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Deep scattering layers
| Морской словарь |
Strata of ocean organisms which scatter or echo sound waves such as sonar. the organisms migrate downward to 150–200 fathoms during the day, but come close to the surface at night.
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Deep sea exploration, английский
The investigation of physical, chemical, and biological conditions on the abyssal sea bed, an area we know less about than the surface of mars. beyond the continental shelf, the bottom slopes into deeper water known as the abyssal plain. this is a vast, mostly flat, and generally unexplored area comprising about 40 percent of the ocean floor and lying between one and three thousand fathoms (6,000 to 18,000 feet/1,830 to 5,490 meters) below the surface. at these depths it is permanently dark, bone-chillingly cold, and pressure can reach more than 1,125 kg/sq.cm (16,000 pounds/sq.in). sensing from air and space provides an overview, and photographs taken by cameras towed along the bottom can be studied to determine places worthy of examination. but detailed observation relies on submersible vehicles. remotely operated vehicles (rovs) and unmanned underwater vehicles (uuvs) excel at large area exploration, but periodically have to have their batteries recharged or replaced. oceanographers have begun to replace them with “sea gliders” that do not have engines and propellers, but “fly” through the water on stubby wings, moving vertically by changing buoyancy. their electricity demands are minimal, giving them much longer endurance. but as yet there is deck 94 no substitute for human eyes, so manned submersibles usually make the final observations. however, with the expanded use of fiber optics, satellites, and more advanced remote-controlled robots, scientists may eventually be able to explore from computer screens in laboratories without having to venture into the depths themselves. deep-sea line: (pronounced dipsyline). the heavy leadline used for sounding deep waters before the advent of echo sounders. the standard weight was 50 pounds (22.7 kg) and the line was normally 100 fathoms, but occasionally longer. william falconer’s description in his 1780 dictionary of the marine is still appropriate: the deep-sea-lead is marked with two knots at 20 fathom, 3 at 30, 4 at 40, and so on to the end. it is also marked with a single knot in the middle of each interval, as at 25, 35, 45 fathoms, &c. to use this lead more effectually at sea, or in deep water on the sea-coast, it is usual previously to bring to the ship,
Deep air support, английский
Aerial action at such a distance that the possibility of “friendly fire” casualties is not a consideration (cf. close air support).
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