426 



SURFACE VESSEL TARGET STRENGTHS 



40 



<n 



-J 



bJ 

 ffi 



O 

 hi 



a 



30 



o 



z 



UJ 



a: 



I- 

 to 



I- 



UJ 



o 



20 



10 





 BOW 



20 



40 



60 



120 



140 



80 100 



BEAM 

 ASPECT ANGLE IN DEGREES 



Figure 3. Aspect dependence for moving vessels (New York). 



160 



180 

 STERN 



40 



30 



20 



-10 



, ■ 



• t • « ' • * •' • • 



^! — • : • 



Table 2. Aspect dependence at different ranges for 

 moving destroyers (San Diego). 





 BOW 



20 



40 60 80 100 



BEAM 

 ASPECT ANGLE IN DEGREES 



120 



Figure 4. Aspect dependence for moving vessels (San 

 Diego). 



leads to much the same results, which are illustrated 

 in Figure 4. Since the target strengths measured at 

 San Diego were found to depend markedly on range 

 (see Section 24.4), they were separated according to 

 range in order to examine the dependence on aspect 

 angle. The data were broken down into three groups, 

 for ranges of 100 to 300 yd, 300 to 500 yd, and 500 to 

 700 yd, and each group was analyzed for a possible 

 dependence on aspect angle. Average target strengths 

 for aspects within 20 degrees of the beam, and for all 

 other aspects are shown in Table 2 for each range 

 group. 



The scatter of the individual values from the aver- 

 ages in Table 2 is less than the scatter from the 

 overall averages in Table 1, and a slight change of 

 target strength with aspect seems significantly 

 shown. Some dependence of this nature might be 

 expected from a diffusely reflecting surface, if all the 

 target were in the path of the sound beam. However, 

 any change with aspect angle as great as that found 

 for submerged submarines seems ruled out by Table 

 2. These results are generally consistent with the 

 hypothesis that bubbles along the side of the ship 

 are responsible for the echoes observed from moving 

 ships. More accurate data would be required, how- 

 ever, for verification of this theory. 



24.4 



R4NGE DEPENDENCE 



In Sections 20.4.4 and 23.4.1 it was pointed out 

 that the target strength of submarine depends on 

 the range at ranges less than the maximum radius. 



