Optical properties of terrestrial clouds

The aim of this review is to consider optical characteristics of terrestrial clouds. Both single and multiple light-scattering properties of water clouds are studied. The numerous results discussed can be used for solutions to both inverse and direct problems of cloud optics. An introduction to main microphysical characteristics of water and ice clouds, including the effective size, the liquid water content and path, the concentration of particles, is given. The refractive index of water and ice, which is of importance for optical waves propagation in clouds, is also considered. We consider extinction and absorption coefficients, phase functions, and asymmetry parameters of water and ice clouds and their relationships with the size, shape, and concentration of water droplets and ice crystals. Simple analytical results for absorption, reflection, and transmission characteristics of cloudy media are given. They are valid for optically thick clouds with optical thickness larger than 5. We have reviewed studies of polarization of solar light reflected from clouds. Image transfer problems have been considered as well. Modern methods of passive remote sensing of water and ice clouds are discussed. The review is finished by the discussion of optical properties of inhomogeneous clouds, which is a main topic of modern cloud optics research.