Measurements of target strength spectra of metal spheres and live fish by using broad band sonar signals of dolphin

This paper describes a method and results of measurements of the target strength (TS) spectra of metal spheres and live fish using sonar signals of dolphins with a broadband system. First, we measured the broadband form function of a tungsten carbide and a copper sphere in a water tank and confirmed good agreements with the theoretical values. Second, we measured the TS spectra of three species of anaesthetized fish in a water tank. Although the spectra showed nearly similar tendencies of past measurements, they varied considerably among the species, the individuals, and the tilt angles. Third, we measured the TS spectra of tethered live fish suspended from a ship at the sea. In this case we removed the directivity of transducers by the tungsten carbide sphere suspended near the fish. The sonar signals of dolphin are effective to measure TS spectra of fish.