Multi-source radiation coupled target infrared polarization characteristic inversion method

Abstract

The invention provides a multi-source radiation coupled target infrared polarization characteristic inversion method. The method comprises the following steps: S1, acquiring temperature parameters of a background, a target and an incident source, an angle parameter of the incident source and a surface material parameter of the target; s2, calculating the equivalent black body radiation brightness of the background, the target and the incident source; s3, calculating a first specular reflection heat radiation component and a second specular reflection heat radiation component; s4, calculating a first diffuse reflection heat radiation component and a second diffuse reflection heat radiation component; s5, calculating a self-heating radiation component of the target; s6, obtaining three parameters in a reflection Stokes vector according to the first specular reflection thermal radiation component, the second specular reflection thermal radiation component, the first diffuse reflection thermal radiation component, the second diffuse reflection thermal radiation component and the target self-heating thermal radiation component; and S7, obtaining the target polarization degree of the target according to the three parameters. The method has the beneficial effect that the accuracy of target infrared polarization feature inversion can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of imaging measurement, and in particular to a method for inverting infrared polarization characteristics of a target with multi-source radiation coupling. Background Art

[0002] Compared with traditional infrared imaging, infrared polarization imaging technology can not only obtain the spatial distribution, temperature radiation and other characteristics of scene targets, but also obtain additional effective information such as polarization degree and polarization angle, which provides an effective way to solve the problem of efficient and accurate identification of targets in complex environments. At present, domestic and foreign scholars have conducted extensive and in-depth research on infrared polarization imaging technology, and have achieved some breakthrough results in application aspects such as target detection, road detection, and facial recognition. However, the infrared polarization characteristics of the target are affected by many factors such as spatial observation, time evolution, background distribution and its own properties, which makes it difficult to scientifically and meticulously demonstrate the scene adaptability and capability boundaries of infrared polarization imaging technology only by complicated field tests and lack of application experience. Therefore, in order to accurately study the infrared polarization characteristics of various targets and backgrounds and reduce research costs and research cycles, the measurement and modeling of reflected / spontaneous radiation polarization characteristics has become one of the current research hotspots in this field of technology.

[0003] At present, in order to further explore the coupling mechanism between the target material properties and surface characteristics and the reflection / spontaneous radiation characteristics, and reveal the target polarization radiation transmission mechanism of polarization imaging under multi-environment and multi-factor conditions, many researchers have carried out research work such as polarized bidirectional reflectance distribution function (pBRDF) model of coated targets and natural background objects, material characteristics analysis and inversion, and polarization characteristics analysis model construction, which provide theoretical support for target detection in complex environments at the mechanism level. For example, in 2015, Renhorn et al. in Sweden [Optics Express, 2015, 23(24): 31253-31273.] added material surface roughness parameters to the existing basis, proposed a polarized bidirectional reflectance distribution function model based on infrared polarization characteristics, and applied it to the simulation of polarization characteristics of paint samples with different roughness, effectively promoting the development of polarization models and their detection and identification applications. However, this model only considers the polarization characteristics in the process of specular reflection, ignores the polarization effect of the diffuse reflection part in the interaction between light and matter, and does not consider the occlusion and shadow effects between adjacent face elements. In 2020, Xie Jian from Xidian University [Research on Simulation Method of Infrared Polarization Characteristics of Typical Targets, Master's Thesis of Xidian University, 2020] introduced a dual diffuse reflection component including anisotropic directional diffuse reflection and isotropic ideal diffuse reflection to model the polarization characteristics of reflected radiation based on the traditional PG (Priest-Germer) model, achieving a more accurate inversion of target polarization characteristics. In 2022, Haodong Shi et al. from Changchun University of Science and Technology [Optics and Laser Technology, 2022: (151): 108069] established an analytical model of infrared polarization characteristics of rough surfaces with shadow occlusion functions, and quantitatively analyzed the influence of incident angle and surface roughness on target polarization characteristics, which provides theoretical guidance for the study of target polarization characteristics in real environments.

[0004] Among the above existing methods, domestic and foreign scholars have conducted extensive research on pBRDF and established many theoretical models that are more in line with practical applications, which has greatly promoted the development of polarization research. However, in actual applications, the infrared polarization characteristics of the target are easily affected by background radiation, target spontaneous radiation and incident source radiation. This multi-source radiation coupling mechanism leads to the following three deficiencies in the existing target infrared polarization characteristic inversion methods: 1) Lack of consideration of the actual effect of background radiation, especially the sky background in the actual field and the environmental background in the laboratory, resulting in low accuracy in polarization characteristic inversion; 2) Ignoring the impact of the temperature difference between the target and the background on the polarization characteristics, which in turn affects the accuracy of infrared polarization information; 3) Failure to effectively model the interaction of multi-source radiation coupling, making it difficult to accurately invert the infrared polarization characteristics of the target.

