ASSESSING THE SPATIAL-DISTRIBUTION OF EVAPOTRANSPIRATION USING REMOTELY SENSED INPUTS

The evaporation of water from soil and plant surfaces is of vital environmental interest. The importance of this process becomes apparent when one considers that the scales involved range from water loss from leaf stomata to the circulation of the planetary atmosphere. Since the launch of the first earth observing satellite in 1972, the idea of using remotely sensed data to evaluate the spatial distribution of evaporation has moved from the conceptual to the developmental phase. Problems that currently impede the development of operational systems include spatial resolution, atmospheric interference, estimation of aerodynamic resistance, spatial extrapolation of ground-based meteorological data, partial vegetation cover, and the extension of instantaneous values to daily totals. In this review, efforts to evaluate evaporation using remotely sensed data on both local and regional scales are reviewed, and some impediments that must be resolved before an operational system can be developed are discussed.