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Comparison of Large Aperture Scintillometer and Satellite-based Energy Balance Models in Sensible Heat Flux and Crop Evapotranspiration Determination

2012; Volume: 2; Issue: 1 Linguagem: Inglês

2226-4361

Mcebisi Mkhwanazi, José L. Chávez, Evan H. Rambikur,

Climate variability and models

The estimation of crop water use or evapotranspiration (ET) is an important aspect of water management especially in arid and semi-arid regions. Various methods have been used in the estimation of ET including remote sensing (RS) based models, and these have an added advantage of estimating ET over a large area (e.g., regionally). This study looked at two models of estimating ET; Mapping evapotranspiration at high Resolution with Internalized Calibration (METRIC) and the Surface Energy Balance Algorithm for Land (SEBAL). Satellite images from Landsat 5 for 2010 for two alfalfa fields in Rocky Ford, Colorado, were processed and analyzed to obtain sensible heat flux (H). Both RS models employ the energy balance (EB) method and estimate net radiation (Rn) and soil heat flux (G) similarly. However they differ in the approach to calculate H. Since ET is determined as a residual in the EB equation, the accurate estimation of H becomes critical. The objective of the study was to assess the RS estimates of H with H measured using a Large Aperture Scintillometer (LAS). Further comparison was done for ET. Results indicated that METRIC more accurately estimated H and ET than SEBAL. For hourly ET, SEBAL showed a relative error up to 38% while METRIC resulted in a relative error up to 11%. Both models reported larger errors for dry fields depicting smaller fractional vegetation cover values. The results of this study indicate that there is an opportunity to improve the RS methods discussed by incorporating surface heterogeneity and perhaps the correction of radiometric surface temperature for atmospheric effects.