Data comparison

As often occurs with models of this type and particularly in mountainous regions, availability of spatially distributed measurements for model verification is very limited. Direct measurements of actual evapotranspiration were not available for Valmasino.

In order to analyse model accuracy, aETd values were computed for the grass land cover using meteorological measurements available at the Bagni di Masino station on the basis of Priestley-Taylor (1972) and the Penman-Monteith's (Monteith, 1965) equations. Evapotranspiration estimates given by the model using remotely-sensed data in correspondence to the meteorological station were averaged for 3 x 3 pixel area to represent the spatial averaging done by ground sensor and were compared with Priestley-Taylor and the Penman-Monteith values. Histograms in Figure 8 show a substantial agreement among estimates of remote sensing and traditional methodologies for herbaceous rangeland class. Remote sensing estimates are the highest, whereas the Penman-Monteith are the lowest in both seasons. Moreover, differences between results given by traditional equations appear greater than those between aETd values given by RS and Priestley-Taylor techniques.

Figure 8. Values oiaETj as derived from the winter season Landsat TM image in relation to topography and land cover classes
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