| Summary: | World-wide a concern exists about the influence of man-made sound on marine life and particularly on marine mammals. One of the acoustic polluters of the world’s oceans is high-power active sonar. An early warning system at the sound source, which is based on passive detection of marine mammals, could avoid exposure of marine mammals to dangerous sound levels. For this purpose an experimental towed array is developed at TNO. The problem with detection of marine mammals is the wide variety of produced sounds. The frequencies may range from 10 Hz (calls from baleen whales), up to more than 100 kHz (clicks from porpoises). The newly developed Delphinus array has a directional detection mode up to 12 kHz and an omni-directional mode up to 40 kHz. It should be able to detect most mammal marine vocalisations. The performance of the Delphinus array was tested at sea, where the added value of a high-frequency towed array was clearly demonstrated. Ultra-sonic clicks, probably of beaked whales that are highly vulnerable to high-intensity sound, were detected with the arra
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