406 



SUBMARINE TARGET STRENGTHS 



TARGET STRENGTH IN DECIBELS 

 BOW 



BEAM 



BEAM 



STERN 

 Figure 20. Dependence of target strength on signal length for an S-boat at 24 kc. 



23.5.2 



Observations 



Since evidence showing a dependence of target 

 strength on pulse length could be found only in the 

 direct measurements, these measurements have been 

 examined and analyzed from this point of view. 

 Different signal lengths have been employed in 

 direct target strength measurements at San Diego, 

 where pulses from 0.5 to 200 msec long have been 

 used. 



Peak echoes from 5-msec signals were found to 

 average about 4 db lower than echoes from 33-msec 

 signals, according to early runs at San Diego on an 



S-class submarine, using JK gear at a frequency of 

 24 kc.'^ Further studies showed a minimum depend- 

 ence of target strength on pulse length at beam 

 aspects, and a maximum, nearly linear, dependence 

 at bow and quarter aspects.^" Later measurements, 

 however, reported no very significant dependence of 

 target strength on signal length for signal lengths of 

 10, 30, and 100 msec' These measurements are illus- 

 trated in Figures 17 and 18 for an S-boat and a fleet- 

 type submarine respectively; the difference in target 

 strengths between 100- and 30-msec signals and 

 100- and 10-msec signals were greatest at aspects 

 near the bow and stern and are plotted against the 



