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 SONAR IN ICE 



During the 1947 Antarctic Development Project (Operation HIGH- 

 JUMP) , sonar proved invaluable in detecting ice targets and assisting 

 in navigation. The value of sonar in navigating ice-laden waters, 

 when visibility was restricted, lay not in its ability to classify targets, 

 but in the positive warning it was able to give the conning officer of 

 the ship's approach to ice. 



In the cold waters of the Antarctic, ranging in temperatures from 

 34° to as low as 29° F., conditions were found to be excellent for 

 propagation of sound, and very good results in the use of sonar with 

 all kinds of targets were obtained. The excellence of sonic conditions 

 produced very nearly 100 percent reliability in sonar to detect ob- 

 struction within dangerous ranges. 



Ice targets were found to give solid echoes at moderate ranges. 

 Growlers, which constitute a hazard in radar navigation in rough seas, 

 were detectable well in excess of hazardous ranges, even when swells 

 up to 6 or 8 feet were encountered. Observed sound ranges and those 

 predicted from the temperature data were coincident. 



Hig'h water noise and heavy rolling of the ship had a decided effect 

 upon the range. Best results were obtained when the vessel was 

 making less than 10 knots. Some difficulty was reported in detecting 

 growlers when bearing between 170° and 180° relative, due to the 

 interference caused by the noise of the screws. 



On Operation NANOOK the Atule reported that bergs could best 

 be detected by sonar listening. They gave off a loud noise similar to 

 high-speed screws on a ship, possibly caused by the release of air bub- 

 bles under fairly high pressure. Echo ranging in the Arctic was not 

 dependable, often failing to indicate bergs at ranges where they were 

 a distinct hazard. The U. S. S. Edisto found sonar of little value 

 during summer Arctic operation as the ice shield had to be closed 

 upon entering ice to avoid certain damage to the sound dome. Never- 

 theless, sonar gear is regarded as a valuable aid to navigation in polar 

 waters. 



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