Number 181 (Story #4), June 3, 1994 by Phillip F. Schewe and Ben Stein ACOUSTIC COLOR is the name for the process by which sound waves scatter from an object at characteristic frequencies ("colors" in analogy with optical color) depending on the object's composition, shape, and other properties. Nicholas Makris at the Naval Research Laboratory (202-767-9037) has demonstrated an acoustic-color imaging technique that can map 200 square kilometers of ocean floor at a time from a single point at sea. Using a trio of ships with underwater instruments, Makris and his colleagues first obtain a "black and white" image of a region of the Mid Atlantic Ridge, by radiating a powerful, single-frequency sound wave that "illuminates" a vast region of the ocean floor. The echoes received from different parts of the ocean floor are detected by a 300-meter-long string of underwater sensors, yielding a rough topographical map. Then, a more detailed "color" image is obtained by radiating sound waves over a spectrum of frequencies from 200-300 Hz. Whereas conventional surveying techniques take a month to map 200 square kilometers of ocean floor, the acoustic color technique can map an equivalent area in minutes. (Paper to be presented at an upcoming meeting of the Acoustical Society of America in Cambridge, MA.)