HR: 0830h
AN: SH11A-02    [Abstracts]
TI: Evaluation of the Accuracy of the CAU Multiple-Wavelength Sun Photometer for Spectral Measurements of Total Atmospheric Extinction
AU: * Brown, D
EM: douglasbrown1982@yahoo.com
AF: Department of Computer and Information Sciences, Clark Atlanta Univeristy, 223 James P. Brawley Drive, SW Mail Stop 241, Atlanta, GA 30314 United States
AU: Mandock, R L
EM: rmandock@cau.edu
AF: Earth System Science Program, Department of Physics, Clark Atlanta Univeristy, 223 James P. Brawley Drive, SW Mail Stop 241, Atlanta, GA 30314 United States
AU: Grams, G W
EM: ggrams@cau.edu
AF: Earth System Science Program, Department of Physics, Clark Atlanta Univeristy, 223 James P. Brawley Drive, SW Mail Stop 241, Atlanta, GA 30314 United States
AU: Blyler, M L
EM: mblyler.ee80@gtalumni.org
AF: Earth System Science Program, Department of Physics, Clark Atlanta Univeristy, 223 James P. Brawley Drive, SW Mail Stop 241, Atlanta, GA 30314 United States
AU: Tucker, D
EM: dorielle_t@yahoo.com
AF: GE Consumer and Industrial, Appliance Park, Lexington, KY 40225 United States
AB: Researchers at Clark Atlanta University have developed a second-generation LED sun photometer with significant improvements over the LED haze sensor distributed to high schools by NASA. We compared sun photometer results obtained in the Atlanta area with simultaneous observations that used a more expensive, handheld, 5-filter Microtops II Sunphotometer, manufactured by Solar Light Company, Inc. This device measures precipitable water (using a 940 nm filter with 10 nm bandwidth) and aerosol optical depth (using a 1020 nm filter with 10 nm bandwidth). It also measures ozone column depth using 3 filters for wavelengths in the Huggins ozone absorption band. Our most recent sun photometer results agreed within expected errors when comparing LED results at the 3 longest wavelengths (660, 860, and 940 nm) with the Microtops aerosol optical thicknesses. However, some problems were encountered with data obtained at the shortest wavelength (400 nm), and that issue needs to be resolved. We are evaluating the performance of our instrument using a series of computer calculations that address the finite bandwidth of the LED detectors. The Bouguer-Beer law assumes the light source is monochromatic. However, the LED bandwidth varies from 30-50 nm (widest at the longest wavelengths). We must determine whether this bandwidth is narrow enough to justify the use of a standard Langley plot. MODTRAN4 is used to obtain the transmissivity of light at relative high resolution through a variety of atmospheric conditions. By assuming realistic concentrations of water vapor, ozone and aerosol content, the wavelength-dependent overlap between radiation reaching the surface and the spectral response of the LEDs is computed to determine the magnitude of any deviations from Beer's law.
DE: 0800 EDUCATION
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2005 Joint Assembly