Huge Waves That Hit Reunion Island Tracked From Space

WATER WORLD

Still of the animation of observed swell generated by a storm south of Cape Town, South Africa, on 9 May 2007 propagating across the Indian Ocean. Colour correlates to the wavelength of the waves tracked by the Envisat ASAR Wave mode, with red being the longest. Credits: IFREMER - BOOST Technologies. For the full animation please go here.

Residents flee after waves batter Indonesia's coastline
Jakarta (AFP) May 19 - More than a thousand people have fled inland along Indonesia's coastline after tidal waves destroyed houses and fishing boats this week, officials said Saturday. Residents have taken refuge in schools and other government buildings after high waves pounded coastlines from northern Sumatra island to the southern tourist resort island of Bali, officials said. "The number of people that fled their houses has reached 1,246 people," Setio Sutarto from the National Disaster Management Agency told AFP.

He said West Java and West Sumatra were the regions worst hit by the tidal waves, which started hitting the coast late Thursday. Eleven provinces have been affected, including Aceh, which was devastated by the 2004 Asian tsunami, the Kompas daily said. Hundreds of homes have been badly damaged and others swept away in fishing villages dotting the coastlines, the newspaper said.

Television pictures showed wooden homes flattened and residents searching through water-soaked debris for their belongings. Fishermen have been advised against going out to sea in affected areas, Kompas said. On the resort island of Bali, tourists and vendors have been warned to keep off the main beach of Kuta after waves pounded the coastline, destroying stalls, officials said.

Surfers have also been told to keep out of the water in Bali, they said. The popular restaurant strip on Bali's Jimbaran beach was shut down on Friday after waves pounded fishing huts and boats, the Jakarta Post said.

Metres-high waves, caused by monsoon winds on the Indian Ocean, are set to continue to smash the coastline for several more days, the national meteorology office told AFP. "Our prediction shows that waves would be reduced tomorrow on Sumatra island but people along coastlines of West Java island must be careful of more possible high waves," said Sugarin from the office, in Jakarta. A tsunami alert has not been issued for Indonesia, the nation worst hit by the Indian Ocean tsunami in 2004. No casualties have been reported.

by Staff Writers
Paris, France (SPX) May 18, 2007
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 data for global swells available to scientists and users by the end of the year as a demonstration. The products will be useful for weather centres to complement the accuracy of their sea forecast models.

Envisat is equipped with an advanced version of the SAR instrument, Advanced Synthetic Aperture Radar (ASAR), flown on the ERS-1 and ERS-2 missions. Its wave mode acquires 10 by 5 km small images, or 'imagettes', of the sea surface every 100 km along the satellite orbit.

These small 'imagettes', which depict the individual wave heights, are then mathematically transformed into averaged-out breakdowns of wave energy and direction, called ocean-wave spectra, which ESA makes available to scientists and weather centres.

A typical SAR satellite images a swath of 400 km, enough to capture complete 'mesoscale' phenomena such as tropical storms. While optical satellite images show the swirling cloud-tops of a hurricane, a SAR image pierces through the clouds to show the sea surface roughness and its modulation through the combination of wind wave and currents.

Waves of all wavelengths and travelling in several directions are generated by storms. Upon leaving the storm, they disperse and those with the longest wavelengths travel the fastest. During the Envisat Symposium held in Montreux, Switzerland, from 23 to 27 April 2007, Chapron and Collard presented for the first time a demonstration of swell tracking across the Pacific Ocean over a period of 12 days using Envisat ASAR Wave Mode.

The same swell tracking was applied for the identification of the waves that hit Reunion Island last weekend. Independent satellite wind observations confirmed the position of the storm as the origin of the huge waves.

As part of the Global Monitoring for Environment and Security (GMES), a joint initiative of the European Commission and ESA, the space agency has undertaken the development of Sentinel-1, a European polar-orbiting satellite system for the continuation of SAR operational applications. The Sentinel-1 SAR instrument will have a dedicated wave mode allowing the Near Real Time tracking and forecasting of swell for European users.

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WATER WORLD

Welcome Rain Falls On Parched Australia

Sydney (AFP) May 18, 2007
Parts of parched Australia received their heaviest rainfall in years on Friday, but farmers warned much more is needed if the six-year drought is to be broken. Towns in eastern Australia have experienced at least 25 millimetres (one inch) of rain since a wet weather system arrived on Thursday. The National Farmers Federation said the rain was vital to winter crops but more was needed to break the drought which is crippling farm production and threatening water supplies in major cities.

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