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Climate Monitoring | Drought-stricken States Await Crop of New Satellite Sensors

ESA's Soil Moisture Ocean Salinity (SMOS) satellite. Credit: ESA/AOES Medialab

SAN FRANCISCO — As communities along the U.S. East Coast continue to repair the damage caused by coastal flooding in the wake of Hurricane Sandy, Western states are girding for increasing water shortages. A study published Nov. 11 in the journal Nature Climate Change warns that agricultural regions in California and other areas of the Northern Hemisphere that rely heavily on melting snow to irrigate crops are likely to see a significant drop in snowfall in the years ahead.

That type of forecast is fueling the desire among weather and climate scientists to obtain data from new sensors designed to assist them in forecasting drought conditions and monitoring scarce water resources. For years, researchers have relied on U.S. government Landsat imagery satellites, U.S. National Oceanic and Atmospheric Administration geostationary and polar-orbiting spacecraft, the twin Gravity Recovery and Climate Experiment satellites developed by NASA and the German Aerospace Center, and the European Space Agency’s Soil Moisture Ocean Salinity (SMOS) mission to gather data on droughts. For the next two years, space agencies are preparing to launch increasingly sophisticated drought-monitoring sensors.

The first one, scheduled to launch in mid-February, will fly on NASA’s Landsat Data Continuity Mission. The satellite — which many refer to as Landsat 8 — includes two instruments: the Operational Land Imager built by Ball Aerospace & Technologies Corp. of Boulder, Colo.; and the Thermal Infrared Sensor (TIRS) built by NASA’s Goddard Space Flight Center in Greenbelt, Md. The two sensors are designed to extend Landsat’s 40-year archive of imagery, which researchers around the world rely on to track changes in land use, including deforestation, agricultural irrigation and urban sprawl. Although Landsat began gathering data in 1972, it was not until Landsat 4 was launched a decade later that its instruments began collecting thermal data as part of its multispectral imagery. Those data quickly proved its utility because water resource managers in the Western United States discovered that they could combine it with imagery from Landsat’s other spectral bands to determine the amount of water absorbed by individual agricultural fields and urban landscapes. Well-irrigated plants release much more water into the atmosphere through transpiration than dry grass, crops and trees. Transpiring plants can be identified in thermal imagery because they are cooler than plants that lack adequate water.

In an effort to reduce spending, NASA proposed a plan in 2008 to fly Landsat 8 without a thermal imager. When that plan was met with an outcry from the governors of Western states, TIRS was added to the project already under way. Although Landsat Data Continuity Mission program officials have encountered problems with TIRS, including most recently helium leaking from the sensor’s cryogenic cooler, those issues have been resolved and the sensor is ready for its planned Feb. 11 launch on a United Launch Alliance Atlas 5 rocket, said James Irons, NASA’s Landsat Data Continuity Mission project scientist. In order to reach its near-polar orbit, the satellite will be launched from California’s Vandenberg Air Force Base.

The European Space Agency’s Sentinel-1A environmental satellite, part of the European Union’s Global Monitoring for Environment and Security program, also is designed to assist scientists in predicting and monitoring droughts. Sentinel-1A is slated to carry a C-band Synthetic Aperture Radar, built by EADS Astrium, to gather data on land, ice and ocean conditions. For water resource managers specifically, those radar data can be used to track changes in soil moisture, which helps them anticipate flooding or drought. Sentinel-1A is scheduled to launch in late 2013 on a Soyuz rocket from Europe’s Guiana Space Center in French Guiana.

Information drawn from Sentinel-1A will supplement Earth observations the European Space Agency currently obtains from SMOS, a mission launched in 2009 to provide aide in hydrological studies, investigations of ocean circulation patterns, extreme weather forecasts and climate models. SMOS carries an L-band microwave radiometer to detect variations in the amount of water in the soil and salinity in the oceans.

In late 2014, NASA plans to launch the Soil Moisture Active Passive, or SMAP, mission. Like SMOS, the NASA mission includes an L-band radiometer, but it also features an L-band radar. By combining data drawn from the two instruments, scientists hope to obtain extremely detailed information on soil moisture. “This is the first [soil moisture] mission to fly with both a radiometer and a radar,” said Eni Njoku, SMAP project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., which manages the mission. “SMAP will combine the coarse-resolution radiometer measurements that are made at fairly high accuracy with the high-resolution radar measurements that have somewhat lower accuracy. It combines both of these into an optimum product.”

With those data, researchers will be able to pinpoint areas of extremely high or low soil moisture content. “This mission will help to improve our knowledge of, and our ability to predict, hydrological extremes from droughts to floods,” Njoku said.

Detailed data on soil moisture also will help scientists forecast crop yields and improve atmospheric models used to predict weather and climate, Njoku said. “No satellite mission has been able to do this with the accuracy and resolution that SMAP will provide,” he added.

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