Remote Sensing of ET Over U.S. Southwest Irrigated Agriculture

Remote sensing of ET is now well-recognized as an effective way to monitor, manage, and forecast crop water requirements. The practical implementation of remote sensing observations to realize these activities, however, has been limited by inadequate spatial resolution or temporal sampling. Either the images were too coarse to resolve individual fields, or they were too infrequent, making decision support difficult and inaccurate. Recent satellite deployments are overcoming these limitations. They will transform the quality and utility of ET mapping over agriculture. This presentation aims to highlight that transformation by illustrating the quality of daily ET estimates obtainable from Landsat 8, Sentinel 2, Venus, and ECOSTRESS. Highlighted will be ET studies over Yuma and Central Arizona. Since Fall 2016 the studies have collected in situ observations of water deliveries and ET over economically significant crops, among them: lettuce, wheat, barley, potato, melons. Each site was monitored with an eddy covariance station throughout the growing season, then re-visited as a new crop was planted. Visible- near infrared and thermal infrared data were collected for the same locations and times, then used in 3 ET models: two temperature-driven approaches (TSEB and METRIC), and a vegetation-index only approach (VISW). Accuracy and model uncertainties for each will be reported, the results from which will address questions about the importance of spatial resolution, overpass frequency, and the benefit of thermal observations.