[0005] Therefore, how to explore the influence of background radiation on the target polarization characteristics, construct the coupling mechanism of multi-source radiation (background radiation, target spontaneous radiation and incident source radiation), and establish a target infrared polarization characteristic inversion method that is more in line with actual application conditions is a technical problem that needs to be solved urgently in this field. Summary of the invention

[0006] The technical problem to be solved by the present invention is to improve the accuracy of target infrared polarization feature inversion. In order to overcome the defects of the above-mentioned prior art, the present invention provides a target infrared polarization feature inversion method with multi-source radiation coupling.

[0007] The present invention provides a method for inverting target infrared polarization characteristics by multi-source radiation coupling, comprising the following steps: Step S1, obtaining temperature parameters of the background, target and incident source, angle parameters of the incident source and surface material parameters of the target; Step S2, based on Planck's blackbody radiation law, obtaining the equivalent blackbody radiation brightness of the background, the target and the incident source within the detector working band when the temperature is T according to the temperature parameter; Step S3, obtaining a first specular reflection thermal radiation component and a second specular reflection thermal radiation component based on the polarized bidirectional reflectance distribution function and according to the angle parameter, the surface material parameter, the background and the blackbody radiation brightness of the incident source; Step S4, based on the microfacet theory, obtaining a first diffuse reflection thermal radiation component and a second diffuse reflection thermal radiation component according to the angle parameter, the surface material parameter, the blackbody radiation brightness of the background, and the blackbody radiation brightness of the incident source; Step S5, obtaining the target self-heating radiation component according to the angle parameter and the blackbody radiation brightness of the target; Step S6, obtaining three parameters in the reflection Stokes vector according to the first specular reflection heat radiation component, the second specular reflection heat radiation component, the first diffuse reflection heat radiation component, the second diffuse reflection heat radiation component and the target self-heating radiation component; Step S7, obtaining the target polarization degree corresponding to the target according to the three parameters in the reflected Stokes vector.

[0008] Compared with the prior art, the target infrared polarization characteristic inversion method of multi-source radiation coupling of the present invention has the following advantages: 1) The present invention comprehensively considers the multi-source radiation coupling of background radiation, target spontaneous radiation and incident source radiation. By applying Planck's blackbody radiation law and microfacet theory, the contribution of different radiation components to the target infrared polarization characteristics is effectively distinguished and quantified. It can be applied to complex radiation environments and improves the accuracy and robustness of the target infrared polarization characteristics inversion; 2) The present invention combines Kirchhoff's law, the law of conservation of energy and the Stokes matrix method to systematically calculate the polarization characteristic components and polarization degree information of the target surface. Compared with the traditional method, it can more comprehensively extract the infrared polarization information of the target surface, improve the ability to analyze the properties and state of the target surface, and provide richer information for infrared imaging in complex scenes; 3) The present invention innovatively separates and calculates the first specular reflection thermal radiation component, the second specular reflection thermal radiation component, the first diffuse reflection thermal radiation component and the second diffuse reflection thermal radiation component. Combined with the principle of polarization imaging, it can adapt to the diversity of various infrared radiation sources and target materials, has higher adaptability and versatility, and provides theoretical and application support for infrared target detection, tracking and recognition technology.

[0009] In a possible implementation, the temperature parameters include background environment temperature, incident source temperature and target temperature. In step S2, the equivalent blackbody radiation brightness of the background, the target and the incident source in the detector working band is obtained by the following calculation formula: ; ; ; in, represents the blackbody radiation brightness of the background; represents the blackbody radiation brightness of the incident source; represents the blackbody radiation brightness of the target; represents a preset first radiation constant; represents the wavelength of the incident light of the incident source; represents a preset second radiation constant; represents the background ambient temperature; represents the incident source temperature; represents the target temperature.

[0010] In a possible implementation, the angle parameters include the light source zenith angle, the light source azimuth angle, the observation zenith angle, and the observation azimuth angle, and the surface material parameters include the real part of the refractive index, the imaginary part of the refractive index, the roughness, and the specular reflection coefficient of the surface material of the target, and the step S3 includes: Step S31, based on spherical trigonometry and inverse trigonometric functions, obtaining a first angle between a microfacet normal and a macro surface normal, and a second angle between the microfacet normal and an incident light ray according to the light source zenith angle, the light source azimuth angle, the observation zenith angle, and the observation azimuth angle; Step S32, obtaining a third angle between the plane where the macro surface normal and the micro facet normal are located and the incident light, and a fourth angle between the plane where the macro surface normal and the micro facet normal are located and the reflected light according to the light source zenith angle, the observation zenith angle, the first angle and the second angle; Step S33, obtaining the target surface according to the light source zenith angle, the real part of the refractive index, the imaginary part of the refractive index and the second angle s wave and p Fresnel reflection coefficient of the wave; Step S34, obtaining a 2×2 Jones matrix according to the third angle, the fourth angle, the light source azimuth, the observation azimuth, and the Fresnel reflection coefficient, obtaining an incident Stokes vector, and obtaining a Mueller matrix in combination with the Jones matrix; Step S35, obtaining shielding and shading factors according to the first angle, the second angle, the light source zenith angle, and the observation zenith angle; Step S36, obtaining a first distribution function corresponding to the first specular reflection thermal radiation component according to the Mueller matrix, the occlusion and shading factor, the roughness, the specular reflection coefficient, the first angle, and the second angle; Step S37, obtaining the first specular reflection thermal radiation component according to the blackbody radiation brightness of the incident source and the first distribution function; Step S38, integrating the first distribution function in the hemispherical space to obtain a second distribution function corresponding to the second specular reflection thermal radiation component, and obtaining the second specular reflection thermal radiation component according to the blackbody radiation brightness of the background and the second distribution function.

