Multistatic lidar measurements of aerosol properties

Laser remote sensing techniques provide important tools for determining most of the characteristics of aerosols, including their physical and chemical properties. A better understanding of the spatial and temporal distribution of aerosols is needed to study the sources, processes of formation and growth, and the role they play in establishing the planetary albedo and the radiative transfer into space. Multi-wavelength backscatter measurements using Rayleigh and Raman lidar techniques provide signals that profile the optical propagation to describe the transmission of radiation through an atmospheric column. The Rayleigh lidar signals provide backscatter coefficients and the Raman lidar signals from N2 and O2 provide true optical extinction profiles. The combination of these two sets of data gathered simultaneously makes an important contribution to understanding the radiation transmission through the lower atmosphere. However, another approach provides an even better way of characterizing aerosol properties. Bistatic and multistatic lidar measurements use the polarization ratio of the scattering phase function to calculate profiles of the aerosol number density, size, size distribution, and type. These parameters can be determined for spherical particles in the size range between about 50 nm and 20 microns. Analysis of the aerosol concentration and size distribution requires adopting a mathematical shape function, usually a log-normal distribution of spherical particles. Information on aerosol type can be roughly determined based on the refractive index of the scatterers and depolarization of the scattered radiation as a function of wavelength. The development of the hardware for making aerosol measurements and results from recent simulations and field tests are used to show the capabilities and limitations of the technique.