428 



SURFACE VESSEL TARGET STRENGTHS 



100 



150 200 



250 



300 350 400 4 50 



RANGE IN YARDS 



500 



550 600 650 



Figure 7. Range dependence at beam aspects for moving vessels (San Diego). 



X 



a,,- 



. • — t "• ~ « " 



% ~ - o 



•• • — • • • 



ISO 



200 



350 400 450 

 RANGE IN YARDS 



500 



650 



700 



Figure 8. Range dependence at off-beam aspects for moving vessels (San Diego). 



,40 



m 



o 



ui30 



IE 



I- 



m 



20 



10 



o 



DC 



< 



r— 



— ^^ ^S-^ 



! ^i — !^i • 



— • — — ; — 



200 250 300 350 400 

 RANGE IN YARDS 



450 



500 



Figure 9. Range dependence at beam aspects for 

 moving vessels (New York). 



of curvature of the submarine. The target strength 

 of a still ship would be expected to behave in the 

 same way under similar conditions. Because ship 

 hulls may be flatter and may have a larger radius of 



curvature than submarines, this dependence on 

 range might extend to much longer ranges than for 

 submarines. On the other hand, the target strength 

 of a moving ship might be expected to increase as the 

 range increases, as more and more of the scattering 

 surface lies in the path of the direct sound beam. 



Accordingly, target strength was examined as a 

 function of range, for beam and off-beam echoes, for 

 all three sets of data. The results of this analysis are 

 illustrated in Figures 5 to 10, where in each graph 

 the solid line represents the least squares solution 

 based on an assumed linear relation between the tar- 

 get strength and the range. The slopes of these lines 

 are listed in Table 3. It is apparent that in all cases 

 the dependence of target strength on range is most 

 pronounced (1) for still vessels and (2) at beam 

 aspect. 



Three explanations may be suggested to account 

 for the increase in target strength with range: (1) 

 failure Of the sound beam to cover the target at short 



