Three-dimensional localization of sperm whales using a single hydrophone

TLDR

Ray‑trace acoustic propagation modeling is used to exploit multipath click arrivals, accounting for waveguide physics such as bathymetry interaction and ray refraction. The study demonstrates a three‑dimensional localization method for tracking sperm whales using as few as one sensor. The method compares recorded click arrival patterns to depth‑, range‑, and azimuth‑dependent ray‑trace models, automatically matching multipath arrivals without explicit ray identification, and uses azimuthally dependent bathymetry to estimate 3‑D whale location from a single hydrophone. Using real data from one or two hydrophones, the authors produced multiple whale tracks—including a simultaneous visual‑acoustic localization—and found that foraging depth is shallower when a longline haul is present.

Abstract

A three-dimensional localization method for tracking sperm whales with as few as one sensor is demonstrated. Based on ray-trace acoustic propagation modeling, the technique exploits multipath arrival information from recorded sperm whale clicks and can account for waveguide propagation physics like interaction with range-dependent bathymetry and ray refraction. It also does not require ray identification (i.e., direct, surface reflected) while utilizing individual ray arrival information, simplifying automation efforts. The algorithm compares the arrival pattern from a sperm whale click to range-, depth-, and azimuth-dependent modeled arrival patterns in order to estimate whale location. With sufficient knowledge of azimuthally dependent bathymetry, a three-dimensional track of whale motion can be obtained using data from a single hydrophone. Tracking is demonstrated using data from acoustic recorders attached to fishing anchor lines off southeast Alaska as part of efforts to study sperm whale depredation of fishing operations. Several tracks of whale activity using real data from one or two hydrophones have been created, and three are provided to demonstrate the method, including one simultaneous visual and acoustic localization of a sperm whale actively clicking while surfaced. The tracks also suggest that whales’ foraging is shallower in the presence of a longline haul than without.