Satellites are put into orbit for a variety of tasks. From sending television signals to our homes to enabling GPS devices, to helping us see weather on a global scale, satellites collect information and provide us with modern conveniences. One new use for a proposed satellite scheduled to launch this winter is soil moisture monitoring at a local level.
Regions across the globe face drought from time to time. Right now, about 60 percent of California is experiencing "exceptional drought," the U.S. Drought Monitor's most dire classification. California's last two winters have been among the driest since records began in 1879. Without enough water in the soil, seeds can't sprout roots, leaves can't perform photosynthesis, and agriculture can't be sustained.
In order to monitor drought, farmers, scientists and resource managers can place sensors in the ground, but these only provide spot measurements and are rare across some critical agricultural areas in Africa, Asia and Latin America. For this reason, NASA's Soil Moisture Active Passive (SMAP) satellite was created. The mission will collect the kind of local data agricultural and water managers need.
SMAP uses two microwave instruments to monitor the top 2 inches of soil on Earth's surface. Together, the instruments create soil moisture estimates with a resolution of about 6 miles, mapping the entire globe every two or three days.
"Agricultural drought occurs when the demand for water for crop production exceeds available water supplies from precipitation, surface water and sustainable withdrawals from groundwater," said Forrest Melton, a research scientist in the Ecological Forecasting Lab at NASA Ames Research Center in Moffett Field, California.
"Based on snowpack and precipitation data in California, by March we had a pretty good idea that by summer we'd be in a severe agricultural drought," Melton added. "But irrigation in parts of India, the Middle East and other regions relies heavily on the pumping of groundwater during some or all of the year." Underground water resources are hard to estimate, so farmers who rely on groundwater have fewer indicators of approaching shortfalls than those whose irrigation comes partially from rain or snowmelt. For these parts of the world where farmers have little data available to help them understand current conditions, SMAP's measurements could fill a significant void.