Aerosol mapping of the atmosphere using a multiple wavelength polarization lidar

A multiple wavelength volume scanning lidar employing polarization techniques is being built to characterize the size and shape distribution of aerosols in the boundary layer and the troposphere. The technical opportunities of using multiple wavelength lidar have been studied in order to discriminate between various particle sizes in the lower and middle atmosphere. Though these techniques have been used to classify aerosols and other particles by size it has proved difficult to distinguish water droplets from ice crystals. Based on the Mie scattering theory, it has been stated that particles of different shapes alter the polarization of the illuminating light due to internal reflections and scattering. Hence, the depolarization observed in the backscatter of the lidar beam is a measure of the different shapes of the constituent aerosols. Our system uses three wavelengths: 355 nm, 532 nm, and 1064 nm, in addition, the polarization information from each channel is measured. This triple wavelength approach gives better particle size discrimination as well as distinct depolarization signatures. In addition, the incorporation of shorter wavelengths yields a higher resolution. A special opportunity which has been incorporated in the design of this system is its volume mapping feature. By scanning a given volume segment, it is possible to map cloud systems. Incorporation of these three techniques; multiple wavelengths, polarization measurements and volume mapping into a single lidar, will result in an extremely powerful system capable of mapping the scattering properties of clouds and aerosols more accurately. This system is designed to gather enough data to study the complex intricacies of cloud microphysics. Information gathered by this technique promises a clearer understanding of cloud composition and atmospheric thermodynamics.