Eddies are relatively small, contained pockets of moving water that break off from the main body of a current and travel independently of their parent. They can form in almost any part of a current, but are especially pronounced in western boundary currents. An almost constant string of eddies is visible off of the northern coast of South America as an equatorial current from Africa crashes into South America.

An eddy arises out of fast-moving currents if the current leaves the confining influence of land, it will become unstable and begin to meander and bend. If a current becomes so tightly bent that it doubles back on itself, that section of flow may “pinch off” and separate from the main body. These swirling features can take the shape of warm-core (masses of warm water turning in colder ocean waters) or cold-core (masses of cold water in warm) eddies and can travel for months across hundreds or thousands of miles of open ocean.

Strong currents and eddies influence shipping routes and have been known to damage oil platforms. Knowledge of how and where these phenomena occur as well as how they might be changing can be used by fishing fleets to locate schools of fish, by the Coast Guard to respond to search-and-rescue emergencies or oil spills, and by policy makers to help formulate marine conservation plans.

Hermess is developing a method to improve the accuracy in the localisation of eddies. The localisation is done using AIS data. The solution will make offshore operations safer, prediction of oil spills better and can be life-saving in search and rescue operations.

An overview of the results obtained in a case study off the east coast of South Africa is given at https://www.melodiesproject.eu/content/tracking-ocean-eddies-ais. More details on this case study can be found in the graduation thesis of Ruben van der Neut.