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



I should mention a few additional aspects of the effects of the 

 ice layer on propagation. For an ice layer 3 m thick, the effect on 

 pressure amplitudes at depth and on dispersion is small. But this thin 

 ice sheet causes a large change in particle motions near the surface. 

 Waves are elliptically polarized in the ice in the plane of propaga- 

 tion. Particle motion is retrograde elliptical at the surface and 

 prograde elliptical at the bottom of the ice. This orbital motion 

 is similar to that of flexural waves in the ice. Flexural waves 

 generated by large-scale ice deformation at the boundaries of floes 

 are the principal source of ambient ice vibrations. 



Figure 26 shows the ratio of horizontal to vertical particle 

 motion at the surface for flexural waves and hydroacoustic waves. 

 The ice is an antinode for vertical particle velocity and thus geo- 

 phones are useful devices to detect low-frequency waves.. 



721 



