Road surface mirage:A bunch of hot air?  

作　　者：ZHOU HuaiChun HUANG ZhiFeng CHENG Qiang LU We QIU Kui CHEN Chen HSU Pei-feng 

机构地区：[1]State Key Laboratory of Coal Combustion, School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China [2]Department of Mechamcal and Aerospace Engineering, Florida Institute of Technology, Melbourne, FL 32901-6975, USA

出　　处：《Chinese Science Bulletin》2011年第10期962-968,共7页

基　　金：supported by the National Natural Science Foundation of China(50636010,50721005);the Program of Introducing Talents of Discipline to Universities of China(B06019)

摘　　要：The inferior mirage from road surfaces is a common phenomenon,which can be easily seen in everyday life.It has been recognized in the literature as a light refraction phenomenon due to the refractive index gradient caused by the temperature gradient in the air strata above the road surfaces.However,it was also suggested that the mirage is just a phenomenon of specular reflection at grazing incidence.Because of the lack of reasonable and quantitative evidence,the generally accepted light refraction theory has not yet been refuted.Here we show some mirror-like reflection images captured from a road surface stretch in Yujiashan North Road,Wuhan,China,when there was no obvious temperature gradient on or above the road,measured on a winter day in December 2009.This provided direct evidence to doubt the temperature induced light refraction mechanism of the inferior mirage.Furthermore,the critical grazing angle of about 0.2° to the road plane where the mirror-like reflection appears could not make the rough surface scatter incident light as a smooth surface according to the Rayleigh criterion.Therefore the phenomenon is a mirrorlike observation effect of scattering from the surface,which cannot be entirely explained by light refraction via air strata.The results demonstrate that the image-formation mechanism and the observer-based-analysis method shown here potentially offer a means of understanding a wide range of scattering phenomena from rough surfaces at grazing angle;for example,the superior mirages of unusual brightness occasionally observed over frozen lakes and the off-specular reflection phenomenon.The inferior mirage from road surfaces is a common phenomenon, which can be easily seen in everyday life. It has been recog- nized in the literature as a light refraction phenomenon due to the refractive index gradient caused by the temperature gradient in the air strata above the road surfaces. However, it was also suggested that the mirage is just a phenomenon of specular reflection at grazing incidence. Because of the lack of reasonable and quantitative evidence, the generally accepted light refraction theory has not yet been refuted. Here we show some mirror-like reflection images captured from a road surface stretch in Yujiashan North Road, Wuhan, China, when there was no obvious temperature gradient on or above the road, measured on a winter day in December 2009. This provided direct evidence to doubt the temperature induced light refraction mechanism of the inferior mirage Furthermore, the critical grazing angle of about 0.2~ to the road plane where the mirror-like reflection appears could not make the rough surface scatter incident light as a smooth surface according to the Rayleigh criterion. Therefore the phenomenon is a mirror- like observation effect of scattering from the surface, which cannot be entirely explained by light refraction via air strata. The results demonstrate that the image-formation mechanism and the observer-based-analysis method shown here potentially offer a means of understanding a wide range of scattering phenomena from rough surfaces at grazing angle; for example, the superior mirages of unusual brightness occasionally observed over frozen lakes and the off-specular reflection phenomenon.

关 键 词：海市蜃楼 热空气 路面 表面散射 温度梯度 镜面反射 折射现象 光线折射 

分 类 号：P427.112[天文地球—大气科学及气象学]