Abstract
We discuss the acoustic characteristics of the three-dimensional target strength (3DTS) of defrosted Japanese Jack mackerel and Chub mackerel. The target strength of fish in the whole aspect was measured in a tank by changing the horizontal incident angle from 0° to 360° by 1° steps and the pitch angle from 0° to 90° by 10° steps. Prior to measurement of TS, morphological parameters including swim bladder size and shape were measured by soft X-ray for theoretical estimation. The theoretical TS of fish were calculated using the prolate-spheroid model based on morphological parameters and were compared with the measured values. Results showed that both the maximum and the minimum TS were proportional to body length, and the directivity of the TS was strongly associated with its orientation. The TS of fish changed significantly with the changing yaw and pitch angle of the fish, but remained fairly constant as the roll angle of the fish changed. The maximum and minimum TS were found at the broadside and end-on aspects of the fish, respectively.
