Localization and tracking of marine animals can reveal key insights into their behaviors underwater that would otherwise remain unexplored. A promising nonintrusive approach to obtaining location information of marine animals is to process their bioacoustic signals, which are passively recorded using multiple hydrophones. In this paper, a data processing chain that automatically detects and tracks multiple odontocetes (toothed whales) in three dimensions (3-D) from their echolocation clicks recorded with volumetric hydrophone arrays is proposed. First, the time-difference-of-arrival (TDOA) measurements are extracted with a generalized cross-correlation that whitens the received acoustic signals based on the instrument noise statistics. Subsequently, odontocetes are tracked in the TDOA domain using a graph-based multi-target tracking (MTT) method to reject false TDOA measurements and close gaps of missed detections. The resulting TDOA estimates are then used by another graph-based MTT stage that estimates odontocete tracks in 3-D. The tracking capability of the proposed data processing chain is demonstrated on real acoustic data provided by two volumetric hydrophone arrays that recorded echolocation clicks from Cuvier's beaked whales (Ziphius cavirostris). Simulation results show that the presented MTT method using 3-D can outperform an existing approach that relies on manual annotation.

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Cuvier’s beaked whales (Ziphius cavirostris) are difficult to study due to infrequent sightings and their deep-diving behavior. One approach to studying their behavior is to use arrays of hydrophones to localize and track individual beaked whales. We collected over one year of small aperture (∼1 m) broadband acoustic array recordings at different sites offshore of the coast of Southern California, a region with a considerable presence of Cuvier’s beaked whales. We use the time difference of arrival between hydrophone pairs in our arrays to determine the direction of an echolocating beaked whale. When the source directions are cross-fixed from multiple arrays, the location of an animal can be determined and sequential locations can be used to form tracks. Tracks were used to determine a number of signal characteristics, such as source sound pressure level, beam directionality, and click temporal patterns as well as a number of animal behaviors including swim speed, group size, descent angle, and foraging depth.