ESA's SMOS probe has launched to track the world's water. Credit: ESA

The European Space Agency has successfully launched its Soil Moisture and Ocean Salinity (SMOS) satellite to track the world's water.

The probe will measure the moisture in soil, allowing climate scientists and weather forecasters to better predict droughts and floods. The mission will also measure the salt content of the oceans.

Both should improve water-management strategies and reveal how Earth's water cycle is changing in response to global warming, explains Yann Kerr, principal investigator on the mission and director of the Center for the Study of the Biosphere from Space in Toulouse, France. "The impact of climate change on water resources in totally unknown," Kerr says.

The wet look

SMOS is fitted with an instrument called MIRAS (Microwave Imaging Radiometer using Aperture Synthesis), which will measure the volume of microwaves coming from Earth at roughly 1.4 gigahertz, in the frequency band known as the L-band.

"At this frequency the signal is very sensitive to the moisture," says Kerr. Dry soil emits much more electromagnetic radiation at this frequency than does wet soil, and so appears brighter — in the same way that hotter objects look brighter when viewed by a thermal-imaging camera, he explains. This should improve flood prediction, for example, because wet land is much less able to absorb the water from a sudden downpour.

As the probe orbits Earth, it will produce a complete global map of these microwave emissions every three days, with a spatial resolution of about 50 kilometres.

Changes in the salt content of the oceans cause similar, but much smaller, variations in microwave emissions. These will be monitored by comparing the averages of 30 days' observations from MIRAS, says Kerr, and should allow global salinity maps to be created that are an improvement on the current system, which generally involves only very localized measurements from floating buoys. Changes in salinity have a big impact on ocean circulation, which affects the distribution of heat among the world's oceans.

Final preparations

Following today's launch from the Plesetsk Cosmodrome in Russia, the probe's three arms, carrying the 69 antennae of the MIRAS instrument, will be extended tomorrow. After that comes a six-month commissioning phase to calibrate the instrument.

SMOS has been a long time coming: ESA approved the mission almost 11 years ago. The mission was developed in cooperation with the French space agency (CNES) and Spain's Centre for the Development of Industrial Technology (CDTI).

"Almost everything has been developed from scratch, as very few measurements existed at this L-band frequency," says Jordi Font, an oceanographer from the Institute of Marine Sciences (CSIC) in Barcelona, Spain, and lead investigator for the ocean salinity measurements. If SMOS proves successful, a second satellite could eventually join it on its moisture mission, he says.