Seapower - Seapower201105

ARGO ILLUSTRATION
The global Argo array features more than 3,000 autonomous floats gathering and transmitting data around the world.
The U.S. component of Argo is supported primarily by the National Oceanic and Atmospheric Administration through
the National Oceanographic Partnership Program.

The unit has a 10-day cycle, diving to 1,000 meters and drifting with the current for nine days, then dropping to 2,000 meters and ascending while taking data on temperature and salinity on the way back up.

At the surface, the unit’s antenna transmits its position along with the data collected during its journey from 2,000 meters to the surface. The data is sent to NOAA satellites, and then on to data-collection centers.

While drifting at the 1,000-meter level, the float may travel as little as a kilometer a day, 30 kilometers in a strong current. In places like the circumpolar Southern Ocean current, 200 kilometers is not unheard of.

It is safer to drift submerged.

“All the bad things that can happen to the Argo float happen on the surface — hit by a boat, picked up by a fisherman, sensors get fouled — so the less time spent on top of the ocean the better,” Roemmich said.

Buoyancy Gliders

Spray gliders are autonomous underwater vehicles that, like floats, take vertical profiles of data, giving scientists a clearer understanding of the temperature, salinity and turbidity of specific areas of the oceans. But they also can be programmed to steer to waypoints and redirected to make course changes as needed.

Each Spray Glider is 2 meters ( 6. 5 feet) in length, and has a wingspan of 1. 2 meters ( 3. 9 feet), according to Dan Rudnick, a professor of oceanography at Scripps.

The gliders have no external moving parts or motors. Instead, they move on a preprogrammed course vertically and horizontally in the water by pumping mineral oil between two bladders, one internal and the other external to the hull. The movement of the oil and the subsequent shrinking of the external bladder decreases the glider’s volume. This action changes the volume of the glider, making it denser or lighter than the surrounding water.

Power for onboard electronics and communications comes from lithium batteries. Data is sent to the National Oceanic and Atmospheric Administration’s National Data Buoy Center at Stennis Space Center in Bay St. Louis, Miss.

The gliders are deployed from shore or a research ship using a Zodiac boat. A mission may last three to five months.

“We send them out for months at a time. They are not expendable. We bring them back, turn them around and send them back out. Every time we take one out we put another one in,” Rudnick said.

The gliders have been used in the Pacific from Monterey Bay on the U.S. West Coast to the Solomons Sea and Palauan Islands, and in the Gulf of Mexico to look for oil in the water during the Deepwater Horizon spill last year.