​y in two directions on the virtual aperture surface θmax ,y θmin , The size of the rectangular aperture surface is obtained; when the ray tube is generated, its division step is 1 / 10 of the wavelength λ of the electromagnetic wave.

[0016] Preferably, step 3 at least includes the following steps:

[0017] Step 3.1, discretize the target into triangular surface elements;

[0018] Step 3.2, for different triangle face elements, calculate the intersection points between the ray and the triangle face element;

[0019] Step 3.3: Calculate the reflection direction and reflection field intensity of the multiple reflections of the ray on the surface of the surface element.

[0020] Preferably, step 3.2 at least includes the following steps:

[0021] Step 3.2.1, according to the coordinates of the three points of the triangle surface element, they are: The normal unit vector of the triangle surface element is Establish the equation of the plane where the triangle lies:

[0022]

[0023] Step 3.2.2: According to the ray exit point and the ray propagation direction vector Establish the ray equation:

[0024]

[0025] Step 3.2.3, solve the intersection point and t value of the ray and triangle element.

[0026] Preferably, step 3.3 at least includes the following steps:

[0027] Step 3.3.1: Based on Snell's law, the unit vector of the incident ray direction Unit normal vector at the reflection point Calculate the reflected ray direction vector

[0028]

[0029] Step 3.3.2, calculate the incident field strength: E i (r′) is the incident field strength when parallel polarization is used, H i (r′) is the incident field strength when vertically polarized; calculate the reflected field strength: E r (r′) is the reflected field strength when parallel polarization is used, H r (r′) is the reflected field strength when vertically polarized, as follows:

[0030]

[0031] in:

[0032]

[0033] In the formula, R ∥ is the reflection coefficient of the target surface for parallel polarization, R ⊥ is the reflection coefficient of the target surface when vertically polarized; E e∥ and E e⊥ are the amplitudes of the electric field vector in the two polarization directions respectively;

[0034] Step 3.3.3: Update the ray reflection direction and field intensity reflection using steps 3.3.1 and 3.3.2 to iterate the calculation until the ray leaves the target.

[0035] Preferably, step 4 at least includes the following steps:

[0036] Step 4.1, calculate the scattered field of a single ray tube in the receiving direction:

[0037]

[0038] in, is the receiving direction of the scattered field in polar coordinates, A θ , It is a function of the field strength at each point on the output ray tube and the quadrilateral surrounded by the ray tube;

[0039] Step 4.2, traverse all ray tubes, and superimpose the scattered fields of all ray tubes to obtain the scattering cross-section gain value of the target at a typical azimuth angle and the scattering cross-section gain value at a typical high and low angle;

[0040]

[0041] In the formula, σ Vv is the scattering cross-section gain value of the target at a typical azimuth angle, σ HH is the scattering cross-section gain value at typical high and low angles.

[0042] Preferably, step 5 at least includes the following steps:

[0043] Step 5.1, setting the calculated target radar cross section gain value for the typical azimuth, connecting the radar cross section gain values ​​corresponding to each typical azimuth, and drawing a horizontal cross section gain diagram of the ship target;

[0044] Step 5.2: Set the target radar cross-section gain values ​​calculated for typical elevation and low angles, connect the radar cross-section gain values ​​corresponding to each typical elevation and low angle, and draw a vertical cross-section gain diagram for the ship target.

[0045] Preferably, step 6 at least includes the following steps:

[0046] Step 6.1, calculate the azimuth and elevation angle of the radar device relative to the large ship target;

[0047] Step 6.2: Calculate the target radar cross-sectional area by interpolation.

[0048] Preferably, step 6.1 at least includes the following steps:

[0049] Step 6.1.1, calculate the horizontal distance Δx and height difference Δy between the radar equipment and the large ship target:

[0050]

[0051] Δy=(lat m -lat s )·60·1852

[0052] Among them, lon m is the longitude of the radar equipment location, lat m is latitude, h m is the height; lon s is the longitude of the ship target, lat s is latitude;

[0053] Step 6.1.2, calculate the azimuth angle α and elevation angle β of the radar equipment relative to the large ship target:

[0054] α=atan2(Δx,Δy)

[0055]

[0056] Preferably, step 6.2 at least includes the following steps:

[0057] Step 6.2.1: Interpolate the horizontal gain of the target radar cross-sectional area:

[0058]

[0059] Where α1 and α2 are typical azimuth angles;

[0060] Step 6.2.2: Interpolate the vertical gain of the target radar cross-sectional area:

[0061]

[0062] Where β1 and β2 are typical high and low angles.

