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help - unknown underwater broadband sounds

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Subject: help - unknown underwater broadband sounds
From: Nino Pierantonio <>
Date: Wed, 9 May 2012 15:30:03 +0200
Dear list members,

I am writing to ask you help to identify a strange underwater noise.
I use a wide-band two-elements (Benthos AQ4 sensors) towed array to listen and track some species of cetaceans in the Mediterranean Sea. The system also includes two pre-amplifiers, a pressure sensor for depth readouts and a final amplifier connected to an external E-MU audio board feeding to the PC. I use 96 kHz or 192 kHz sampling frequency, depending on the species I am dealing with

Lately I am experiencing a weird unknown broadband click-like noise with a clear repetition pattern (some audio files can be downloaded at The noise starts with a small inter-click-interval, pauses for a few seconds and restarts always with an increased inter-click-interval, into a continuous loop that always restart with the same inter-click-interval. I observed no significant changes in the frequency domain during the loop. Interestingly the sound appears mostly when the research boat stops and the hydrophone sinks between 50 and about 200 m. As soon the boat moves and the array rises up towards the surface, the noise disappear.

I have been told that noise could be due to an intermittent connection of the Depth Meter, which does result in strange noise being seen in the acoustic channels. If this is the case, how can I test any potential failures of the pressure sensor/depth reader without disassembling the whole system? If the component failure is not the main cause of the noise, what could possibly be the origin of those clicks? Any advice and suggestion will be greatly appreciated.

Best regards,

Nino Pierantonio

Mobile: +39 349.532.9370
Skype: pierantonio_nino

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