Photoelectric sensor simulation platform and SAR imaging method in simulation platform

Abstract

The invention provides a photoelectric sensor simulation platform and a synthetic aperture radar (SAR) imaging method in the simulation platform. The method comprises the following steps: step 1, subdividing a target three-dimensional model; step 2, acquiring a propagation path of a ray by using a ray tracing method homologous with that in an optical imaging system; and step 3, performing simulation calculation on the far-region scattered field of the target by using a bounce ray method, and performing data processing on the far-region scattered field to obtain a synthetic aperture radar image of the target. According to the technical scheme, the working frequency of the sensor simulation platform and the photoelectric sensor simulation platform is successfully expanded to the field of radar microwaves. Radar SAR and optical homologous simulation imaging lay a good foundation for subsequent research in the fields of image registration, feature fusion, target recognition and the like.

Description

Technical Field

[0001] The present application relates to the field of optical imaging and synthetic aperture radar imaging, and in particular to a photoelectric sensor simulation platform and a SAR imaging method in the simulation platform. Background Art

[0002] Synthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR) are two radar imaging technologies that can obtain high-resolution images of targets even in complex environments, which makes them important in both military and civilian fields. Since both SAR and ISAR use the relative motion between the radar and the target to obtain high-resolution two-dimensional images of the target, there is no essential difference between the two in computer simulation, so they are collectively referred to as radar SAR images in the present invention. Chinese patent document "A SAR Radar Imaging Method and System" (Publication No. CN113917465A) discloses a technical solution, which uses a synthetic virtual array obtained by SAR technology and uses a new imaging algorithm to process the array signal to obtain imaging information of the target.

[0003] The bouncing ray method is an electromagnetic high-frequency approximation algorithm that combines physical optics and geometric optics. It uses geometric optics to trace the path of rays acting multiple times on the target surface or inside the medium, and then uses physical optics to calculate the contribution of rays to scattering after leaving the target surface, thereby obtaining the far-field scattering field of the target. At the same time, the same ray tracing method is also used in optical imaging to obtain the influence of the target's visible light / infrared material on light propagation and optical imaging, thereby obtaining an accurate visible light / infrared image of the target. Chinese patent document "Bistatic scattering center modeling method based on bouncing ray method" (publication number CN112799063A) discloses a technical solution, which forms a target grid model through target geometric modeling and segmentation, and then realizes the construction of the target bistatic scattering center model through a bistatic ray path and scattering field calculation method based on the bouncing ray method, a bistatic ray position equivalence method, a three-dimensional bistatic ISAR image rapid generation method based on image domain ray tube integration, and a scattering center extraction algorithm based on CLEAN.

[0004] Visible light / infrared imaging has a long wavelength and is difficult to penetrate shielding and camouflage, and the optical imaging system is greatly affected by weather and light. However, SAR imaging can image at all times of the day and in all weather conditions, can penetrate certain shielding and camouflage, and its imaging resolution remains unchanged as the distance between the radar and the target increases. However, SAR images also have problems such as not being able to be intuitively interpreted. Summary of the invention

[0005] In view of this, the present application proposes a synthetic aperture radar imaging method and a photoelectric sensor simulation platform in a photoelectric sensor simulation platform with an optical imaging system.

[0006] According to one aspect of the present application, a synthetic aperture radar imaging method in an optoelectronic sensor simulation platform having an optical imaging system is provided, the method comprising:

[0007] Step 1, segmenting the target three-dimensional model;

[0008] Step 2, using the ray tracing method homologous to that in the optical imaging system to obtain the propagation path of the ray;

[0009] Step 3: Use the bouncing ray method to simulate and calculate the far-field scattering field of the target, and perform data processing on the far-field scattering field to obtain a synthetic aperture radar image of the target.

[0010] Preferably, the method further comprises:

[0011] In the optoelectronic sensor simulation platform, an optical imaging system that is homologous to the synthetic aperture radar imaging system is used to perform visible light and infrared imaging of the target in the same imaging plane, and the synthetic aperture radar image of the target is matched with the optical image.

