Ocean Salt
To further understand Earth's environmental changes, a satellite was launched to map the planet's salty seas.
The 12-story rocket reached a 408-mile-high sun-synchronous orbit.
Built by Argentina, the SAC-D satellite is equipped with multiple scientific instruments from several countries including NASA's Aquarius sensor package designed to make exceptionally precise global measurements of salt content at the ocean surface.
Standing 16.4 feet tall and 9 feet wide within the Delta rocket's protective nose cone, the SAC-D spacecraft weighed 2,977 pounds at launch. The two-stage launcher reached a preliminary parking orbit about 11 minutes after liftoff, then coasted around the South Pole and soared towards Africa when the booster performed a final maneuver to inject the satellite into the desired orbit. Deployment of the payload occurred as expected 56-and-a-half minutes into flight.
The large oval antenna reflector and three microwave radiometers at the heart of Aquarius will work like highly sensitive radio receivers to detect variations in the electrical conductivity of seawater, enabling scientists to deduce the ocean salinity levels.
"Salinity is the glue that bonds two major components of Earth's complex climate system: ocean circulation and the global water cycle," said Aquarius principal investigator Gary Lagerloef of Earth & Space Research in Seattle. "Aquarius will map global variations in salinity in unprecedented detail, leading to new discoveries that will improve our ability to predict future climate."
The satellite will orbit the planet every 98 minutes, covering a swath 242 miles wide for Aquarius to accumulate entire global maps of the planet each week.
"Salinity is the amount of salt dissolved in seawater and you might be surprised to know it varies through the ocean," Lindstrom said. "It's measured in grams of salt in kilograms of seawater. It's typical range is from 32 parts per thousand to 38 parts per thousand. These are small numbers, small differences, but they make enormous difference in the circulation and climate."
Scientists have collected a few million measurements of ocean salinity over the last hundred years, but vast stretches of the planet have never been sampled. Gaining a complete picture every seven days should revolutionize scientists' knowledge of the oceans by unveiling for the first time how salinity changes across the entire globe month-to-month, season-to-season and year-to-year.
Aquarius and SAC-D join a constellation of other environmental research satellites and ocean observers that study sea temperatures, levels, colors and surface winds.
"The addition of Aquarius to this suite of instruments helps create a more complete picture of our oceans and the impact on Earth's climate," said Eric Ianson, Aquarius program executive from NASA Headquarters.
"This important Earth science mission is NASA's first attempt to measure ocean surface salinity from space. Obtaining global measures of salinity is key to our better understanding of ocean circulation, climate and the Earth's water cycle."
A 50-year trend of the limited sampling shows that salty places are getting saltier and the freshwater places are getting fresher.
"Is this an indication we're having an acceleration of the planet's water cycle? The salty places in the subtropical (areas) are having more evaporation, the rain belts are having more precipitation and the ocean is giving us this signal," said Lindstrom.
"This is an indicator but there could be other explanations for this. It could be the ocean circulation is changing, it could be ocean mixing is changing. What we really need to do as oceanographers is dig into this more deeply and Aquarius will help us illuminiate these processes. It's a diagnostic for the water cycle but it can also help us tell about ocean circulation and mixing."
Once Aquarius is commissioned and ready for service in about three months, scientists plan a field campaign with ships, buoys, floats and gliders to compare data with the satellite instrument as the mission commences in earnest.
http://www.spaceflightnow.com/delta/d354/..
