Estimating the Soil Surface Evaporation and Transpiration Components from Satellite Images in the Absence of a Thermal Band
Publication: World Environmental and Water Resources Congress 2008: Ahupua'A
Abstract
With the expected failure of Landsat 5 within the next five years and the likelihood of no thermal sensor on Landsat 8 scheduled for launch in 2011, the prospect of energy balance determination of evapotranspiration (ET) from Landsat scale resolution (30 m) is dim. An alternative to the computation of a full energy balance is to use the presence of vegetation cover, characterized using a vegetation index, to estimate the relative rate of transpiration from a pixel and then add an additional evaporation amount that stems from a wet soil surface. The wet surface is modeled using precipitation and irrigation amounts and weather data. This approach, while lacking accuracy of the full energy balance, provides means to create ET images using short wave reflectances produced by future medium resolution satellites. The relatively simple evaporation model of FAO-56 is used to compute daily evaporation losses in the context of transpiration from vegetation. These evaporation losses are added to transpiration derived from a vegetation index to produce a complete estimate for ET. Because of the enormous number of pixels in a Landsat scale image (30 million), it is not possible to know specific irrigation timings by field, so that synthetic irrigation events are simulated. Comparisons between synthesized ET from the described approach and ET from a full energy balance computed using METRIC are explored for parts of south central Idaho and error is quantified.
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Copyright
© 2008 American Society of Civil Engineers.
History
Published online: Apr 26, 2012
ASCE Technical Topics:
- Aerial photography
- Computing in civil engineering
- Continuum mechanics
- Dynamics (solid mechanics)
- Ecosystems
- Engineering mechanics
- Environmental engineering
- Evaporation
- Evapotranspiration
- Geomatics
- Hydrologic engineering
- Irrigation
- Irrigation engineering
- Solid mechanics
- Surface waves
- Surveying methods
- Transpiration
- Vegetation
- Water and water resources
- Waves (mechanics)
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