Surface albedo is a very scale-dependent variable. The numbers in Table 5.3 refer to albedos that would be measured with upward and downward facing pyranometers (instruments used to measure solar radiation) from typically 1-10 m above the surface. The higher that the reflected component is measured above the surface, the greater the areal integration of albedo. Hence, some distinction should be made between local albedos, such as listed in Table 5.3, and regional albedos. The regional surface albedo ar can be expressed as:
where at is the albedo of the different surfaces (i) over a region and At is the area covered by each surface. Developing appropriate parameterizations of regional albedo over heterogeneous surfaces such as snow-covered vegetation or sea ice for use in climate models is an area of active research (see Barry, 1996). For example, the SHEBA program combined local measurements of albedo with aircraft surveys to determine the areal coverage of different surface types.
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