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Where When How N/D 2017 - J/F 2018 : Page 91

68 F (20 C) and salinity of 35 parts per thousand, sound travels, near the water’s surface, at 4,996 feet (1.514 m) per second (3,407 mph [5,451 kmph]). SOFAR So Good With the basics out of the way, let’s look at how we’ve come to understand sound in the sea. In the spring of 1944, two scien-tists from the Woods Hole Institute of Oceanography, Maurice Ewing and J. Lamar Worzel, set out on the research ves-sel R/V Saluda to test a theory. They pro-posed that low-frequency sound should travel long distances in the deep ocean. On April 3 of that year, a hydrophone was hung overboard and the Saluda recorded the sound of an explosive charge deto-nated by a ship nearly 400 miles (640 km) away. Ewing and Worzel had heard the first sound transmission through what was eventually termed the SOund Fixing And Ranging (SOFAR) channel. Interestingly, the explosion was not heard as a single sound, but, characteristic of SOFAR trans-missions, as a number of separate, gradu-ally intensifying sounds. In fact, the final signal was so intense that, according to re-search, “the end of the sound channel transmission was so sharp that it was im-possible for the most unskilled observer to miss it.” Later experiments would make these first test results pale in comparison. For example, during a test in the 1960s, Navy depth charges were detonated and heard 2,290 miles (3,664 km) away from the explosion. The U.S. Navy soon realized that the ability of low-frequency sound to travel long distances in the deep ocean could be used to increase the range at which they could detect submarines. So, in the great secrecy of the Cold War, the Navy launched Project Jezebel (later to be known as SOund SUrveillance System or SOSUS). The SOSUS project placed arrays of hydrophones on the ocean bottom throughout the world, which were con-nected by cables to top-secret processing centers on shore. This became one of the most successful programs of the Cold War, easily detecting and tracking the noisy So-viet submarines of that era. One aspect of the SOSUS project, which at first was quite mysterious, turned out to be a scientific treasure house. Oper-Diving as it should be Diving • Snorkelling • Instruction Tel: 649.946.5040 • • • • • 91 Visit the Turks & Caicos Islands at NOV/DEC/JAN/FEB 2017/2018

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