Remote Sensing of Evapotranspiration
The generation of evapotranspiration maps using Landsat Satellite images is based on METRIC (Mapping EvapoTranspiration at high Resolution and Internalized Calibration). This process was initially funded in the early 2000s by the Idaho Department of Water Resources (IDWR). Since then, evapotranspiration maps for eastern southern Idaho have been generated for 1986, 1996, 2000, 2006, 2008, 2009, 2010, 2011, 2013, 2016 and 2017. We are currently preparing to perform "Near Real Time" METRIC processing for 2018. The images/maps are available on line from the IDWR ET GIS website. Additionally, we are working on generation of METRIC evapotranspiration maps for the Treasure Valley area (Boise to Fruitland) for select years to support IDWR and USGS Treasure Valley aquifer modeling project. The process has also been applied at various locations throughout the United States and the world.
In 2009, the Idaho Department of Water Resources — University of Idaho partnership that applies METRIC-based ET in IDWR hydrology and water rights and operations was awarded the prestigious Innovations in American Government Award by the Ash Institute of the Kennedy School of American Governance of Harvard University. The award announcement is at: "Mapping Evapotranspiration from Satellites."
Animations of ET in Idaho are available at: "Evapotranspiration from Landsat."
A single Landsat satellite is insufficient to produce annual evapotranspiration (ET) products due to impacts of clouds. This link summarizes the impacts of clouds on one versus two satellites for southern Idaho annual ET (pdf). The likelihood of producing annual ET products increases by nine times with two. Most of the continental US requires 16 satellites for a clear image every 16 days 70% of the time. This power point shows the number of satellites and probability of cloud free images (16 and 32 day) for the continental US.