Development of AUV-based system for acoustic tracking of diving sperm whales

Sperm whales are known to dive to a depth of over two thousand meters. They emit loud impulsive broadband sounds called "clicks" during their diving. To investigate the sperm whale behavior, we attempt to apply the autonomous underwater vehicle (AUV) as an observation platform for sperm whales. AUV recognizes sperm whales individually and tracks them by listening to their clicks. As an initial stage for these objectives, we set up an experiment to test our observation system using two boats without an AUV. The observation system consists of two sets of 4-hydrophone arrays. Each hydrophone array works as a short baseline (SBL) system. The SBL system detects sperm whale clicks and calculates the orientation to sperm whales. Two relative directions from the two SBL arrays separated over a long base line (LBL) tell us the position of whale by triangulation. In the middle of August 2003, we carried out an experiment of the test system off Chichijima Island in Ogasawara. We deployed two boats each with a hydrophone array. An acoustic link between the SBL arrays was established to obtain the LBL length. During the experiments over five days we encountered at least fourteen sperm whales and succeeded in tracking some sperm whales by our observation system. Later in September 2004, we will perform another experiment using an AUV that works as one of the SBL systems. We expect this AUV-based observation system will give us a better understanding of sperm whale diving behavior and eco-system