74. What is sonar? 



The word "sonar" was coined fronn the ternn describing the opera- 

 tion and functions of certain undersea equipment, "sound /7avigation 

 and ranging." Equipment using sound for underwater navigation and 

 ranging is called sonar. It operates on the same principle as radar, but 

 transmits sound waves instead of radio waves. Sonar may be either 

 active or passive. In an active system, a sound is transmitted and the 

 echo received. Distance is computed as one-half of elapsed time multi- 

 plied by speed of sound in sea water. A passive system is a listening 

 system, and only direction can be determined. 



The speed of sound is affected by water temperature, salinity, and 

 pressure. An increase in any of these results in an increase in sound 

 velocity. 



Sonar is used for submarine detection, navigation, fish finding, and 

 depth determination. The depth finding sonar is commonly called a 

 fathometer but the correct general name for a depth finding sonar is 

 echo sounder. The word "Fathometer" is a registered trademark of the 

 Raytheon Company and should be used to describe electronic sounders 

 made by Raytheon only. 



Coombs, Charles 



Deep-Sea World, William Morrow and Company, 1966. 

 Hull, Seabrook 



The Bountiful Sea, Prentice-Hail, 1964. 

 U. S. Naval Oceanographic Office 



Oceanography and Underwater Sound for Naval Applications, 



Special Publication No. 84, October 1965. 



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