Abstract
In order to estimate areal evapotranspiration, a system which is adopted modified Penman method and utilized Landsat and elevation data is developed. After extraction of study area and its geometric correction, Landsat MSS data is consequently classified into one of land use categories, which gives empirical parameters for calculation of evapotranspiration. Elevation data, which is originally given by 7.5″×11.25″, is interpolated and fitted to each pixel of land use image data. This is used to evaluate the total shortwave radiation at each pixel. Calculation of evapotranspiration is executed by using empirical functions in terms of meteorological elements which are linearly regressed with height from data at several observatories. The calculated result would be taken the form not only statistical quantities but also transformed image data. Monthly change of estimated evapotranspiration is consistent with its rise and fall characteristics depending on climatic condition. Distribution at mountaneous area, represented as image data, reasonablly shows the effect of topographic condition. As a result, this system could reliably estimate and reproduce actual evaportranspiration of wide area as much as several hundreds square kilometers. This system also has a potential to give us a useful information for water management of river basin.
