Hot Topic – Listening to Monterey Bay

Hydrophone Provides Continuous, Live Stream of Deep Sea Sounds from Monterey Bay

Location of the MARS hydrophone, on the Smooth Ridge, at the edge of Monterey Canyon, approximately 30 km (18 mi) from shore. Image credit: MBARI.

The Monterey Accelerated Research System (MARS) cabled observatory, the first cabled oceanographic observatory on the U.S. West Coast, provides electrical power and data connections for research instruments deployed at 900 m (3,000 ft) below the surface of Monterey Bay. On July 28, 2015, the Monterey Bay Aquarium Research Institute (MBARI) connected a broadband hydrophone to the MARS observatory, approximately 30 km (18 mi) west/northwest of Monterey, CA. Underwater sounds recorded by this hydrophone are now available via continuous live stream. In addition to hearing the underwater sounds from the Bay, spectrograms allow visitors to visualize the sounds in a live video display.

To accurately capture the full ambient sounds of the Bay, the hydrophone is capturing acoustic data across a very broad spectrum (10-128,000 Hertz) and sampling more than 250,000 times each second.  This frequent sampling of underwater sound across a broad spectrum generates a tremendous amount of data. Acoustic data recorded by the hydrophone (about two terabytes each month) are relayed back to shore in real time. Human experts cannot analyze all of the hydrophone’s data. Thus, computer systems are now being tested to sift through the data, recognize different sounds, and classify them accordingly (e.g., whale vocalizations).

Deployment of the MARS hydrophone, at 900 m (3,000 ft) depth in Monterey Bay. Image credit: MBARI.

Although the MARS hydrophone is located on the seafloor, most of the sounds it detects are from animals and activity higher in the water column.  The hydrophone has recorded sea lion and dolphin vocalizations, as well as the sounds of rain, waves, and ships. MBARI researchers are collaborating with scientists at the Monterey Bay National Marine Sanctuary, U.S. Naval Postgraduate School, Moss Landing Marine Laboratories, University of California-Santa Cruz, the Scripps Institution of Oceanography, and other organizations to analyze the sounds from the MARS hydrophone and characterize the soundscape of Monterey Bay.  Recorded sounds have already provided surprising information, including evidence that beaked whales, though rarely seen, are common in the outer bay. Scientists also hope to use the hydrophone’s acoustic data to understand how relatively “quiet” Monterey Bay is compared to busier areas such as the Southern California Bight.



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