Analysis of the Echo for Identifying the Temporal Structure of the Fish by Using the Broadband Sonar Signal of Dolphin

Dolphins can recognize prey by using the broadband sonar signals. The echo from the fish contains components resulting from multiple reflections, for example, the swimbladder and body surface of the fish. It is necessary for identification of fish species to estimate the positions and amplitudes of these reflections. In this paper, we analyzed the echo from the fish by using the sonar signal of the bottlenose dolphin. Firstly, we analyzed echoes which were measured from the anaesthetized fish in a water tank. It was verified that the numbers and delays of reflections are varied with both the species and the tilt angle. Secondary, we analyzed the echo which was measured from the live fish suspended by nylon monofilament line in the open sea. It was verified that the delays and amplitudes of reflections are varied with the orientation and movement of the fish.