Cetaceans (whales and dolphins) are highly vocal animals. The sounds they emit have become familiar: consider the haunting songs of singing whales and the clicks and whistles of dolphins. By studying the sounds these animals employ gives one a window on their world.
Background
Technological advances have meant that the collection of long-term acoustic data from monitoring is becoming much more common place. The analysis of the massive datasets that these activities can generate requires the use of automated computer analysis. This work develops and studies such methods. The specific tasks we address are:
Detection
- Determining whether cetaceans are present.
Classification
- Identifying which species are present.
Localisation
- Estimating the position of an animal relative to the sensors.
Tracking
- Linking together a sequence of detections from a single source.
Source separation
- Estimating the sounds of one animal from recordings of multiple animals.
Whales and dolphins mainly produce clicks and/or whistles . These sounds cover a wide frequency range, some are about five times higher in frequency than most people can hear, whereas some whales produce sounds whose pitch is below that we are able to perceive. These sounds are often received against a background noise and with multiple calls occurring simultaneously. This possesses a series of significant signal processing challenges.
We work in a variety of locations and on a range of species, devising processing strategies tailored to call types and species. This includes humpback whale sings in Madagascar, fin whale calls off the Galician coast, spotted and spinner Dolphins collected from around the world, sperm whales clicks and pilot whales whistles in Norway.
Detection
Whistle detection
Many cetacean species emit narrow band frequency modulated calls (whistles). We have developed methods for detecting and extracting whistles from noisy environments, when the animals are also producing echolocation clicks.
Click detection
Odontocetes (toothes whales) use echolocation to sense their environment. The sound pulses they emit to achieve this are short duration pulses (clicks). Detecting these can betray the presence of the animals and may allow one to localise an individual, whilst studying these sounds allows one to gain insights into odontocete feeding behaviour.
Signal Processing