Modeling And Simulation Of Skylight Polarization Pattern

During the process of atmospheric transmission of the sunlight, plenty of polarized light is produced by light-scattering caused by air molecules and aerosol particles, as well as reflection caused by the non-metallic surfaces, such as cloud layers and the earth's surfaces. The specific distribution of the polarized light in the sky is called skylight polarization pattern. Skylight polarization pattern is not only the theoretical foundation of the research in the navigation by making use of polarized light and the detection of various air targets, but also an important object for the remote sensing and the atmospheric optical analysis. The investigation of modeling and simulation of skylight polarization pattern as well as computing and analysis of the characteristics and variation of the pattern can provide a theoretical basis for these applied research above. A novel description of light waves is used in this thesis. On that basis, an ideal and a real skylight polarization model are built separately. Furthermore, combined with the real state of environment, simulation and analysis of skylight polarization data are investigated principally. The main work of this thesis includes:(1) Status of current skylight polarization modeling and simulation are summarized. And the problems existed in current model are pointed. The forming hypostasis of skylight polarization pattern is studied. And the simplified models of the process of light scattering and surface reflection in sunlight's atmospheric transmission are analyzed.(2) For the purpose of modeling needs, electric vector and Stokes vector are proposed to describe light waves in this paper. On this basis, a analytical method of Rayleigh scattering of a single particle based on electric vector is proposed. The physical meaning of polarization angle in current models is explained effectively by use of the characteristics of electric vector of light waves. Besides, a novel representation of skylight polarization information is defined.(3) A modeling method of ideal skylight polarization pattern based on electric vector is proposed. The celestial coordinate system and the north-east-up coordinate system are established respectively. Utilizing transformation between the two coordinate systems, the analytical method of Rayleigh scattering of a single particle can be applied to any measured point over the celestial hemisphere on an earthbound observer. The results of simulation experiments show that the proposed method can not only give an accurate description of the major features of skylight polarization pattern under ideal atmospheric conditions, but also solves the problem that current ideal-models can't be extended to the real issues.(4) A modeling method of real skylight polarization pattern based on the process of sunlight's atmospheric transmission is proposed. The relationship between the status of climate and the visibillity distance is studied. According to this, the model of atmospheric transport of skylight is set up. Then, Fresnel formula is applied to the celestial coordinate system, and the model of surface reflection of skylight is also established. Moreover, through combination of the model of light scattering, the model of atmospheric transport and the model of surface reflection, polarized skylight all over the sky can be described. Finally, combined with the real situation of the surface environment and the weather, simulation experiments are designed. Through the results of simulation experiments, variation of real skylight polarization pattern is analyzed preliminarily.