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Ocean-Observing Satellites Help Break Current Records
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 was 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. 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. Topex/Poseidon and its successor Jason-1 are joint missions of NASA and the French space agency, Centre National d'Estudes Spatiales.
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 our Web site 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, 2007. "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.
More information on the "Base 3 Rowing Challenge" is available at http://www.basefx.com.au/expedition/?cat=3 and on the "Crossing the Ditch" kayak expedition at http://www.crossingtheditch.com.au/ .
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