Lu Jia, Zhou Huaichun
Appl Opt. 2017 Jul 1;56(19):5550-5558. doi: 10.1364/AO.56.005550.
The mirror-like reflection image of the road surface under grazing-angle scattering can be easily observed in daily life. It was suggested that road surface mirages may occur due to a light-enhancing effect of the rough surface under grazing-angle scattering. The main purpose of this work is to explain the light-enhancing mechanism of rough surfaces under grazing-angle scattering. The off-specular reflection from a random rough magnesium oxide ceramic surface is analyzed by using the geometric optics approximation method. Then, the geometric optics approximation method is employed to develop a theoretical model to predict the observation effect of the grazing-angle scattering phenomenon of the road surface. The rough surface is assumed to consist of small-scale rough surface facets. The road surface mirage is reproduced from a large number of small-scale rough surface facets within the eye's resolution limit at grazing scattering angles, as the average bidirectional reflectance distribution function value at the bright location is about twice that of the surface in front of the mirage. It is suggested that the light-enhancing effect of the rough surface under grazing-angle scattering is not proper to be termed as "off-specular reflection," since it has nothing to do with the "specular" direction with respect to the incident direction.
在日常生活中，很容易观察到掠角散射下路面的镜面反射图像。有人认为，由于掠角散射下粗糙表面的光增强效应，可能会出现路面海市蜃楼现象。这项工作的主要目的是解释掠角散射下粗糙表面的光增强机制。利用几何光学近似方法分析了随机粗糙氧化镁陶瓷表面的非镜面反射。然后，采用几何光学近似方法建立理论模型，预测路面掠角散射现象的观测效果。假设粗糙表面由小尺度粗糙表面小面组成。在掠射散射角下，在眼睛分辨率极限内，从大量小尺度粗糙表面小面再现了路面海市蜃楼，因为明亮位置的平均双向反射分布函数值约为海市蜃楼前方表面的两倍。有人认为，掠角散射下粗糙表面的光增强效应不宜称为“非镜面反射”，因为它与相对于入射方向的“镜面”方向无关。
