ARCTIC UNDERWATER ACOUSTICS

[Music] In 1958, the United States submarine Nautilus crossed the Arctic Ocean submerged. The crews proved the Arctic to be a usable operating area for nuclear submarines, but one with many unique characteristics. Today we know very little about this ocean. But should submarine warfare become important in the area, we need to know more. Sonar, the ears of submarine and anti-ubmarine forces, depends on underwater sound. More knowledge of underwater sound in the Arctic is the objective of this research program. We made our permanent station on Ice Island T3, which is drifting 450 mi north of Barrow, Alaska. Unlike the pack ice, the ice island never breaks up. It is ideal for permanent installations such as our Deeus project. The T3 camp is at the edge of the ice island on Kby Bay where the ice is 12 to 15 ft thick and is also protected by the island from breakup. We spotted our array site 1 half mile out, far enough to avoid man-made sounds from the camp. The complete array system consists of hydrophone holes accurately positioned by theolyte survey and equally spaced around the circumference of the circle. Hydrophones are lowered to 100 ft. Seismometers are frozen into the ice at the bottom of each hole. Radial cables connect all the holes to the array wanigan in the center. Finally, the telemetry cable runs to the electronics trailer at the main camp. This actual scene from the air shows the permanent installation. The system enables formation of preformed beams arranged equally over 360° of bearing. The Deeus processor provides a wide selection of averaging times and frequency discrimination for underwater signal analysis. While installing the Deeus system, we sent a second party to Arlus 4, a temporary station on the pack ice about 100 miles from Barrow. The stations, 360 mi apart, were linked by radio telephone. At T3, the field crew leader receives the call and arranges for sound signal. One of the experiments on Arlo 4 required signals to reach that hydrophone from considerable distance. The crew on the Deus site at T3 participated. These signals are generated by Mark 61 underwater sound sources detonated under the ice at specific intervals. Explosions from the 2-lb TNT bombs detonated hundreds of feet below station P3 are picked up by the electronics equipment at Arles 4. Only the low frequency sounds are received. The rough under surface of the ice scatters higher frequencies. Ambient noises heard and analyzed include the creaking and popping of ice, voices of seals and whales, and many other sounds not yet identified. With the Deeus system permanently established at T3 and the Arles 4 work completed, the GM Defense Research Laboratory's expedition of 1965 completed its installation task for the year.