Comparison of Satellite Based Models for Estimating Evapotranspiration of Soybean Crop

Precise estimates of actual crop evapotranspiration (ETa) are important for managing water use effectively under different climatic conditions. The ETa can be accurately estimated by using standard models and appropriate models, and by employing advanced cloud-based geospatial technologies. In this study, daily ETa values of soybean crop were estimated using Decision Support System for Irrigation Water Management (DSS-IWM), Earth Engine Evapotranspiration Flux (EEFlux). The estimated values of ETa were compared with that of computed from the standard FAO-56 Penman-Monteith model. This study utilized six satellite images of Landsat to monitor the ETa during crop growing season of Soybean. The ETa values estimated by DSS-IWM, EEFlux and FAO-56 Penman-Monteith model ranged from 0.26 to 2.86, 0.96 to 4.70 and 1.10 to 6.41 mm day^-1 with the mean values of 2.45, 1.40 and 3.05 mm day^-1, respectively. The results revealed that both the DSS-IWM and EEFlux models underestimated the seasonal ETa values by 54.17% and 19.72%, respectively, as compared to that obtained from the FAO-56 Penman-Monteith model. The results of the DSS-IWM model showed a moderate level of agreement with the FAO-56 Penman-Monteith model with value of index of agreement (IA) as 0.55, root mean square error (RMSE) of 1.88 mm day^-1, and normalized root mean square error (NRMSE) of 0.61. On the other hand, the results of the EEFlux model revealed more closeness to the FAO-56 Penman-Monteith model with values of IA as 0.87, RMSE as 0.81 mm day^-1, and NRMSE as 0.27. These findings indicated that the EEFlux model can be used for estimating the field-scale ETa values accurately for soybean crop. The study demonstrated potential of EEFlux model for regional scale assessment of ETa.