[0012] Preferably, said segmenting the target three-dimensional model comprises: segmenting the metal surface of the target three-dimensional model by using triangular facets, and segmenting the medium part of the target three-dimensional model by using tetrahedrons.

[0013] Preferably, it is characterized in that step 2 comprises:

[0014] Step 201, using a geometric optics method to track the propagation path distance of a plurality of parallel rays equivalent to an electromagnetic field when bouncing on a target metal or coating surface, and the angle at which the rays are simultaneously reflected and transmitted at the interface between two medium tetrahedrons;

[0015] Step 202, calculating the ray field intensity during the ray propagation process.

[0016] Preferably, step 3 comprises:

[0017] Step 301, calculating the far-field scattering field of the ray according to the intersection point of the ray with the target surface when the ray leaves the target surface and the ray field intensity, and superimposing to obtain the far-field scattering field of the target;

[0018] Step 302, obtaining a three-dimensional shape function according to the far-field scattering field of the target;

[0019] Step 303: Project the three-dimensional shape function onto the imaging plane to obtain a target synthetic aperture radar image.

[0020] The present application provides a photoelectric sensor simulation platform, which has an optical imaging system and includes:

[0021] A segmentation module, used for segmenting the target three-dimensional model;

[0022] An acquisition module, used for acquiring the propagation path of the ray using a ray tracing method homologous to that in the optical imaging system;

[0023] The synthetic aperture radar image module is used to simulate and calculate the far-field scattering field of the target by using the bouncing ray method, and to perform data processing on the far-field scattering field to obtain the synthetic aperture radar image of the target.

[0024] Preferably, the simulation platform also includes:

[0025] The matching module is used to use an optical imaging system homologous to the synthetic aperture radar imaging system to perform visible light and infrared imaging of the target in the same imaging plane, and to match the target radar synthetic aperture radar image with the optical image.

[0026] Preferably, the segmentation module is further used to segment the metal surface of the target three-dimensional model using triangular facets, and segment the medium part of the target three-dimensional model using tetrahedrons.

[0027] Preferably, the acquisition module is also used to track the propagation path distance of several parallel rays equivalent to the electromagnetic field when they bounce on the target metal or coated surface through geometric optics, as well as the angle at which the rays are simultaneously reflected and transmitted at the tetrahedral interface of two media; and calculate the ray field intensity during ray propagation.

[0028] Preferably, the synthetic aperture radar image module is further used to calculate the far-field scattering field of the ray according to the intersection point with the target surface when the ray leaves the target surface and the ray field intensity, and superimpose to obtain the far-field scattering field of the target; obtain a three-dimensional shape function according to the far-field scattering field of the target; and project the three-dimensional shape function onto an imaging plane to obtain a synthetic aperture radar image of the target.

[0029] According to the technical solution of this application, the operating frequency of the photoelectric sensor simulation platform has been successfully extended to the radar microwave field. Radar SAR and optical homologous simulation imaging have also laid a good foundation for subsequent research in the fields of image registration, feature fusion, and target recognition. SAR imaging and optical imaging homologous simulation have expanded the operating frequency range of the simulation platform and solved the problem of insufficient information obtained in a single mode, enabling the simulation platform to adapt to the increasingly complex electromagnetic environment and various imaging needs.

[0030] The present application adds a simulation module of target SAR image to the photoelectric sensor simulation platform, thereby expanding the operating frequency range; the SAR imaging system, which is homologous to optical imaging, solves the problem of heavy reliance on light and environment under a single optical imaging system; optical imaging and SAR imaging use the same ray tracing method, which reduces simulation time while also reducing computer memory requirements; after the SAR image and the optical image are imaged and matched on the same imaging plane, the optical image can be enhanced to a certain extent, which also makes up for the deficiency that the SAR image cannot be intuitively interpreted.

