Recalibrating the Department of National Defence approach to active sonar impact management.

Fielding a well-trained, combat-ready military, and observing Canada's responsibility as environmental stewards are at times conflicting priorities for the Department of National Defence (DND). As new low frequency sources are introduced into service, DND must review and update policies and procedures regarding the use of active sonar to minimize its impacts on marine mammals with an evidence-based approach. Risk is mitigated primarily through avoidance, which requires an understanding of marine mammal distribution in order to avoid the most sensitive species and their habitats. In parallel, a research and development program evaluates and develops technological solutions to minimize the risk of harm. By first embracing an empirical framework to assess acute and chronic impacts, DND has been able to partner with other government departments and researchers to develop technology targeted towards the residual risks to marine mammals posed by sonar operations.

Range-dependent impacts of ocean acoustic propagation on automated classification of transmitted bowhead and humpback whale vocalizations.

Significant effort has been made over the last few decades to develop automated passive acoustic monitoring (PAM) systems capable of classifying cetaceans at the species level. The utility of such systems depends on the systems' ability to operate across a wide range of ocean acoustic environments; however, anecdotal evidence suggests that site-specific propagation characteristics impact the performance of PAM systems. Variability in propagation characteristics leads to differences in how each cetacean vocalization is altered as it propagates along the source-receiver path. A propagation experiment was conducted in the Gulf of Mexico to investigate the range-dependent impacts of acoustic propagation on the performance of an automated classifier. Modified bowhead and humpback vocalizations were transmitted over ranges from 1 to 10 km. When the classifier was trained with signals collected near the sound source, it was found that the performance decreased with increasing transmission range-this appeared to be largely explained by decreasing signal-to-noise ratio (SNR). Generation of performance matrices showed that one method to develop a classifier that maintains high performance across many ranges is to include a varied assortment of ranges in the training data; however, if the training set is limited, it is best to train on relatively low SNR vocalizations.

Automated aural classification used for inter-species discrimination of cetaceans.

Passive acoustic methods are in widespread use to detect and classify cetacean species; however, passive acoustic systems often suffer from large false detection rates resulting from numerous transient sources. To reduce the acoustic analyst workload, automatic recognition methods may be implemented in a two-stage process. First, a general automatic detector is implemented that produces many detections to ensure cetacean presence is noted. Then an automatic classifier is used to significantly reduce the number of false detections and classify the cetacean species. This process requires development of a robust classifier capable of performing inter-species classification. Because human analysts can aurally discriminate species, an automated aural classifier that uses perceptual signal features was tested on a cetacean data set. The classifier successfully discriminated between four species of cetaceans-bowhead, humpback, North Atlantic right, and sperm whales-with 85% accuracy. It also performed well (100% accuracy) for discriminating sperm whale clicks from right whale gunshots. An accuracy of 92% and area under the receiver operating characteristic curve of 0.97 were obtained for the relatively challenging bowhead and humpback recognition case. These results demonstrated that the perceptual features employed by the aural classifier provided powerful discrimination cues for inter-species classification of cetaceans.