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Ocean Surface Topography from Space
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Breaking Current Records
January 01, 2008

This map shows how currents could affect the rowers' course. On Dec. 27, the rowers (magenta line) reached the outer edge of the most energetic zone, where the risk of strong adverse currents is high. The latest information suggested that the simple strategy of paddling due west would land them close to Sydney (located about 34 on the scale on the left) because the effects of meridional currents on either side of an anticyclonic eddy would cancel out.

Image credit: CSIRO

Two different teams of ocean adventurers set records this winter crossing the Tasman Sea. One was the first expedition to kayak from Australia to New Zealand; the other became the first Australians to row across the Tasman Sea. Both took advantage of something that sailors have been relying on since the launch of Topex/Poseidon in 1992 -maps of ocean currents made possible by ocean altimetry.

The teams consulted with David Griffin, a research scientist with Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO).
Griffin creates maps of the local waters using sea surface height measurements from the Jason-1, Envisat and Geosat satellites to calculate the location,
speed and direction of currents. These maps, which also include sea surface temperature, are available online at http://www.cmar.csiro.au/remotesensing/oceancurrents/.

"The difficult thing about this region is the strong and variable currents," says Griffin, who has worked with many different groups including fishermen, yachtsmen, police, search and rescue personnel, and environmental protection agencies. Griffin is a principal investigator on the Ocean Surface Topography Science Team, an international group of researchers selected to work on the Jason mission.

A sudden change in the currents gave the rowers a boost. The anticyclonic feature 'pinched off' from the main flow of the East Australian Current to form an isolated warm core eddy, the northern edge of which propelled the rowers' boat homeward at about 1 meter per second, the equivalent to having one extra rower.



Image credit: CSIRO

The rowers set off for Australia from New Zealand on Nov. 29, and Griffin received hourly notices of their boat's position. "We had a script going that updated, every hour, what their trajectory would be if they choose various headings to paddle on," says Griffin. "Andrew Johnson, the expedition's navigator, had studied the maps on the CSIRO website during preparation for the voyage, so he had a pretty good idea of the array of obstacles and opportunities the ever-changing eddy field of the East Australian Current was likely to present."

"We were certainly lucky with the currents," says Johnson, "but being aware of them was half the battle. At least then you could minimize the negative impact and maximize the positive."

After 32 days at sea, the four Australian rowers successfully completed the 2,200-kilometer (1,400-mile) journey on Dec. 30, 2007. The first rowing crossing, done by a single New Zealander in 1970, took 67 days.

The kayakers began their voyage across the "ditch," slang for the Tasman Sea, on Nov. 13. "They made their tactical decisions by using Google Earth to overlay their waypoints on a map of sea surface temperature imagery and altimetric currents that we provide on our web site," says Griffin. They had hoped to make it to New Zealand by Christmas. Instead, they arrived on Jan. 13 after 62 days at sea. "We were biting our fingernails," says Griffin.
The launch of the Ocean Surface Topography Mission on the Jason-2 satellite this summer will help ensure that critical ocean altimetry measurements continue into the next decade.

Get more information on the "Base 3 Rowing Challenge" and on the "Crossing the Ditch" kayak expedition.


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