TRANSDUCER HORIZONTAL 



293 



40 



RANGE IN YARDS 

 80 400 800 



4000 8000 



o 



UJ 



> 



Ul 



-100 



120 



O -140 



-160 — 



!5 



o: 



UJ 



o 



111 



> 



ec -ISO 



0.01 



0.05 0.1 0.5 1 



TIME IN SECONDS 



10 



Figure 17. Surface reverberation levels with strong downward refraction. Transducer depth 20 feet. 



RANGE IN YARDS 



400 800 



4000 8000 



at 



o 



lU 



> 



Ul 



!i 



o: 

 111 

 at 



K 



111 



> 

 111 



-100 



-120 



-140 



-160 



-180 



o EXPERIMENTALLY OBSERVED POINTS 



• OBSERVED POINTS CORRECTED FOR 

 TRANSDUCER DIRECTIVITY 

 I THEORETICAL INVERSE-CUBE DEPENDENCE 



I I I I I Hill I I I I I nil 



0.01 0.05 0.1 0.5 1 



TIME IN SECONDS 



Figure 18. Surface reverberation levels with strong downward refraction. Transducer depth 60 feet. 



and 18. Figure 19 shows the bathythermograph 

 record and the calculated limiting rays for the two 

 depths. The points marked A in Figures 17 and 18 

 show the range where the Umiting ray leaves the sur- 

 face. Just as in Figure 16, the observed reverberation 

 levels at short range can be expected to differ from 

 a straight line with —30 log r slope because of the 

 correction factor h(d — Ob'{6 — ?)/cos d. To facili- 

 tate comparison with this Une, the observed levels 



zoo 400 600 800 1000 56 60 64 68 

 RANGE IN YARDS DEGREES F 



Figure 19. Refraction conditions for data in Figures 

 17 and 18. 



