Research Of Bidirection Reflection Distribution Function For Polytype Materials In Diffrent Wavelength

The trend of advanced weapons is high-precision tracking, guidance and target recognition in modern military. The essential problem is to discover and hide the scattering characteristics of military targets using different methods in the design and use of weapons. With the complication of military targets, the requirement of detection accuracy raises and the range of detection bands are broadened. So it is exigent to in-depth research on the scattering characteristics of targets, infrared and laser radiation. BRDF can be used to evaluate bi-directional reflection, absorption characteristic and radiative characteristic of all kinds of material surfaces in the domain of visible light or infrared laser spectrum. it is mainly determined by the surface roughness, dielectric constant, exposure or reflective wavelength and polarization etc。The physical surface is usually irregular and height random various, but the surface scattering condition is effected by the surface form, so the tool which could investigate the irregular surface is needed. Fractal theory is a powerful tool of studying and dealing with the irregular figure with the scale characteristic. It can describe the complexity of the surface topography through the simple parameter, so fractal theory has offered a kind of effective means of describing the surface topography from microscopic molecule to macroscopical yardstick. In this paper, the roughness of certain granite surface (grinding and polishing treatment) was measured by needle touched method firstly and the simple outline profile was drawn. On the basis of measuring the parameter in experiment, the random rough surface is simulated utilizing the fractal theory, it is compared with surface measured actually; light scattering from randomly rough surfaces is investigated by numerical simulation.The main content as follows: Combined with the fractal theory, the theoretical model of random surface is obtained. On the basis of Kirhoff approximate, Monte-Carlo method with the theories of radiation, optics and electromagnetism scattering is employed to analyze the scattering characteristics of theory surfaces and random surfaces. Furthermore, parametric studies are conducted to investigate the effects of surface roughness and incidence angles for scattering characteristics. A two-dimensional FBM fractal model is used to dessrible the actual rough surface the kirhh off approximation is considered, and the expressions of electromaynetic scattering field and the normalized radar cross section from thise fractal surface are obtained, Numerical results of the normalized radar cross section as a function of fractal dimension, characteristic length and incident frenquency are given .the FBM model is also compared with the classical models of Gaussian exponential correlation. Measurement method is studied for BRDF of actual surfaces and the corresponding experimental platform is built. The work of calibration and error analysis are given and the distributions of BRDF of four military target materials (foaming Al, graphite fiber (Al), graphite fiber (Mg) and carbon fiber) surfaces are obtained in visible and infrared bands. A temperature control to our experiment table. The BRDF of Cu is measured in visible and infrared bands from 20oC~500 oC given the analysis and interpretation of the results.