NASA’s SMAP Satellite To Slake Thirst for Soil Moisture Data

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SAN FRANCISCO — The U.S. Agriculture Department’s Foreign Agricultural Service issues frequent forecasts on the health of crops worldwide to help individual farmers, businesses and government agencies anticipate supply and demand. Accurate information can be difficult to obtain, however, for areas that lack gauges to measure precipitation or soil moisture, one of the most important indicators of future plant health.

The areas without gauges also tend to be places where people face food shortage or food insecurity, said John Bolten, a physical scientist in the Hydrological Sciences Laboratory at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Those places are likely to benefit greatly from the type of data that will be provided by NASA’s Soil Moisture Active Passive (SMAP) satellite, he added.

SMAP, a mission designed to produce global maps showing the moisture content of the top five centimeters of soil every three days, was a top-priority identified by the National Research Council’s Earth science decadal survey released in 2007. SMAP is scheduled to launch Jan. 29 on a United Launch Alliance Delta 2 rocket from Vandenberg Air Force Base in California into near-polar, sun-synchronous orbit. The satellite, which is roughly the size of a small school bus, is equipped with a lightweight conically scanning deployable mesh reflector built by Northrop Grumman’s Astro Aerospace of Carpinteria, California, an L-band radiometer and an L-band nonimaging synthetic aperture radar.

The satellite’s radar and radiometer will work in concert to provide information on soil moisture that is more precise than anything currently available, said Simon Yueh, SMAP project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California.

That information is likely to improve global weather and climate forecasts because soil moisture levels have a significant impact on temperature and precipitation, he added.

SMAP data also are likely to improve forecasting of droughts, wildfires and floods, said Kent Kellogg, SMAP project manager at JPL.

Researchers, emergency management agencies, meteorologists and climatologists will have to wait for that data, however. After launch, NASA officials plan to spend approximately 90 days commissioning the spacecraft, including two weeks deploying the large mesh antenna to its six-meter aperture and another ten days spinning the antenna up to its intended speed of 14.6 revolutions per minute. The initial public release of instrument data is scheduled for late July, with initial soil moisture products issued three months later.  NASA plans to make final verified soil moisture data products available by May 2016, Kellogg said.

In addition to measuring soil moisture levels, SMAP will provide data showing where the ground is frozen or thawed. NASA plans to begin releasing that information to the public by November 2015, with a verified product published in July 2016, Kellogg said.

SMOS. Credit: European Space Agency artist’s concept

“It will take a while to calibrate the instruments and validate the data because we will be acquiring measurements over diverse soil types, vegetation, terrain and in different climates,” Kellogg said. “We have to make sure the satellite data agrees with information drawn from ground sensors in all these different circumstances.”
NASA and Agriculture Department officials have been working for years with organizations that have identified ways to use SMAP data for a variety of purposes. Many of those organizations currently use observations gathered by the European Space Agency’s Soil Moisture Ocean Salinity (SMOS) spacecraft launched in 2009.

SMOS data, for example, helped the Foreign Agricultural Service improve food production forecasts for many areas of the world where soil moisture gauges were sparse or nonexistent, said Susan Moran, a hydrologist with the USDA’s Agricultural Research Service.

Susan Moran, a hydrologist with the USDA’s Agricultural Research Service. Credit: USDA/Jack Dykinga
Susan Moran, a hydrologist with the USDA’s Agricultural Research Service. Credit: USDA/Jack Dykinga

SMAP is expected to further improve those forecasts. In contrast to SMAP, SMOS carries only one instrument, an interferometric radiometer, that provides data resolution of between 35 and 50 kilometers. SMAP will provide soil moisture data with a resolution of ten kilometers, Kellogg said.

“That difference is important because suddenly applications that need finer resolution [than SMOS offers] become feasible,” Moran said.

Another significant difference between SMAP and SMOS is that the new satellite includes features designed to detect and remove radio frequency interference stemming from terrestrial sources or other spacecraft. “L-band has become a busy region of the spectrum,” Kellogg said. “Removing that interference will help us refine the data.”