Whence follOws: F $ Fapp, where equality Occurs Only if a(v) are equal tO cOnstants within the intervals Vs and Vl: In Other wOrds, the less the spectral albedO changes within the used spectral intervals, the mOre exact Our approximatiOn will be. HOwever, the apprOximate value Of exergy is always lOwer than its exact value.

UnfOrtunately, we were nOt able tO achieve a mOre exact estimation Of the error. In One example Of the direct calculatiOn Of the errOr, in which the necessary spectral characteristics were measured for a surface cOvered by grass (Wilmers, 1984), it was shown that the error is maximal when a day is sunny and clear, and decreases when a day is cloudy. However, even in the worst case it is not higher than 12%. These data were collected in several different research sites:

1. 100-year-old beech forest in North Germany (Kiel);

2. crop rotation field in North Germany (Kiel);

3. grass community in North Germany (Hamburg);

4. pine forest in Central Germany;

5. wheat field in Oklahoma, USA;

6. moderately managed pine forest in South Germany.

Let us consider the seasonal dynamics of the following observed and calculated parameters as the radiation (energy) balance, exergy, exergy and radiation efficiency coefficients, and Kullback's measure. We take the Kiel sites as an example (see Fig. 10.1).

Forest Crop Field

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