Simple approximate formula for the reflection function of a homogeneous, semi-infinite turbid medium

A simple, approximate analytical formula is proposed for the reflection function of a semi-infinite, homogeneous particulate layer. It is assumed that the zenith angle of the viewing direction is equal to zero (thus corresponding to the case of nadir observations), whereas the light incidence direction is arbitrary. The formula yields accurate results for incidence-zenith angles less than approximately 85degrees and can be useful in analyzing satellite nadir observations of optically thick clouds. (C) 2002 Optical Society of America.