Determination of cloud microphysical properties by laser backscattering and extinction measurements

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Abstract
The extinction and backscattering of 514-nm laser radiation in polydisperse water droplet clouds have been studied in the laboratory. Three cloud size distributions with modal diameters of 0.02, 5, and 12 μm have been investigated. The relationships between the cloud optical parameters (attenuation coefficient σ and volume backscattering coefficient βπ) and the cloud water content C have been measured for each size distribution. It has been found that a linear relationship exists between σ and C and between βπ and C for cloud water content values up to 3 g/m3. The linear relationships obtained, however, have slopes which depend on the droplet size distribution. For a given water content both σ and βπ increase as the modal diameter decreases. The measured data are compared with existing theoretical analyses and discussed in terms of their application to lidar measurements of atmospheric clouds. It is concluded that the empirical information obtained can serve as a basis for quantitative lidar measurements.