Radiative-Transfer and Effective-Medium Theories: A Current Outlook

To be sufficiently accurate, radiation-budget and remote-sensing applications involving clouds, aerosols, precipitation, the ocean body, and various types of surface must be based on advanced theories of light scattering and radiative transfer. From the perspective of physics, these theories must originate in the Maxwell equations. However, direct computer solutions of these equations for particulate media had been impracticable until quite recently. This has led to a widespread use of various simplistic approaches such as the phenomenological radiative-transfer and effective-medium theories originally proposed more than a century ago. Recently, however, a new modeling approach has emerged directly based on advanced analytical and computer solutions of the Maxwell equations. The main objective of this talk is to formulate the general theoretical framework of electromagnetic scattering rooted in Maxwell’s electromagnetics and analyze its most fundamental consequences. I will discuss in particular how the radiative transfer theory can be derived from first physical principles and how the widely used effective-medium approximations can be tested versus direct numerical solutions of the Maxwell equations. The talk will conclude with an outlook of future advances needed to establish the disciplines of atmospheric radiation and remote sensing on a firm footing of first-principles physics.