[0031] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings constituting a part of the present application are used to provide a further understanding of the present application, and the schematic implementation modes and descriptions of the present application are used to explain the present application. In the accompanying drawings:

[0033] Figure 1 A flow chart of a synthetic aperture radar imaging method in an optoelectronic sensor simulation platform with an optical imaging system provided in the present application;

[0034] Figure 2 Schematic diagram of the triangular face element and tetrahedron provided in this application respectively dividing the metal surface and dielectric body of the target

[0035] Figure 3 Schematic diagram of the transmission and reflection angles of the non-uniform plane wave provided in this application at different medium interfaces;

[0036] Figure 4-Figure 7 The three-dimensional schematic diagram of the model, visible light imaging results, infrared imaging results, and SAR imaging results provided in this application are respectively;

[0037] Figure 8 Schematic diagram of the photoelectric sensor simulation platform provided for this application. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments of the present application and the features in each embodiment may be combined with each other.

[0039] The present application will be described in detail below with reference to the accompanying drawings and in combination with implementation modes.

[0040] In order to improve the simulation platform, this application provides a SAR imaging method that is homologous to optical imaging. In this method, optical imaging and SAR imaging use the same ray tracing technology, which reduces the computing time and memory while effectively expanding the operating frequency range of the photoelectric sensor simulation platform, solving the problem of insufficient information obtained in a single mode, and enabling the simulation platform to adapt to increasingly complex electromagnetic environments and various imaging requirements. In this application, homologous refers to the same sensor-carrying platform, the same imaging perspective or imaging plane.

[0041] To achieve the above technical objectives, the present application provides a SAR imaging method that is homologous to optical imaging, such as Figure 1 As shown, the method includes:

[0042] Step 1, segmenting the target three-dimensional model;

[0043] Step 2, using the ray tracing method homologous to that in the optical imaging system to obtain the propagation path of the ray;

[0044] Step 3: Use the bouncing ray method to simulate and calculate the far-field scattering field of the target, and perform data processing on the far-field scattering field to obtain a synthetic aperture radar image of the target.

[0045] Preferably, the present application also uses an optical imaging system homologous to the radar imaging system in the photoelectric sensor simulation platform to perform visible light and infrared imaging of the target in the same imaging plane, and matches the target radar SAR image with the optical image.

[0046] In step 1, triangular face elements and tetrahedrons are used to segment the metal surface and dielectric body of the target, respectively, as follows: Figure 2 As shown, the segmentation size is generally selected as 1 / 10 of the wavelength, and then a number of parallel rays equivalent to electromagnetic waves are used to illuminate the target, and the geometric optics method is used to trace the ray paths after reflection and transmission on the target surface and inside.

[0047] In step 2, we first analyze the rays reflected on the target metal surface, assuming that the starting point of the ray is a point in space. The direction of ray propagation is The propagation distance is t, then the propagation path of the ray is expressed as:

[0048]

[0049] If any point within a triangular element of the target metal surface is known Then the plane equation of the triangular surface element is expressed as:

[0050]

[0051] in, is the three-dimensional coordinate of any vertex in the triangular face element, that is, the coordinates of the three vertices are expressed as: is the unit normal vector of this triangle surface element:

[0052]

[0053] By combining the above three equations, we can find the propagation distance of the ray reflected on the target surface:

[0054]

[0055] For rays propagating in a dielectric tetrahedron, the center point of the bright triangle of the dielectric tetrahedron is used as the starting point of the ray. At this time, the ray propagates in a straight line and will inevitably intersect with one of the other three triangles of this tetrahedron. Therefore, the remaining three faces of the tetrahedron are first cycled to find the triangle that intersects with the ray. Then calculate the transmission and reflection angles generated at different dielectric interfaces when the non-uniform plane wave propagates in a lossy medium, such as Figure 3 As shown:

[0056] in is the surface normal vector of the medium, is the amplitude vector of the incident wave, is the phase vector of the incident wave, and The angle between them is δ1, and the incident wave propagation vector can be expressed as When the phase vector of the incident wave is When the angle is θ1, the phase vector of the transmitted wave is and The angle between them is θ2, at this time and The angle is δ2.

[0057] The transmission angle of rays at the interface of different media can be obtained by calculation:

[0058]

[0059] Among them, θ′ and θ″ are two critical values ​​where angle blur occurs, Γ2=θ2+δ2.

[0060] In step 3, the change of the ray field intensity during the ray propagation process is calculated.

