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



(1963) , and Mellen and Marsh (1965) in terms of ray and normal-mode 

 theory. An unexplained feature of the early experiments was the 

 large variations (up to 40 dB) observed at each frequency of propaga- 

 tion loss as a function of range. Experiments made during the past 

 6 years by Buck, Diachok and Kutschale, combined with computer 

 modeling by Weinstein, Chow and Kutschale, have gone a long way to 

 \inscramble the causes of these variations. The recent investigations 

 strongly suggest that reliable estimates of propagation loss as a 

 function of range for fixed source and detector depths can be ob- 

 tained from airborne measurements of surface ice roughness combined 

 with computer modeling of loss. An important test of prediction of 

 loss will come when the data are analyzed from large-scale experiments 

 conducted by Diachok and Kutschale during May 1974. These experiments 

 will be described briefly to illustrate the airborne techniques 

 presently in use to obtain coincident data of propagation loss as a 

 function of range and surface ice roughness. 



The central Arctic Ocean is covered by ice the year round. The 

 pack ice averages about 10 feet thick. The ice is in continual, very 

 slow motion under the influence of winds and currents. The pack ice 

 is not of uniform thickness, but it is broken by leads of open water 

 and pressure ridges. The irregularity of the pack ice boundaries 

 is strongly dependent upon location and time of year. This seasonal 

 and spatial dependence of ice roughness is of great importance for 

 long-range sound propagation because of scattering of waves impinging 

 upon the ice. Figure 1 shows a photograph of the pack ice taken 

 from a plane. 



In contrast to the variability of the ice cover, the sound speed 

 structure in the water is very uniform as a function of location and 

 season. Sound speed is generally an increasing function of depth 

 from the surface to the bottom. Sounds are transmitted to long 



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