Lidar aerosol ratio: Measurements and models

Lidar offers an effective means for monitoring and characterizing global aerosol properties. While relative backscatter maps provided by spaceborne lidar measurements such as those obtained with LITE are valuable for delineating global aerosol structural features, obtaining more quantitative information needed for assessing aerosol radiative effects, namely, retrieval of aerosol extinction and backscatter, requires more information/constraints than what is provided by simple, single-direction lidar soundings. The aerosol extinction-to-backscatter ratio, or lidar aerosol ratio, S_a, is a key parameter which, if known, permits retrieval of aerosol backscatter and extinction profiles from the lidar measurements. This paper assesses S_a determinations obtained from a number of lidar, nephelometer and solar radiometer/sky radiance observations. Results of modeling studies to relate different aerosol models to various ranges of S_a values are also considered. The goal is to establish an S_a climatology that can be used to aid aerosol retrievals from satellite lidar observations such as those to be provided by GLAS and PICASO-CENA.