Two methods to measure target strength (TS) are introduced and compared with each other. One is the suspension method, and the other is the split-beam method. Each of them is representative of control and in situ methods, respectively. In addition, a morphological investigation of a swimbladder in a pressure tank, and the development of an instrumented package of acoustic and optical systems, are also introduced. The former is to reveal the degree of TS variation by the vertical movement of fish, and the latter is to obtain precise TS and fish behavior by the echo trace analysis method.

Two methods to measure target strength (TS) are introduced and compared with each other. One is the suspension method, and the other is the split-beam method. Each of them is representative of control and in situ methods, respectively. In addition, a morphological investigation of a swimbladder in a pressure tank, and the development of an instrumented package of acoustic and optical systems, are also introduced. The former is to reveal the degree of TS variation by the vertical movement of fish, and the latter is to obtain precise TS and fish behavior by the echo trace analysis method.