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



laser profiling system was not available aboard the Navy aircraft, 

 and we had to rely on visual observation. In the recent experiments 

 we had the benefit of previous experience and new devices such as 

 inertial navigation, ice-penetrating SUS, a laser profiling system 

 and specially modified sonobuoys. We employed two Navy P-3 aircraft 

 and made four runs radiating from T-3. These two aircraft subsequent- 

 ly worked together north of Banks Island in the smooth ice area and 

 completed three more runs using sonobuoys as listening devices. Coin- 

 cident measurements were thus obtained of propagation loss and surface 

 roughness in areas showing the greatest known contrast of roughness. 

 I would like to point out that it is not easy to hit a small lead 

 with a SUS charge dropped by air, but the Navy personnel did a supreme 

 job in this respect to give us a generally high density of shots with 

 range . 



A few words are in order about how the dB loss per bounce is 

 derived from the field data. This is done by comparing the measured 

 propagation loss with computed curves for various loss per bounce 

 until the measured and computed curves coincide. This, of course, 

 puts a severe requirement on the reliability of the computer model. 

 Experience has shown that the FFP is most useful at frequencies below 

 100 Hz where wave effects are significant, but both ray theory and 

 the FFP are reliable above 100 Hz up to 315 Hz, the upper limit of 

 measurement. Figure 25 illustrates this for an identical model of 

 surface loss. The curves by ray theory were computed by M. S. Weinstein 

 of Underwater Systems, Inc., Silver spring, Maryland. 



For predictive purposes the process is reversed. One obtains 

 an estimate of loss per bounce from airborne measurements of surface 

 roughness to enter in the computer program. 



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