SPECTRAL ALBEDO MEASUREMENTS IN THE UV AND VISIBLE REGION OVER DIFFERENT TYPES OF SURFACES

The spectral albedo of the earth's surface, i.e. the ratio between spe ctral irradiance reflected by the ground to all directions and global irradiance, was measured by a spectroradiometer in the UV and visible region from 290 nm to 800 nm with a spectral resolution of 1.5 nm at s teps of 2 nm in the UV (290-400 nm) and 10 nm in the visible (400-800 nm) region. The measurements were performed over bare fertile soil, sa nd at the beach, concrete (autobahn) and snow as well as over differen t types of vegetation (grass, oats, rye, sugar-beet, stubble). As the albedo increases with increasing wavelengths for most types of surface s considered, it is smaller in the UV than in the visible region. In t he UVB region (lambda < 315 nm) the measured albedo is as small as 0.0 16-0.017 over vegetation, 0.04-0.05 over bare fertile soil, 0.07-0.10 over concrete (''autobahn'') and 0.62-0.76% over polluted snow with a small wavelength dependence. A somewhat higher albedo occurs in the UV A region (315 < lambda < 400 nm) with values ranging from 0.02 over ve getation to 0.05 to 0.08 over bare soil. The albedo over dry bright sa nd, which is typically found at the beach, is significantly higher (0. 14 at 300 nm to 0.24 at 400 nm) than over other snow-free surfaces, th us leading to an enhanced dose of biologically effective radiation at the beach.