Estimation of Rice Evapotranspiration Using Reflective Images of Landsat Satellite in Sefidrood Irrigation and Drainage Network

More accurate estimation of crop evapotranspiration (ET_c) in a regional scale has always been one of the most important challenges. Temporal and spatial monitoring of ET_c using satellite images can help to enhance accuracy of estimations. In this study, the (ET_c)_rice maps were produced by using statistical/experimental methods based on crop coefficient (K_c) maps derived from vegetation index (VI). K_c was estimated using four methods, including linear relationship between K_c and VI (K_c-VI), calibrated model of K_c-VI, linear relationship between K_cb (the basal crop coefficient) and VI (K_cb-VI), and calibrated model of K_cb-VI. The results showed that calibrated model of K_c-VI had a better performance compared to the other methods, with normalized root mean square errors (NRMSE), mean absolute error and root mean square error being 5.7%, 0.05 mm/d and 0.06 mm/d, respectively. (ET_c)_rice maps were produced by using calibrated model of K_c-VI and reference evapotranspiration (ET₀) from FAO Penman-Monteith method. The NRMSE was 21.3% for using FAO Penman-Monteith method. Therefore, calibrated K_c-VI model in combining with ET₀ based on the Landsat 7 ETM+ images could be provided a good estimation of (ET_c)_rice in regional scale, and can be applied to estimate water requirement due to the free and facilitate access.