The spectral albedo of snow: effects of age, depth, cloud cover, sun angle, and impurities

We present a method for calculating the spectral albedo of snow which can be used at any wavelength in the solar spectrum and which accounts for diffusely or directly incident radiation at any zenith angle. For deep snow, the model contains only one adjustable parameter, an effective grain size, which is close to observed grain sizes. The model agrees well with observations for wavelengths in the near-infrared above 0.8 micro m. In the visible and near-UV, on the other hand, the model for pure snow may predict albedos up to 15% higher than those which are actually observed. The discrepancy is due to the presence in snow of trace amounts of small highly-absorbing particles of desert dust or carbon soot. At concentrations of only 1 part per million by weight or less, they can lower snow albedo in the visible by 5-15%.