power density is in the low-frequency region. The power spectra 

 decrease monotonically with increase in frequency until a frequency 

 of about 0.02 cpm, at which point they fall off less rapidly with 

 frequency at about f-5/3 (k"!) . At a frequency of about 0.8 cpm there 

 appears to be another transition zone corresponding to decay at a rate 

 of f-5/2 (k-2). 



d. Acoustic Propagation and Internal Waves 



Horizontal thermoclines show a shadow zone beyond the limiting 

 ray in the duct. Within the duct, more or less acoustic energy is 

 trapped depending upon whether the limiting ray is steeper or shallower 

 than with an undisturbed thermocline. The effect of internal waves 

 on acoustic propagation is to form regions of convergence and divergence 

 of rays below the thermocline. In particular, figure 6-11 demonstrates 

 the effect on propagation in and below a surface duct. There is an 

 increase of energy leakage out of the duct bounded by a wavy thermocline. 

 In addition, there are alternating regions of high and low intensity 

 below it. 



22 



