Backscatter and extinction measurements in cloud and drizzle at co₂laser wavelengths

The backscatter and extinction of laboratory generated cloud and drizzle sized drops have been measured at CO₂laser wavelengths (predominately at λ = 10.591 jtm). Measurements of volume backscatter coefficient cf, and volume extinction coefficient σ_efor laboratory cloud of predominantly 20-μm radius droplets are dependent on the form of the size distribution in agreement with numerical prediction. For drops of 20m af λ = 10.591 μm the relation between ae and has the appealingly simple size distribution independent form of σ_eσ_e=8π/G_∞, (formula presented)is the asymptotic value of the backscatter gain, where n and k are the real and imaginary indices of refraction. The linear relation is in good agreement with extinction and backscatter measurements made on laboratory generated drizzle sized drops (r 20 μm). This suggests that the extinction coefficient at CO₂laser wavelengths could be inferred from lidar backscatter return signals without requiring knowledge of the size distribution for drizzle and spherical precipitation sized water drops.