DKPENDENCE ON ORIEINTATION 



393 



TARGET STRENGTH IN DECIBELS 



BOW 



BEAM 



BEAM 



STERN 

 Figure 5. Aspect dependence (MIT). 



made at Mountain Lakes on a model of the U570 are 

 reproduced in Figure 6, for an altitude angle of de- 

 gree, a full-scale range of 340 yd, and a full-scale 

 frequency of 26 kc.'^ Bow and stern target strengths 

 in Figures 5 and 6 are considerably lower than in 

 Figure 2, probably because the ellipsoid used in the 

 theoretical calculations was rounded at either end 

 while the optical and acoustical models were pointed. 

 Other discrepancies at bow and stern are discussed 

 in Sections 23.8.2 and 23.8.3. 



23.1.2 



Altitude Angle 



Target strength varies with altitude angle, but in 

 most cases this variation does not appear to be im- 



portant practically. Figure 7 illustrates the theoretical 

 predictions of the target strength of the U570 at beam 

 aspect as a function of altitude angle for a range of 

 about 16 yd; ^ since target strengths were found only 

 for certain intervals of the altitude angle, they are 

 represented as sectors in the polar plot of Figure 7. 

 The sharp sectors at particular altitudes are attrib- 

 uted to the sum of two separate reflections — from 

 the blister tank and from the hull itself — neglecting 

 interference phenomena. Figure 8 shows the same 

 plot for the optical measurements made on a model 

 of the USS Perch (SS313) for echo-ranging distances; 

 the peak at 90 degrees, when the projector is directly 

 above the submarine, arises from a strong reflection 



