NASA’s SMAP satellite will capture microwave radiation from the Earth to measure soil moisture. (NASA)
Thursday morning a rocket was scheduled to lift off from Vandenberg Air Force Base on California’s Central Coast, tricked out with instruments that could provide better weather forecasts and more clues to where the drought is headed. (Update: NASA rescheduled Thursday’s launch for Saturday due to high winds and technical problems).
It’s not one of NASA’s catchier names, but the satellite known as SMAP, for “Soil Moisture Active Passive” is designed to provide — for the first time — highly precise maps of water stored in topsoil around the world. Scientists say that’s an important cog in the planet’s water cycle.
“Much like when you perspire, your sweat evaporates and cools your body,” offers Kent Kellogg, the mission’s project director at the Jet Propulsion Lab in Pasadena.
“As it evaporates it seeds the atmosphere with moisture, so that clouds can form, and then precipitation can occur.”
From more than 400 miles up, SMAP will measure differences in natural microwave radiation coming off the Earth. Kellogg likens it to a big pair of night vision goggles in the sky, but measuring radiation on a much lower frequency (so, no, it doesn’t mean NASA can watch you skulking around at night). Wetter soil is cooler and drier soil warmer. From that, scientists can derive water content accurate down to about 6 square miles. Kellogg says that could improve local flood forecasting and drought management.
“If you know how much water is in the soil, if you think of soil as a sponge and you know how full of water that soil or that sponge is, you can have a much better prediction of the likelihood for flooding to occur,” explains Kellogg.
Currently soil moisture is mapped using a relatively sparse network of individual ground-level probes. SMAP will constantly map soil conditions globally. Record high temperatures have stoked evaporation from soils, making California’s current drought even worse.
“SMAP will give us a much more accurate measurement of the rate of change of drought-prone areas,” says Kellogg. “Are they getting larger or getting smaller?”
They’ve been getting larger in California lately, given the historically dry January that’s just winding down, with little precipitation on the horizon. Of course, it’s hard to see clearly more than about ten days out with current weather models. NASA expects SMAP to help with that as well, possibly adding days to the range of reliable regional forecasts.
“Understanding soil moisture conditions in regional areas can give us a lot of insight into the likelihood for rain to form and for the regional temperatures,” says Kellogg.
But SMAP will have its limitations.
“We do not expect to use SMAP data at this point,” says Roger Bales, a climate scientist at the University of California, Merced, “in part because we do not expect it to provide relevant soil moisture information for the areas where we work.” Bales has spent years developing a ground-based network of sensors to measure soil and other hydrologic conditions in the Sierra Nevada, much of which is heavily forested.
“SMAP has some limitations on measurements of soil moisture when the soil is covered by canopy,” or snow in a wet year, Bales points out. “We also understand that SMAP will mainly measure moisture in a thin surface layer of soil, and our interest is more on the deeper soil profile.”
But with its 20 or so ground passes per day, Kellogg expects SMAP to provide useful data on more exposed ground, such as the millions of acres of irrigated land in California.
SMAP will be the fifth and final addition to a suite of recently launched earth science satellites that track attributes ranging from precipitation to the carbon cycle.