[0011] In a possible implementation, in step S31, the first distribution function is obtained by the following calculation formula: ; ; in, represents the first distribution function; represents the specular reflection coefficient; represents the Mueller matrix; represents the occlusion and shading factor; represents the first angle; represents the second angle; represents said roughness; represents the zenith angle of the light source; represents the observation zenith angle; exp() represents the natural exponential function operation; represents the azimuth of the light source; represents the observation azimuth; Represents the difference between the observation azimuth and the light source azimuth.

[0012] In a possible implementation, in step S32, the second distribution function is obtained by the following calculation formula: ; in, represents the second distribution function; represents the first distribution function; represents the zenith angle of the light source; represents the azimuth angle of the light source.

[0013] In a possible implementation, the angle parameters include an observation zenith angle, a light source zenith angle, and a light source azimuth angle, and the surface material parameters include a directional diffuse reflectance, a roughness, and an ideal diffuse reflectance, and step S4 includes: Step S41, obtaining a third distribution function corresponding to the first diffuse reflection thermal radiation component according to the directional diffuse reflection coefficient, the roughness, the observation zenith angle and the ideal diffuse reflection coefficient; Step S42, integrating the third distribution function in a hemispherical space to obtain a fourth distribution function corresponding to the second diffuse reflection thermal radiation component; Step S43, obtaining the first diffuse reflection thermal radiation component according to the third distribution function and the blackbody radiation brightness of the incident source; Step S44: obtaining the second diffuse reflection thermal radiation component according to the fourth distribution function and the blackbody radiation brightness of the background.

[0014] In a possible implementation, in step S41, the third distribution function is obtained by the following calculation formula: ; in, represents the third distribution function; represents the directional diffuse reflectance; represents said roughness; represents the observation zenith angle; represents the ideal diffuse reflectance.

[0015] In a possible implementation, in step S42, the fourth distribution function is obtained by the following calculation formula: ; in, represents the fourth distribution function; represents the directional diffuse reflectance; represents said roughness; represents the observation zenith angle; represents the zenith angle of the light source; represents the azimuth of the light source; represents the ideal diffuse reflectance.

[0016] In a possible implementation, the angle parameters include an observation zenith angle, an observation azimuth angle, a light source zenith angle, and a light source azimuth angle, and the surface material parameters include roughness, a real part of a refractive index, an imaginary part of a refractive index, and a specular reflection coefficient, and step S5 includes: Step S51, obtaining the hemispherical reflectivity of the target surface according to the observation zenith angle, the observation azimuth angle, the light source zenith angle and the light source azimuth angle; Step S52, based on Kirchhoff's law and the law of conservation of energy, the emissivity of the target surface is obtained according to the hemispherical reflectivity and the pre-acquired blackbody emissivity; Step S53, obtaining the target self-heating radiation component according to the emissivity and the blackbody radiation brightness of the target.

[0017] In a possible implementation, step S6 includes: Step S61, converting the blackbody radiation brightness corresponding to the background, the incident source, and the target into vector expressions in the form of Stokes vectors respectively; Step S62, combining each of the vector expressions with the first specular reflection thermal radiation component, the second specular reflection thermal radiation component, the first diffuse reflection thermal radiation component, the second diffuse reflection thermal radiation component and the target self-heating radiation component to obtain the three parameters within the reflection Stokes vector. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the infrared polarization characteristic source of the object of the present invention; Figure 2 is a flow chart of the steps of the present invention; Figure 3 It is a geometrical schematic diagram of the incident source and the detector of the present invention; Figure 4 It is a schematic diagram comparing the measured results of the present invention with different inversion methods. DETAILED DESCRIPTION

[0019] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present invention, and are not intended to limit the protection scope of the embodiments of the present invention. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0020] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] See also Figure 1 In order to clearly explain the method proposed in the present invention, the basic principles and concepts of infrared polarization imaging are first described. Figure 1As shown in the figure, the infrared polarization characteristics of the target are mainly composed of the polarization effects of the target's own thermal radiation and the target's surface reflected thermal radiation. Therefore, in the actual imaging measurement process, the total radiation energy of the target is the sum of the reflected radiation generated by the incident source and the background environment through the material surface, the energy emitted by the self-radiation, and the path radiation, that is: ; in, Indicates the target infrared radiation energy received by the imaging detector, represents the target's self-heating radiation component, Represents the background ambient thermal radiation component reflected by the target surface, represents the incident source thermal radiation component reflected by the target surface, It represents the radiant brightness transmitted from the target to the imaging detector.

