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Surf's up: an artist's impression of a rogue wave. Credit: BBC HORIZON/FREAK WAVE

They are known as ‘rogue waves’ — the towering walls of water that, some experts suspect, sink tens of ships every year. Now oceanographers are planning to use satellite images to produce a global map of where and how often the rogues occur.

The WaveAtlas initiative follows a trial using three weeks' worth of radar images obtained by the European Space Agency (ESA) from its two European Remote Sensing (ERS) satellites. The trial data covered February and March 2001, a period during which two tourist liners, the Bremen and the Caledonian, had their windows smashed by 30-metre waves in separate incidents in the Southern Ocean.

The trial's results make hair-raising reading. Besides the two 30-metre giants, the team identified at least eight other waves topping 25 metres across the world. It is a wake-up call for anyone who views rogue waves as a nautical myth, says project member Wolfgang Rosenthal of the GKSS Research Centre in Geesthacht, Germany.

The full project, which will encompass two years' worth of images from 1998 to 2000, could help to explain the staggering number of unexplained sinkings worldwide. “There are many more accidents than you would think — around two a week,” says Rosenthal. “They simply get put down to bad weather.”

As the ERS satellites circle the globe, they each take a representative radar snapshot of an area 10 kilometres by 5 kilometres for every 200 kilometres of the Earth's surface they cover. The WaveAtlas team uses the amount of radar reflected to determine the incline of the ocean surface, and therefore the size of the waves captured in the image. The researchers have received 75% of the requested images from ESA, and hope to complete the analysis early next year.

Project leader Susanne Lehner, a marine physicist at the University of Miami, Florida, suspects that rogue waves can form when existing waves are chased by a storm system moving at roughly the same speed. “We want to see what weather patterns they are associated with,” she says.

The project could also inform the design of ships and oil platforms, Rosenthal argues. Most current platforms are built with a clearance of 15 metres, he says. “The designers think they did a good job, but officers on the platform say ‘we get wet feet’.”