Laboratory studies of scattering matrices for randomly oriented particles:: potentials, problems, and perspectives

A number of issues relevant to laboratory studies of scattering matrices as functions of the scattering angle for randomly oriented particles in the visible part of the spectrum are discussed. The usefulness of experiments is compared with that of numerical computations, in particular, for ensembles of natural nonspherical particles with broad ranges of sizes and shapes. It is argued that measurements of the entire scattering matrix have considerable advantages over measurements of only the intensity and polarization of the scattered light for incident unpolarized light. Results of special test experiments are presented which show that our experimental results for scattering matrices are not significantly contaminated by multiple scattering and that the orientation of the particles can be adequately described as random. Some ways are pointed out to overcome the lack of measurements for very small and very large scattering angles. A possibility to reduce the amount of material needed in the experiments is indicated. Finally, characterizations of the particles in terms of sizes, shapes and refractive indices are discussed. (C) 2003 Elsevier Science Ltd. All rights reserved.