TRANSDUCER DIRECTED DOWNWARD 



285 



40 



80 



RANGE IN YARDS 



400 600 



4000 5000 



-80 



se -100 



-120 



-UO 



0.01 



0.09 0.1 0.5 



TIME IN SECONDS 



10 



TEMPERATURE IN DEGREES F 

 46 48 SZ 56 60 64 



100 



ZOO 



SOO 



400 



900 



Figure 5. Volume reverberation levels with scattering layer at several depths. 



plot of the estimated depth of the deep layer ob- 

 served for each position and frequency along the line 

 connecting positions III and VIII. Figure 9 illustrates 

 the persistence of the layer throughout the area of 

 observations. 



According to equation (24) of Chapter 12, it should 

 be possible to determine log m from the experimen- 

 tally observed reverberation levels, provided the 

 values of the transmission anomaly term —2A -\- A\ 

 are known. Since horizontal velocity gradients in the 

 ocean are usually negligible, refraction can be neg- 

 lected in measurements with a directional transducer 

 pointed vertically downward, and Ax can thus be set 

 equal to zero. Furthermore, if the acoustic properties 

 of the ocean do not change much with increasing 

 depth, the transmission anomaly resulting from ab- 

 sorption and scattering should be a linear function of 

 range (see Section 5.2.2 of Part I). In other words, if 



the ocean is approximately homogeneous, the term 

 — 2A -f Ai in equation (24) of Chapter 12 should 

 equal —2ar/ 1,000 where r, the range of the rever- 

 beration in yards, is equal to the depth of the scat- 

 terers giving rise to the reverberation. It follows 

 that if the "uncorrected" scattering coefficient M is 

 determined from the equation 



R'{t) = 10 log ^ + 10 log M - 20 log r + /„, 



then 



10 log M = 10 log TO 



2a?- 

 1,000 ' 



(1) 



In equation (1) to, the true value of the scattering 

 coefficient, is constant if the properties of the ocean 

 do not change with depth. Thus, for a homogeneous 

 ocean, with m and a constant with depth, a plot of 

 10 log M against depth on a linear scale should be a 



