Airborne measurements of ground and cloud spectral albedos under low aerosol loads

Spectral albedo measurements have been made by three airborne systems (two aircraft and one balloon) over the flat arable land of East Anglia, UK, and above clouds. The spectral albedos measured at the various flight altitudes include the backscattering of the atmosphere beneath the aircraft/balloon, which has to be removed to get the areal spectral surface albedo. Data derived from the airborne spectroradiometers showed the areal surface albedo to be about 0.02 in the UVB (wavelength range between 280 320 nm), increasing with wavelength to about 0.05 at 500 nm. The cloud albedos were measured above two different stratus layers, one completely overcast and one broken. Above the overcast cloud sheet the albedo was independent of wavelength with values between 0.62 and 0.85 depending on position above cloud and altitude. Above the broken cloud layer the averaged albedo spectra showed clear spectral reflection features from the underlying surface mixed with the cloud albedo signatures. Copyright 2004 by the American Geophysical Union.