STRUCTURE AND ORIGIN OF ECHOES 



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occur at the same place in successive echoes; rather, 

 they usually appear to be distributed unsystemati- 

 cally though generally nearer the center of the echo 

 than either end. 



In some cases, however, repeatable peaks seem to 

 be present in submarine echoes. A series of nine con- 

 secutive echoes from 5-msec signals at 60 kc are repro- 

 duced in Figure 36 and show two separate peaks or 

 groups of peaks at the same places in each echo. In 

 these measurements the submarine aspect was held 

 nearly constant at about 330 degrees. Thus no defi- 

 nite conclusions can be drawn at the present time as 

 to how often an echo peak will reproduce itself. It is 

 therefore uncertain whether these peaks represent 

 highlights on the submarine or random interference 

 between several reflected sound waves. 



In general, the process of reflection of sound from a 

 submerged submarine at off-beam aspects is still im- 

 perfectly understood. The entire submarine appears 

 to contribute to the reflected sound, yet specific, 

 repeatable highlights have not been observed in most 

 examinations of echo oscillograms. It is difficult to 

 understand how nonspecular reflection from the sub- 

 marine hull or from protuberances and fixtures on the 

 outside of the submarine can account tor these 

 echoes. Until the origin of these off-beam echoes from 

 actual submarines is satisfactorily explained, the ap- 

 plicability to actual echo ranging of the results ob- 

 tained with the indirect optical and acoustical tests 

 is open to question. 



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Figure 36. Repeatable peaks in submarine echoes. 



