Light Scattering Reviews 5: Single Light Scattering and Radiative Transfer

Light scattering by densely packed inhomogeneous media is a particularly ch- lenging optics problem. In most cases, only approximate methods are used for the calculations. However, in the case where only a small number of macroscopic sc- tering particles are in contact (clusters or aggregates) it is possible to obtain exact results solving Maxwell’s equations. Simulations are possible, however, only for a relativelysmallnumberofparticles,especiallyiftheirsizesarelargerthanthewa- length of incident light. The ?rst review chapter in PartI of this volume, prepared by Yasuhiko Okada, presents modern numerical techniques used for the simulation of optical characteristics of densely packed groups of spherical particles. In this case, Mie theory cannot provide accurate results because particles are located in the near ?eld of each other and strongly interact. As a matter of fact, Maxwell’s equations must be solved not for each particle separately but for the ensemble as a whole in this case. The author describes techniques for the generation of shapes of aggregates. The orientation averaging is performed by a numerical integration with respect to Euler angles. The numerical aspects of various techniques such as the T-matrix method, discrete dipole approximation, the ?nite di?erence time domain method, e?ective medium theory, and generalized multi-particle Mie so- tion are presented. Recent advances in numerical techniques such as the grouping and adding method and also numerical orientation averaging using a Monte Carlo method are discussed in great depth.

The 5th volume of LIGHT SCATTERING REVIEWS is devoted to modern knowledge and milestones in both experimental and theoretical techniques related to radiative transfer and optics of such highly reflective objects as snow and ice. Twelve leading world experts in their respective fields provide important contributions to this fascinating subject.

The first chapter has three parts: In the first, the main optical properties of large particles such ice crystals in snow and clouds are presented. The second part gives recent results in the understanding of light polarization and brightness near opposition, which is important for the observation of atmosphereless solar-system objects. The chapter ends with a summary of previous studies based on both approximate and rigorous methods of numerical light scattering simulations for fractal aggregates, such as soot particles.

The second chapter of the book describes recent results in the broad area of radiative transfer. In the first three parts, several radiative transfer codes are presented and explained in detail: DISORT, the general-purpose discrete-ordinate algorithm for radiative transfer; SHARM, fast and accurate radiative transfer with atmospheric gaseous absorption and spatially variable anisotropic surfaces; and SCIATRAN, a new tool to study the polarized radiative transfer in the terrestrial atmosphere – underlying surface system. Part 4 studies optical properties of paper in the framework of radiative transfer theory, while the fifth part reviews the theoretical foundations of the inverse problems of radiative transfer. Part 6 concentrates on the linearization of atmospheric radiative transfer in spherical geometry, which is important for satellite remote sensing applications, such as limb mode observations of the atmosphere from space. The chapter ends with the radiative transfer modeling of the Ring effect, which is observed where the solar spectrum shows the so-calledFraunhofer lines of low intensity, caused by rotational Raman scattering by nitrogen and oxygen molecules in the Earth's atmosphere. Fundamental theoretical results from studies of the Ring effect are reported in this volume.

Chapter 3 describes in two parts the optical properties of snow and ice, which are particularly relevant to studies of climate change. Part 1 considers the complex scattering optics of natural snow cover, while Part 2 describes novel theoretical and observational techniques for estimating light scattering in Arctic sea ice.

Summing up, this book will be a valuable addition to the library of any scientist dealing with light scattering and radiative transfer problems.