A fisheries application of a dual-frequency identification sonar acoustic camera

The uses of an acoustic camera in fish-passage research at hydropower facilities are being explored by the U.S. Army Corps of Engineers. The Dual-Frequency Identification Sonar (DIDSON) is a high-definition imaging sonar that obtains near-video quality images for the identification of objects underwater. Developed originally for the U.S. Navy by the University of Washington's Applied Physics Laboratory, it bridges the gap between existing fisheries-assessment sonar and optical systems. The images within 12 m of this acoustic camera are sufficiently clear such that fish can be observed undulating as they swim and their orientation ascertained in otherwise zero-visibility water. In the 1.8 MHz high-frequency mode, this system comprises 96 beams over a 29degrees field-of-view. The high resolution and fast frame rate provide target visualization in real time. The DIDSON can be used where conventional underwater cameras would be limited by low light levels and high turbidity. (C) 2003 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.