[0061] For the ray reflected on the target surface, it is assumed that the electric field strength of the ray at a point P in space is After being reflected on the target metal surface, it reaches point P'. The field intensity at point P' can be calculated by the geometric optics method as follows:

[0062]

[0063] Where d is the distance the ray travels from point P to point P', R is the reflection coefficient, DF is the divergence factor, j is the imaginary unit, k is the wave number, and jk is the wave vector.

[0064] When the ray leaves the target surface after one or more impacts, the position and field intensity of the intersection with the target surface can be used to calculate the far-field scattering field of the ray.

[0065] The far-field scattering of a single ray tube can be approximately expressed as:

[0066]

[0067] Among them, A θ and yes and Two amplitude components in the direction. r is the distance the electromagnetic wave propagates, θ and φ are two directions centered on the emission source, Represent unit vectors in two directions respectively.

[0068] For rays propagating inside a dielectric body, its far-field electric field can be expressed as:

[0069]

[0070] Where η is the wave impedance in free space, is the direction of the far-field scattering field, is the intersection point of the ray at the boundary between the air and the target surface, is the equivalent current density.

[0071] By superimposing the contributions of all rays to the far-field scattering field of the target, the far-field scattering field of the entire target can be obtained.

[0072] In addition, the target shape function is defined to calculate the relationship between the target shape and the far-zone scattered field.

[0073] Assume that the incident electric and magnetic fields are:

[0074]

[0075] in, is the wave vector, is the position vector, ω is the angular frequency, and μ0 is the magnetic permeability. represents the time of the time-harmonic electric field, and E0 is the electric field intensity, which is a scalar.

[0076] Where the surface of an object is irradiated by electromagnetic waves, that is, the bright area, a surface current will be generated, which can be expressed as:

[0077]

[0078] in, is The normal vector at is the surface current.

[0079] The far-field scattered field of the induced current on the target surface can be expressed as follows when the boundary conditions are met:

[0080]

[0081] in is the free space Green's function:

[0082]

[0083] Then the target far-zone scattered field can be expressed as:

[0084]

[0085] Defining shape functions for:

[0086]

[0087] in, is the impulse function;

[0088] Assume that the radar receives the target far-field scattered field component, it can be expressed as

[0089]

[0090] The three-dimensional Fourier transform of the shape function is defined as:

[0091]

[0092] That is, the target can be The far-field scattered field in the direction is expressed as:

[0093]

[0094] It can be seen from the above formula that the shape function of the target has a corresponding relationship with the three-dimensional Fourier transform of the far-field field. Therefore, after obtaining the far-field scattering field of the target, the three-dimensional shape of the target can be obtained by performing an inverse Fourier transform on it. At the same time, the two-dimensional SAR image of the target can be obtained by projecting the three-dimensional shape function onto a certain imaging plane. Assuming that the imaging plane is the xoz plane, then:

[0095]

[0096] Let the two-dimensional shape function be Substituting into the above formula, we can get:

[0097]

[0098] So The scattered field component in the direction is:

[0099]

[0100] In k y = 0, the two-dimensional shape function of the target can be obtained by performing a two-dimensional inverse Fourier transform on its far-field scattering field:

[0101]

[0102] in, Represents the direction of radar observation, which can also be other angles Therefore, the above formula can be rewritten as:

[0103]

[0104] It can be seen from this that after obtaining the far-field scattering field of the target, that is, the echo data, it is only necessary to perform a two-dimensional inverse Fourier transform on it to obtain a two-dimensional SAR image of the target in the corresponding imaging plane.

[0105] After obtaining the target radar far-zone scattering field and its relationship with the target two-dimensional image, its radar SAR image can be obtained.

[0106] At the same time, because the SAR imaging process uses the same ray tracing method as optical imaging, in the same imaging plane, when the optical imaging system in the photoelectric sensor simulation platform obtains the visible light and infrared images of the target, it can be used to reduce the calculation process in the optical imaging, so as to speed up the simulation process and reduce the need for computer memory. It is also possible to match the radar SAR image with the optical image, which can not only expand the working frequency range of the simulation platform, but also solve the problem of insufficient information obtained in the single mode of the original platform.

