Surface Reflectivity

Surface Reflectivity

The capability of a surface to reflect solar energy is measured by its albedo or reflectivity in the visible portion of the energy spectrum. The table of albedos gives values for different surfaces and materials (Figure 3).

We can relate values in this table with our experience by remembering that surfaces with high albedos are surfaces that appear bright when illuminated with visible light. So if we consider a photograph of the earth taken from the Space Shuttle, the brightest features are clouds and the large ice masses of Greenland and Antarctica. Deserts are brighter than vegetated surfaces, and the ocean is darker than land (except that at certain angles light is highly reflected off the surface of the ocean in what we call sun glint). NASA has produced a nice albedo map of the Earth.

A scan of the table will confirm these general observations, with clouds reflecting 70 to 90% of incident energy and clean snow reflecting 75 to 95% (you will note that "old snow reflects less). Sand has a relatively high reflectivity for a natural surface, and typical soil is somewhat less. Deciduous forests have a relatively low value of 10 to 20%.

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