Freak waves aren't such rare events after all, a conference in Galway heard. Lorna Siggins, Marine Correspondent, reports on the phenomenon
A simple radar antenna mounted on a ship or oil rig is now central to a new European system geared towards forecasting "freak" or "rogue" waves. Early results suggest that these supposedly rare events may be far more common than assumed.
Preliminary information also highlights the need for far more analysis to improve safety for international shipping, according to Konstanze Reichert of OceanWaves GmbH, of Luneburg, Germany. She was speaking at the recent Eurocean conference, hosted in Galway by the Marine Institute and the European Science Foundation.
Reichert was one of several researchers employed at the State-funded research centre, GKSS in Hamburg, which developed the use of radar to monitor wave energy, height and surface currents. The technology became marketable in the 1990s, and she used it to start up her own company, OceanWaves.
The firm was commissioned to conduct two research projects - EuroROSE and MaxWave - focusing on the forecasting and measurement of currents and waves.
The system comprises a conventional navigational x-band radar, a high-speed video digitising and storage device, and the standard computer. Measurements are based on the backscatter of microwaves from the ocean surface, which is visible as "sea clutter" on the nautical radar.
That sea clutter is analysed to deliver information on waves and surface currents, she explains.
During the EuroROSE project, data from ground-based radars, sensors and numerical models was combined to provide the best forecast for coastal and port approaches, such as dangerous harbour entrances.
Specific focus on "rogue" waves was an integral part of the subsequent MaxWave project, also funded by the EU until late last year. The project had been triggered by the high number of large ships lost over recent years, with freak waves of exceptional height being the assumed cause.
Global statistics on reports of extreme waves and Lloyds accident records on international shipping routes from 1995 to 1999 were used to calculated the probability of extremes in general forecasts.
Tonnes of raw data was collected on the Phillips Petroleum rig, Ekofisk, in the North Sea, and correlations between the movement of currents such as the Gulf Stream over particular water depths, current interaction, and wave action were focused on, explains Reichert.
The MaxWave project involved using conventional wave sensors, and x-band radar for remote sensing.
New algorithms to estimate single wave events were developed which could be identified on board ships' radars.
The results indicate that the probability of freak waves is much greater than previously estimated, she says, and she believes the research is imperative for ship designers.
"There is a lot more work to be done on probabilities."
Reichert, an oceanographer, hasn't had direct experience of a rogue wave. "My experience of the sea has always been positive, but I have to say after this research that I am more inclined to be staying close to the office."
Speaking at the same Eurocean session on maritime transport, Peter Ryder, chairman of the European meteorological network, Eurogoos, notes that climate change was already posing a significant challenge to weather forecasters analysing sea areas.
Such change casts doubts on the representative nature of environmental information gathered over many years, and the suitability of structures such as offshore rigs that were built some time ago, he notes.
The Eurocean conference involved over 500 scientists, policy makers and planners from the EU, Norway, Romania and the US, and was held by the Marine Institute in Galway as part of Ireland's EU presidency programme.
Full proceedings of Eurocean are due to be published by the European Commission in October, but powerpoint presentations by speakers and rapporteurs can be found on the website www.eurocean2004.com