548 



SCHEVILL, BACKUS, AND HERSEY 



[chap. 14 



as the instruments just described. An instrument of this type has been recently 

 completed at Woods Hole using one hundred Rayspan filters (Raytheon Mfg. 

 Co.) and a multichannel recorder (Alden Products Co.). A recording is shown 

 in Fig. 5. It is to be compared with a vibralyzer analysis of the same sound 

 shown in Fig. 4. 



O 0.1 0.2 0.3 0,4 0.5 0,6 0.7 ' 



TIME (sec) 



Fig. 5. Sound spectrogram of Delphinus delphis calls including those of Fig. 4 made on 

 the W. H. O. I. Rayspan-Alden combination. 



Inside the broken line is the part of the record represented by Fig. 4. The fre- 

 quency response of the tape playback used for Fig. 5 is different from that of Fig. 4, 

 accounting for some of the difference between the two spectrograms. 



D. Instruments for Identifying Sound Makers at Sea 



Methods and instruments for locating, tracking, and finally closing range on 

 sound-making animals in the open sea is the most pressing need in this field. 

 Real progress toward identification of sound makers will await such develop- 

 ments. Versatile and convenient directional hydrophone arrays are needed ; 

 they must be coupled with analyzers instantaneously presenting significant 

 information about the chase. Probably these will have to operate from com- 

 paratively small craft having very quiet propulsion. Furthermore, identification 

 means deliberate visual inspection or capture of the animal, probably both. 

 This appears a formidable instrumentation problem. Nevertheless, many 

 elements of such systems have been used for other purposes in the past decade. 



Directional high-frequency echo-ranging equipment has been used to locate 

 sound sources such as whales or porpoises. The many sharp transient sounds 

 heard in the ocean, only a few of which have been identified, might well be 

 located by travel time difference measurements from a suitably disposed 



