Enhancing the Simplified Surface Energy Balance (SSEB) approach for estimating landscape ET: Validation with the METRIC model |
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Authors: | G.B. Senay |
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Affiliation: | U.S. Geological Survey (USGS), Earth Resources Observation and Science (EROS) Center, 47914 252nd St, Sioux Falls, SD 57198, United States |
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Abstract: | Evapotranspiration (ET) can be derived from satellite data using surface energy balance principles. METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) is one of the most widely used models available in the literature to estimate ET from satellite imagery. The Simplified Surface Energy Balance (SSEB) model is much easier and less expensive to implement. The main purpose of this research was to present an enhanced version of the Simplified Surface Energy Balance (SSEB) model and to evaluate its performance using the established METRIC model. In this study, SSEB and METRIC ET fractions were compared using 7 Landsat images acquired for south central Idaho during the 2003 growing season. The enhanced SSEB model compared well with the METRIC model output exhibiting an r2 improvement from 0.83 to 0.90 in less complex topography (elevation less than 2000 m) and with an improvement of r2 from 0.27 to 0.38 in more complex (mountain) areas with elevation greater than 2000 m. Independent evaluation showed that both models exhibited higher variation in complex topographic regions, although more with SSEB than with METRIC. The higher ET fraction variation in the complex mountainous regions highlighted the difficulty of capturing the radiation and heat transfer physics on steep slopes having variable aspect with the simple index model, and the need to conduct more research. However, the temporal consistency of the results suggests that the SSEB model can be used on a wide range of elevation (more successfully up 2000 m) to detect anomalies in space and time for water resources management and monitoring such as for drought early warning systems in data scarce regions. SSEB has a potential for operational agro-hydrologic applications to estimate ET with inputs of surface temperature, NDVI, DEM and reference ET. |
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Keywords: | α, correction coefficient to convert grass reference ET to alfalfa (maximum) reference ET, it can be assumed or developed using local calibration DEM, elevation data from a digital elevation model ETf, reference (maximum) ET fraction from the SSEB model ETo, standardized clipped grass reference ET ETm, maximum ET (αETo) ETrF, reference (alfalfa) ET fraction from the METRIC model KL, lapse rate correction LST, land surface temperature LSTc, elevation corrected LST METRIC, Mapping EvapoTranspiration at high Resolution with Internalized Calibration NDVI, normalized difference vegetation index SSEB, Simplified Surface Energy Balance model SSEBel, SSEB with elevation correction alone SSEBelvi, SSEB with both elevation and NDVI correction Ta, air temperature (weather data) Ts, land surface temperature (as observed by remotely sensed data) |
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