An alternative means of estimating the spatial distribution of evaporation is through the use of remotely sensed images, obtained by either aircraft- or spacecraft-based sensors. Images obtained from existing satellite sensors can cover swaths ranging from 60 to 2050 km (at resolutions ranging from 10 m to 1 km) and include information about surface reflectance, temperature, and general backscatter properties (Table 2).
In this section, recent developments in the evaluation of evaporation using remotely sensed images are discussed, with emphasis on several problems that must be resolved before an operational satellite-based system for monitoring areal evaporation from land surfaces can be realized. These methods have been divided into two basic classes: (a) statistical and analytical approaches that calculate H and XE "directly" from the remote-sensing data and (b) modeling approaches that use remote-sensing data to "define" or serve as boundary conditions in the estimation of XE and H.
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