A large scene SAR echo fast generation method based on scene grid database

Abstract

The application relates to a large-scene SAR echo fast generation method based on a scene grid database, relates to the electrical field, and comprises the following steps: importing triangular surface elements of a scene, dividing the size of a grid according to the far-field condition of a sensor to form a scene grid; performing ray tracing on the scene grid according to the relationship of incident electromagnetic fields of the sensor to obtain a ray tube representing electromagnetic wave propagation; performing integral summation on all ray tubes in the scene grid to obtain the scattering coefficient of the scene network at a given frequency and angle; calculating the scattering coefficient for the frequency and angle required in SAR echo simulation to form a scene network scattering coefficient library; combining the scattering coefficients of each scene grid to form a large-scene electromagnetic response frequency domain system function; and obtaining the total echo of the scene through time domain convolution or frequency domain multiplication, so that the application has the advantages of solving the problems of large calculation amount and poor real-time performance of a traditional direct simulation SAR echo method.

Description

Technical Field

[0001] This invention relates to the field of electrical technology, and in particular to a method for rapid generation of large-scene SAR echoes based on a scene grid database. Background Technology

[0002] Synthetic Aperture Radar (SAR) echo simulation technology is based on the interaction mechanism between electromagnetic waves and targets and the environment, as well as the SAR imaging mechanism. It uses mathematical modeling to simulate SAR echoes between targets and the environment. It is commonly used to verify the performance of SAR systems, evaluate various imaging algorithms, and analyze the effectiveness of algorithms based on different models. Furthermore, due to the nonlinearity of SAR echoes, accurately extracting ground feature information is very difficult; therefore, SAR echo simulation technology can be used to build models to help explain this complex echo mechanism.

[0003] Based on whether or not electromagnetic scattering processes are considered, SAR raw data simulation methods can be divided into two categories: image-level simulation and echo signal-level simulation. Image-level simulation methods only simulate the characteristics of SAR images, without considering the electromagnetic scattering processes between targets and the environment in the scene. They use existing or hypothetical scattering coefficient maps (such as optical or SAR images) to simulate SAR raw data. Echo signal-level simulation methods, on the other hand, focus on the electromagnetic scattering process, considering the interaction between electromagnetic waves and targets and the environment. They simulate SAR raw data by modeling complex terrain scenes and the motion of the SAR platform, combined with electromagnetic calculation methods.

[0004] Because real-world SAR systems and operating scenarios are extremely complex, SAR image-level simulations are often based on simple electromagnetic scattering models using point scattering sources. In contrast, SAR echo signal-level simulations can more realistically simulate the electromagnetic scattering process of SAR. SAR echo signal-level simulations first establish a SAR simulation scenario model to accurately describe the spatial geometric relationship between the radar and the target / environment, analyzing geometric distortion characteristics such as near-range compression, perspective contraction, overlay, and shadows in the SAR image. Secondly, by establishing electromagnetic scattering models for the target, the environment, and the coupled electromagnetic scattering model between the target and the environment, the electromagnetic interaction mechanism between electromagnetic waves and the SAR scene is accurately described. Based on the aforementioned simulation scenario model and electromagnetic scattering model, sweep frequency data for large-scale scenes is calculated. Finally, SAR time-domain echo data and SAR images are obtained through time-frequency transformation and imaging processing. However, many calculations of the coupled electromagnetic scattering between the target and the natural environment are based on numerical methods, resulting in enormous computational and storage requirements, far from meeting the needs of SAR echo simulation engineering applications.

[0005] Therefore, to address the above shortcomings, a method for rapid generation of large-scene SAR echoes based on a scene grid database is needed. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] The technical problem to be solved by this invention is to address the issues of high computational complexity and poor real-time performance in traditional methods for directly simulating SAR echoes.

