Optical depth

Optical depth is the dimensionless path integral of a medium’s extinction coefficient. It quantifies how strongly the medium attenuates radiation along a specified path.

Beer–Lambert law: The law stating that transmitted intensity decays exponentially with the path-integrated absorption coefficient. It converts optical depth into transmitted intensity for a uniform, non-emitting absorber.
Absorption (electromagnetic radiation): The transfer of electromagnetic radiation energy to matter. Absorption contributes to extinction and therefore to optical depth.
Atmospheric optical depth: The optical depth of an atmospheric layer or the full atmosphere at a specified wavelength. It quantifies how aerosols, gases, and clouds attenuate sunlight or thermal radiation.
Absorption optical depth: The path integral of the absorption coefficient, excluding scattering extinction. It isolates true energy absorption from the broader attenuation measured by total optical depth.
Radiative transfer equation: An equation describing how radiation intensity changes through absorption, emission, and scattering in a medium. Optical depth is a path coordinate that simplifies this equation.
Scattering: The redirection of waves or particles through interactions with matter or other waves. Scattering removes radiation from a direct beam and contributes to extinction.
Aerosol optical depth: The wavelength-dependent optical depth contributed by airborne particles in a vertical atmospheric column. It is a standard measure of aerosol loading inferred from sunlight attenuation.
Scattering optical depth: The path integral of the scattering coefficient along a specified route. It separates beam redirection from absorption within total optical depth.
Extinction coefficient: A local measure of how strongly a medium removes radiation from a beam per unit path length. Integrating this quantity along the path gives optical depth.
Path length: The distance traveled by radiation through a medium along a specified route. A longer route generally accumulates greater optical depth at fixed extinction.

Linked from 31 pages