Parameter Tree:
EARTH SCIENCE > ATMOSPHERE > CLOUDS > CLOUD MICROPHYSICS > CLOUD OPTICAL DEPTH/THICKNESS

Definition:
The degree to which a cloud prevents light from passing through it.
Optical thickness depends upon the physical constitution (crystals, drop,
droplets), the form, the concentration of particles, and the vertical
extent of the cloud. 


Reference:
The Glossary of Meteorology, American Meteorological Society, 1998.