[0022] The embodiment of the present invention takes an aluminum plate sprayed with black paint as the analysis object, and inverts its infrared polarization characteristics, wherein the measured data comes from: using a laser as the incident light source in a laboratory environment to irradiate the target area to be measured, and using an infrared polarization imaging camera to realize data acquisition; keeping the difference between the azimuth angle of the incident source and the azimuth angle of the camera at 180°, that is, fixed on the same reflecting surface; the incident source is incident on the center of the target at a zenith angle of 40°; the observation zenith angle of the camera starts from 0°, with a step size of 0°, and gradually increases to a zenith angle of 80°.

[0023] The present invention proposes a method for inverting infrared polarization characteristics of a target coupled with multi-source radiation. The technical scheme adopted is: on the basis of obtaining temperature characteristics of different sources, the background radiation brightness, the target spontaneous radiation brightness and the incident source radiation brightness are calculated based on Planck's blackbody radiation law; secondly, the first specular reflection thermal radiation component under the radiation of the incident source is calculated by using the microfacet theory, Fresnel's reflection law and Snell's law, and the second specular reflection thermal radiation component under the background radiation is calculated according to the hemispherical reflection theory; then, the first diffuse reflection thermal radiation component under the radiation of the incident source and the second diffuse reflection thermal radiation component under the background radiation are calculated; then, according to Kirchhoff's law and the law of conservation of energy, the polarization characteristic component of the target infrared spontaneous radiation is calculated; on this basis, the Stokes matrix method is applied to establish a target surface infrared polarization characteristic model under the coupling of multi-source radiation (background radiation, target spontaneous radiation and incident source radiation), and the acquisition of target polarization degree information is further realized according to the principle of polarization imaging.

[0024] See also Figure 2 The specific process of the method of the present invention includes: Step S1, obtaining temperature parameters of the background, target and incident source, angle parameters of the incident source and surface material parameters of the target; Step S2, based on Planck's blackbody radiation law, the temperature is obtained according to the temperature parameter T The equivalent blackbody radiation brightness of the background, target and incident source in the detector working band; Step S3, based on the polarized bidirectional reflectance distribution function, obtaining the first specular reflection thermal radiation component and the second specular reflection thermal radiation component according to the angle parameters, the surface material parameters, the background and the black body radiation brightness of the incident source; Step S4, based on the microfacet theory, obtaining the first diffuse reflection thermal radiation component and the second diffuse reflection thermal radiation component according to the angle parameter, the surface material parameter, the black body radiation brightness of the background and the black body radiation brightness of the incident source; Step S5, obtaining the target self-heating radiation component according to the angle parameter and the blackbody radiation brightness of the target; Step S6, obtaining three parameters in the reflection Stokes vector according to the first specular reflection heat radiation component, the second specular reflection heat radiation component, the first diffuse reflection heat radiation component, the second diffuse reflection heat radiation component and the target self-heating radiation component; Step S7, obtaining the target polarization degree corresponding to the target according to the three parameters in the reflected Stokes vector.

[0025] Furthermore, the temperature parameter in step S1 includes the background ambient temperature , incident source temperature and target temperature ; Surface material parameters include the real part of the refractive index of the target surface material , imaginary part of refractive index , Roughness , Specular reflection coefficient , Directional diffuse reflectance and ideal diffuse reflectance ; Angle parameters include the zenith angle of the light source and the light source azimuth , and the observation zenith angle and the observation azimuth .

[0026] Further, in step S2, according to Planck's blackbody radiation law, the blackbody radiation brightness at temperature T The general calculation formula is: ; in, represents the first radiation constant, and , represents the second radiation constant, and , Indicates wavelength; Therefore, combining the temperature parameters of different radiation sources obtained in step S1 and Planck's blackbody radiation law, the equivalent blackbody radiation brightness of the background, incident source and target in the detector working band (8~14μm) can be calculated as follows: ; ; ; From the above formula, the blackbody radiation brightness of the background, incident source and target are: .

[0027] Further, the first specular reflection thermal radiation component and the second specular reflection thermal radiation component generated by the incident source and the background environment in step S3 are calculated using a polarized bidirectional reflectance distribution function (pBRDF), see Figure 3 As shown, pBRDF describes the reflection polarization characteristics of the target surface at any observation angle from the perspective of radiometry on the basis of geometric optics. It is related to many factors such as the incident source angle, observation angle, roughness and surface refractive index. The specific expression is: ; in, Represents the pBRDF function of the target surface, in units of ; and They represent the light source zenith angle and light source azimuth angle of the incident source respectively; and They represent the observation zenith angle and observation azimuth angle of the observation position respectively; Indicates that the target is apparently from Directional differential radiation brightness, which reflects the magnitude of infrared radiation received by the target surface from the incident source; Indicates that the target surface is Specular thermal radiation component in the direction; subscript and represent incident and reflected respectively.

