New analysis of satellite images has proven the existence of rogue waves: massive surges of water rising more than 25 metres above the ocean. Scientists are now starting to understand the factors that combine to produce such huge waves, long dismissed as myths.
The MaxWave project, was initiated by the European Union in 2000 specifically to identify, understand and model the waves. The European Space Agency (ESA) allocated two of its weather satellites - ERS-1 and 2 - to see how frequently the waves occur: statistical analysis suggested that such waves should only show up once every 10,000 years.
ERS1 and ERS2 both have a Synthetic Aperture Radar (SAR) as their main instrument. This collects what the ESA calls "imagettes" of the ocean surface, taking five-by-ten kilometre snapshots every 200m. Scientists use these images to produce ocean-wave spectra from which they can identify anomalous waves.
Sailors have long reported sightings of these waves, but reports had mainly been dismissed either as exaggeration or outright fibs. However, in the last 20 years, more than 200 supercarriers have been lost at sea with eyewitness reports suggesting rogue waves were responsible. As more ships and rigs survived encounters with the massive waves, scientists decided to investigate.
The list of encounters the ESA cites is impressive. On 1 January 1995 the Draupner oil rig in the North Sea was hit by a wave whose height was measured by an onboard laser device at 26 metres, with the highest waves around it reaching 12 metres. Then, in early 2001, two cruising vessels - the Bremen and the Caledonian Star - had their bridge windows smashed by 30-metre rogue waves in the South Atlantic.
The project ran for three years, collecting radar images of the ocean's surface. Over 30,000 images were collected, approximately a three-week period, around the time of the Bremen and Caledonian Star's encounters. Ten rogue waves were identified in these pictures.
The ESA says that the results of the research will have implications for ship and platform design. ®