DEPENDENCE ON ORIENTATION 



391 



TARGET STRENGTH IN DECIBELS 

 BOW 



BEAM 



BEAM 



STERN 

 Figure 3. Aspect dependence (San Diego). 



depth of 150 ft. The values reported are of the order 

 of 40 db, so much larger than any reported previously 

 by any method that they appear to be the result of 

 faulty calibration; the systematic error of about 

 20 db at all aspects is difficult to explain in any other 

 way. 



It might iDe pointed out, however, that the trans- 

 mission loss as measured aboard the submarine was 

 about 15 db greater than that expected from the pre- 

 vailing oceanographic conditions. Therefore an at- 

 tenuation coefficient of 4 db per kyd was assumed, in 

 addition to inverse square divergence. In spite of 

 such a transmission loss, however, the target strengths 



are more than 10 db greater than the highest values 

 previously observed on a similar submarine. 



Figures 2 to 6 show typical variations of target 

 strengths with aspect angle. Figure 2 is a plot of the 

 theoretical calculations of the target strength of the 

 U570 {Graph) for an echo-ranging frequency of 25 kc 

 and a range of 1,000 yd.* They are based on approxi- 

 mating the submarine by an ellipsoid of appropriate 

 dimensions, with a conning tower of "tear drop" 

 cross section; details of this method are described in 

 Section 20.5. 



Figure 3 shows the result of a typical target 

 strength run at 24 kc on a fleet-type submarine at 