[0008] (II) Technical Solution

[0009] To address the aforementioned technical problems, this invention provides a method for rapid generation of large-scene SAR echoes based on a scene grid database, comprising the following steps:

[0010] I. Import the triangular facets of the scene, and divide the mesh size according to the far-field conditions of the sensor to form the scene mesh;

[0011] II. Based on the relationship of the incident electromagnetic field of the sensor, ray tracing is performed on the scene mesh to obtain the ray tubes representing the propagation of electromagnetic waves. The scattering coefficients of the scene network with a given frequency and angle are obtained by integrating and summing all the ray tubes in the scene mesh. The scattering coefficients of the scene network with a given frequency and angle are calculated for the frequency and angle required in SAR echo simulation, forming a scene network scattering coefficient library.

[0012] III. Combine the scattering coefficients of each scene grid to form the frequency domain system function of the electromagnetic response of the large scene, and obtain the total echo of the scene through time domain convolution or frequency domain multiplication.

[0013] As a further explanation of the present invention, preferably, the scene mesh size satisfies:

[0014]

[0015] Where L is the scene mesh size;

[0016] R is the distance from the sensor to the center of the grid;

[0017] λ is the wavelength corresponding to the center frequency of the transmitted signal.

[0018] As a further explanation of the present invention, preferably, the scene grid size is close to the size of the SAR image pixels.

[0019] As a further explanation of the present invention, preferably, the integral summation formula for all ray tubes within the scene mesh is:

[0020]

[0021] As a further explanation of the present invention, preferably, the large scene is divided into an M×N grid, and the scattering coefficient of each scene grid is... Then the frequency domain system function E(f,r) is:

[0022]

[0023]

[0024] Where f is the frequency;

[0025] Let be the displacement vector from the sensor to the center of the scene grid in row m and column n;

[0026] u mn This indicates whether the scene grid in the m-th row and n-th column is within the sensor beam illumination range. 1 indicates that it is within the beam illumination range, and 0 indicates that it is not within the beam illumination range, meaning that the scene grid does not contribute to the echo.

[0027] for The unit vector;

[0028] r is the position of the sensor relative to the origin of the scene coordinate system;

[0029] r mn This represents the position of the scene grid center relative to the scene coordinate origin.

[0030] As a further explanation of the present invention, preferably, when the transmitted signal spectrum is s(f) and the frequency domain system function of the scene electromagnetic response is E(f,r), then the total echo E(t,r) of the scene is:

[0031] E(t,r)=IFT{E(f,r)·s(f)}

[0032] Wherein, IFT stands for Inverse Fourier Transform;

[0033] s(f) = FT{s(t)} is the spectrum of the time-domain waveform s(t) of the transmitted signal;

[0034] FT stands for Fourier Transform.

[0035] (III) Beneficial Effects

[0036] The above-described technical solution of the present invention has the following advantages:

[0037] This invention designs three main steps: scene mesh generation, offline construction of scene mesh scattering coefficient library, and online generation of SAR echo. It can solve the problems of large computational load and poor real-time performance of traditional methods for directly simulating SAR echo, and can be used for the design of SAR sensor hardware-in-the-loop simulation radio frequency signal generator. Attached Figure Description

[0038] Figure 1 This is the logic diagram of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] A method for rapid generation of large-scene SAR echoes based on a scene grid database, such as Figure 1 As shown, it includes the following steps:

[0041] I. Scene Mesh Generation. First, import the triangular elements of the scene. Then, divide the mesh size according to the sensor's far-field conditions. The mesh size L must meet the sensor's far-field conditions to ensure that the path difference deviation of the scattering points within the mesh relative to the sensor is less than 45° (π / 8).

[0042]

[0043] Right now:

[0044]

[0045] Where L is the scene mesh size;

[0046] R is the distance from the sensor to the center of the grid;

[0047] λ is the wavelength corresponding to the center frequency of the transmitted signal.

[0048] To ensure the accuracy of the SAR sensor's beam illumination range edge, the size of the scene grid can be close to the size of the SAR image pixels. Finally, the scene grid is formed for further use.

