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An experimental apparatus to measure the scattering properties of hexagonal icelike particles in the analog manner at the helium neon laser wavelength of 0.633 m has been designed and built. The instrument consists of an array of 36 highly sensitive and linear photodiode detectors that are positioned to measure the light between the scattering angles of 2.8Њ and 177.2Њ in approximately 2.5Њ increments and at any desired azimuthal angle. This array is calibrated such that the retrieved light signals are corrected to the actual light seen by the detectors to within approximately 6% at all applicable scattering and azimuthal angles. A system of electro-mechanical positioners places the sample at the desired and known position. A glass sphere and a glass fiber configured to scatter light like an infinite cylinder was used to test the operational effectiveness and calibration of the experimental apparatus. The phase functions for the parallel and perpendicular components determined from the experimental results match closely with the results computed from Mie theory.

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The scattering properties of hexagonal icelike crystals as measured in the analog manner by the experimental apparatus described in Part I are presented. The crystals are made out of sodium fluoride (NaF), which has an index of refraction similar to that of water ice. The experimentally determined light intensities scattered from fixed and integrated random orientations of a NaF hexagonal crystal, oriented to produce a two-dimensional scattering profile, compares favorably to the expectations derived from geometric ray tracing methods. Also, the three-dimensional scattering properties of a simulated NaF Parry column, a NaF crystal aggregate, and a NaF plate with a rough surface are compared to results computed from the geometric ray tracing approach. From these comparisons the authors conclude that within the experimental measurement uncertainties and to the degree in which the NaF crystal models approach the geometric and optical ideal, the geometric ray tracing approach is an excellent method to determine the single-scattering properties of hexagonal ice crystals of various shapes in the geometric optics domain.

In a preliminary experimental program, the measured bidirectional reflection properties between 1.0 and 3.5 mum from a grating spectrometer with a resolution of approximately 0.1 mum for ice crystal clouds generated in a cold chamber are compared with theoretical results computed from a line-by-line equivalent solar radiative transfer model. The theoretical calculations are based on the measured habits, concentrations, and sizes of the ice particles from replicas of the ice crystals that show a mean maximum size of approximately 7 mum. The experimental design was first tested with transmission measurements in a pure water-vapor environment that compare closely with theoretical expectations. Within the uncertainties and in consideration of the assumptions necessitated by the preliminary nature of this program, there is a close comparison between the experimental and theoretical results.