Airborne spectral measurements of surface-atmosphere anisotropy during theSCAR-A, Kuwait oil fire, and TARFOX experiments

During the SCAR-A, Kuwait Oil Fire Smoke Experiment, and TARFOX deployments , angular distributions of spectral reflectance for various surfaces were m easured using the scanning Cloud Absorption Radiometer (CAR) mounted on the nose of the University of Washington C-131A research aircraft. The CAR con tains 13 narrowband spectral channels between 0.47 and 2.3 mu m with a 190 degrees scan aperture (5 degrees before zenith to 5 degrees past nadir) and 1 degrees instantaneous field of view. The bidirectional reflectance is ob tained by flying a clockwise circular orbit above the surface, resulting in a ground track approximately 3 km in diameter within about 2 min. Spectral bidirectional reflectances of four surfaces are presented: the Great Disma l Swamp in Virginia with overlying haze layer, the Saudi Arabian Desert and the Persian Gulf in the Middle East, and the Atlantic Ocean measured east of Richmond, Virginia. Although the CAR measurements are contaminated by at mospheric effects, results show distinct spectral characteristics for vario us types of surface-atmosphere systems, including hot spots, limb brighteni ng and darkening, and Sun glint. In addition, the-hemispherical albedo of e ach surface-atmosphere system is calculated directly by integrating over al l high angular-resolution CAR measurements for each spectral channel. Compa ring the nadir reflectance with the overall hemispherical albedo of each su rface, we find that using nadir reflectances as a surrogate for hemispheric al albedo can cause albedos to be underestimated by as much as 95% and over estimated by up to 160%, depending on the type of surface and solar zenith angle.