Abstract
An overview of the commonly applied evapotranspiration (ET) models using remotely sensed data is given to provide insight into the estimation of ET on a regional scale from satellite data. Generally, these models vary greatly in inputs, main assumptions and accuracy of results, etc. Besides the generally used remotely sensed multi-spectral data from visible to thermal infrared bands, most remotely sensed ET models, from simplified equations models to the more complex physically based two-source energy balance models, must rely to a certain degree on ground-based auxiliary measurements in order to derive the turbulent heat fluxes on a regional scale. We discuss the main inputs, assumptions, theories, advantages and drawbacks of each model. Moreover, approaches to the extrapolation of instantaneous ET to the daily values are also briefly presented. In the final part, both associated problems and future trends regarding these remotely sensed ET models were analyzed to objectively show the limitations and promising aspects of the estimation of regional ET based on remotely sensed data and ground-based measurements.
Highlights
Speaking, evapotranspiration (ET) is a term used to describe the loss of water from the Earth’s surface to the atmosphere by the combined processes of evaporation from the open water bodies, bare soil and plant surfaces, etc. and transpiration from vegetation or any other moisturecontaning living surface
The Intergovernmental Panel on Climate Change (IPCC) was established by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) in 1988 to evaluate the risk of climate change caused by human activity
The commonly applied ET models using remote sensing data can be categorized into two types:empirical methods and analytical methods. (Semi-)empirical methods are often accomplished by employing empirical relationships and making use of data mainly derived from remote sensing observations with minimum ground-based measurements, while the analytical methods involve the establishment of the physical processes at the scale of interest with varying complexity and requires a variety of direct and indirect measurements from the remote sensing technology and groundbased instruments
Summary
Evapotranspiration (ET) is a term used to describe the loss of water from the Earth’s surface to the atmosphere by the combined processes of evaporation from the open water bodies, bare soil and plant surfaces, etc. and transpiration from vegetation or any other moisturecontaning living surface. In 1970s, when the split-window technique for surface temperature retrieval was not yet developed, ET evaluation was often accomplished by regressing thermal radiances from remote sensors and certain surface meteorological measurement variables (solar radiation, air temperature) to in-situ ET observations or by simulating a numerical model of a planetary boundary layer to continuously match the thermal radiances from satellites [1,19,21,22] These methods and the refinements have been successfully used in mapping ET over local areas. This paper provides an overview of a variety of methods and models that have been developed to estimate land surface ET on a field, regional and large scales, based mainly on remotely sensed data. The commonly applied ET models using remote sensing data can be categorized into two types: (semi-)empirical methods and analytical methods. (Semi-)empirical methods are often accomplished by employing empirical relationships and making use of data mainly derived from remote sensing observations with minimum ground-based measurements, while the analytical methods involve the establishment of the physical processes at the scale of interest with varying complexity and requires a variety of direct and indirect measurements from the remote sensing technology and groundbased instruments
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