The effect of particle shape and composition on microwave attenuation and scattering by precipitation

Shape factors for scattering and attenuation in precipitation are normally less than 2, because raindrops are not normally distorted much, and because snow or ice crystals, though distorted, have a relatively small dielectric constant. Very distorted water drops would have large shape factors because of the great dielectric constant of water. A thin water coating, however, raises the attenuation by an ice sphere up to or beyond that of a water sphere, and the scattering, nearly up to that of a water sphere. If, similarly, it raises attenuation and scattering by a non-spherioal ice particle to that of a similarly shaped water particle, then the shape factors for spheroidal water drops are good approximations to the shape factors for randomly oriented wet ice crystals. This is based on the assumption that the theory of small spheroids can still be applied when the particle is comparable with the wavelength and that the results on water coatings apply to spheroids as well as to spheres. A full theoretical investigation of these assumptions would be a heavy undertaking, and exper1mental verification appears preferable. If these assumptions are justified the scattering of melted snow would exceed that of rain of the same precipitation rate and the attenuation would rise to many times that of rain.