Satellite measures globe's salty seas

SEATTLE, June 13 (UPI) -- A NASA instrument has completed a year of measuring ocean salinity from space, providing important data about Earth's water cycle, the space agency said.

Launched June 10, 2011, the satellite mission -- a combined effort between NASA and Argentina's Comision Nacional de Actividades Espaciales -- is compiling a more complete picture of the salty sea and how it varies on a global scale, the agency reported Wednesday.

NASA's Aquarius instrument aboard the Argentine satellite is the first such device specifically designed to study surface ocean salinity from space, making 300,000 measurements per month. It uses three passive microwave sensors, called radiometers, to record the thermal signal from the oceans' top 10 millimeters, about 0.4 inches.

Aquarius has confirmed what oceanographers have known for many years, that the Atlantic Ocean is saltier than the Pacific and Indian oceans, and that rivers such as the Amazon carry tremendous amounts of fresh runoff from land and spread plumes far into the sea.

In the tropics, particularly near the Pacific's Inter-Tropical Convergence Zone, extra rainfall makes equatorial waters somewhat fresher, researchers said.

"An overarching question in climate research is to understand how changes in the Earth's water cycle -- meaning rainfall and evaporation, river discharges and so forth -- ocean circulation, and climate link together," said Gary Lagerloef, Aquarius principal investigator at Earth and Space Research in Seattle.

"Salinity is the variable we can use to measure that coupling. It's a critical factor, and it will eventually be used to improve climate forecasts," he said.