[0063] Step 6.2.3, calculate the target radar cross section rcs of the ship relative to the radar equipment:

[0064] rcs=rcs ref ·krcs α ·krcs β

[0065] In the formula, rcs ref is the typical reference cross-section value for the target.

[0066] Compared with the prior art, the present invention has the following advantages:

[0067] The invention provides a large ship target radar scattering cross-sectional area equivalent model calculation method. Based on the physical optics method, combined with optical ray tracing, the scattering field is reflected on the surface of a complex target, and then all reflected ray fields are superimposed to obtain the total field, which greatly improves the calculation accuracy and speed of the scattering of large ship targets, helps to evaluate the stealth of large ship targets, and is beneficial to the design and optimization of radar systems for enemy large ship targets.

[0068] The present invention establishes a geometric model of large ship targets, divides the scattering source structure of large ships, adopts the emission ray method (bouncing ray method), and integrates the geometric optics method, physical optics method, geometric diffraction theory, physical diffraction theory and equivalent electromagnetic flow method. It can discretize the complex structure into several facets for physical optics calculation to ensure the accuracy of the mirror direction, and can handle ray tracing and various diffraction problems. It is suitable for the calculation and analysis of the RCS of large ships. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 This is a flow chart of a method for calculating an equivalent model of radar cross-sectional area of ​​a large ship target in the present invention;

[0070] Figure 2 Schematic diagram of the conversion relationship between target coordinates and virtual aperture surface coordinates in an embodiment of the present invention;

[0071] Figure 3 A schematic diagram of generating a ray tube in an embodiment of the present invention;

[0072] Figure 4 Schematic diagram of the reflection relationship of the reflection point in the embodiment of the present invention;

[0073] Figure 5 It is a horizontal cross-section gain diagram of a ship target in an embodiment of the present invention;

[0074] Figure 6 This is a vertical cross-section gain diagram of a ship target in an embodiment of the present invention. DETAILED DESCRIPTION

[0075] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0076] like Figure 1 As shown, the technical solution of the present invention provides a method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target, comprising the following steps:

[0077] Step 1: Establish a three-dimensional geometric model of a large ship target;

[0078] Step 2: According to the target geometry, a virtual electromagnetic wave incident aperture plane is established at an infinite distance, and the aperture plane is discretized to obtain a single ray tube;

[0079] Step 3, tracking the reflection direction of each ray tube on the target surface until the ray leaves the target surface;

[0080] Step 4, calculate the scattered field of each ray tube in the receiving direction, and superimpose the scattered fields of all ray tubes to obtain the total scattered field of the target;

[0081] Step 5: Draw the ship target horizontal cross section and vertical gain diagram according to the calculated target radar scattering gain at typical horizontal azimuth angles and vertical elevation angles;

[0082] Step 6: Based on the target radar scattering gain map, use the interpolation formula to calculate the radar scattering cross-sectional area of ​​the ship target when the radar equipment detects in different directions.

[0083] In one embodiment of the present invention, in step 1, a 3D model of a large ship is produced by using 3D modeling software 3dsMax, which specifically includes:

[0084] Step 1.1, obtain the specific physical parameters of the ship target from reliable channels, such as: ship length, side width, hull structure parameters, main scattering source structure parameters on the ship, superstructure structure parameters, mast and antenna size parameters arranged on the mast, weapon equipment deployment position and size parameters on the deck, etc.

[0085] Step 1.2, start 3ds Max, create basic model blocks according to the physical parameters of the ship target, select "Convert to Editable Polygons", and start the "NURMS" tool, set the appropriate number of iterations and smoothness, and realize the three-dimensional modeling of the ship target. In this embodiment, the geometric model of the ship target is constructed by combining NURBS (Non-Uniform Rational B-Spline) surface and plane element approximation, which can flexibly and arbitrarily approximate the target shape, eliminate redundant information that does not participate in the calculation, and consider multiple scattering mechanisms, and is suitable for dealing with occlusion problems.