[0107] In order to verify the effectiveness of the present invention, SAR and optical homologous simulation imaging of the T90 tank target is performed in the same imaging plane in the photoelectric sensor simulation platform. The radar parameter settings are shown in Table 1 below, and the photoelectric sensor parameters are shown in Table 2.

[0108] Table 1 Radar parameters

[0109] Center frequency 6GHz bandwidth 1.5GHz Sweep times 101 Pitch Angle 73° Azimuth -7.15°～7.15° Sweep angle times 101

[0110] Table 2 Sensor parameters

[0111]

[0112] Table 3 Time and memory required for separate / homogeneous simulation of SAR and optical systems

[0113]

[0114] When performing SAR and optical homologous simulation imaging of the T90 tank target in the same imaging plane in the optoelectronic sensor simulation platform, different observation angles need to be set for the SAR imaging system and the optical imaging system. This is because there is an essential difference in the imaging principles between the two. In the SAR imaging system, the propagation direction of the radar electromagnetic wave is the direction represented by the distance of the image.

[0115] Figure 4 is a three-dimensional schematic diagram of the model. The visible light imaging results in the optical imaging system are shown in Figure 5 , infrared imaging results are shown in Figure 6 , the imaging results of the SAR imaging system are shown in Figure 7 . After the homologous SAR image and optical image are matched, the target details in the visible light and infrared images are more obvious and more consistent with the actual situation, which can help understand the SAR image; and compared with the optical image, the SAR image has more prominent special parts such as tracks and gun barrels, which can effectively know the key parts of the target. At the same time, it can be seen from Table 3 that after the homologous simulation is adopted for the SAR imaging and optical imaging systems, the simulation time is less than the sum of the simulation times of the two, and the required computer memory is also reduced accordingly. This example not only illustrates that SAR imaging and optical imaging are accurate, but also embodies the homologous simulation of SAR imaging and optical imaging, solves the problem of insufficient information obtained in a single mode, and successfully expands the advantages of the working frequency range of the simulation platform, speeds up the simulation speed and reduces the demand for computer memory, verifying the effectiveness of the present invention.

[0116] This application proposes a SAR imaging method that is homologous to optical imaging. It uses a ray tracing method that is homologous to optical imaging to determine the path of ray reflection and transmission inside and on the surface of the target, so as to reduce simulation time and computer memory. Then, the bouncing ray method is used to obtain the far-field scattering field data of the target, and a high-resolution radar SAR image of the target is obtained through subsequent processing. At the same time, an optical imaging system is used in the photoelectric sensor simulation platform to perform visible light and infrared imaging of the target. In addition to achieving the purpose of expanding the operating frequency range of the simulation platform, it also solves the problem of insufficient information under the single optical imaging system of the original simulation platform.

[0117] This application provides a photoelectric sensor simulation platform, such as Figure 8 As shown, the simulation platform has an optical imaging system, which includes: a segmentation module for segmenting the target three-dimensional model; an acquisition module for acquiring the propagation path of the ray using a ray tracing method homologous to that in the optical imaging system; a synthetic aperture radar image module for simulating and calculating the far-field scattering field of the target using a bouncing ray method, and performing data processing on the far-field scattering field to obtain the synthetic aperture radar image of the target. The simulation platform also includes: a matching module for performing visible light and infrared imaging of the target in the same imaging plane using an optical imaging system homologous to the synthetic aperture radar imaging system, and matching the target radar synthetic aperture radar image with the optical image. The segmentation module is also used to segment the metal surface of the target three-dimensional model using triangular facets, and to segment the medium part of the target three-dimensional model using tetrahedrons. The acquisition module is also used to track the propagation path distance of several parallel rays equivalent to electromagnetic fields when bouncing on the target metal or coating surface, and the angle of simultaneous reflection and transmission of the rays at the interface of the tetrahedron of the two media through the geometric optics method; and calculate the ray field intensity during ray propagation. The synthetic aperture radar image module is also used to calculate the far-field scattering field of the ray based on the intersection point with the target surface when the ray leaves the target surface and the ray field intensity, and superimpose to obtain the far-field scattering field of the target; obtain the three-dimensional shape function based on the far-field scattering field of the target; and project the three-dimensional shape function onto the imaging plane to obtain the synthetic aperture radar image of the target. The three-dimensional shape function is related to the shape of the target and is an electromagnetic wave function that can reflect the three-dimensional shape characteristics of the target.

