PEDERSEN, GORDON, AND WHITE: SURFACE DECOUPLING EFFECTS 



This curve provides some practical "rule of thumb" values. One - 

 half the decoupling depth is 3 dB loss. One-third depth is 6 dB loss. 

 One-fifth depth is 10 dB loss. One-tenth depth is 16 dB loss. 



Observe that for a given receiver depth the loss will decrease 

 with increasing frequency because the surface decoupling depth 

 decreases with increasing frequency. This phenomenon is believed 

 to be the controlling factor which causes the ambient noise in the 

 ocean to increase in the region from about 10 Hz to 80 Hz. 



In summary, a new ray theory model of surface decoupling loss 

 has been developed which is adequate for frequencies above 10 Hz. 

 Investigation of the surface decoupling phenomena by mode theory 

 has resulted in several new conclusions: The highest levels for 

 shipping noise are predicted to occur at receiver depths somewhat 

 in excess of the decoupling depth. Under conditions of severe near- 

 surface gradients, there is marked disagreement between convergence 

 propagation losses in the decoupling region as calculated by the 

 ray theory and by normal mode theory. 



An exercise known as CAPER was conducted in late August 1974 

 by NUC, MPL, and HIG under LRAPP sponsorship. Part of this 

 exercise consisted of measuring convergence zone propagation loss 

 at 104 Hz on five receivers distributed from 10-foot to 150-foot 

 depth and covering the surface decoupling region. These data will 

 be analyzed to determine if they confirm the theory presented here. 



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