[0049] II. Offline Construction of Scene Mesh Scattering Coefficient Library. First, ray tracing is performed on the scene based on the relationship of the incident electromagnetic field from the sensor, obtaining ray tubes representing electromagnetic wave propagation. The scattering coefficient of a scene mesh with a given frequency and angle can be solved by integrating and summing all ray tubes within the scene mesh.

[0050]

[0051] For SAR echo simulation, the frequency and angle scattering coefficients are calculated, and a scene grid scattering coefficient library is formed for further use.

[0052] III. Online SAR Echo Generation. When the transmitted signal spectrum is s(f) and the frequency domain system function of the scene's electromagnetic response is E(f,r), then the total echo E(t,r) of the scene is:

[0053] E(t,r)=IFT{E(f,r)·s(f)}

[0054] Wherein, IFT stands for Inverse Fourier Transform;

[0055] s(f) = FT{s(t)} is the spectrum of the time-domain waveform s(t) of the transmitted signal;

[0056] FT stands for Fourier Transform.

[0057] Assume a large scene is divided into an M×N grid, and the scattering coefficient of each scene grid is... Then the frequency domain system function E(f,r) is:

[0058]

[0059]

[0060] Where f is the frequency;

[0061] Let be the displacement vector from the sensor to the center of the scene grid in row m and column n;

[0062] u mn This indicates whether the scene grid in the m-th row and n-th column is within the sensor beam illumination range. 1 indicates that it is within the beam illumination range, and 0 indicates that it is not within the beam illumination range, meaning that the scene grid does not contribute to the echo.

[0063] for The unit vector;

[0064] r is the position of the sensor relative to the origin of the scene coordinate system;

[0065] r mn This represents the position of the scene grid center relative to the scene coordinate origin.

[0066] By treating the electromagnetic scattering process of a large scene as a linear system, given the spectrum of the transmitted signal and the frequency domain system function of the scene's electromagnetic response, the total echo of the scene can be obtained through time-domain convolution or frequency-domain multiplication. Furthermore, the frequency domain system function of the large scene's electromagnetic response can be composed of the scattering coefficients of each scene grid.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for rapid generation of large-scene SAR echoes based on a scene grid database, characterized in that: Includes the following steps, I. Import the triangular facets of the scene, and divide the mesh size according to the far-field conditions of the sensor to form the scene mesh; The scene mesh size meets the following requirements: in The scene grid size is approximately equal to the pixel size of the SAR image. The distance from the sensor to the center of the grid; The wavelength corresponds to the center frequency of the transmitted signal; II. Based on the relationship of the incident electromagnetic field of the sensor, perform ray tracing on the scene mesh to obtain the ray tubes representing the propagation of electromagnetic waves. Integrate and sum the integrals of all ray tubes within the scene mesh. The formula for the summation of the integrals of all ray tubes within the scene mesh is: Solving this equation yields the scattering coefficients of the scene network at a given frequency and angle; calculating the scattering coefficients for frequencies and angles required in SAR echo simulations creates a scene network scattering coefficient library. III. When the transmitted signal spectrum is The frequency domain system function of the electromagnetic response of the scene is The total echo of the scene is for: in, This is the inverse Fourier transform; The time-domain waveform of the transmitted signal The spectrum; Fourier transform; Let the large scene be divided into The grid is such that the scattering coefficient of each scene grid is... Then the frequency domain system function for: in For frequency; Let be the displacement vector from the sensor to the center of the scene grid in row m and column n; This indicates whether the scene grid in the m-th row and n-th column is within the sensor beam illumination range. 1 indicates that it is within the beam illumination range, and 0 indicates that it is not within the beam illumination range, meaning that the scene grid does not contribute to the echo. for The unit vector; This refers to the sensor's position relative to the scene's coordinate origin. The position of the scene grid center relative to the scene coordinate origin; the scattering coefficients of each scene grid are combined to form the frequency domain system function of the electromagnetic response of the large scene, and the total echo of the scene is obtained by time domain convolution or frequency domain multiplication.

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