[0028] Further, step S3 is extended to include: S31: Based on spherical trigonometry and inverse trigonometric functions, a first angle between a microfacet normal and a macro surface normal, and a second angle between a microfacet normal and an incident light ray are obtained according to a light source zenith angle, a light source azimuth angle, an observation zenith angle, and an observation azimuth angle; The parameters required to obtain the first specular reflection thermal radiation component and the second specular reflection thermal radiation component in step S1 include: the zenith angle of the light source and the light source azimuth Observation zenith angle and the observation azimuth ; The real part of the refractive index of the target surface material , imaginary part of refractive index , Roughness , Specular reflection coefficient ; The first angle between the microfacet normal and the macro surface normal can be obtained by using the vector calculation method of spherical trigonometry. , the second angle between the microfacet normal and the incident light They are: ; in, ; Then, the first angle can be obtained by calculating the inverse trigonometric function: and the second angle They are: ; Combining the above two formulas, we can calculate the first angle between the microfacet normal and the macro surface normal. , the second angle between the microfacet normal and the incident light ; Step S32, obtaining a third angle between the plane formed by the macro surface normal and the micro facet normal and the incident light, and a fourth angle between the plane formed by the macro surface normal and the micro facet normal and the reflected light according to the light source zenith angle, the observation zenith angle, the first angle and the second angle; Using the vector calculation method of spherical trigonometry, we can get the third angle between the incident light and the plane composed of the macro surface normal and the micro surface element normal. , the fourth angle between the plane formed by the reflected light and the macro surface normal and the micro surface element normal They are: ; Then, the third angle can be calculated based on the inverse trigonometric function: and the fourth angle They are: ; Combining the above two formulas, we can calculate the third angle between the incident light and the plane formed by the macro surface normal and the micro surface element normal: , the angles between the reflected light and the planes formed by the macro surface normal and the microfacet normal ; Step S33, obtaining the target surface according to the light source zenith angle, the real part of the refractive index, the imaginary part of the refractive index and the second angle s wave and pFresnel reflection coefficient of the wave; For metal materials with complex refractive index, the Fresnel reflectivity and It can be expressed as: ; ; in, ; In the formula, n and k represent the real part and imaginary part of the refractive index of the target surface material respectively; Calculate the target surface s wave and p Fresnel reflection coefficient of the wave and The expression is ; ; Combining the above two formulas, the Fresnel reflectivity can be calculated and ; Fresnel reflection coefficient and ; Step S34, obtaining a 2×2 Jones matrix according to the third angle, the fourth angle, the light source azimuth, the observation azimuth, and the Fresnel reflection coefficient, obtaining an incident Stokes vector, and obtaining a Mueller matrix in combination with the Jones matrix; Usually, the incident radiation and reflected radiation have two mutually orthogonal components, namely s Quantity and p The electric field vector transmission relationship of the components can be expressed by a 2×2 Jones matrix: ; in, and represent the complex electric field components perpendicular to the incident and reflected planes, respectively; and represent the complex electric field components parallel to the incident plane and the reflected plane respectively; and For s wave and p Fresnel reflection coefficient of the wave; T is the Jones matrix; Then, the four elements of the Jones matrix T , , , It is obtained by two rotation matrices and a Fresnel reflection matrix, namely: ; Combining the above two formulas, we can get the four elements of the Jones matrix T , , and ; Considering that both the background environment and the incident source such as the sun or black body are unpolarized light, that is, the incident Stokes vector , so the 4×4 Mueller matrix With the incident Stokes vector After the operation, only four elements in the first column remain, namely , , and ; According to the conversion relationship between Mueller matrix and Jones matrix, The expression is: ; in, Represents complex conjugate, and the Mueller matrix can be calculated using the above formula The elements in are , , ; Step S35, obtaining the shielding and shading factors according to the first angle, the second angle, the light source zenith angle and the observation zenith angle; Occlusion and shading factors It reflects the geometric attenuation effect of the undulating state of the target surface on the light. That is, the rougher the target surface, the more obvious the shielding effect, and thus the more obvious the impact on its surface scattering and radiation characteristics. According to the research theory of Torrance Sparrow and Blinn et al. [Josa, 1967,57(9):1105], the shadow and occlusion function in the specular reflection component It is expressed as: ; Using the above formula, we can get the shadow and occlusion function ; Step S36, obtaining a first distribution function corresponding to the first specular reflection thermal radiation component according to the Mueller matrix, the shading and shadowing factor, the roughness, the specular reflection coefficient, the first angle and the second angle; The first distribution function of the first specularly reflected thermal radiation component under the action of the incident source can be expressed as: ; in, is the distribution function of the normal direction of the microfacet; is the Mueller matrix of the target surface; is the occlusion and shading factor; is the roughness of the target surface; is the specular reflection coefficient; is the first angle between the microfacet normal and the macro surface normal; is the second angle between the incident light and the microfacet normal; The distribution of the normal direction of the microfacet can be regarded as a Gaussian slope distribution, so The functional form of can be expressed as: ; in, is the first angle between the microfacet normal and the macro surface normal, is the roughness; Combining the above formula, we can get the first distribution function of the first specular reflected thermal radiation component: The elements in are: , and ; Step S37, obtaining a first specular reflection thermal radiation component according to the blackbody radiation brightness of the incident source and a first distribution function; The first distribution function of the first specularly reflected thermal radiation component is the ratio of the directional radiance increment from the surface to the directional reflected radiance increment caused by it. Therefore, the first specularly reflected thermal radiation component of the target surface is It can be expressed as: ; Combined with the above formula, the first specular reflection thermal radiation component of the target surface is The elements in are: , , ; Step S38, integrating the first distribution function in the hemispherical space to obtain a second distribution function corresponding to the second specular reflection thermal radiation component, and obtaining the second specular reflection thermal radiation component according to the black body radiation brightness of the background and the second distribution function; The second specular reflection thermal radiation component comes from the background environment in the hemispherical space, which is at the zenith angle of the incident light source. and the light source azimuth Therefore, the second distribution function of the second specular reflection thermal radiation component can be obtained by integrating the first distribution function in the hemispherical space. The specific expression is: ; The second distribution function of the second specular reflected thermal radiation component can be calculated using the above formula: The elements in are: , and ; According to the calculated second distribution function of the second specularly reflected thermal radiation component, the second specularly reflected thermal radiation component of the target surface It can be expressed as: ; Combining the above formula, we can get the first specular reflection thermal radiation component of the target surface: The elements in are: , , .

