MULTIPLE-SCATTERING EFFECTS ON DIFFERENTIAL ABSORPTION FOR THE TRANSMISSION OF A PLANE-PARALLEL BEAM IN A HOMOGENEOUS MEDIUM

The transmission, including all scattering orders, of a plane-parallel beam in a homogeneous scattering medium containing aerosols (e.g., wa ter cloud) mixed with an absorbing gas (e.g., ozone) is computed with a two-stream radiative transfer model. From differential transmission the concentration of the gas is deduced. The effect of multiple-scatte ring on the deduced concentration is shown for conservative scattering aerosols for which the multiple scattering by the aerosols is differe ntially absorbed by the gas and for nonconservative scattering aerosol s for which the multiple scattering is differentially absorbed by the aerosols as well as differentially absorbed by the gas. The two-stream analytical model (with no dependence on the field of view) shows good qualitative agreement (especially for a small field of view) with a n umerical radiative transfer model in which the trace gas concentration is computed for the different detector's field of view. (C) 1997 Opti cal Society of America.