Simulation And Analysis Method Of Infrared Polarization Characteristics Of Typical Targets

When target shares the similar temperature and emissivity with its background,it's difficult to distinguish target's contour and textural details from the thermal images with similar radiation intensity.The polarization of target is closely related to the refractive index,roughness,texture and geometric shape of its material surface,and the polarization of different materials have obvious differences.The infrared polarization imaging system uses this kind of difference to image the scene,so as to improve the contrast between the target and the background.The infrared polarization model is a mathematical and physical description of the polarization characteristics of the target while simulation is an intuitive way to visualize and verify the model.Therefore,the modeling and simulation methods of infrared polarization characteristics are of great significance to the research of target's polarization characteristics.At the microscopic level,most targets do not have the most ideal mirror surface,but a rough surface with certain distribution.Target infrared radiation often has multiple reflection,volume scattering,shielding and shadow effects on rough surfaces,which influence the polarization of infrared radiation to some extent.Many researches have been using the lambert model to model the diffuse reflection component of rough surface's polarization,but the diffuse reflection on the surface of actual object is not isotropic,but has certain direction correlation,therefore the simulation value of the model is still different from the measured value of the target.In addition,most existing polarization models study the visible band and only model light's reflection polarization,but not the polarization characteristics generated by spontaneous radiation in the infrared band.In order to solve the above problems,this paper focuses on the modeling and simulation of the polarization characteristics of typical rough surfaces of targets in the infrared band.Firstly,through the infrared polarization imaging experiment on typical targets,this paper qualitatively analyzes the differences and characteristics between traditional infrared intensity imaging and polarization imaging.Secondly,a long-wave infrared target pBRDF(polarized Bidirectional Reflectance Distribution Function)measurement platform has been built to illuminate different coating targets with a long-wave laser light source,then to gain the pBRDF measured data at different geometric angles for further experimental analysis.In addition,according to the features of rough surface,the polarization of reflected radiation is modeled more accurately by introducing the double diffuse reflection components including anisotropic diffuse reflection and isotropic ideal diffuse reflection.On this basis,the polarization model of spontaneous radiation is derived from the law of energy conservation and Kirchhoff's law,and a modified semi-empirical infrared polarization model is established by combining reflected radiation and spontaneous radiation.The model in this paper is simulated and compared with the measured data and the P-G(Priest-Germer)model.The result shows that the model established in this paper is more consistent with the measured data,which proves the effectiveness of this model.Finally,through visualization technologies,infrared polarization characteristics of hemispheric space and typical targets are 3D modeled and simulated by using the model in this paper,and the results are analyzed and summarized in this thesis.