44 THE NAVY OCEAN SCIENCE PROGRAM 



phase of our defense on understanding of the environmental 

 effects on underwater sound gives an extremely high priority 

 to this phase of ocean science. The dependence of underwater 

 weapon effectiveness and countermeasures on acoustic per- 

 formance further enhances this priority. 



Propagation of Sound in the Oceans 



Since the ocean is not a homogeneous medium with plane 

 boundaries, acoustic energy does not travel in straight lines 

 for any significant distance. It is refracted by the varying sound- 

 speed structure of the water masses, scattered by biological 

 or other suspended materials, reflected and scattered at the ocean 

 surface and bottom, and absorbed by the water mass through 

 which it travels. To exploit acoustic phenomena, we must 

 understand the mechanisms by which acoustic energy is trans- 

 mitted from one point to another at ranges from a few feet to 

 many miles, at frequencies from sub-audio to ultrasonic, and 

 how the transmission process is affected by the oceans and its 

 boundaries. Research is being pursued along lines discussed 

 in the following paragraphs. 



The paths by which acoustic energy is transmitted through 

 ocean-water masses of differing temperature, salinities, etc., 

 are being identified and evaluated. This program includes 

 measurement of the acoustic properties of sea water and the 

 structure of these properties within the ocean. It also includes 

 theoretical analysis of the paths followed by sound through the 

 ocean and even beneath it, through sediment and rock, and 

 experimental measiu'ement of sound transmission at sea and 

 in laboratory model studies. 



Reflection mechanisms and losses at the ocean bottom are 

 being studied as a function of composition, roughness, and 

 acoustic frequency. The ocean flooi* has the same general charac- 

 ter as the land areas of the world— mountains, plains, channels, 

 canyons, exposed rocks, and very soft muddy areas. Because 

 underwater sound propagation is markedly affected by the 

 ocean bottom and the underlying materials, extensive measure- 

 ments have been made with an evolving series of precision echo 



