Calibration of a Steered Phased-Array Sonar for use in Fish Detection

A stationary acoustical-optical observation system is being developed to detect groundfish presence and to estimate biomass at multiple, discrete geographic locations in New England waters. Electrically steered, phased-array sonars mounted on platforms deployed on the seabed make measurements of scattering from aggregations (e.g., layers or shoals) of fish, while simultaneously having sufficient resolution to detect and quantify the reflectivity (target strengths) of individual fish around the instrument package. The acoustical system is composed of commercially available obstacle avoidance sonars, which were not designed for fine-scale fisheries applications. For this reason, it was necessary to perform detailed tank calibrations to provide the quantitative information needed to relate energy from backscattered echoes to target strengths of fish. When individuals can be simultaneously observed on the sonar and the video imaging sensors, one can accumulate data that will relate the fish size, target aspect (observation angle), and the target strength