UCLA

This paper investigates the radiative properties of bubbles or particles embedded in an absorbing medium. It aims first at determining the conditions under which the absorption by the surrounding medium must be accounted for in the calculation of the e±ciency factors by comparing results from the (1) Mie theory, (2) far-field, and (3) near-field approximations. Then, it relates these approximations for a single particle to the effective radiation characteristics required for solving the radiative transfer in an ensemble of scatterers embedded in an absorbing medium. The results indicate that the efficiency factors for a spherical particle can differ significantly from one model to another, in particular for large particle size parameter and matrix absorption index. Moreover, the effective scattering coefficient should be expressed based on the far-field approximation. Also, the choice of the absorption efficiency factor depends on the model used for estimating the effective absorption coefficient. However, for small void fractions, absorption by the matrix dominates and models for the absorption coefficient and effciency factor are unimportant. Finally, for bubbles in water, the conventional Mie theory can be used between 0.2 and 200 microns except at some wavelengths where absorption by water must be accounted for.