A method for solving sea surface size in sea surface and ship coupling scattering calculation

Abstract

The application discloses a sea surface size solving method in sea surface and ship coupling scattering calculation, comprising: determining the radar wave incidence pitch angle, frequency polarization mode of the sea surface and ship coupling scattering calculation; generating a sea surface with more than twice the ship length and more than three times the ship width in the sea surface model based on the required simulated sea state; fusing the ship model and the sea surface model, obtaining the HRRP calculation under different azimuth angles through electromagnetic scattering simulation, and obtaining the scattering energy source distribution of the sea surface and ship coupling scattering calculation under different angles; continuously increasing the sea surface size, obtaining the HRRP change under different sizes, and if the HRRP scattering energy source distribution around the ship model does not change, the sea surface under the size can cover the sea surface and ship coupling scattering path under the current incidence angle. The application can effectively cover the main sea surface and ship coupling scattering points and paths, effectively control the sea surface model size, improve the calculation efficiency, and has strong practical value.

Description

Technical Field

[0001] The present invention relates to the technical field of ship-sea-surface coupled scattering calculation, and in particular to a method for solving sea surface size in sea surface-hull coupled scattering calculation. Background Art

[0002] In real-world environments, a ship's radar scattering characteristics are closely coupled to the ocean environment, which in turn has a complex impact on the ship's scattering field. This is especially true for newer-generation ships, whose RCS levels have significantly decreased, reducing the signal-to-clutter ratio of the ship's echo signal. When the ship's target characteristics drop below a certain level, ignoring the coupled scattering between the sea surface and the hull will inevitably lead to deviations from the ship's actual state in simulation and evaluation results. For highly stealthy ships, coupled scattering between the sea surface and the hull can cause changes in the ship's radar scattering intensity and bright spot distribution, rendering existing radar stealth measures ineffective.

[0003] The size of the sea surface that couples with the ship varies at different pitch angles. Compared to high-grazing-angle scattering, the area of ​​sea surface that couples with the ship under low-grazing-angle radar illumination can be significantly larger. Therefore, further clarification is needed on how to set the sea background size and boundary conditions in simulation evaluations. Setting a sea background that is too large will dramatically increase the computational complexity of sea-ship scattering, while setting a sea background that is too small may not fully account for all points and paths of coupled scattering between the sea surface and the ship.

[0004] Therefore, in order to meet the needs of stealth assessment of future ships under low-grazing angle detection, it is urgent to establish a reasonable and feasible method for solving the sea surface model size. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for solving the sea surface size in the sea surface and hull coupled scattering calculation in response to the defects in the existing technology. The method can effectively cover the main points and paths of the sea surface and hull coupled scattering, and can also effectively control the size of the sea surface model, improve the calculation efficiency, and has strong practical value.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] The present invention provides a method for solving sea surface size in sea surface and hull coupled scattering calculation, the method comprising the following steps:

[0008] Step 1: Establish an integrated sea surface and ship model, including a sea surface model and a ship model, and determine the radar wave incident pitch angle and frequency polarization mode for the sea surface and hull coupled scattering calculation;

[0009] Step 2: Based on the sea conditions to be simulated, generate a sea surface that is more than twice the length of the ship and more than three times the width of the ship in the sea surface model;

[0010] Step 3, the ship model and the sea surface model are fused, electromagnetic scattering simulation is carried out, HRRP calculation under different azimuth angles is acquired, and the scattering energy source distribution under different angles of the sea surface and ship coupling scattering calculation is acquired;

[0011] Step 4, the sea surface size is continuously increased by 1 times of the ship length or 2 times of the ship width, HRRP changes under different sizes are acquired, when the sea surface size is increased to a certain degree, if the HRRP scattering energy source distribution around the ship model does not change, the sea surface size under the current incident angle can cover the sea surface and ship coupling scattering path, and the acquired sea surface size is output.

[0012] Further, in the sea surface and ship integrated model of step 1, the following parameters are included: ship length, ship width, distance from the ship bow direction sea surface edge to the ship geometric center, distance from the ship side direction sea surface edge to the ship geometric center, and distance from the ship stern direction sea surface edge to the ship geometric center.

[0013] Further, in step 2, if there is no sea state requirement, a calm sea surface is selected, and the sea surface medium attribute is set to a metal good conductor material.

[0014] Further, in step 3, the azimuth angle is taken as the ship bow direction, the side direction and the stern direction.