[0086] In one embodiment of the present invention, a single ray tube acquisition method for step 2 is provided, wherein a virtual electromagnetic wave incident aperture plane is established at an infinite distance according to the target geometry, and the aperture plane is discretized according to a certain rule to obtain a single ray tube, which at least includes the following steps:

[0087] Step 2.1: Figure 2 As shown in the figure, the three-dimensional point information (X, Y, Z) on the target is projected onto a virtual aperture surface at a certain distance from the target and perpendicular to the incident direction of the plane wave through coordinate transformation. The transformed coordinates are Where θ is X r The angle between the Z axis and Yes X r The angle between the projection in the xoy plane and the positive x-axis;

[0088] The conversion relationship is:

[0089]

[0090] Assume that the coordinates of the two-dimensional point are Then there is

[0091]

[0092] Step 2.2: Traverse all two-dimensional points and obtain the maximum and minimum values ​​y in two directions on the virtual aperture surface θmax ,y θmin , Get the size of the rectangular aperture surface; Figure 3As shown in the figure, when the ray tube is generated, in order to ensure the calculation accuracy, the division step of the ray tube is at least 1 / 10 of the electromagnetic wave wavelength λ. Let M and N be y θ , The number of ray tubes in the direction (each ray tube includes a central ray and four corner rays), then the number of ray tubes is:

[0093]

[0094] In one embodiment of the present invention, in step 3, when each ray tube irradiates the target surface, it is necessary to determine whether the incident ray illuminates the target surface element. If so, it is necessary to determine the reflection direction of the ray according to Snell's theorem until the ray leaves the target surface, which specifically includes the following steps:

[0095] Step 3.1: Discretize the target into triangular face elements. Specifically:

[0096] The target is discretized into triangular face elements. The coordinates of the three points of the triangular face element can be calculated based on the modeling and segmentation information:

[0097] Step 3.2: For different triangle face elements, calculate the intersection points between the ray and the triangle face element:

[0098] Step 3.2.1, according to the coordinates of the three points of the triangle surface element, they are: The normal unit vector of the triangle surface is Establish the equation of the plane where the triangle lies:

[0099]

[0100] Step 3.2.2: According to the ray exit point and the ray propagation direction vector Establish the ray equation:

[0101]

[0102] Step 3.2.3, solve the intersection point and t value of the ray and triangle element.

[0103] The intersection point of the ray and the target surface element has been obtained above. If the reflection direction of the ray on the surface element can be obtained, the equation of the reflected ray can be calculated. Snell's law can be used to calculate the reflection direction of the ray after the intersection of the ray and the surface element at the target surface.

[0104] Step 3.3: Calculate the reflection direction and reflection field intensity of the multiple reflections of the ray on the surface of the surface element.

[0105] Step 3.3.1: Figure 4As shown, based on Snell's law, the unit vector of the incident ray direction is Unit normal vector at the reflection point Calculate the reflected ray direction vector

[0106]

[0107] Step 3.3.2: Figure 4 As shown, when the ray is incident and reflected on the target surface, its field strength also satisfies a certain corresponding relationship. According to the different polarization modes of the radar antenna, the incident field strength E under the horizontal polarization condition is calculated respectively. i (r′), reflected field strength E r (r′) and the incident field strength H under vertical polarization conditions i (r′), reflected field strength H r (r′):

[0108]

[0109] in:

[0110]

[0111] In the formula, R ∥ is the reflection coefficient of the target surface for parallel polarization, R ⊥ is the reflection coefficient of the target surface when vertically polarized; E e∥ and E e⊥ are the amplitudes of the electric field vector in the two polarization directions respectively;

[0112] Step 3.3.3: Update the reflected ray to the incident ray and the reflected field intensity to the new incident field intensity based on the ray reflection direction and field intensity. Continuously iterate the calculation using steps 3.3.1 and 3.3.2 until the ray leaves the target.

[0113] In one embodiment of the present invention, in step 4, the scattered field of each ray tube in the receiving direction is calculated, all ray tubes are traversed, and the scattered fields of all ray tubes are superimposed to obtain the total scattered field of the target, which at least includes the following steps:

[0114] Step 4.1, calculate the scattered field of a single ray tube in the receiving direction:

[0115]

[0116] in, is the receiving direction of the scattered field in polar coordinates, A θ , It is a function of the field strength at each point on the output ray tube and the quadrilateral surrounded by the ray tube;

[0117] Step 4.2, traverse all ray tubes, and superimpose the scattered fields of all ray tubes to obtain the scattering cross-section gain value of the target at a typical azimuth angle and the scattering cross-section gain value at a typical high and low angle;

[0118]

[0119] In the formula, σ VV is the scattering cross-section gain value of the target at a typical azimuth angle, σ HH is the scattering cross-section gain value at typical high and low angles.

