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 ca...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.展开更多
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)
文摘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.