[0015] Further, the method for HRRP calculation in step 3 includes:

[0016] Each scattering center of the ship model is distinguished by the radar, at this time, the electromagnetic scattering of the ship is equivalent to a combined scattering body composed of multiple discrete scattering centers, that is, a "scattering center model", when the radar pulse width τ of the pulse radar is greater than 2L / c, the echo signals of each scattering center of the target are in the same distance resolution unit, by coherently combining the RCS of each discrete scattering center, the total RCS of the ship target is obtained, and the specific mathematical form is as shown in the following formula:

[0017]

[0018] In the formula, N is the number of discrete scattering centers, σ n is the RCS of the nth scattering center, φ n becomes the phase of the scattering field of the nth scattering center relative to the first one.

[0019] The radar high resolution one-dimensional range profile HRRP is regarded as the echo vector sum of each scattering center of the target in the radar line of sight direction acquired by the wideband radar, and reflects the scattering center distribution of the radar target along the distance dimension of the radar wave propagation direction.

[0020] Further, the method for HRRP calculation in step 3 includes:

[0021] The sea surface and ship integrated model is set to have N scattering center groups in the distance direction of the radar, and is divided into M distance resolution units in the distance direction, so the total echo signal X of the ship target is N The echo signal of the ship in the distance direction of each scattering center is considered as the sum of the echo signals of the scattering centers:

[0022]

[0023] In the formula, Δf is the interval of the frequency step, c is the speed of light, k is the wave number, R n is the distance of the scattering center from the radar;

[0024] The echo signal of the target and its high-resolution one-dimensional range image form a pair of Fourier transforms, that is, the ship target scattering center distribution in each distance unit is obtained by performing inverse Fourier transform on the formula:

[0025] The imaging radar uses a frequency-stepped radar signal to realize one-dimensional range image imaging, that is, a pulse train with a step change in carrier frequency is transmitted, then the echo signal of the target is sampled, windowed and pulse compressed, and then fast inverse Fourier transform (IFFT) processing is performed according to the energy and phase information between the echo pulses of different carrier frequencies, so as to obtain the high-resolution one-dimensional range image A(R k ) of the target:

[0026]

[0027] The present application has the following beneficial effects:

[0028] The size of the sea surface coupled with the ship is different at different pitch angles. The present application performs HRRP one-dimensional range image imaging on the sea surface and ship coupling scattering model under different sea surface scales, obtains the discrete scattering center positions of all the sea surface and ship coupling echoes, and determines the size of the sea surface size based on the scattering center positions. It can be considered that the RCS calculation result of the sea surface and ship coupling model under the sea surface size can be included in the sea surface and ship coupling part, and the error introduced by the too large sea surface can be reduced, the mapping calculation between the ship and the sea surface in the non-coupling area can be avoided, and the invalid calculation amount can be significantly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0029] The present application will be further described below in combination with the drawings and examples, and the drawings are as follows:

[0030] Figure 1 The sea surface and ship integrated model of the embodiment of the present application;

[0031] Figure 2 The sea surface size setting schematic diagram of the embodiment of the present application;

[0032] Figure 3is the HRRP simulation result of 0° direction under different sea surface sizes of the embodiment of the application;

[0033] Figure 4 is the HRRP simulation result of 90° direction under different sea surface sizes of the embodiment of the application. DETAILED DESCRIPTION

[0034] In order to make the objects, technical solutions and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0035] Embodiment 1

[0036] The sea background size solving method in the sea surface and ship coupling scattering calculation of the embodiment of the application has the following specific calculation process:

[0037] (1) Different sea areas affect the calculation results of the sea surface and ship coupling scattering under different pitch angles. First, the radar wave incidence pitch angle and frequency polarization mode of the coupling scattering calculation are determined.

[0038] (2) Based on the simulated sea conditions, a sea surface model with more than twice the length of the ship and more than three times the width of the ship is generated. If there is no sea condition requirement, a calm sea surface is selected. In order to better reflect the sea surface echo, the sea surface medium property is set to a metal good conductor material.

[0039] (3) The ship model and the sea surface model are fused, and the HRRP calculation under different azimuth angles is obtained through electromagnetic scattering simulation, and the scattering energy source distribution under different angles of the sea surface and ship coupling scattering calculation is obtained. If there is no special requirement, the azimuth angle is taken as the bow direction, the lateral direction and the stern direction.

[0040] (4) The sea surface size is continuously increased by 1 times the length of the ship (in the length direction) or 2 times the width of the ship (in the width direction), and the HRRP change under different sizes is obtained. When the size increases to a certain degree, if the HRRP energy distribution around the ship model does not change, it is considered that the sea surface under the size can cover the sea surface and ship coupling scattering path under the current incidence angle.

[0041] The sea background size solving method in the sea surface and ship coupling scattering calculation of the embodiment of the application can effectively cover the main sea surface and ship coupling scattering points and paths, and can also effectively control the size of the sea surface model, improve the calculation efficiency, and has strong practical value.

