Chapter 1. Optical properties of small particles and their aggregates, 1.1. Numerical light scattering simulations and optical properties of aggregates 1.2. Application of scattering theories to the characterization of precipitation processes Chapter 2. Modern methods in radiative transfer 2.1. Using a 3D radiative transfer Monte-Carlo model to assess radiative effects on polarized reflectances above cloud scenes,2.2. Linearization of radiative transfer in spherical geometry: an application of the forward-adjoint perturbation theory, 2.3. Convergence acceleration of radiative transfer equation solution at strongly anisotropic scattering, 2.4. Code SHARM: fast and accurate radiative transfer over spatially variable anisotropic surfaces, 2.5. General invariance relations reduction method and its applications to solutions of radiative transfer problems for turbid media of various configurations Chapter 3. Optical properties of bright surfaces and regoliths,3.1. Theoretical and observational techniques for estimating light scattering in first-year Arctic sea ice,3.2 Reflectance of various snow types: measurements, modeling, and potential for snow melt monitoring, 3.3. Simulation and modeling of light scattering in paper and print applications, 3.4. Coherent backscattering in planetary regoliths

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.