Extended Abstract (48K)P2.22
Aerosol optical depth over land from the AVHRR pathfinder atmosphere data set
Kenneth R. Knapp, CIRA/Colorado State Univ. and NOAA/NESDIS/ORA, Camp Springs, MD
The Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmosphere (PATMOS) data set provides daily observations for nearly twenty years (1981-1999) binned into approximately (110km)^2 equal area grid cells. This extraordinarily long period of observation allows explicit characterization of the Earth's surface reflectance properties through retrieval of the bi-directional reflectance distribution functions (BRDF) and estimate of aerosol burden. Both aerosols and the surface contribute to the magnitude and angular variability of clear-sky visible reflectances over land (besides molecular extinction, which is well understood). The aerosol contribution depends on the AOD and optical properties (single scatter albedo and scattering phase function). The surface contribution depends on its topography and vegetation, which determine the BRDF and make it seasonally variable. While both contributions can be accurately simulated with a radiative transfer model, the dependent parameters of neither are available on a global basis. However, using the extensive PATMOS data together with radiative transfer models and surface measurements of AOD, these two contributions can be separated. PATMOS data is used to estimate surface BRDF parameters. These parameters are then used to calculate the top-of-the-atmosphere reflectance for an aerosol-free atmosphere from a radiative transfer model. Deviations in the PATMOS clear-sky reflectances from model estimates are used to retrieve AOD , which is compared to ground-based measurements. The study will show BRDF and AOD retrievals for land surface types which show signs of an aerosol signal.
Supplementary URL: http://orbit-net.nesdis.noaa.gov/crad/sat/atm/aerosol/kknapp/
Poster Session 2, Climatology and Long-term Satellite Studies
Monday, 15 October 2001, 2:15 PM-4:00 PM
Previous paper Next paper