Monday, July 27, 2015

Feeling HARPy

 The main event of this research cruise is putting out an array of hydrophone (underwater microphone) receivers and transmitting sound to them from a ship-based source, which we will get to in a few days, but there are a lot of other things going on as well!  Today we are steaming to the location of a HARP, which stands for High-frequency Acoustic Recording Package.  This instrument package has been out here for a year recording the sounds of the Arctic, also called the Arctic soundscape.

Bruce Thayre
Bruce Thayre from John Hildebrand’s lab at the Scripps Institution of Oceanography is here to recover the HARP, grab the data, make sure it is still in good operating condition, put new batteries in it, and redeploy it so that it will continue listening for another year.  Bruce has also been preparing another HARP (see photo), so there will be two HARPs measuring the soundscape for the coming year. 

The HARP is on a small mooring with an anchor at the bottom, then 4 meters of chain, then acoustic releases, then another 4 meters and then the HARP package, which consists of 3 tubes containing the recording electronics, the disks, and the batteries.  The hydrophone itself is attached by a rope and sits above the recording package.

The HARP records at a rate of 200,000 samples per second (200 kHz).  The HARP could record for 10 months continuously at this rate, but scientists are really interested in knowing how the soundscape changes through the cycle of an entire year, so the HARP is programmed to record at a duty cycle of 2/3, which means it samples 2/3 of the time, and lasts for the entire year.

HARPs have been deployed up here in the Arctic since 2006 and have recorded sounds from bowhead whales, beluga whales, ringed seals, bearded seals, ribbon seals, and once even a walrus.  They also record passing ships, wind and rain sounds, and lots and lots of ice breaking. 

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