A new airborne Polar Nephelometer for the measurement of optical and microphysical cloud properties. Part II: Preliminary tests

摘要

A new optical sensor, the airborne PolarNephelometer, has been tested in an open wind tunnel. The wind tunnel wasoperated in cloudy conditions including either cloud water droplets or icecrystals, or a mixture of these particles. The sensor is designed to measure theoptical and microphysical parameters of cloud particles sized from a fewmicrometers to about 500 μm diameter. Basically, the probe measures thescattering phase function of an ensemble of cloud particles which intersect acollimated laser beam near the focal point of a paraboloidal mirror. From themeasured scattering phase function the retrieval of the droplet-size spectra andsubsequent derived quantities such as liquid water content and size parameterscan be calculated using an inversion method. The particle phase discrimination(water droplets/ice particles) can be derived from the shape of the scatteringphase function and the sensitivity of the probe allows the detection of smallice crystals (typically of 5 μm diameter). The paper describes the preliminaryresults obtained by the prototype version of the Polar Nephelometer in variouscloudy conditions. These results are compared with direct microphysicalmeasurements obtained by usual PMS probes also mounted in the wind tunnel.Complementary results obtained in a cold chamber are presented in order toillustrate the reliability of the Polar Nephelometer in the presence of smallice crystals.