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Aircraft measurements of spectral and broadband shortwave radiative fluxes during the Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) experiment
William L. Smith Jr., NASA/LRC, Hampton, VA; and T. P. Charlock, C. K. Rutledge, T. Zhang, V. E. Roback, J. Redemann, and P. V. Hobbs
The Chesapeake Lighthouse and Aircraft Measurements for Satellites (CLAMS) field campaign was successfully executed over the middle Atlantic eastern seaboard from July 10-August 2, 2001. CLAMS is a radiative closure experiment designed to validate and improve EOS TERRA satellite data products, namely, radiative flux profiles retrieved from CERES (Clouds and Earth's Radiant Energy System) and aerosol properties retrieved from MISR (Multi-angle Imaging Spectro-Radiometer) and MODIS (MODerate Resolution Imaging Spectroradiometer). Central to CLAMS experimental strategy is the Chesapeake Lighthouse located in the Atlantic Ocean, 13 miles east of Virginia Beach near the mouth of the Chesapeake Bay and the site of an ongoing CERES Ocean Validation Experiment (COVE). An impressive suite of radiometric instrumentation operates continuously at COVE including BSRN radiometers, AERONET and an ocean scanning spectralphotometer to measure BRDF. Unlike a ship or bouy, the Chesapeake Lighthouse is a stable sea platform, elevated 25-40 meters above the sea surface, above the most intense sea spray and well offshore. Nevertheless, the measurement of upwelling radiation may be problematic owing to the possible effect of the platforms legs both directly (enhanced reflectance?) or indirectly (foam and bubble generator?). This paper focuses on analyses of the shortwave radiation measurements made from the NASA Langley OV-10 aircraft during CLAMS. The OV-10 aircraft is instrumented with commercial uplooking and downlooking broadband and spectral radiometers. The spectral radiometers are the Analytical Spectral Devices, Inc. Full-Range Fieldspec which measure hemispheric solar irradiance from 350-2200 nm with a resolution of 7-10 nm. During CLAMS, the OV-10 was primarily flown at low-altitude (100-600 ft) to characterize ocean optical properties in the vicinity of COVE and to compliment spectral BRDF measurements made from the Cloud Absorption Radiometer (CAR) aboard the University of Washington Convair-580. Broadband and spectral albedos derived from the aircraft data are compared to measurements from COVE to help understand the platform effects. The variabilitiy in ocean optical properties in the vicinity of COVE is also examined. Downwelling spectral irradiances are computed from MODTRAN and compared to the aircraft measurements. Finally, a shortwave spectral flux profile derived from the OV-10, CLAMS in-situ aerosol observations made from the Convair 580 and a radiative transfer model are used to determine the aerosol radiative forcing on CLAMS "golden day" (July 17), a day in which aerosol optical thickness was observed to be about 0.5 at 500 nm.
Session 1, Radiative Effects of Aerosols
Monday, 3 June 2002, 9:00 AM-11:45 AM
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