KUTSCHALE: LOW-FREQUENCY PROPAGATION IN THE ICE-COVERED ARCTIC OCEAN 



ranges in this sound channel by upward refraction in the water and 

 repeated reflection from the ice. Figure 2 compares the Arctic 

 profile with a profile of the temperate Atlantic. The Arctic sound 

 channel is the polar extension of the deep soiind channel or SOFAR 

 channel of the nonpolar oceans. Figure 3 shows typical ray paths 

 computed at one -degree intervals from a source at depth in the Arctic 

 channel. The deep penetrating waves arrive first, and the waves 

 traveling near the axis last. 



The Arctic SOFAR signals are often quite different in character 

 from those signals observed in the deep channel, largely because of 

 the predominance of low-frequency waves in the Arctic. Waves above 

 40 Hz are strongly scattered by the rough ice boundaries so that at 

 ranges beyond 700 nautical miles (1200 km) , waves in the band from 8 to 

 40 Hz generally predominate in the signal. The dispersion observed in 

 the Arctic signals shows that the waves are coherent over long dis- 

 stances. In each normal mode, both phase and group velocity decrease 

 with increasing frequency. 



Figure 4 shows the major bathymetric features of the central 

 Arctic Ocean. Three submarine ridges are separated by deep abyssal 

 plains. It is apparent that the Soviet Union borders on a major 

 portion of the central Arctic Ocean. The Siberian continental 

 shelf is the widest in the world. Certainly shallow-water propaga- 

 tion is of great importance, not only to the Navy but also to the 

 oil industry, but time will not permit me to discuss this important 

 area of under-ice acoustics. 



Some sample propagation paths are shown on the map of Figure 4, 

 and the corresponding signals will be shown on the next two 

 figures. Signals for paths 1 to 4 were transmitted between three 

 manned floating ice stations: ARLIS II, T-3, and Polar Pack I. Path 



688 