[0120] In one embodiment of the present invention, in step 5, drawing a horizontal cross-sectional gain diagram and a vertical cross-sectional gain diagram of a ship target respectively according to the calculated target radar scattering gain at a typical horizontal azimuth angle comprises at least the following steps:

[0121] Step 5.1: Figure 5 As shown in the figure, the target radar cross section gain value calculated for the typical azimuth setting is connected with the radar cross section gain value corresponding to each typical azimuth. The typical azimuth values ​​are: 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270°, 300°, and the horizontal cross section gain diagram of the ship target is drawn;

[0122] Step 5.2: Figure 6 As shown in the figure, the target radar cross-section gain value calculated for the typical elevation and low angle settings is connected to the radar cross-section gain values ​​corresponding to each typical elevation and low angle. The typical elevation and low angle values ​​are: -22.5°, 0°, 22.5°, 45°, 67.5°, and 90°, and the vertical cross-section gain diagram of the ship target is drawn.

[0123] In one embodiment of the present invention, a method for calculating the radar cross-sectional area of ​​a ship target when the radar device detects in different directions in step 6 is provided, which adopts an interpolation formula for calculation and specifically includes the following steps:

[0124] Step 6.1: Calculate the azimuth and elevation angle of the onboard radar relative to the large ship target, including:

[0125] Step 6.1.1, calculate the horizontal distance Δx and height difference Δy (in meters) between the radar equipment and the large ship target:

[0126]

[0127] Δy=(lat m -lat s )·60·1852

[0128] Among them, lon mis the longitude of the radar equipment location, lat m is latitude, h m is the height; lon s is the longitude of the ship target, lat s The latitude is in radians, the longitude is in meters, and the altitude is in meters.

[0129] Step 6.1.2, calculate the azimuth angle α and elevation angle β of the radar equipment relative to the large ship target:

[0130] α=atan2(Δx,Δy)

[0131]

[0132] Step 6.2, interpolation calculation of target radar cross-section of ship target relative to airborne radar, specifically including:

[0133] Step 6.2.1, interpolate and calculate the horizontal gain of the ship target radar cross-sectional area:

[0134]

[0135] Where α1 and α2 are typical azimuths, and the azimuth α of the radar equipment relative to the ship target falls within the interval [α1, α2].

[0136] Step 6.2.2: Interpolate the vertical gain of the ship target radar cross-sectional area:

[0137]

[0138] Where β1 and β2 are typical elevation angles, and the elevation angle β of the airborne radar equipment relative to the ship target falls within the interval [β1, β2]. Step 6.2.3, calculate the target radar cross-sectional area rcs of the ship target relative to the airborne radar:

[0139] rcs=rcs ref ·krcs α ·krcs βγ

[0140] In the formula, rcs ref is the typical reference cross-section value for the target.

[0141] The present invention solves the limitation of using a single method to calculate the target radar cross-sectional area for ship target characteristics, and provides a bouncing ray method that combines the geometric optics principle with the physical optics method. Based on a constructed three-dimensional model of a ship target, a typical horizontal radar cross-sectional gain value and a vertical radar cross-sectional gain value of the ship target are calculated through processes such as ray tube generation, ray tube tracking update and far-field integration, and a horizontal cross-sectional gain diagram and a vertical cross-sectional gain diagram of the ship target are drawn. When different radar devices detect the target, a simple and fast calculation of the ship target radar cross-sectional area can be achieved through an interpolation formula based on the horizontal cross-sectional gain diagram and the vertical cross-sectional gain diagram.

[0142] The above are preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target, characterized by: The method comprises the following steps: Step 1: Establish a three-dimensional geometric model of a large ship target; Step 2: According to the target geometry, a virtual electromagnetic wave incident aperture plane is established at an infinite distance, and the aperture plane is discretized to obtain a single ray tube; Step 3, tracking the reflection direction of each ray tube on the target surface until the ray leaves the target surface; Step 4, calculate the scattered field of each ray tube in the receiving direction, and superimpose the scattered fields of all ray tubes to obtain the total scattered field of the target; Step 5: Draw the ship target horizontal cross section and vertical gain diagram according to the calculated target radar scattering gain at typical horizontal azimuth angles and vertical elevation angles; Step 6: Based on the target radar scattering gain map, use the interpolation formula to calculate the radar scattering cross-sectional area of ​​the ship target when the radar equipment detects in different directions.

2. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 1, characterized in that: The step 2 at least comprises the following steps: Step 2.1: Project the three-dimensional point information (X, Y, Z) on the target onto a virtual aperture plane at a certain distance from the target and perpendicular to the incident direction of the plane wave through coordinate transformation. The transformed coordinates are Where θ is X r The angle between the Z axis and Yes X r The angle between the projection in the xoy plane and the positive x-axis; The conversion relationship is: Step 2.2: Traverse all two-dimensional points and obtain the maximum and minimum values ​​y in two directions on the virtual aperture surface θmax ,y θmin , The size of the rectangular aperture surface is obtained; when the ray tube is generated, its division step is 1 / 10 of the wavelength λ of the electromagnetic wave.

3. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 1, characterized in that: The step 3 at least comprises the following steps: Step 3.1, discretize the target into triangular surface elements; Step 3.2, for different triangle face elements, calculate the intersection points between the ray and the triangle face element; Step 3.3: Calculate the reflection direction and reflection field intensity of the multiple reflections of the ray on the surface of the surface element.

4. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 3, characterized in that: The step 3.2 at least includes the following steps: Step 3.2.1, according to the coordinates of the three points of the triangle surface element, they are: The normal unit vector of the triangle surface element is Establish the equation of the plane where the triangle lies: Step 3.2.2: According to the ray exit point and the ray propagation direction vector Establish the ray equation: Step 3.2.3, solve the intersection point and t value of the ray and triangle element.

5. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 4, characterized in that: The step 3.3 at least includes the following steps: Step 3.3.1: Based on Snell's law, the unit vector of the incident ray direction Unit normal vector at the reflection point Calculate the reflected ray direction vector Step 3.3.2, calculate the incident field strength: E i (r ′ ) is the incident field strength when parallel polarization is applied, H i (r ′ ) is the incident field strength when vertically polarized; calculate the reflected field strength: E r (r ′ ) is the reflected field strength when parallel polarization is applied, H r (r ′ ) is the reflected field strength when vertically polarized, as follows: in: Where R|| is the reflection coefficient of the target surface when parallel polarization is used, R ⊥ is the reflection coefficient of the target surface when vertically polarized; E e || and E e⊥ are the amplitudes of the electric field vector in the two polarization directions respectively; Step 3.3.3: Update the ray reflection direction and field intensity reflection using steps 3.3.1 and 3.3.2 to iterate the calculation until the ray leaves the target.

6. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 1, characterized in that: The step 4 at least comprises the following steps: Step 4.1, calculate the scattered field of a single ray tube in the receiving direction: in, is the receiving direction of the scattered field in polar coordinates, A θ , It is a function of the field strength at each point on the output ray tube and the quadrilateral surrounded by the ray tube; Step 4.2, traverse all ray tubes, and superimpose the scattered fields of all ray tubes to obtain the scattering cross-section gain value of the target at a typical azimuth angle and the scattering cross-section gain value at a typical high and low angle; In the formula, σ VV is the scattering cross-section gain value of the target at a typical azimuth angle, σ HH is the scattering cross-section gain value at typical high and low angles.

7. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 1, characterized in that: The step 5 at least comprises the following steps: Step 5.1, setting the calculated target radar cross section gain value for the typical azimuth, connecting the radar cross section gain values ​​corresponding to each typical azimuth, and drawing a horizontal cross section gain diagram of the ship target; Step 5.2: Set the target radar cross-section gain values ​​calculated for typical elevation and low angles, connect the radar cross-section gain values ​​corresponding to each typical elevation and low angle, and draw a vertical cross-section gain diagram for the ship target.

8. The method for calculating the equivalent model of radar cross-sectional area of ​​a large ship target according to claim 1, characterized in that: The step 6 at least comprises the following steps: Step 6.1, calculate the azimuth and elevation angle of the radar device relative to the large ship target; Step 6.2: Calculate the target radar cross-sectional area by interpolation.

9. A large ship target radar cross-sectional area equivalent model calculation method as claimed in claim 8, characterized in that: The step 6.1 at least comprises the following steps: Step 6.1.1, calculate the horizontal distance Δx and height difference Δy between the radar equipment and the large ship target: Δy=(years m -years s ) 60 1852 Among them, lon m is the longitude of the radar equipment location, lat m is latitude, h m is the height; lon s is the longitude of the ship target, lat s is latitude; Step 6.1.2, calculate the azimuth angle α and elevation angle β of the radar equipment relative to the large ship target: α=atan2(Δx,Δy) 10. A large ship target radar cross-sectional area equivalent model calculation method as claimed in claim 9, characterized in that: The step 6.2 at least comprises the following steps: Step 6.2.1: Interpolate the horizontal gain of the target radar cross-sectional area: Where α1 and α2 are typical azimuth angles; Step 6.2.2: Interpolate the vertical gain of the target radar cross-sectional area: In the formula, β1 and β2 are typical high and low angles; Step 6.2.3, calculate the target radar cross section rcs of the ship relative to the radar equipment: rcs=rcs ref ·krcs α ·krcs β In the formula, rcs ref is the typical reference cross-section value for the target.

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