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Response Characteristics of Two Automatic Ice Particle Counters

Robert C. SheetsNational Hurricane Research Laboratory, NOAA, Miami, Fla. 33124

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F. K. OdencrantzEarth and Planetary Sciences Division, U. S. Naval Weapons Center, China Lake, Calif.

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Abstract

Two automatic ice particle counters, one operating in the visible and the other in the infrared spectrum, were tested. The operation of both units is based upon the cross-polarization technique for discriminating between ice and water particles. The results indicate that, although even small water droplets produce a signal, it is possible to distinguish between large water drops and small ice crystals because of the relatively large sensitivity for solid or crystalline materials. The signal strength depends upon the structure of the particle as well as its size. That is, smooth-sided crystals result in larger signals than similar sized, rough-sided particles. The capability of these instruments to provide real-time readouts of ice crystal counts is quite important for operational use in cloud modification experiments.

Abstract

Two automatic ice particle counters, one operating in the visible and the other in the infrared spectrum, were tested. The operation of both units is based upon the cross-polarization technique for discriminating between ice and water particles. The results indicate that, although even small water droplets produce a signal, it is possible to distinguish between large water drops and small ice crystals because of the relatively large sensitivity for solid or crystalline materials. The signal strength depends upon the structure of the particle as well as its size. That is, smooth-sided crystals result in larger signals than similar sized, rough-sided particles. The capability of these instruments to provide real-time readouts of ice crystal counts is quite important for operational use in cloud modification experiments.

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