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

Abstract 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 (ET 0 ) 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 ET 0 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.