Passive Acoustic Monitoring Arrays

Assembled from 14 blocks · 2 evidence · 10 related

1. Story
2. Seafloor and moored hydrophones that record low-frequency whale calls continuously, over ranges that a ship or an aircraft cannot cover. Blue whale calls are very low in frequency and propagate efficiently in the deep sound channel, so a single recorder covers a large area. The technique was inherited rather than invented for whales: the US Navy SOSUS arrays, built from the mid-1950s to track submarines, were declassified for their mission in 1991, and the distinctive 52 Hz call had already been identified from Navy hydrophone data in 1989 by William Watkins at Woods Hole. The Antarctic application is now large - the IWC-SORP acoustic trends group had access to more than 300,000 hours of Southern Ocean passive acoustic recordings as of March 2020, principally listening for the three-part Antarctic blue whale Z-call that sweeps from about 28 Hz to about 17 Hz over as much as 18 seconds.
3. Knowledge
4. Passive Acoustic Monitoring Arrays
5. Connections
6. Antarctic Summer Feeding Migration
7. IWC Southern Ocean Research Partnership
8. The 52 Hz call is identified in Navy hydrophone data
9. The SOSUS mission is declassified
10. Blue whale song frequencies are observed falling worldwide
11. Blue whales are found back at South Georgia
12. Evidence
13. Antarctic blue whales produce a characteristic three-part Z-call: a first unit of 8-12 s at about 28 Hz, a short downsweep from 28 to 19 Hz, and a third unit of 8-12 s between 19 and 17 Hz, lasting up to about 18 s in total. The SORP Acoustic Trends working group had access to more than 300,000 hours of Southern Ocean passive acoustic data as of March 2020, collected over roughly twenty years from ships and moored recorders. V55 verification basis: retrieved in search summary attributed to these sources; neither paper was fetched.
14. SOSUS was installed by the US Navy from the mid-1950s as a network of seafloor hydrophone arrays across the Atlantic and Pacific, exploiting the deep sound channel so that low-frequency sound travels great distances; its mission was declassified in 1991. The 52 Hz call was first identified in 1989 by William Watkins of the Woods Hole Oceanographic Institution from Navy hydrophone data, and the same call was tracked seasonally across the North Pacific over hundreds to thousands of kilometres between recordings. V55 verification basis: retrieved in search summary; neither the Watkins publication nor a Navy declassification record was consulted.