Research On The Scattering Characteristics Of Fractal Surfaces

The fractal theory performs as a useful tool dealing with on the unsmooth andnondiferentiable geometric object generated by a nonlinear system. It has gainextensively attention since it was proposed. Fractal structure can be attained throughthe duplicate, scaling and interaction of its initial simple part. Studies have shownthat it is more useful and suitable to use fractal theory todescribe natural objectssuch as the boundary the profile of the mountain peak, coastline, plant coverage,seawaves and so on.BRDF(Bidirectional Reflectance Distribution Function) is usually used todescript the space distribution characteristic and spectrum characteristic ofEM(Electromagnetic field) scattering from rough surfaces in the studies of targetand environment light characteristics. Extensive applications of BRDF have beenapplied in the field of remote sensing, target recognizing, radar stealth techniquesand image processing. The distribution of BRDF can be affected by many elementssuch as the surface roughness of material, the zenith angle, azimuth and polarizationof incident light. Changing the position of light source can affect the BRDFcharactristics and it may bring new features into it.Based on the fractal theory, a2-D band limited WM(Weierstrass–Mandelbrot)model is set up to imitate the rough surfaces. It was contrasted with the traditionalGaussian model and exponential model. Numberical analysis of scatteringcharacteristics from fractal rough surfaces is carried out in the COMSOLMultiphysiscs. The effects of fractal dimension, wavelength, zenith angle andpolarization of incident light on the BRDF are studied at the same time. The effectof the time varying feature of EM on the scattered EM is also researched. Thesimulation results of the rough surfaces illuminated by a moving light are discussedespecially. The chaos time series analysis is applied in the scattered electric fields,and the largest Lyapunov exponent is positive. At last, a practical BRDF measure iscarried out in a BRDF measurement system designed by HIT. The BRDF from roughsurfaces of different materials are tested. The materials are black Nickel, carbonfiber, SiC and quart glass. The BRDF of different incident lights are studied and acontradiction with the simulation data is performed.