[0118] The above description is only a preferred implementation mode of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A synthetic aperture radar (SAR) imaging method in a photoelectric sensor simulation platform with an optical imaging system, characterized in that: The method includes: Step 1, segmenting the target three-dimensional model; Step 2, using the ray tracing method homologous to that in the optical imaging system to obtain the propagation path of the ray; Step 3: Use the bouncing ray method to simulate and calculate the far-field scattering field of the target, and perform data processing on the far-field scattering field to obtain a synthetic aperture radar image of the target.

2. The SAR imaging method according to claim 1, characterized in that: The method further includes: In the optoelectronic sensor simulation platform, an optical imaging system that is homologous to the synthetic aperture radar imaging system is used to perform visible light and infrared imaging of the target in the same imaging plane, and the synthetic aperture radar image of the target is matched with the optical image.

3. The synthetic aperture radar imaging method according to claim 1, characterized in that: The segmentation of the target three-dimensional model includes: segmenting the metal surface of the target three-dimensional model by using triangular facets, and segmenting the medium part of the target three-dimensional model by using tetrahedrons.

4. The synthetic aperture radar imaging method according to claim 3, characterized in that: Step 2 includes: Step 201, using a geometric optics method to track the propagation path distance of a plurality of parallel rays equivalent to an electromagnetic field when bouncing on a target metal or coating surface, and the angle at which the rays are simultaneously reflected and transmitted at the interface between two medium tetrahedrons; Step 202, calculating the ray field intensity during the ray propagation process.

5. The synthetic aperture radar imaging method according to claim 4, characterized in that: Step 3 includes: Step 301, calculating the far-field scattering field of the ray according to the intersection point of the ray with the target surface when the ray leaves the target surface and the ray field intensity, and superimposing to obtain the far-field scattering field of the target; Step 302, obtaining a three-dimensional shape function according to the far-field scattering field of the target; Step 303: Project the three-dimensional shape function onto the imaging plane to obtain a target synthetic aperture radar image.

6. A photoelectric sensor simulation platform, the simulation platform having an optical imaging system, characterized in that: The simulation platform includes: A segmentation module, used for segmenting the target three-dimensional model; An acquisition module, used for acquiring the propagation path of the ray using a ray tracing method homologous to that in the optical imaging system; The synthetic aperture radar image module is used to simulate and calculate the far-field scattering field of the target by using the bouncing ray method, and to perform data processing on the far-field scattering field to obtain the synthetic aperture radar image of the target.

7. The simulation platform according to claim 6, characterized in that: The simulation platform also includes: The matching module is used to use an optical imaging system homologous to the synthetic aperture radar imaging system to perform visible light and infrared imaging of the target in the same imaging plane, and to match the target radar synthetic aperture radar image with the optical image.

8. The simulation platform according to claim 6, characterized in that: The segmentation module is also used to segment the metal surface of the target three-dimensional model using triangular facets and to segment the medium part of the target three-dimensional model using tetrahedrons.

9. The simulation platform according to claim 8, characterized in that: The acquisition module is also used to track the propagation path distance of several parallel rays equivalent to the electromagnetic field when they bounce on the target metal or coated surface through the geometric optics method, as well as the angle at which the rays are simultaneously reflected and transmitted at the tetrahedral interface of two media; and calculate the ray field intensity during the ray propagation process.

10. The simulation platform according to claim 9, characterized in that: The synthetic aperture radar image module is also used to calculate the far-field scattering field of the ray based on the intersection point with the target surface when the ray leaves the target surface and the ray field intensity, and superimpose to obtain the far-field scattering field of the target; obtain a three-dimensional shape function based on the far-field scattering field of the target; and project the three-dimensional shape function onto the imaging plane to obtain a synthetic aperture radar image of the target.

Images