GACP Projects
Validation of the Lidar Retrieval of Aerosol Extinction
David S. Covert, PI
Theodore L. Anderson, PI
Abstract: Understanding potential climate change depends upon improved quantification of climate forcing by anthropogenic aerosols, including clear-sky backscattering of solar radiation to space. Because of its exquisite precision, vertical resolution, and the relative ease of data acquisition, lidar technology has a great potential to contribute to this research. However, this potential remains largely unrealized due to calibration and retrieval uncertainties, especially with regard to an optical property known as the lidar ratio - the ratio of light extinction to 180-degree backscatter. We have modified an integrating nephelometer to allow direct and highly accurate measurements of 180-degree backscatter and will deploy this device at a coastal station under existing funding. We request, herein, logistical support for a small but crucial field experiment and salary support for a subsequent data analysis project intended to enable quantitative use of lidar data (past and future) in the development of a global climatology of aerosol forcing. Under the field project our 180° nephelometer will be deployed at the NOAA/CMDL aerosol research station at Bondville, IL in order to obtain systematic, empirical data on the lidar ratio and to carry out a rigorous lidar validation experiment in conjunction with a horizontally-pointing Micro-Pulse Lidar (MPL). Subsequent data analysis efforts, based on these results, will include the development of an empirically-based climatology of lidar ratios for lower tropospheric aerosols and a general assessment of uncertainties for lidar retrievals of aerosol properties. Lidar data sets that could potentially be brought to bear on the aerosol forcing issue include ground-based monitoring with MPL (e.g. at the DoE ARM site), extensive airborne campaigns with NASA's DIAL system, the space shuttle lidar mission (LITE), and possible future satellite lidars (GLAS and PICASSO).
