The origin and movement of waves reaching up to 11 metres that devastated France's Reunion Island in the Indian Ocean on Saturday evening have been detected with ESA's Envisat satellite.
The waves that thrashed the southern port of Saint Pierre, leaving two fishermen missing, causing several piers to collapse and flooding several homes and businesses, originated south of Cape Town, South Africa, and travelled northeast for nearly 4000 km over a period of three days before slamming into Reunion Island.
Dr Bertrand Chapron of IFREMER, the French Research Institute for Exploitation of the Sea, and Dr Fabrice Collard of France's BOOST Technologies in Brest located and tracked the swells using standard processed Synthetic Aperture Radar (SAR) ESA products.
"Swells are still surprise factors, which can unfortunately be deadly," Chapron said. "The SAR Wave Mode product allows us to locate and systematically track swells globally. In the near future we anticipate using SAR wave data to predict their arrival time and intensity."
Although waves were forecast to hit Reunion Island, their intensity was predicted to be only a couple of metres, Collard explained.
"Because strong swells are preceded by calm water, it is impossible to detect their arrival from shore," Collard said. "SAR is the swell instrument and can typically observe swell periods in the range of 12 to 25 seconds."
A larger wave period correlates to a more extreme wind event. The one that hit Saint Pierre, Reunion Island, had a 19-second range and initially originated from very intense storm winds on 8 May.
Approaching the coastline, the wave system slows down and individual waves increase to reach at least two times the mean average of their initial wave height easily. For instance, a 5-metre significant wave height system can hit the coast with the height of 10 metres.
Chapron and Collard are working on a project that will make
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Contact: Mariangela D'Acunto
mariangela.dacunto@esa.int
39-069-418-0856
European Space Agency
16-May-2007