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Airborne Sunphotometer Measurements of Aerosol Optical Depth and Columnar Water Vapor During the Puerto Rico Dust Experiment, and Comparison with Land, Aircraft, and Satellite MeasurementsAnalyses of aerosol optical depth (AOD) and columnar water vapor (CWV) measurements obtained with the six-channel NASA Ames Airborne Tracking Sunphotometer (AATS-6) mounted on a twin-engine aircraft during the summer 2000 Puerto Rico Dust Experiment are presented. In general, aerosol extinction values calculated from AATS-6 AOD measurements acquired during aircraft profiles up to 5 km ASL reproduce the vertical structure measured by coincident aircraft in-situ measurements of total aerosol number and surface area concentration. Calculations show that the spectral dependence of AOD was small (mean Angstrom wavelength exponents of approximately 0.20) within three atmospheric layers defined as the total column beneath the top of each aircraft profile, the region beneath the trade wind inversion, and the region within the Saharan Air Layer (SAL) above the trade inversion. This spectral behavior is consistent with attenuation of incoming solar radiation by large dust particles or by dust plus sea salt. Values of CWV calculated from profile measurements by AATS-6 at 941.9 nm and from aircraft in-situ measurements by a chilled mirror dewpoint hygrometer agree to within approximately 4% (0.13 g/sq cm). AATS-6 AOD values measured on the ground at Roosevelt Roads Naval Air Station and during low altitude aircraft runs over the adjacent Cabras Island aerosol/radiation ground site agree to within 0.004 to 0.030 with coincident data obtained with an AERONET Sun/sky Cimel radiometer located at Cabras Island. For the same observation times, AERONET retrievals of CWV exceed AATS-6 values by a mean of 0.74 g/sq cm (approximately 21 %) for the 2.9-3.9 g/sq cm measured by AATS-6. Comparison of AATS-6 aerosol extinction values obtained during four aircraft ascents over Cabras Island with corresponding values calculated from coincident aerosol backscatter measurements by a ground-based micro-pulse lidar (MPL-Net) located at Cabras yields a similar vertical structure above the trade inversion. Finally, AATS-6 AOD values measured during low altitude aircraft traverses over the ocean are compared with corresponding AOD values retrieved over water from upwelling radiance measurements by the MODIS, TOMS, and GOES-8 Imager satellite sensors, with mixed results. These exercises highlight the need for continued satellite sensor comparison/validation studies to improve satellite AOD retrieval algorithms, and the usefulness of airborne sunphotometer measurements in the validation process.
Document ID
20020073067
Acquisition Source
Ames Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Livingston, John M.
(SRI International Corp. Menlo Park, CA United States)
Russell, Philip B.
(NASA Ames Research Center Moffett Field, CA United States)
Reid, Jeffrey
(Space and Naval Warfare Systems Command San Diego, CA United States)
Redemann, Jens
(Bay Area Environmental Research Inst. Sonoma , CA United States)
Schmid, Beat
(Bay Area Environmental Research Inst. Sonoma , CA United States)
Allen, Duane A.
(NASA Ames Research Center Moffett Field, CA United States)
Torres, Omar
(Maryland Univ. Baltimore County Catonsville, MD United States)
Levy, Robert C.
(Science Systems and Applications, Inc. Lanham, MD United States)
Remer, Lorraine A.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Holben, Brent N.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Hipskind, R. Stephen
Date Acquired
August 20, 2013
Publication Date
January 1, 2002
Subject Category
Environment Pollution
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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