June 8, 2011
Aquarius To Study The Power Of Sea Salt
By Dauna Coulter, Science@NASA
A new observatory is about to leave Earth to map a powerful compound of global importance: Common everyday sea salt.
"Based on decades of historical data gathered from ocean areas by ships and buoys, we know the salinity has changed over the last 40 years," says Aquarius principal investigator Gary Lagerloef. "This tells us there's something fundamental going on in the water cycle."
Salinity is increasing in some ocean regions, like the subtropical Atlantic, which means more fresh water is being lost through evaporation at the sea surface. But no one knows why this is happening; nor can anyone pinpoint why other areas are experiencing more rainfall and lower salinity. To solve these mysteries, scientists need a comprehensive look at global salinity.
Within a few months, Aquarius will collect as many sea surface salinity measurements as the entire 125-year historical record from ships and buoys.
"Salinity, along with temperature, governs the density of seawater," says Lagerloef. "The saltier the water, the denser it is, and density drives the currents that determine how the ocean moves heat around the planet. For example, the Gulf Stream carries heat to higher latitudes and moderates the climate. When these currents are diverted by density variations, weather patterns such as rainfall and temperature change."
Scientists have gathered an ensemble of measurements over the ocean--e.g., wind speed and direction, sea surface heights and temperatures, and rainfall. But these data do not provide a complete picture.
"We've been missing a key element "“ salinity," says Lagerloef. "A better understanding of ocean salinity will give us a clearer picture of how the sea is tied to the water cycle and help us improve the accuracy of models predicting future climate."
Aquarius is one of the most sensitive microwave radiometers ever built, and the first NASA sensor to track ocean salinity from space.
"It can detect as little as 0.2 parts salt to 1,000 parts water -- about the same as a dash of salt in a gallon of water. A human couldn't taste such a low concentration of salt, yet Aquarius manages to detect it while orbiting 408 miles above the Earth."
The Aquarius radiometer gets some help from other instruments onboard the satellite. One of them helps sort out the distortions of the choppy sea. CONAE's Sandra Torrusio, principal investigator for the Argentine and other international instruments onboard, explains:
"One of our Argentine instruments is another microwave radiometer in a different frequency band that will measure sea surface winds, rainfall, sea ice, and any other 'noise' that could distort the Aquarius salinity measurement. We'll subtract all of that out and retrieve the target signal."
Torrusio is excited about the mission.
"I've met so many new people, not only from Argentina, but from the US and NASA! It's been a great experience to work with them and exchange ideas. We may come from different places, but we all talk the same language. And it isn't English "“ it's science."
Working together, these international "people of science" will tell us more about the ocean's role in our planet's balance "“ and in our own "“ no matter where we live.
Image Caption: Artist's concept of the Aquarius/SAC-D spacecraft, a collaboration between NASA and Argentina's space agency, with participation from Brazil, Canada, France and Italy. Aquarius, the NASA-built primary instrument on the spacecraft, will take NASA's first space-based measurements of ocean surface salinity, a key missing variable in satellite observations of Earth that links ocean circulation, the global balance of freshwater and climate. The mission is scheduled to launch in June. Image credit: NASA
On the Net: