Obscuration Of Light By Resonance-Sized, Nonspherical Particulates

A selected number of our microwave extinction measurement results on preferentially/randomly oriented nonspherical particles are presented. These particles span in size near the first major resonance, possess refractive indexes characteristic of natural aerosols, and have axisymmetry in shape, such as spheroids, cylinders and dumbbells. Subtle dependence of light obscuration on particle orientation is shown in our standardized form of P,Q plots. Such a P,Q plot is a cartesian display of the complex scattering amplitude S(0) versus particle orientation (X,ψ) at scattering angle 0 = 0 and contains detailed information on the single-particle obscuration process in perhaps the most comprehensive form. We also routinely deduce C ext , the extinction cross section ext' averaged over random particle orientations, from such a P,Q plot. The ensuing, vivid overall pictures of obscuration by a number of randomly oriented nonspherical particles are also depicted in graphs of Q ext,v versus ρv, showing the volume-equivalent extinction - efficiency averaged over random orientations versus the volume-equivalent phase-shift parameter of each particle. Comparisons with theoretical predictions, where applicable, are also shown in these graphs.