TRANSDUCER HORIZONTAL 



291 



10 



20 



40 



10 



20 40 



FREQUENCY IN KC 



80 



10 



20 



40 



80 



Figure 12. Variation of 10 log M with frequency (mean values of 10 log M for depths less than 250 feet). Positions III 

 and III2 refer to measurements made at Position III on two separate days. 



-70 



FREOUENCT IN KC 



Figure 13. Variation of scattering coefficient with 

 frequency (mean values of 10 log M at all nine positions 

 for depths less than 250 feet). 



10 log m! /2 and J^{d) in equation (39) are also inde- 

 pendent of range. This simple inverse cube depend- 

 ence is observed only rarely. Figure 15 shows the 

 reverberation intensities observed on May 8, 1942, 

 with the QCH-3 transducers. On this date ground 

 swells were long and low, and a few whitecaps were 

 forming. The QCH-3 transducers were at a depth 

 of 20 ft with their long dimensions horizontal and 

 with the transducer axes parallel to the sea surface. 



m 



-I 

 lu 

 > 

 III 



-J 



-50 



-70 



-90 



2 -110 



< 



111 

 o 

 a: 



UJ 



> 



UJ 



tc 



-130 



•150 



0.01 



RANGE IN YARDS 

 40 00 400 



800 



0.05 0.1 0.5 



TIME IN SECONDS 



Figure 14. Comparison of reverberation from hori- 

 zontally and vertically directed beams. 



In this position the QCH-3 transducers are prac- 

 tically nondirectional in the vertical plane, so that 

 in equation (41), Chapter 12, the correction factor 

 hifi — ^fi)b'(d — ^,0)/cos 6 is very nearly unity at 

 all angles of importance. Since this correction factor 

 is the only part of Ja{0} which can depend on range, 



