BOTTOM SCATTERING COEFFICIENTS 



315 



RANGE IN YARDS 



RANGE IN YARDS 



S -110 



100 



1000 



K -120 



-130 



-140 



-150 



o 



110 



1000 



-120 



-■ -130 



0.1 0.2 as 



TIME IN SECONDS 



COARSE SAND DEPTH 170 PEET 

 AUGUST 18, 1943 



-140 



\ -ISO 



ai 



0.2 



0.5 

 TIME IN SECONDS 



SAND-AND-MUD DEPTH 315 FEET 

 SEPTEMBER 27, 1943 



RANGE IN YARDS 



RANGE IN YARDS 



•110 



■120 



-130 



■140 



-150 



100 



1000 



-no 



a. -120 



100 



1000 



id 



-130 



0.2 0.5 



TIME IN SECONDS 



MUD DEPTH 255 FEET 

 OCTOBER 9,1943 



-140 



-150 



0.2 0.5 



TIME IN SECONDS 



ROCK DEPTH 370 FEET 

 SEPTEMBER 27, 1943 



I CALCULATED RANGE AT WHICH 

 I 6» RAY STRIKES BOTTOM 



Figure 7. Typical bottom reverberation levels with horizontal transducer. 



The reverberation level at any range could be trans- 

 lated into the bottom scattering coefficient by use of 

 equation (54) of Chapter 12, and the grazing angle of 

 the sound at this range could be computed from the 

 temperature-depth information. However, it will be 

 seen in the following subsection that this procedure 

 is not workable, briefly because the value of m" com- 

 puted in' this way is accurate only for the portion of 

 the bottom struck by the central portion of the pro- 

 jected beam, and within this limited area there is not 

 much variation in the grazing angle. Thus, in order to 

 determine the form of the function m"(0), specifically 

 designed experiments are necessary. 



An Experiment Designed to Measure m''{S) 



Data casting light on the angular dependence of m" 

 were obtained in a series of experiments, made in 

 August, September, and October of 1943, and de- 

 scribed in an internal report by UCDWE..^ On each 

 day that measurements were taken, the transducer 

 was set either at degrees (main transducer beam 

 horizontal) or at 30 degrees (main transducer beam 

 pointed 30 degrees down from the horizontal), and 

 lowered to a depth of 9 ft. Bottom reverberation for 

 a number of 10-msec 24-kc pings was then recorded 

 as a function of time, by using the equipment de- 

 scribed as 2) in Section 13. 1 . 1 . By comparing measure- 



