Hundreds of people die at sea every year due to ship and airplane accidents. Emergency teams have little time to rescue those in the water because the probability of finding a person alive fall dramatically after six hours. Beyond tides and challenging weather conditions, unsteady coastal currents often make search and rescue operations extremely difficult.
New insight into coastal flows gained by an international research team led by George Haller, Professor of Nonlinear Dynamics at ETH Zurich, promises to enhance the search and rescue techniques currently in use. Using tools from dynamical systems theory and ocean data, the team has developed an algorithm (算法) to predict where objects and people floating in water will go. "Our work has a clear potential to save lives," says Mattia Serra, the first author of a study recently published in Nature Communications.
In today's rescue operations at sea, complicated models of ocean dynamics and weather forecasting are used to predict the path of floating objects. For fast-changing coastal waters, however, such predictions are often inaccurate due to uncertain boundaries and missing data. As a result, a search may be launched in the wrong location, causing a loss of precious time.
Haller's research team obtained mathematical results predicting that objects floating on the ocean's surface should gather along a few special curves (曲线) which they call TRansient Attracting Profiles (TRAPs). These curves can't be seen with our eyes but can be tracked from instant ocean surface current data using recent mathematical methods developed by the ETH team. This enables quick and precise planning of search paths that are less sensitive to uncertainties in the time and place of the accident.
In cooperation with a team from MIT, the ETH team tested their new, TRAP-based search algorithm in two separate ocean experiments near Martha's Vineyard, which is on the northeastern coast of the United States. Working from the same real-time data available to the Coast Guard, the team successfully identified TRAPs in the region in real time. They found that buoys and manikins (浮标和人体模型) thrown in the water indeed quickly gathered along these emerging curves. "Of several competing approaches tested in this project, this was the only algorithm that consistently found the right location," says Haller.
"Our results are rapidly obtained, easy to interpret and cheap to perform," points out Serra. Haller stresses: "Our hope is that this method will become a standard part of the tool kit of coast guards everywhere. "
