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).
