Experimental Result of AUV-based Acoustic Tracking System of Sperm Whales

Abstract

Sperm whales are known to dive to a depth of over two thousand meters and it is also known that they emit loud impulsive broadband sounds called "clicks" during their diving. But little is known about sperm whales' behavior because they dive more than one thousand meters. So authors propose to use the autonomous underwater vehicle (AUV) as an observation platform of sperm whales. Our final goal is to develop and construct the system so that AUV can estimate the position of sperm whales by a passive technique listening to their clicks, and can track a specific sperm whale. The tasks of the AUV are to recognize sperm whales individually and track them in real time by listening to sperm whale's clicks with 4-hydrophone array and detecting its direction. In September 2005, we carried out an experiment to test this AUV-based observation system off Ogasawara Islands using AUV AE2000 in the depth of 1000 meters. During the experiments over eight days, we had ten dives and succeeded in recording of the click sound by both the AUV and the mother vessel. But it was difficult to calculate the direction of a whale in real-time on the AUV because the sound level of clicks was low and the sound noise generated by AUV itself was high. According to the off-line analysis, we found out that clicks can be detected by the AUV while all actuators on the AUV were stopped.