Polar nephelometer for light-scattering measurements of ice crystals

We report on a small, lightweight polar nephelometer for the measurement of the light-scattering properties of cloud particles, specifically designed for use on a balloonborne platform in cirrus cloud conditions. The instrume nt consists of 33 fiber-optic light guides positioned in a two-dimensional plane from 5 degrees to 175 degrees that direct the scattered light to phot odiode detectors-amplifier units. The system uses an onboard computer and d ata acquisition card to collect and store the measured signals. The instrum ent's calibration is tested by measurement of light scattered into a two-di mensional plane from small water droplets generated by an ultrasonic humidi fier. Excellent comparisons between the measured water-droplet scattering p roperties and expectations generated by Mie calculation are shown. The meas ured scattering properties of ice crystals generated in a cold chamber also compare reasonably well with the theoretical results based on calculations from unified theory of light scattering by ice crystals that use the parti cle size distribution measured in the chamber. (C) 2001 Optical Society of America OCIS codes: 010.1310, 290.1090, 290.5820, 290.5850.