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Proceedings Paper

Goddard UV aerosol absorption closure experiment (2002-03)
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Paper Abstract

Compared to the visible spectral region very little is known about aerosol absorption in UV. Without such information it is impossible to quantify a cause to the observed discrepancy between modeled and measured UV irradiances and photolysis rates. We report preliminary results of an aerosol closure experiment where a UV-shadow-band radiometer (UVMFRSR, USDA UVB Monitoring and Research Network) and well-calibrated sun-sky radiometer (CIMEL, NASA AERONET network) were run side-by-side for several months at NASA/GSFC site in Greenbelt, MD. The aerosol optical thickness, τ, was measured at 340nm and 380nm by the CIMEL direct-sun technique. These results compared well with independent MFRSR τ measurements at 368nm (using total minus diffuse irradiance technique). Such comparisons provide an independent check of both instrument’s radiometric and MFRSR’s angular calibration and allow precise tracking of the UV filter degradation by repeating the comparisons made at somewhat regular time intervals. The τ measurements were used as input to a radiative transfer model along with AERONET retrievals of the column-integrated particle size distribution (PSD) to infer an effective imaginary part of the UV aerosol refractive index (k). This was done by fitting the MFRSR diffuse fraction measurements to the calculated values for each UV spectral channel. Inferred values of refractive index and PSD allow calculation of the single scattering albedo, ω, in the UV and comparisons with AERONET ω retrievals. The advantage of utilizing diffuse fraction measurements is that radiometric calibration is not needed for the MFRSR since the same detector measures both the total and diffuse flux. The additional advantage is that surface albedo is much smaller in the UV than in the visible spectral range and has much less effect on aerosol measurements.

Paper Details

Date Published: 4 November 2003
PDF: 9 pages
Proc. SPIE 5156, Ultraviolet Ground- and Space-based Measurements, Models, and Effects III, (4 November 2003); doi: 10.1117/12.508967
Show Author Affiliations
Nickolay A. Krotkov, Univ. of Maryland/Baltimore County (United States)
Pawan K. Bhartia, NASA Goddard Space Flight Ctr. (United States)
Jay R. Herman, NASA Goddard Space Flight Ctr. (United States)
James R. Slusser, Colorado State Univ. (United States)
Gwendolyn R. Scott, U.S. Dept. of Agriculture (United States)
Colorado State Univ. (United States)
Gordon Labow, Science Systems and Applications, Inc. (United States)
Alexander P. Vasilkov, Science Systems and Applications, Inc. (United States)
Tom Eck, Univ. of Maryland/Baltimore County (United States)
Oleg Dubovik, Univ. of Maryland/Baltimore County (United States)
Brent Holben, NASA Goddard Space Flight Ctr. (United States)


Published in SPIE Proceedings Vol. 5156:
Ultraviolet Ground- and Space-based Measurements, Models, and Effects III
James R. Slusser; Jay R. Herman; Wei Gao, Editor(s)

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