Array Measures Ice Cloud Scattering

Scattering from nonspherical ice crystals in the upper atmosphere interferes with satellite remote-sensing applications and can play a significant role in climatic changes.

Employing a temperature- and humidity-controlled cold-vapor chamber to create clouds of uniform ice crystals, researchers from the University of California, Los Angeles, and the Desert Research Institute in Reno, Nev., have achieved the comprehensive measurement of the angular scattering properties of plate- and column-shaped ice crystals similar to those found in the atmosphere.

The measurements, which are reported in the Sept. 20 issue of Applied Optics, were obtained via a special fiber-coupled photodiode detector array, called a nephelometer, that detected scattering from a 670-nm diode laser beam. The researchers found that the measurements agreed with scattering patterns predicted by geometric ray-tracing calculations. These predictions included 22° and 46° halo patterns, with the 46° pattern being more prominent for clouds formed mainly from plate-shaped crystals.