Simple methods for locating, counting, and tracking sperm whales underwater in three dimensions

Abstract

Sperm whales’ clicks can be used to locate source animals in three dimensions using volumetric arrays of four or more sonobuoys. Clicks are detected using algorithms that depend on gender. Males are easier to track: their clicks are loud and distinctive, and there is usually only one male nearby. A simple envelope detector suffices. Females click more quietly, at a higher rate, and they often occur in large groups, resulting in a continuous barrage of clicks. Using a single click as a matched filter detector enhances the detection of clicks coming from a particular animal. Arrival time differences between the different sonobuoys are used to locate the source in three dimensions. A particular animal can be tracked by determining its location over time. An estimate of the number of phonating animals can be made by locating all the source animals during a particular time interval. During NOAAs SWAPS97 sperm whale survey, arrays of four sonobuoys each were placed around groups of diving sperm whales. Clicks from the animals were recorded at 48ksamples/s. Analyses of these data will be presented. [Work sponsored by NOAA and ONR.]