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 instrument 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 photodiode detectors-amplifier units. The system uses an onboard computer and data acquisition card to collect and store the measured signals. The instrument's calibration is tested by measurement of light scattered into a two-dimensional plane from small water droplets generated by an ultrasonic humidifier. Excellent comparisons between the measured water-droplet scattering properties and expectations generated by Mie calculation are shown. The measured 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 particle size distribution measured in the chamber. (C) 2001 Optical Society of America OCIS codes: 010.1310, 290.1090, 290.5820, 290.5850.