[0029] Furthermore, the first diffuse reflection thermal radiation component and the second diffuse reflection thermal radiation component generated by the incident source and the background environment in step S4 are calculated using the micro-facet theory proposed by Torrance and Sparrow, that is, the rough surface is composed of a group of randomly oriented tiny mirror facets that follow the Fresnel reflection law, and when the facet directions are different, diffuse reflection can describe the effects such as occlusion and shadow, volume scattering, and multiple scattering.

[0030] Further, step S4 is extended to include: Step S41, obtaining a third distribution function corresponding to the first diffuse reflection thermal radiation component according to the directional diffuse reflection coefficient, the roughness, the observation zenith angle and the ideal diffuse reflection coefficient; In step S1, the first diffuse reflection thermal radiation component and the second diffuse reflection thermal radiation component are extracted to obtain the parameters required for solving the problem, including the observation zenith angle , Roughness , Directional diffuse reflectance and ideal diffuse reflectance ; According to the material properties of the target surface, the third distribution function of the first diffuse thermal radiation component is composed of directional diffuse reflection and ideal diffuse reflection, and has no polarization characteristics, that is: ; in, and Represent the directional diffuse reflection component and the ideal diffuse reflection component respectively; The directional diffuse component can then be expressed as: ; Ideal diffuse reflection is the radiation formed by the interaction between the incident light and the particles inside the material, which moves in all directions on the surface with equal probability. Therefore, the ideal diffuse reflection component can be expressed as: ; Therefore, the third distribution function of the first diffuse thermal radiation component can be expressed as: ; The third distribution function of the first diffuse thermal radiation component can be calculated using the above formula: ; Step S42, integrating the third distribution function in the hemispherical space to obtain a fourth distribution function corresponding to the second diffuse reflection thermal radiation component; The second diffuse reflection thermal radiation component comes from the background environment in the hemispherical space. Therefore, the fourth distribution function of the second diffuse reflection thermal radiation component can be obtained by integrating the third distribution function of the first diffuse reflection thermal radiation component in the hemispherical space. The specific expression is: ; The fourth distribution function of the second diffuse thermal radiation component can be calculated using the above formula: ; Step S43, obtaining a first diffuse reflection thermal radiation component according to the third distribution function and the blackbody radiation brightness of the incident source; The third distribution function of the first diffuse reflection thermal radiation component is the ratio between the directional radiance increment from the surface and the directional reflection radiance increment caused by it. Therefore, the first diffuse reflection thermal radiation component of the target surface is It can be expressed as: ; Combining the above formula, we can get the first diffuse thermal radiation component: The elements in are ; Step S44, obtaining a second diffuse reflection thermal radiation component according to the fourth distribution function and the blackbody radiation brightness of the background; According to the fourth distribution function of the second diffuse reflected thermal radiation component, the second diffuse reflected thermal radiation component of the target surface It can be expressed as: ; Combining the above formula, the second diffuse thermal radiation component can be obtained: The elements in are .

[0031] Further, step S5 is extended to include: Step S51, obtaining the hemispherical reflectivity of the target surface according to the observation zenith angle, the observation azimuth angle, the light source zenith angle and the light source azimuth angle; In step S1, the parameters required for solving the target spontaneous radiation component are extracted, including the observation zenith angle Roughness ; The real part of the refractive index of the target surface material , imaginary part of refractive index , Specular reflection coefficient ; According to Kirchhoff's law and the law of conservation of energy, the emissivity and reflectivity of opaque objects satisfy the following relationship: ; In order to obtain a specific expression for the emissivity, it is necessary to introduce the concept of hemispherical reflectance (directional hemispherical reflectance DHR). Hemispherical reflectance refers to the integral of the reflectance of the surface in the hemispherical space when the target surface receives radiation from a certain angle, that is: ; Step S52, based on Kirchhoff's law and the law of conservation of energy, the emissivity of the target surface is obtained according to the hemispherical reflectivity and the pre-acquired blackbody emissivity; Emissivity of the target surface It can be expressed as: ; in, represents the blackbody emissivity. Since the ideal blackbody has no polarization, its corresponding Stokes vector is ; The emissivity of the target surface can be calculated using the above formula: The elements in are: , and ; Step S53, obtaining the target self-heating radiation component according to the emissivity and the blackbody radiation brightness of the target; Target self-heating radiation brightness It can be expressed as: ; In the above formula, is the directional emissivity function; is the blackbody radiation brightness of the target; Combining the above formula, we can get the target self-heating radiation brightness: The elements in are: , and .

