DEPENDENCE ON CLASS 



397 



90 



BEAM 



ASPECT ANGLE IN DEGREES 



ISO 

 STERN 



Figure 11. Target strength-aspect curves at different altitudes (acoustical). 



good agreement with values at periscope depth. At 

 an aspect angle of 150 degrees, however, a target 

 strength of 27 db was obtained, much higher than 

 any other values reported at that aspect, directly or 

 indirectly. An S-boat, for example, measured in the 

 same series of runs, gave a target strength of 14 db 

 at the same aspect. 



This high value of 27 db may result from overcor- 

 recting for the transmission loss by assuming an 

 excessively large attenuation coefficient, since the 

 range of the Tilefish was 760 yd compared to 150 yd 

 for the corresponding measurements on the S-boat. 

 The attenuation coefficient assumed was 10 db per 

 jkyd of sound travel at a frequency of 45 kc. However, 

 high target strengths may actually be characteristic 

 of deep submarines at certain aspects. It may be men- 



tioned that at Fort Lauderdale, one of the strongest 

 series of echoes was obtained when echo ranging at 

 stern aspect on a fleet-type submarine submerged to 

 a depth of 250 ft, at ranges between 220 and 700 yd. 



23.2 



DEPENDENCE ON CLASS 



Submarines of different sizes and shapes may be 

 expected to reflect sound differently; the echoes from 

 an R-boat 186 ft long and those from a new fleet-type 

 submarine more than 300 ft long are not likely to be 

 the same. In particular, specular reflection of sound 

 from a submarine would be expected to depend 

 rather critically on the shape of the hull and espe- 

 cially on the different radii of curvature. 



