Mapping Evapotranspiration Using Landsat, Sentinel-2, ECOSTRESS, and MODIS Remote Sensing Data

Most consumptive crop water use returns to the atmosphere through evapotranspiration (ET). In California, where our water resources are limited and heavily utilized, the need for a cost-effective, timely, and consistent spatial estimate of crop ET, from the farm to watershed level, is becoming increasingly important. The Priestley-Taylor (PT) approach, calibrated with field data and driven by satellite observations, shows great promise for accurate ET estimates across diverse ecosystems. We improved the robustness of the PT approach in agricultural lands, to enable growers and farm managers to tailor irrigation management based on in-field spatial variability and in-season variation. We optimized the PT coefficients for each crop type with ET measurements from eddy covariance towers and/or surface renewal stations for seven crop types (Alfalfa, Citrus, Corn, Pasture, Pistachio, Grape and Tomato) in California. In addition to MODIS and Landsat data, we used data from Sentinel-2 and the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) mission to estimate daily 24 hours mean ET. ECOSTRESS, launched in June-2018, provides the most detailed and accurate land surface temperature measurements ever acquired from space. While good agreement was found between satellite-based estimates and field measurements of net radiation and crop type specific optimization, our results demonstrate that ECOSTRESS thermal data can reduce uncertainties in estimating daily ET at field scale resolution. A continuous monitoring of the dynamics and spatial heterogeneity of canopy and consumptive water use at a field scale, will help prepare and inform decisions in adaptively manage water, canopy, and grove density to maximize yield per drop of water.