Editing Hydrophone (section)

===Arrays===
Multiple hydrophones can be arranged in an [[microphone array|array]] so that it will add the signals from the desired direction while subtracting signals from other directions. The array may be steered using a [[beamforming|beamformer]]. Most commonly, hydrophones are arranged in a "line array"<ref>{{Cite book|url=https://books.google.com/books?id=azuIDwAAQBAJ&q=hydrophones+are+arranged+in+a+%22line+array%22&pg=PA39|title=Underwater Acoustic Signal Processing: Modeling, Detection, and Estimation|last=Abraham|first=Douglas A.|date=2019-02-14|publisher=Springer|isbn=978-3-319-92983-5|language=en}}</ref> but may be in many different arrangements depending on what is being measured. As an example, in the article <ref>[https://www.bksv.com/en/knowledge/blog/sound/hydrophone-array Measuring noise at sea with hydrophone arrays systems]</ref> measuring propeller noise from fleet ships required complex hydrophone array systems to achieve actionable measurements.

[[SOSUS]] hydrophones, laid on the seabed and connected by underwater cables, were used, beginning in the 1950s, by the [[U.S. Navy]] to track movement of [[Soviet Union|Soviet]] submarines during the [[Cold War]] along a line from [[Greenland]], [[Iceland]] and the [[United Kingdom]] known as the [[GIUK gap]].<ref>Mackay, D.G. "[http://theses.gla.ac.uk/347/01/2008mackayMPhil.pdf Scotland the Brave? US Strategic Policy in Scotland 1953–1974]". ''Glasgow University, Masters Thesis (research).'' 2008. Accessed 12 October 2009.</ref> These are capable of clearly recording extremely low frequency [[infrasound]], including many [[list of unexplained sounds|unexplained ocean sounds]].