Modeling the effect of an inhomogeneous surface albedo on incident UV radiation in mountainous terrain: determination of an effective surface albedo

We compare three different methods for determining an average 'effective' U V albedo. These methods are applied to spectral irradiance data from a meas urement campaign held in the German Alps during the spring of 1999. The fir st method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a functi on of the surface albedo. In the third method, the surrounding area is part itioned into snow-covered and snow-free regions, and the effective albedo e stimated by applying a higher or lower reflectivity to each facet before in tegrating over the surroundings. We present the differences and the correla tions between the various methods as well as the results for the different locations.