Space station to improve monitoring of Earth's plant health

A new space-based instrument to study how effectively plants use water is being developed at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif. The instrument, called the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), will monitor one of the most basic processes in living plants: the loss of water through the tiny pores in leaves.

When people lose water through their pores, the process is called sweating. The related process in plants is known as transpiration. Because water that evaporates from soil around plants also affects the amount of water that plants can use, ECOSTRESS will measure combined evaporation and transpiration, known as evapotranspiration.

"When a person sweats during a workout, it helps cool their body, and if they get enough water they can keep exercising," said Simon Hook, a research scientist at JPL and the project's principal investigator. "If they do not get enough water, they show signs of overheating and stress and eventually collapse. Similarly, if plants do not get enough water, they show signs of stress. By measuring evapotranspiration, we get an early indicator of that stress, and we can do something about it before the plants collapse."

ECOSTRESS's science instrument is a high-resolution thermal infrared radiometer, which works like a giant thermometer from space to measure the temperature of plants and the amount of heat radiating from Earth's surface. "If we find a plant is too hot, that's because it's not getting enough water to cool itself down," said Josh Fisher, a JPL research scientist and science lead for ECOSTRESS.

Existing satellite instruments that monitor evapotranspiration offer either high spatial resolution but low time frequency (a couple of measurements a month), or high time frequency and coarse spatial resolution. Scientists, farmers and water managers need both high resolution and high frequency.

The International Space Station provides a particularly beneficial vantage point not regularly available with traditional free-flying (sun-synchronous polar-orbiting) satellites, which fly over the same spot on Earth at the same time on each pass. The station's orbit shifts so that it flies over any given spot on Earth at different times. By looking at ECOSTRESS imagery of a certain location over the course of days to weeks, scientists will be able to see how evapotranspiration varies in that location throughout the day. This is important, because plants that get enough water in the cool of the morning might shut down in afternoon heat, just as a person stops sweating under extreme heat stress.

Scheduled for completion in 2017 and launch between 2017 and 2019, ECOSTRESS is one of two instruments selected in July for NASA's Earth Venture-Instrument series of missions. These missions are part of the Earth System Science Pathfinder program, managed by NASA's Langley Research Center in Hampton, Va., for NASA's Science Mission Directorate. The ECOSTRESS team includes researchers from the U.S. Department of Agriculture; Princeton University, Princeton, N.J.; and the University of Idaho, Moscow, Idaho. The California Institute of Technology, Pasadena, manages JPL for NASA.