Depth/range localization of diving sperm whales using passive acoustics on a single hydrophone disregarding seafloor reflections

Abstract

Depth and range of sound sources can be estimated using a single hydrophone. Such a passive acoustic technique requires the detection of direct path transmitted, sea surface, and seafloor reflected source signals, so as to measure their time of arrival differences (TOADs). Sperm whales almost continuously emit powerful, directional echolocation sounds (usual clicks) when diving. Sperm whales often dive in deep water, and click seafloor reflections are usually well detected only at the beginning of the dive. Surface echoes may be detected during the entire dive. If the measurement of the surface reflection TOAD of a single click is not enough for estimating the depth/range of the sperm whale at the time when this click was emitted, the joint consideration of delays emitted during the whole dive may provide this estimation. Such delays are indeed the measurements of a single phenomenon: the underwater movements of a single-clicking sperm whale. One can merge such data using a Bayesian technique, as well as use prior information (e.g., range when fluking-up). Such a method could make the single-hydrophone localization technique usable regardless of the properties of the sea bottom, e.g., in deep or high relief areas.