“Independent” and “dependent” scattering by particles in a multi-particle group

The terms “independent” and “dependent” scattering are ubiquitous in the phenomenological discipline of light scattering by particulate media. Yet there is a wide range of ad hoc definitions of these terms, many of which are vague and conceptually inconsequential. In this paper we perform a first-principles analysis of these terms based on the rigorous volume-integral-equation formulation of electromagnetic scattering. We argue that scattering by a multi-particle group can be called independent if certain optical observables for the entire group can be expressed in appropriate single-particle observables. Otherwise one deals with the dependent scattering regime. The prime (and perhaps the only) examples of independent scattering are scattering scenarios described by the first-order-scattering approximation and the first-principles radiative transfer theory.