This fourth volume of Light Scattering Reviews is composed of three
parts. The
?rstpartisconcernedwiththeoreticalandexperimentalstudiesofsinglelightsc-
tering by small nonspherical particles. Light scattering by small
particles such as, for instance, droplets in the terrestrial clouds is a
well understood area of physical optics. On the other hand, exact
theoretical calculations of light scattering p- terns for most of
nonspherical and irregularly shaped particles can be performed only for
the restricted values of the size parameter, which is proportional to
the ratio of the characteristic size of the particle to the wavelength?.
For the large nonspherical particles, approximations are used (e. g.,
ray optics). The exact th- retical techniques such as the T-matrix
method cannot be used for extremely large particles, such as those in
ice clouds, because then the size parameter in the v- iblex=2?a/, wherea
is the characteristic size (radius for spheres), and the associated
numerical codes become unstable and produce wrong answers. Yet another
problem is due to the fact that particles in many turbid media (e. g.,
dust clouds) cannot be characterized by a single shape. Often,
refractive indices also vary. Because of problems with theoretical
calculations, experimental (i. e., la- ratory) investigations are
important for the characterization and understanding of the optical
properties of such types of particles. The ?rst paper in this volume,
written by B. Gustafson, is aimed at the descr-
tionofscaledanalogueexperimentsinelectromagneticscattering.