中文摘要：

对于户外光电成像系统，天空散射光是成像质量下降的一个重要因素。天空散射光偏振特性的研究对于抑制散射光的影响、提高图像对比度具有重要意义。基于偏振图像中信息的提取，从对图像对比度的分析出发，定性地研究了在不同能见度条件下近地面水平方向天空散射光的偏振方向特征，分析了散射角和散射平面方向对天空散射光偏振方向的影响。结果表明，对于能见度好的晴朗天气，天空散射光偏振方向明显，随着能见度条件逐渐变差，偏振方向渐渐变得不明显。但除了能见度非常差（小于5km）的情况，不同能见度条件下的偏振方向特征是比较稳定的，偏振方向基本保持了清洁大气状况下Rayleigh散射偏振的特性。

英文摘要：

Skylight is an important factor in the degrading image quality of outdoor electro-optical imaging system. Research on the polarization characteristic of skylight has a great significance for repressing the effect of scattering light and improving image contrast. Based on extracting information from polarization images, starting from the analysis of image contrast, the polarization direction of near- ground horizontal skylight under different visibilities was studied qualitatively. The effects of scattering angle and the direction of scattering plane on skylight polarization direction were both analyzed. The results indicate that the polarization direction of skylight is apparent in fair weather with good visibility. Otherwise, the polarization direction of skylight becomes unapparent gradually. However, besides extreme low visibility condition （less than 5 kin）, the polarization direction characteristic of skylight under different visibilities is relatively stable, and the polarization direction is similar to that of Rayleigh single scattering polarization in clear atmosphere to a certain extent.