Cao Yunhua

Spectrum BRDF and its Application in Visible Light Scattering of Spatial Object

The spectral bi-directional reflectance distribution function (BRDF) of some satellite coating material and solar plane samples in the band from 380 to 780 nanometres is measured with relative measurement in the laboratory. The spectrum BRDF which can characterize the spectrum reflectance property of samples is obtained by weighting the measured spectral BRDF by the spectral irradiance of the incident spectrum. A new method to calculate the visible light scattering of spatial object is introduced with the aid of the spectrum BRDF. As an application example, the visible light scattering of a simple satellite model is calculated.

Scattering of a general partially coherent beam from a diffuse target in atmospheric turbulence

The second-order and fourth-order statistical moments of the speckle field from a diffuse target in atmospheric turbulence are studied which have great influence on the performance of lidar systems. By expanding a general rotationally symmetric beam as a sum of Gaussian?Schell model (GSM) beams, the mean intensity of the general beam propagating over a distance in an atmospheric turbulence is formulated. Expressions for the degree of coherence (DOC) and the normalized intensity variance of the scattered field of a general beam from a rough surface in turbulence are derived based on the extended Huygens?Fresnel principle. The general expressions reduce to the well-known forms for a GSM beam. Another example for the general beam used in this paper is the collimated flat-topped beam. The results of both kinds of beams show that the intensity profile on the target plane is a key factor affecting the statistical characteristics of the speckle field. A larger beam spot on the target plane induces a smaller coherence length and a smaller normalized intensity variance of the received field. As turbulence gets stronger, the coherence length becomes smaller, and the normalized intensity variance firstly increases and declines to unity finally.

3D BRDF Statistical Modeling and Optimizing of Various Samples

A modified and simplified five-parameter model is presented based on the Torrance-Sparrow model. Multi-angle bistatic data of the surfaces of various materials and roughness are fitted by using this model. The results of five-parameter model are in good agreement with the measured data, and closing to the results of two-dimensional bidirectional reflectance distribution function (BRDF) models. The five-parameter model shows a good applicability to various surface roughness and different optical materials. The combined algorithm of genetic algorithm and simulated annealing algorithm takes a key role on the salvation of the process of optimization to get the parameters. The five parameters model can be used to construct a 3D BRDF distribution based on the spatial measured data, which may provide more information of light scattering from rough surfaces.