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Monday
Jan242011

Putting the world's commercial ships to work

The University of Miami’s Peter Ortner calls the Royal Caribbean cruise ship Explorer of the Seas” the world’s most luxurious research vessel”.  That’s because he and his colleagues affixed instrument packages and even built a small lab on the luxury liner.  Why do this?  Well, if you think about it, cruise ships and commercial ships are criss-crossing the oceans all the time.  What an awesome opportunity to collect data!

Commercial shipping lanes of the world - the ultimate scientific transects?

One of the best sorts of data that Peter’s team collects is called ADCP, for Acoustic Doppler Current Profiling.  Its a sonar method of sorts, but not for measuring the distance to the bottom.  Instead, it can tell you the direction and strength of the current (i.e. its vector) at every depth under the ship.  That’s because the speed that sound travels through the water is distorted by current the same way that the speed of sound through air is distorted by speed (you hear this as, for example, the change in pitch when an ambulance goes by). 

ADCP current vectors (black arrows) recorded by a ship and mapped on temperature of the Gulf Stream. You can see how well they match up

By putting a bunch of ADCPs on a bunch of different ships that cruise regular paths, oceanographers can build up a very detailed picture of currents across ocean basins, on a scale that individual oceanographic vessels could never match.  Along the way, they have discovered new features, especially eddies of various sorts in some unexpected places.  An eddy is a circular current, sort of like a gentle cyclone in water; sometimes they form by themselves, but more often they spin off the edge of a current as it passes through another body of water; these are called frontal eddies.  Eddies can go clockwise or anti-clockwise and they can have a warm core or a cold core or a ring-like structure, depending on how they form.  Eddies are important because they profoundly affect the biology within them - either stimulating or dampening productivity.  They can also be really important for weather and climate, because an eddy can take a lot of heat energy from a warm current like, say, the Gulf Stream, and move it somewhere else.  Climate and weather prediction models work much better when eddies are properly accounted for.

What an eddy looks like by ADCP. The ship travels left to right across the top. Red pixels is where water is coming towards you out of the screen, while blue is it going away from you, into the screen

 

ADCP also gives you BIOLOGICAL data. Here, backscatter shows variations in the distribution of plankton as the ship crosses an eddy like the one in the previous figure

The idea of using commercial ships to collect oceanographic data has proven popular and now a UN committee is working on an implementation plan that would see many ships constantly gathering oceanographic data in all the oceans of the world.  That program is called Oceanscope, and when it reaches maturity, Peter’s dream would have become and reality and he can kick back and watch the data roll in.

 

Reader Comments (3)

To be more precise, the sound emitted by the ADCP is distorted not by the water itself, but by the small animals suspended in it, which scatter the "ping" sent out by the instrument weakly back.

If the returning echo is lower-pitched than the original, the water is moving away from the transducer. If the pitch is higher, the water is moving towards it. Most ADCPs have four separate transducer heads angled slightly outwards, and by comparing the Doppler shift (i.e. pitch change) heard by each one, can figure out the direction of water movement as well.

In addition to the speed and direction of water movement, ADCPs also record the strength of the echoes, providing a relative proxy of animal biomass in the water column.
January 24, 2011 | Unregistered CommenterElOceanografo
Hi Al,
Good post. You probably already are aware of this from your time at Stony Brook, but at marine sciences, they did a project with the Port Jefferson Ferry to install data collection devices on the ships hull, and continuously records samples on each Long Island Sound crossing. Its pretty interesting stuff. Figured it fit in with your post here.
http://www.seagrant.sunysb.edu/article.asp?ArticleID=244
January 24, 2011 | Unregistered CommenterJohnny Scallops
Thanks John, I do remember the Pt Jeff ferry package. I didn't know the idea had grown so widely. Peter tells me that Charlie Flagg, who is still an SBU adjunct, is one of the PI's on the Oceanscope program.

And Sam, thanks for setting me straight! Sometimes as a physical oceanographer, I make a very good parasitologist.
January 25, 2011 | Registered CommenterAl Dove

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