The 27-28 October 1986 FIRE IFO cirrus case study: spectral properties of cirrus clouds in the 8-12 μm window

Abstract

A method for detecting cirrus clouds using 8 μm and 12 μm bands is presented. The 8 μm band is centered on a weak water-vapor absorption line while the 11 μm and 12 μm bands are between absorption lines. The brightness temperature difference between the 8 and 11 μm bands is negative for clear regions, while for ice clouds it is positive. Differences in the 11 and 12 μm channels are positive, whether viewing a cirrus cloud or a clear region. Inclusion of the 8 μm channel therefore removes the ambiguity associated with the use of 11 and 12 μm channels alone. The method is based on the comparison of brightness temperatures observed in these three channels. The HIS and lidar observations were combined to indicate that cirrus clouds cannot be considered gray in the 8-12 μm window region. -from Authors