title: Size parameter for thermally emitting particles.
abstract: For thermal emission from particles the conventional size parameter X = 2 pi a/lambda does not distinguish between small and large particles. We show that the opacity parameter Omega = 4 pi ka/lambda = 2 kX is a more accurate means of demarcating the two emission regimes. Omega is approximately equal to the particle's mean optical depth, and it can be derived from both scattering theory and geometrical optics.
authors.affiliation: Aerospace Corporation, PO Box 92957, Los Angeles, California 90009, USA. david.k.lynch@aero.org
authors.forename: D K
authors.initials: DK
authors.lastname: Lynch
authors.forename: S
authors.initials: S
authors.lastname: Mazuk