Broadband Acoustic Technology Allows ‘High Def’ Underwater Imaging

U.S. researchers have developed broadband acoustic systems that they say will improve the ability to count and classify fish and zooplankton, an advance they liken to jumping from black and white television to high-definition TV. While oceanographers have long used acoustic measurements to determine what lies under the sea, existing technologies use sound waves that measure only one or a few frequencies, producing data that can be ambiguous and open to different interpretations, particularly for small fish and zooplankton. Two new systems developed by researchers at the Woods Hole Oceanographic Institution measure sound over a continuous range of frequencies, producing a broadband acoustic spectrum. Since the acoustic action for most fish occurs at low frequencies, many current echosounders miss their signal, said Tim Stanton, author of a study published in the International Council for Exploration of the Sea. The new broadband system allows researchers to distinguish between fish and other organisms, and identify the size and densities of fish. One of the systems was developed to find fish, while the other was developed to distinguish zooplankton from underwater turbulence.