Space–time and hybrid algorithms for the passive acoustic localisation of sperm whales and vessels
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Abstract
In the frame of the European Sea-floor Observatory Network (ESONET) and in preparation of the Demonstration
Mission Listening to the Deep-Ocean Environment (LIDO) algorithms for the automated real-time
detection, classification and localisation of cetaceans have been developed.
Such Passive Acoustic Monitoring techniques have the potential to play a key role in cetaceans’ conservation
for they allow a non-invasive study of their behaviour, a better knowledge of their population
dynamics, and a better understanding of their dynamic relationship with their environment. This paper
investigates the development of efficient and accurate techniques to be used as the basis of a localisation
module for an automated real-time Passive Acoustic Monitoring system.
An opportunity to assess the capabilities of the developed localisation modules was given by recordings
collected with a bottom-mounted (around 2080 m depth) tetrahedral compact hydrophone array
located offshore the port of Catania (Sicily) during the NEMO-ONDE campaign in the years 2005–2006
by INFN and CIBRA [2]. A well-known class of methods for acoustic source localisation is based on time
differences of arrival (TDOA). Its capabilities have shown to be useful even in adverse situations (i.e.,
few sensors, high noise levels and/or poor calibration). A second class of methods, the space–time
methods, originated in underwater applications such as sonar but reached its most significant achievements
over the last 20 years in digital communications with recent progress in the treatment of broadband
signals. These developments are here revisited under the scope of the localisation and tracking of
cetacean vocalisations.
Various broadband space–time methods were implemented and allowed to map the sound radiated
during the detected clicks and to consequently localise both sperm whales and vessels. Hybrid methods
were also developed which improved the robustness of space–time methods to noise and reverberation
and reduced processing time. In most cases, the small variance obtained for these estimates lessened
the necessity of additional statistical clustering. Even though not independently confirmed by sightings,
the tracks derived in the proposed frame can be considered to be consistent with the known movements
of sperm whales and vessels.Peer Reviewe