Bistatic lidar observation of maritime water cloud particle size

The indirect effect of aerosols in the atmospheric radiation process, which is the effect of aerosols through the formation of clouds, is one of the most uncertain factors in the current climate models for predicting global warming. To study the effect of aerosols on cloud formation quantitatively, a method for measuring cloud particle size is indispensable. A bistatic lidar method was developed for measuring water cloud particle size at the cloud base. The method is based on single scattering Mie theory. A simple measurement system that consists of a single-wavelength laser and dual-polarization bistatic receivers was developed. Experiments were conducted using the 532 nm beam of the Mie scattering lidar on board the research vessel Mirai. An additional bistatic receiver having polarization analyzers was located at a suitable scattering angle. Cloud particle size (mode radius of the assumed size distribution) was derived from the ratio of the polarization components of the scattered light based on the single scattering Mie theory. Particle size of maritime cumulus and stratus near the cloud base was measured. The particle size profiles in the clouds up to a penetration depth of about 50 m were observed with the method. At a larger penetration depth, effect of multiple scattering dominated the return signals.