Made in the 1970s this film THE DEEP SCATTERING LAYER tells the story of the search for a mysterious “second floor” in the ocean, as recorded by sonar devices. This floor — consisting of marine animals such as shrimp, whales and dolphins — moves to different levels at different hours, different days, and different seasons. It is probed by U.S. Navy sonar, deep-trawled nets with hydrophones and instruments, and finally by by ocean going submersibles. While the film presents the research primarily in scientific terms, the study of these sound return layers was also viewed as extremely important by the Navy for tactical reasons to do with submarine operations.
Includes footage of ocean life, sonar / echometer (or ” the echo sounder “) and hydrophones, deep sea and SCUBA diving, and submarine operations. A portion of the film was shot at the Woods Hole Oceanographic Institution. Some of the rare footage shown includes . including the use of small submarines shown at 2:44, the Star III submersible (13:08) and the bathyscaphe Trieste (12:59). At 18:10, the Navy’s Underwater Sound Research Laboratory at the Undersea Research and Development Center San Diego is shown at 18:20. At 25:40, project Ocean Acre is seen, with a research team led by Dr. Charles Brown of the Sound Lab studying a patch of sea water near Bermuda. The study looked at the acoustic signature vs. the biological content of the scattering layer over the seasons and eventually determined that sound scattering occurred due to the presence of millions of tiny fish equipped with swim bladders of the family Myctophidae.
The deep scattering layer, sometimes referred to as the sound scattering layer, is a name given to a layer in the ocean consisting of a variety of marine animals. It was discovered through the use of sonar, as ships found a layer that scattered the sound and was thus sometimes mistaken for the seabed. For this reason it is sometimes called the false bottom or phantom bottom. It can be seen to rise and fall each day in keeping with diel vertical migration.
Sonar operators, using the newly developed sonar technology during World War II, were puzzled by what appeared to be a false sea floor 300–500 metres deep at day, and less deep at night. Initially this mysterious phenomenon was called the ECR layer using the initials of its discoverers. It turned out to be due to millions of marine organisms, most particularly small mesopelagic fish, with swimbladders that reflected the sonar. These organisms migrate up into shallower water at dusk to feed on plankton. The layer is deeper when the moon is out, and can become shallower when clouds pass over the moon. Lanternfish account for much of the biomass responsible for the deep scattering layer of the world’s oceans. Sonar reflects off the millions of lanternfish swim bladders, giving the appearance of a false bottom.
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This film is part of the Periscope Film LLC archive, one of the largest historic military, transportation, and aviation stock footage collections in the USA. Entirely film backed, this material is available for licensing in 24p HD, 2k and 4k. For more information visit http://www.PeriscopeFilm.com
