392 



SUBMARINE TARGET STRENGTHS 



RELATIVE ECHO LEVEL IN DECIBELS 

 BOW 



BEAM 



BEAM 



STERN 



Figure 4. Aspect dependence (New London). Curves (range in yards): (A) 600; (B) 800; (C) 1,000; (D) 1,200. 



San Diego. The submarine followed a straight course 

 at about 2J^ knots at periscope depth, while the 

 Jasper circled it at a range of about 500 yd (see 

 Figure 2 in Chapter 21). Each point on the curve is 

 the average of all echoes obtained within the 15-de- 

 gree sector centered at the indicated aspect angle, and 

 represents, on the average, about 40 individual 

 echoes. 



Figure 4 is a plot of the echo level against aspect 

 angle for a series of tests made on the USS S-48 

 (SS159) at New London and described in Section 

 21.2.2.^^ Each contour represents measurements made 

 at a different range. Since no correction was made 

 either for the transmission loss or for the calibration 



of the equipment, no absolute target strengths are 

 plotted. These echo level values cannot be compared 

 directly with other target strength values, since 

 they are relative to an arbitrary level. However, 

 the differences in echo levels at different aspects 

 correspond to the differences in target strengths at 

 different aspects, as long as the range remains 

 constant. 



Indirect measurements of target strength are il- 

 lustrated in Figures 5 and 6. Figure 5 shows target 

 strength as a function of aspect angle for a model of 

 the USS Perch (SS313), as measured optically at 

 MIT.^ The altitude angle was degrees and the full- 

 scale range 600 yd. The results of the acoustical tests 



