DEPENDENCE ON PULSE LENGTH 



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 BOW 

 STERN 



COS 9 



Figure 17. Dependence of target strength on signal 

 length for an S-boat at 24 kc. 



others, the change in the peak echo intensity, aver- 

 aged over many echoes, turns out to be considerably 

 less than the change in mean echo intensity, aver- 

 aged over the length of the echo and then over many 

 echoes, for the same change in pulse length. 



For example, it is shown that, for a uniformly re- 

 flecting target whose length is 300 ft in the direction 

 of the sound beam, corresponding roughly to a fleet- 

 type submarine at bow or stern aspects, the average 

 peak echo intensity will decrease only 3 db and the 

 average mean echo intensity will decrease 5 db, when 

 the signal length is reduced from 30 to 10 msec. The 

 assumptions on which this analysis is based are so 

 idealized that the exact numerical results are prob- 

 ably not very significant; nevertheless, the general 

 conclusion that the peak amplitude changes less 

 rapidly with the signal length than the average 

 amplitude seems fairly well established theoretically. 



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 BEAM 



0.8 



1.0 



BOW 



STERN 



COS 9 



Figure 18. Dependence of target strength on signal 

 length for a fleet-type submarine at 24 kc. 



ASPECT ANGLE IN DEGREES 



Figure 19. Dependence of relative target strength on 

 signal length at different aspects for an S-class sub- 

 marine at 60 kc. 



