Tuesday, November 21, 2017
 

‘Prawling’ around in the Atlantic

Friday, September 7, 2012

Contact: Lauren Koellermeier, 206-526-6810

A new type of buoy powered by the waves is being used during a large scale field study sampling the salinity – or saltiness – of the mid-Atlantic Ocean.

NASA’s multi-year Salinity Processes in the Upper Ocean Regional Study (or SPURS), started Sept. 6, uses a variety of observational devices to collect much-needed data from this part of the ocean. Instruments will be launched in the Atlantic surface salinity maximum, located halfway between the Bahamas and the west coast of North Africa.

High salinity in a particular part of the ocean is generally caused by low rainfall and high evaporation. Gaining a better understanding of the processes that control and regulate the surface values and cause their variability is one of the aims of this research.

A “Prawler” in the shop

A “Prawler” in the shop

This “Prawler” for the Salinity Processes in the Upper Ocean Regional Study, or SPURS, is ready to be pushed off a ship. The box at the bottom ingeniously serves as a wire spool and an anchor as the wire spools out. Credit: NOAA

Two of the devices to be launched into the Atlantic will be “Prawler” moorings, developed by NOAA’s Pacific Marine Environmental Laboratory in Seattle, Wash. The Seattle lab is known for developing creative and innovative technology to acquire data in the ocean. The lab’s engineers and scientists developed the large anchored buoys that monitor El Niño/La Niña conditions in the Pacific; the deep-water monitoring devices that can help determine if a tsunami is on the move also came out of that laboratory.

“Prawler” is a combination of PICO – the Platform and Instrumentation for Continuous Observation next-generation technology – and “crawler,” because that’s exactly what the instrument package does – it uses the lift from the waves to crawl up the mooring line.

“The instrument package is about the size of a one-gallon paint can,” said William Kessler, an oceanographer at the Seattle laboratory. “It’s attached to an almost 15,000-foot mooring line with a ratchet that locks it in place. But the instrument package only goes up and down the upper 1,600 feet. When a wave lifts the package, the ratchet holds it tight to the line and lifts it up. When the wave trough passes, the ratchet releases and fins keep the package from going down. So it crawls up the line in steps, using only the energy from the waves. Since electrical power is usually the main limitation on ocean instruments, which typically have much of their weight in batteries, the ability to harness the free energy of the waves is a major advance.”

Kessler said when the instrument package reaches the top of the line (or any other pre-programmed spot along the line), it free-falls back to the bottom, making a profile of temperature and salinity on its descent. Once at the bottom, it begins its ascent again, with the whole process taking about an hour. This is fast enough to see the tidal oscillations and turbulence that mixes the surface salinity with slightly fresher ocean water below.

Kessler won’t be aboard the Woods Hole Oceanographic Institution’s R/V Knorr, the ship deploying the Prawlers. But he doesn’t need to be. From his Seattle office he can monitor the instruments, collect their data, and work with the engineers to adjust them if necessary.

While the Prawler was extensively tested during two years of development in Washington’s Puget Sound and in the waters near Hawaii, this is the first real-world science test, meaning there is now enough confidence in the instrument to commit to an experimental objective and scientists will publish the data in a scientific journal.

Watch a video showing how Prawlers are deployed at http://www.pmel.noaa.gov/pico. Learn more at www.pmel.noaa.gov.

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