[0042] For wideband radar, the distance resolution is much smaller than the size of the ship target, so the radar can distinguish the scattering centers of the ship target accurately. The electromagnetic scattering of the ship target can be equivalent to the combined scattering of multiple discrete scattering centers, i.e. the scattering center model. When the pulse width τ of the radar wave is greater than 2L / c, the echo signals of the scattering centers of the target are in the same distance resolution unit, and the total RCS of the ship target can be obtained by coherently combining the RCSs of the discrete scattering centers, which can be expressed as follows:

[0043]

[0044] In the formula, N is the number of discrete scattering centers, σ n is the RCS of the nth scattering center, φ n is the phase of the scattering field of the nth scattering center relative to the first scattering center.

[0045] The high-resolution one-dimensional range profile (HRRP) of the radar can be regarded as the echo vector sum of the scattering centers of the target in the direction of the line of sight of the radar, and reflects the distribution of the scattering centers of the target along the distance dimension of the radar wave propagation direction.

[0046] The ship and sea surface coupling scattering model is divided into N scattering centers in the distance direction of the radar, and is divided into M distance resolution units in the distance direction, so the total echo signal X N of the ship target can be regarded as the sum of the echo signals of the scattering centers of the ship in the distance direction:

[0047]

[0048] In the formula, Δf is the interval of the frequency steps, c is the speed of light, k is the wave number, R n is the distance of the scattering center from the radar. The echo signal of the target and its high-resolution one-dimensional range profile form a pair of Fourier transforms, i.e. the inverse Fourier transform of the formula can obtain the distribution of the scattering centers of the ship target in each distance unit. The imaging radar can use the frequency-stepped radar signal to realize one-dimensional range profile imaging, i.e. a group of pulse trains with step-changed carrier frequencies are transmitted, then the echo signals of the target are sampled, windowed and pulse-compressed, and then the inverse fast Fourier transform (IFFT) processing is performed according to the energy and phase information between the echo pulses with different carrier frequencies, so as to obtain the high-resolution one-dimensional range profile A(R k ) of the target:

[0049]

[0050] Example 2

[0051] As Figure 1The sea surface and ship coupling scattering model, i.e. the sea surface and ship integrated model, is based on the HRRP imaging method to analyze the sea surface size setting principle. The ship length is 150 meters and the ship width is 25 meters. The definition of the sea surface size in the sea surface and ship integrated model is shown in Figure 2 As shown in the figure, the distance between the sea surface edge in the bow direction and the ship geometric center is defined as L, the distance between the sea surface edge in the side direction and the ship geometric center is D, and the distance between the sea surface edge in the stern direction and the ship geometric center is P.

[0052] (1) The electromagnetic scattering model of the calm sea surface and the ship is used to calculate and analyze the HRRP, the grazing angle is set to 3°, the frequency is 10 GHz, the vertical polarization, and the one-dimensional range image resolution is 0.3 m. In order to enhance the sea surface and ship coupling scattering ability, the sea surface is regarded as a metal scatterer.

[0053] (2) The high-resolution one-dimensional range image calculation of the sea surface and ship integrated scattering model for the head-on wave is shown in Figure 3 As can be seen from the figure, the presence of the sea surface leads to a clear increase in the radar wave scattering center energy at the superstructure position, and the superstructure front wall region will produce strong coupling reflection with the sea surface; the presence of the sea surface leads to a clear increase in the background reflection ability.

[0054] Comparison Figure 3 (b) As can be seen from the two curves, the increase of the distance D between the sea surface edge in the side direction and the ship geometric center will not lead to the change of the ship scattering center in the bow direction, and the sea surface and ship coupling mainly occurs on the sea surface in the bow region. As can be seen from the comparison of figure (c) and figure (d), the radar wave scattering center distribution is basically unchanged when the sea surface size in the bow direction is 150 m and 300 m, and only slightly changes when it is increased to 800 m. It can be seen that when the bow sea surface size L is 150 m, it basically contains all the sea surface and ship coupling scattering centers for the bow wave.

[0055] (3) The high-resolution one-dimensional range image calculation for the side wave is shown in Figure 4 As can be seen from Figure 4 (a), the sea surface and ship coupling mainly occurs in the side direction of the ship radar wave; the presence of the sea surface leads to an increase in the background fluctuation; the diffraction of the sea surface edge at ±100 distance produces a relatively strong scattering center.

[0056] Further increase the sea surface in the ship width direction, as shown in Figure 4 (b), (c) and (d), when the sea surface continuously increases, the sea surface and ship coupling also continuously increases, the peak value at the coupling scattering center continuously increases, and the background reflection ability also continuously increases; when D is increased to 300 meters and 400 meters, the two curves are basically coincided, it can be seen that when the sea surface edge is 300 meters away from the ship center, it can basically cover all the coupling scattering for the side wave.

