390 



SUBMARINE TARGET STRENGTHS 



TARGET STRENGTH IN DECIBELS 

 BOW 



BEAM 



BEAM 



STERN 

 Figure 2. Aspect dependence (theoretical). 



weighted as heavily as other measurements. An ap- 

 preciable variation of target strength with aspect 

 angle was observed, in agreement with other meas- 

 urements. Also, an observed difference in these ex- 

 periments of between 10 and 16 db in target strengths 

 at beam and stern aspects, depending on where the 

 beam was focused, seems confirmed by more reliable 

 results. The actual values, however, must be con- 

 sidered doubtful. 



The target strengths of the S-class submarine taken 

 from reference 8 were measured by comparing sub- 

 marine echoes with the echoes from a submerged 

 sphere at a much shorter range than the submarine ; 

 fluctuations were large (see Figure 10 in Chapter 21), 



and the transmission loss was not known accurately. 

 Furthermore, no significant variation in target 

 strength with aspect angle was observed for the 

 S-boat; this result alone makes the reliability of these 

 measurements very dubious. 



The remaining values in Table 1 are in moderately 

 good agreement with each other, especially at beam 

 aspect; values for which no reference is given were 

 found at Fort Lauderdale. The only results out of 

 line are those from the Woods Hole measurements on 

 the Italian submarine Vortice.^° 



These measurements on the submarine Vortice were 

 made at a range of 1,000 yd and frequencies of 12 and 

 24 kc; the submarine was proceeding at 6 knots at a 



