Rescue and salvage operations at sea are particularly challenging for the rescuers, as it usually takes a certain amount of time for the emergency services to arrive on the scene. During this time, the victims may have been carried miles away from the scene of the accident by tides, changing weather conditions or shifting coastal currents. In general, rescuers only have about six hours to save people floating on the water. After that, the probability of finding someone alive drops significantly. This means that hundreds of people drown every year in shipping accidents or plane crashes on the open sea.
An international team of researchers led by George Haller, Professor of Nonlinear Dynamics at the Swiss Federal Institute of Technology (ETH) in Zurich and at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, has now developed a calculation method to facilitate the search at sea. This new algorithm, which the team developed using tools from dynamic systems theories and coast guard data, can predict where people or objects are being driven on the sea surface.
“We hope that our work will help save more lives,” says Mattia Serra, former postdoctoral fellow at ETH Zurich and now a postdoctoral fellow at Harvard, as well as chief author of the study recently published in the journal Nature Communications.
Algorithm shows the way to the missing
Up to now, sea rescuers obtain their information about where a person or object might have drifted off during their missions from elaborate models of ocean dynamics and weather reports. However, these forecasts are often quite inaccurate due to rapidly changing coastal waters, uncertain parameters and lack of data. The consequence is that often the first search is done in the wrong place entirely and much valuable time is lost.
In their mathematical calculations, the scientists have found that objects floating on the sea surface collect along certain curve-like lines. These so-called “TRansient Attracting Profiles” (TRAPs) – profiles with temporary attraction – are not visible to the naked eye. However, with the new algorithm they can be calculated from the flow data of the sea surface. These data would allow “fast and precise planning of routes for rescue operations that are less sensitive to uncertain information about the time and place of the accident,” the researchers say.
First tests successful
The new search algorithm was tested in two separate experiments near the island of Martha’s Vineyard off the northeast coast of North America. Participants in the tests were ETH researchers, a team from MIT’s Department of Mechanical Engineering, a group from the Woods Hole Oceanographic Institute and a team from the American Coast Guard. The teams used the same real-time data as the American Coast Guard and observed how the deployed buoys and test dummies gathered along the calculated curves. “We tested several approaches and this was the only one that worked continuously on site,” Haller emphasises.
“Our results are easy to interpret, quickly available and inexpensive to implement,” explains Serra. The method could also be used to calculate the movement of larger objects floating on the sea surface, such as the spread of an oil spill. The scientists next plan to test the method in other marine regions. “We hope that this method will become a standard tool for the coast guard,” says Haller.
Cover photo: People floating on the surface of the water collect along curve-like lines, called “TRansient Attracting Profiles” (TRAPs) © George Haller/ETH Zurich