[0057] (4) In summary, when the sea surface size L, P is 150m and D is 300m, it can basically cover the centers of all sea surface and hull coupled scattering. Therefore, it can be considered that the RCS calculation results of the sea surface and hull coupled model under this sea surface size can not only include the sea surface and hull coupling part, but also reduce the error introduced by the excessive sea surface, avoid the mapping calculation between the ship and the sea surface in the non-coupling area, and significantly reduce the amount of invalid calculation.

[0058] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0059] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A method for calculating the sea surface size in the calculation of coupled scattering between the sea surface and the ship hull, characterized in that: The method comprises the following steps: Step 1: Establish an integrated sea surface and ship model, including a sea surface model and a ship model, and determine the radar wave incident pitch angle and frequency polarization mode for the sea surface and hull coupled scattering calculation; Step 2: Based on the sea conditions to be simulated, generate a sea surface that is more than twice the length of the ship and more than three times the width of the ship in the sea surface model; Step 3: Fuse the ship model with the sea surface model, and obtain HRRP calculations at different azimuth angles through electromagnetic scattering simulation, and obtain the scattering energy source distribution at different angles of the coupled scattering calculation between the sea surface and the hull; Step 4: Continue increasing the sea surface size by 1 times the ship length or 2 times the ship width to obtain the HRRP changes at different sizes. When the size increases to a certain extent, if the distribution of HRRP scattering energy sources around the ship model does not change, then the sea surface at this size can cover the coupled scattering path between the sea surface and the hull at the current incident angle. Output the obtained sea surface size.

2. The method for calculating the sea surface size in the sea surface and hull coupled scattering calculation according to claim 1 is characterized in that: The sea surface and ship integration model in step 1 includes the following parameters: ship length, ship width, the distance from the edge of the sea surface in the bow direction to the geometric center of the ship, the distance from the edge of the sea surface in the side direction to the geometric center of the ship, and the distance from the edge of the sea surface in the stern direction to the geometric center of the ship.

3. The method for calculating the sea surface size in the sea surface and hull coupled scattering calculation according to claim 1 is characterized in that: In step 2, if there is no sea condition requirement, a calm sea surface is selected; and the sea surface medium attribute is set to a metal good conductor material.

4. The method for calculating the sea surface size in the sea surface and hull coupled scattering calculation according to claim 1 is characterized in that: In step 3, the azimuth angles are the bow, side and stern of the ship.

5. The method for calculating the sea surface size in the sea surface and hull coupled scattering calculation according to claim 1 is characterized in that: The method for calculating HRRP in step 3 includes: The radar can distinguish the scattering centers of the ship model. At this time, the electromagnetic scattering of the ship is equivalent to a combined scatterer composed of multiple discrete scattering centers, that is, the "scattering center model". When the pulse width of the radar wave of the pulse radar is When the echo signals of each scattering center of the target are in the same range resolution unit, the overall RCS of the ship target is obtained by coherently combining the RCS of each discrete scattering center. The specific mathematical form is shown in the following formula: Where N is the number of discrete scattering centers, is the RCS of the nth scattering center, Become the phase of the scattered field of the nth scattering center relative to the first; The radar high-resolution one-dimensional range profile (HRRP) is regarded as the sum of the echo vectors of each scattering center of the target obtained by the broadband radar in the direction of the radar line of sight, which reflects the dispersion of the scattering centers of the radar target along the range dimension of the radar wave propagation direction.

6. The method for calculating the sea surface size in the sea surface and hull coupled scattering calculation according to claim 5 is characterized in that: The method for calculating HRRP in step 3 includes: Assume that the integrated model of sea surface and ship consists of N scattering centers in the distance direction of the radar, and is divided into M range resolution units in the distance direction, so the total echo signal of the ship target is It is regarded as the sum of the echo signals of each scattering center of the ship in the distance direction: Where, is the frequency step interval, c is the speed of light, k is the wave number, is the distance between the scattering center and the radar; A pair of Fourier transforms is formed between the target's echo signal and its high-resolution one-dimensional range image. The inverse Fourier transform of the formula is performed to obtain the distribution of the scattering center of the ship target at each range unit. Imaging radar uses frequency-modulated stepped radar signals to achieve one-dimensional range imaging, that is, it transmits a set of pulse trains with step-by-step carrier frequencies, then samples, windowes, and pulse compresses the target's echo signal, and then performs inverse fast Fourier transform (IFFT) processing based on the energy and phase information between echo pulses of different carrier frequencies, thereby obtaining a high-resolution one-dimensional range image of the target. : 。

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