Sunday, April 18, 2010

Ears in the oceans

On a rocky point at the SW tip of Australia, the Cape Leeuwin lighthouse has warned mariners of the dangerous shoals since the mid-1890s. The light still shines, but today it also serves a less apparent function. From the interpretive signage:

“At ~1000m deep in the ocean, there is a layer of water, called the SOFAR channel, where the speed of sound is at a minimum and sound waves can travel hundreds of kilometers with little loss of signal. A hydro acoustic station is able to record these signals when hydrophones are suspended in the channel.”

P4170019-1 The station monitors a huge part of the world’s oceans (see inset), and is one of a series of stations set up to monitor nuclear explosions and signals from non-explosive sources—earthquakes, volcanic activity, underwater landscapes, shipping noise and even whale songs.

“The Cape Leeuwin Station comprises an array of three hydrophones, a seabed cable, and a shore facility located in the adjacent National Park. The three hydrophones are located ~114km SW of Cape Leeuwin.”

The waters at this point form the boundary between the Indian Ocean and the Pacific Ocean. The next land mass south is Antarctica.