Next week, a new instrument designed to measure plant stress will be plugged into the International Space Station. Once operating, the device will deliver unprecedented data about drought conditions and water conservation all over the planet.
The device was designed and built by scientists at NASA’s Jet Propulsion Laboratory in Pasadena, California. It’s scheduled for launch on June 29 aboard a SpaceX rocket as part of a resupply mission for the space station.
Known as ECOSTRESS, the instrument will measure the temperature of plants on Earth from the space station platform orbiting 254 miles overhead. It will provide imagery sharper than any existing satellite offers – and more often, thanks to the space station’s unique orbit.
Joshua Fisher, NASA’s science lead for the project, refers to it as “space botany.” From the temperature data, scientists will be able to answer all kinds of questions that could help Earthlings use water more wisely.
For instance, if plants are too hot, it means they are experiencing water stress. This could serve as an early warning of drought conditions. The data the device collects could also help farmers decide between different lettuce varieties, for example, to choose one that best handles water scarcity. The data could even gauge the success of urban water conservation measures, such as measuring effectiveness of landscaping choices.
Water Deeply spoke with Fisher to learn more.
Water Deeply: How does ECOSTRESS measure plant temperature from space?
Joshua Fisher: It measures reflectance in the parts of the electromagnetic spectrum that are related to heat. You know those handheld instruments that show you heat maps, like a thermometer? It’s like that except a lot more powerful and from the vantage point of space.
Water Deeply: And how do you get information about water use from that?
Fisher: We’re measuring the temperature of plants on the surface of the Earth, then we convert to water use. So as plants cycle water through their leaves, the water cools them down just like sweating cools us. And if there’s not enough water, then they will heat up because they’re not cycling that water to cool them down. So we can measure that temperature and convert that to water stress.
Water Deeply: How does the space station’s orbit help this project?
Fisher: Most satellites we’re used to are either polar orbiters or geostationary. But the space station has a different type of orbit called a precessing orbit. It doesn’t circle over the poles, but it can see from about 60 degrees north to 60 degrees south. Then it will come over the same spot on Earth every three to five days, depending on latitude. So, at higher latitudes, where its turning around in its orbit, it’s going to be seeing those spots quite a lot. But around the tropics, it will be passing at its normal cadence.
The space station will pass over us at different times every day. That’s really useful for our science because some plants will shut down in the afternoon if there’s water or heat stress, and other plants won’t. But we don’t know where that’s happening globally because we haven’t been able to get it from our polar orbiters. And our geostationary orbiters, which do measure the same area every time are quite coarse because of their orbit.
ECOSTRESS is able to sample that diurnal cycle with a very fine spatial resolution of about 70 meters. That’s basically the size of a large backyard – about 230 feet on a side.
Water Deeply: How can this information be used to improve water efficiency on Earth?
Fisher: Farmers want to water as much as their plants will use. They don’t want to water less, unless they are doing some sort of stress irrigation. In general, you want to basically optimize your irrigation and not any more, because that’s a waste of money. So farmers really want to know how much water to irrigate. ECOSTRESS will tell how much water plants are needing and how much is actually being irrigated.
Then for water managers, similarly, they want to know how much water different areas are using. So our U.S. Department of Agriculture partners are going to be investigating science questions related to drip irrigation versus sprinklers, timing of irrigation, timing of sowing a crop, different types of seed varieties and the like. There are a lot of interesting questions related to water use in just the agricultural arena.
Water Deeply: How often will ECOSTRESS be able to take measurements?
Fisher: The overpass time is every three to five days for a single point on Earth. But we’re always basically measuring and we’re always sending data back to Earth and processing the data. We’ll make big deliveries to the public data archive center in regular increments, every six months or so. The mission itself is a scientific mission. The applications really want near real-time, and we’re producing that and there can be extensions to the mission to enable that. But the prime focus of the mission is for the science.
Even if it’s not near real-time, it can still help farmers. The farmer might be planting a few different varieties of lettuce and won’t know how much water each variety is using. A retrospective analysis will tell a farmer how much water each variety uses for the next season.
Water Deeply: How unique will this data be?
Fisher: We’ve been able to do evapotranspiration using MODIS at 1 kilometer resolution. That’s really good at temporal resolution, but not that great for spatial resolution. We’ve also been able to do evapotranspiration using Landsat data at about the same spatial resolution as ECOSTRESS. But then Landsat passes over us every 16 days, and if there’s a cloud in the way then it’s 32 days.
There are similar instruments on high towers in different forested areas across the globe, including one in Ione, California, in the foothills of the Sierra Nevada. They are part of the Fluxnet network. But the Fluxnet data are limited to plants within a radius of about a mile. It would takes millions of Fluxnets to see the whole picture.
ECOSTRESS kind of hits that sweet spot in terms of really good spatial resolution and really good temporal resolution. The ECOSTRESS instrument is really accurate and our retrieval algorithms to process the data are very mature and good as well. We get the best of all worlds in ECOSTRESS.