|Norman, John - UNIVERSITY OF WISCONSIN|
Submitted to: Hydrological Sciences Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 1996
Publication Date: N/A
Interpretive Summary: Accurate estimates of evapotranspiration (ET) over large areas are important in water resource and agricultural management, crop yield forecasting and evaluating climate change effects on agricultural production. Remote sensing technology can provide information on landscape properties relevant to ET monitoring from field to regional scales. Models of varying complexity are evaluated for their reliability in predicting ET and in their potential to be used operationally with satellite data. The results suggest that several of the semi-empirical approaches are as accurate as the more complicated process-based models for estimating daily ET. However, several of the more complex models have been simplified in order that input parameters can be determined via remote sensing. These models have the greatest potential of being used operationally because they can be applied over different landscapes without recalibration as required by many of the semi-empirical approaches. Application of these ET models will greatly improve forecasts of crop yield and management of our water and agricultural resources.
Technical Abstract: Monitoring evapotranspiration (ET) at large scales is important for assessing climate and anthropogenic effects on natural and agricultural ecosystems. This paper describes many of the techniques used in evaluating ET with remote sensing, which is the only technology that can efficiently and economically provide regional and global coverage of landscape properties. Some of the empirical/statistical techniques have been used operationally with satellite data for computing daily ET at regional scales. With the advent of greater computer processing, numerical models simulating the heat and water flow through the soil-vegetation-atmosphere interface have the potential of being used operationally with satellite data. However, the number of input parameters required by many of these models may limit their application to regions containing a large database of soils and vegetation properties. Current efforts are being directed towards simplifying these models so that only a few parameters estimated by remote sensing data are required. The utility of many of the approaches for estimating ET look promising, especially those models using surface temperature and vegetation indices or a time rate of change in surface temperature coupled to an atmospheric boundary layer model. For many of these approaches, differences with ET observations can be as low as 20% from hourly to daily time scales. This percentage difference is within the level of uncertainty in the measurement of ET and contradicts some recent pessimistic conclusions concerning the utility of remotely sensed radiometric surface temperature for determining the surface energy balance.