Absorption cross section
From AMS Glossary
absorption cross section
The area that, when multiplied by the irradiance of electromagnetic waves incident on an object, gives the radiant flux absorbed and dissipated by the object. Customary usage in radar describes the absorption cross section of an object as the area that, when multiplied by the power density of incident plane-wave radiation, gives the power absorbed and dissipated by the object.
The extinction cross section of an object is the sum of the absorption cross section and the scattering cross section. For a medium consisting of a dispersion of absorbing objects through which radiation propagates, the volume absorption coefficient (units: m2m-3 or m-1) at a given location in the medium is the sum of the absorption cross sections of all the objects in a unit volume centered at that location.