RAFOS floats are submersible devices used to map ocean currents well below the surface. They drift with these deep currents and listen for acoustic "pongs" emitted at designated times from multiple moored sound sources. By analyzing the time required for each pong to reach a float, researchers can pinpoint its position by triangulation. The floats are able to detect the pongs at ranges of hundreds of kilometers because they generally target a range of depths known as the SOFAR (Sound Fixing And Ranging) channel, which acts as a waveguide for sound. The name "RAFOS" derives from the earlier SOFAR floats, which emitted sounds that moored receivers picked up, allowing real-time underwater tracking. When the transmit and receive roles were reversed, so was the name: RAFOS is SOFAR spelled backward. Listening for sound requires far less energy than transmitting it, so RAFOS floats are cheaper and longer lasting than their predecessors, but they do not provide information in real-time: instead they store it on board, and upon completing their mission, drop a weight, rise to the surface, and transmit the data to shore by satellite. Introduction Of the importance of measuring ocean currents The underwater world is still mostly unknown. The main reason for it is the difficulty to gather information in situ, to experiment, and even to reach certain places. But the ocean nonetheless is of a crucial importance for scientists, as it covers about 71% of the planet. Knowledge of ocean currents is of crucial importance. In important scientific aspects, as the study of global warming, ocean currents are found to greatly affect the Earth's climate since they are the main heat transfer mechanism. They are the reason for heat flux between hot and cold regions, and in a larger sense drive almost every understood circulation. These currents also affect marine debris, and vice versa. In an economical aspect, a better understanding can help reducing costs of shipping, since the currents would help boats reduce fuel costs. In the sail-ship era knowledge was even more essential. Even today, the round-the-world sailing competitors employ surface currents to their benefit. Ocean currents are also very important in the dispersal of many life forms. An example is the life-cycle of the European Eel. The SOFAR channel The SOFAR channel (short for Sound Fixing and Ranging channel), or deep sound channel (DSC), is a horizontal layer of water in the ocean at which