Topics in Particle and Dispersion Science

The small-angle approximation (SAA) to the radiative transfer equation (RTE) is used extensively in imaging models for optically-thick dispersions. The SAA is generally considered valid when the particles in a dispersion are very large compared with the wavelength, the relative refractive index of the particles is close to 1, and the optical thickness of the dispersion is not too large. The first two constraints imply that the dominant scattering angle per scattering event is small. The last constraint insures that the cumulative scattering angle (accounting for consecutive scattering events) remains small after more than one scattering event.