[0032] Further, step S6 is extended to include: Step S61, converting the blackbody radiation brightness corresponding to the background, incident source, and target into vector expressions in the form of Stokes vectors respectively; Without considering the atmospheric path radiation and when the target is opaque, the Stokes vector corresponding to the blackbody radiation brightness of the target surface is It can be expressed as: ; In the above formula, , and are the vector expressions of the Stokes vector form corresponding to the target blackbody radiation brightness, background blackbody radiation brightness and incident source blackbody radiation brightness, respectively, and ; Step S62, combining each vector expression with the first specular reflection heat radiation component, the second specular reflection heat radiation component, the first diffuse reflection heat radiation component, the second diffuse reflection heat radiation component and the target self-heating radiation component to obtain three parameters in the reflection Stokes vector; Combined with the first specular reflection thermal radiation component calculated above , the second specular reflection thermal radiation component , the first diffuse thermal radiation component , the second diffuse thermal radiation component and the target self-heating radiation component , the first three parameters of the reflected Stokes vector are: ; Using the above formula, the first three parameters of the reflected Stokes vector are: , , .

[0033] Further, the target polarization degree in step S7 can be calculated by the three parameters of the reflected Stokes vector obtained in step S6, namely: .

[0034] The embodiment of the present invention observes the zenith angle The measured target polarization degree is , and the target polarization degree of inversion is , the inversion error is only 1.74%. It can be seen that the technical solution proposed in the present invention has high inversion accuracy. In addition, by comprehensively considering the multi-source radiation coupling effect, the polarization degree value inverted by the method of the present invention is highly consistent with the experimental data, which further verifies the effectiveness and accuracy of the method.

[0035] In order to further verify the reliability and advancement of the method of the present invention, the actual measurement results are compared with the method of the present invention and the comparison model proposed by Xie Jian [Research on Simulation Method of Infrared Polarization Characteristics of Typical Targets, Master's Thesis of Xidian University, 2020]. Figure 4As shown, it can be seen that: 1) compared with the comparison model, the target infrared polarization characteristic results inverted by the present invention are closer to the actual measured values, wherein the average root mean square error between the model results of the comparison model and the measured values ​​is 0.1805%, while the average root mean square error between the results of the present invention and the measured values ​​is 0.1506%, which reduces the inversion error by 16.57%; 2) in the observation zenith angle range of 0°~40°, the curve change trend of the method of the present invention is more consistent with the measured value distribution, that is, there is a local peak; 3) as the observation zenith angle increases, the curve trend of the method of the present invention also increases, and reaches a maximum value in the range of 70°~80°.

[0036] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0037] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for inverting target infrared polarization characteristics with multi-source radiation coupling, characterized in that: The following steps are involved: Step S1, obtaining temperature parameters of the background, target and incident source, angle parameters of the incident source and surface material parameters of the target; Step S2, based on Planck's blackbody radiation law, the temperature is obtained according to the temperature parameter T The blackbody radiation brightness equivalent to that of the background, the target and the incident source within the detector working band; Step S3, obtaining a first specular reflection thermal radiation component and a second specular reflection thermal radiation component based on the polarized bidirectional reflectance distribution function and according to the angle parameter, the surface material parameter, the background and the blackbody radiation brightness of the incident source; Step S4, based on the microfacet theory, obtaining a first diffuse reflection thermal radiation component and a second diffuse reflection thermal radiation component according to the angle parameter, the surface material parameter, the blackbody radiation brightness of the background, and the blackbody radiation brightness of the incident source; Step S5, obtaining the target self-heating radiation component according to the angle parameter and the blackbody radiation brightness of the target; Step S6, obtaining three parameters in the reflection Stokes vector according to the first specular reflection heat radiation component, the second specular reflection heat radiation component, the first diffuse reflection heat radiation component, the second diffuse reflection heat radiation component and the target self-heating radiation component; Step S7, obtaining the target polarization degree corresponding to the target according to the three parameters in the reflected Stokes vector.

2. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 1 is characterized in that: The temperature parameters include background environment temperature, incident source temperature and target temperature. In step S2, the equivalent blackbody radiation brightness of the background, the target and the incident source in the detector working band is obtained by the following calculation formula: ； ； ； in, represents the blackbody radiation brightness of the background; represents the blackbody radiation brightness of the incident source; represents the blackbody radiation brightness of the target; represents a preset first radiation constant; represents the wavelength of the incident light of the incident source; represents a preset second radiation constant; represents the background ambient temperature; represents the incident source temperature; represents the target temperature.

3. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 1 is characterized in that: The angle parameters include the light source zenith angle, the light source azimuth angle, the observation zenith angle and the observation azimuth angle, and the surface material parameters include the real part of the refractive index, the imaginary part of the refractive index, the roughness and the specular reflection coefficient of the surface material of the target. The step S3 includes: Step S31, based on spherical trigonometry and inverse trigonometric functions, obtaining a first angle between a microfacet normal and a macro surface normal, and a second angle between the microfacet normal and an incident light ray according to the light source zenith angle, the light source azimuth angle, the observation zenith angle, and the observation azimuth angle; Step S32, obtaining a third angle between the plane where the macro surface normal and the micro facet normal are located and the incident light, and a fourth angle between the plane where the macro surface normal and the micro facet normal are located and the reflected light according to the light source zenith angle, the observation zenith angle, the first angle and the second angle; Step S33, obtaining the target surface according to the light source zenith angle, the real part of the refractive index, the imaginary part of the refractive index and the second angle s wave and p Fresnel reflection coefficient of the wave; Step S34, obtaining a 2×2 Jones matrix according to the third angle, the fourth angle, the light source azimuth, the observation azimuth, and the Fresnel reflection coefficient, obtaining an incident Stokes vector, and obtaining a Mueller matrix in combination with the Jones matrix; Step S35, obtaining shielding and shading factors according to the first angle, the second angle, the light source zenith angle, and the observation zenith angle; Step S36, obtaining a first distribution function corresponding to the first specular reflection thermal radiation component according to the Mueller matrix, the occlusion and shading factor, the roughness, the specular reflection coefficient, the first angle, and the second angle; Step S37, obtaining the first specular reflection thermal radiation component according to the blackbody radiation brightness of the incident source and the first distribution function; Step S38, integrating the first distribution function in the hemispherical space to obtain a second distribution function corresponding to the second specular reflection thermal radiation component, and obtaining the second specular reflection thermal radiation component according to the blackbody radiation brightness of the background and the second distribution function.

4. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 3 is characterized in that: In the step S31, the first distribution function is obtained by the following calculation formula: ； ； in, represents the first distribution function; represents the specular reflection coefficient; represents the Mueller matrix; represents the occlusion and shading factor; represents the first angle; represents the second angle; represents said roughness; represents the zenith angle of the light source; represents the observation zenith angle; exp() represents the natural exponential function operation; represents the azimuth of the light source; represents the observation azimuth; Represents the difference between the observation azimuth and the light source azimuth.

5. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 3 is characterized in that: In the step S32, the second distribution function is obtained by the following calculation formula: ； in, represents the second distribution function; represents the first distribution function; represents the zenith angle of the light source; represents the azimuth angle of the light source.

6. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 1 is characterized in that: The angle parameters include the observation zenith angle, the light source zenith angle and the light source azimuth angle, the surface material parameters include the directional diffuse reflection coefficient, the roughness and the ideal diffuse reflection coefficient, and the step S4 includes: Step S41, obtaining a third distribution function corresponding to the first diffuse reflection thermal radiation component according to the directional diffuse reflection coefficient, the roughness, the observation zenith angle and the ideal diffuse reflection coefficient; Step S42, integrating the third distribution function in a hemispherical space to obtain a fourth distribution function corresponding to the second diffuse reflection thermal radiation component; Step S43, obtaining the first diffuse reflection thermal radiation component according to the third distribution function and the blackbody radiation brightness of the incident source; Step S44: obtaining the second diffuse reflection thermal radiation component according to the fourth distribution function and the blackbody radiation brightness of the background.

7. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 6 is characterized in that: In step S41, the third distribution function is obtained by the following calculation formula: ； in, represents the third distribution function; represents the directional diffuse reflectance; represents said roughness; represents the observation zenith angle; represents the ideal diffuse reflectance.

8. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 6 is characterized in that: In step S42, the fourth distribution function is obtained by the following calculation formula: ； in, represents the fourth distribution function; represents the directional diffuse reflectance; represents said roughness; represents the observation zenith angle; represents the zenith angle of the light source; represents the azimuth of the light source; represents the ideal diffuse reflectance.

9. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 1 is characterized in that: The angle parameters include observation zenith angle, observation azimuth angle, light source zenith angle and light source azimuth angle, the surface material parameters include roughness, real part of refractive index, imaginary part of refractive index and specular reflection coefficient, and step S5 includes: Step S51, obtaining the hemispherical reflectivity of the target surface according to the observation zenith angle, the observation azimuth angle, the light source zenith angle and the light source azimuth angle; Step S52, based on Kirchhoff's law and the law of conservation of energy, the emissivity of the target surface is obtained according to the hemispherical reflectivity and the pre-acquired blackbody emissivity; Step S53, obtaining the target self-heating radiation component according to the emissivity and the blackbody radiation brightness of the target.

10. The target infrared polarization characteristic inversion method of multi-source radiation coupling according to claim 1 is characterized in that: The step S6 comprises: Step S61, converting the blackbody radiation brightness corresponding to the background, the incident source, and the target into vector expressions in the form of Stokes vectors respectively; Step S62, combining each of the vector expressions with the first specular reflection thermal radiation component, the second specular reflection thermal radiation component, the first diffuse reflection thermal radiation component, the second diffuse reflection thermal radiation component and the target self-heating radiation component to obtain the three parameters within the reflection Stokes vector.

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