Definitions for "Optical thickness"
In calculating the transfer of radiant energy, the mass of an absorbing or emitting material lying in a vertical column of unit cross-sectional area and extending between two specified levels. Also, the degree to which a cloud prevents light from passing through it; the optical thickness then depends on the physical constitution (crystals, drops, and/or droplets), the form, the concentration, and the vertical extent of the cloud.
Or optical depth. The mass of a given absorbing or emitting material lying in a vertical column of unit cross-sectional area and extending between two specified levels.
The product of the physical thickness of an isotropic optical element and its refractive index. Of an optical system, the total optical path length through all elements.
the normalized extinction coefficient due to absorption and scattering by intervening substances or particles in a direct beam of light