Validation of two Huanjing-1A/B satellite-based FAO-56 models for estimating winter wheat crop evapotranspiration during mid-season

Crop evapotranspiration (ETc) is an important indicator used in managing agriculture water and monitoring crop growth. The objectives of this study were to: (1) analyze the seasonal dynamics of crop coefficients (Kc) and basal crop coefficient (Kcb) derived from vegetation indices (VIs) based on a time series of Huanjing (HJ) satellite images during 2011 and 2013; (2) investigate daily and monthly variations of ETc at key growth stages of winter wheat using lysimeter or eddy covariance systems; (3) compare the performance of two Huanjing-1A/B satellite-based FAO-56 models (the FAO-56 dual-crop coefficient model and the vegetation indices-reference evapotranspiration (VIs-ETo) method) to the ETc measurements; (4) select the best ETc model for estimating daily ETc (mm/day) at the Xiaotangshan experimental site and its surrounding farmland in conjunction with HJ satellite overpasses from March to May 2011. The VIs and concurrent ETc were acquired at the Xiaotangshan experimental site, Beijing, China, during the 2011 and 2013 winter wheat growing seasons. The results showed that the overall tendencies of crop coefficient patterns (Kcb and Kc), ETc and ETo first increased and then decreased at key growth stages of winter wheat. The cumulative ETc of water consumption was highest at the heading-filling stage in May. Similar changes in cumulative ETc were found during April-May 2011 and 2013. The estimation accuracy of ETc was better based on FAO-56 dual-crop coefficient model (R2 = 0.88 and RMSE = 1.06 mm/day in 2011 and R2 = 0.84 and RMSE = 0.55 mm/day in 2013) than the VI-ETo method (R2 = 0.77 and RMSE = 1.22 mm/day in 2011 and R2 = 0.67 and RMSE = 0.81 mm/day in 2013). The results indicated that the FAO-56 dual-crop coefficient model and VI-ETo methods were used to estimate ETc in winter wheat. Two Huanjing-1A/B satellite-based FAO-56 models were used to timely estimate ETc during the winter wheat mid-season, and ETc was used to adjust agricultural water management practices.