SECT. ]] REFRACTION AND REFLECTION TECHNIQUES AND PROCEDURE 37 



correlation. This system gives consistent penetration to the base of the low- 

 velocity sediments; sometimes horizons within the sedimentary column are 

 also recorded. 



Extensive work has been done with non-explosive systems for under-way 

 reflection work. One electromechanical system is discussed by Hersey in this 

 volume. Several versions of underwater arc discharge systems have been used 

 with varying success. One described by Shor et al. (in press) has produced 

 echoes from within the sedimentary column and from the base of the sediments 

 in deep water. All these systems are limited by the noise produced by the motion 

 of the hydrophones through the water; attempts to overcome this have included 

 slacking a single hydrophone, or the use of multiple-hydrophone streamers to 

 cancel noise, or systems by which the echoes from several consecutive signals 

 are added before recording. Future reflection work in the deep sea will 

 undoubtedly be done with high-repetition-rate systems which record in the 

 style of a fathometer whether the source of the energy be high explosives, gas, 

 compressed air, or electricity. 



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 Dow, W., 1952. Three channel ampHfier for use in refraction and sound measurements at 



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