ENVIRONMENTAL FACTORS AFFECTING LOW FREQUENCY 

 PROPAGATION IN THE OCEAN 



David G. Browning 



Naval Underwater Systems Center 

 New London, Connecticut 



A summary is made of our understanding of the effect of 

 environmental factors on low frequency sound propagation, 

 based on recent NUSC experiments and analyses. Modeling 

 programs developed by DiNapoli, Kanabis, Weinberg, and 

 others are used to illustrate the influence of bottom 

 composition, bottom slope and bathymetric features and to 

 determine the low frequency transmission characteristics 

 of ocean sound channels. The present status of our pro- 

 gram to predict the temporal and spatial variations in 

 sound transmission by an understanding of the basic 

 acoustic-oceanographic interaction mechanisms is discussed. 

 Our priorities for further data collection are given. 



Basically, the simplest type of sound channel experiment is 

 illustrated in Figure 1. With both the receiver and source at the 

 sound channel axis, we drop shots as a function of range to get 

 propagation loss as a function of range. 



A very simple model, outlined in Figure 2, is used to get the 

 attenuation as a function of range. Spherical spreading is assiomed 

 out to a certain range R and then cylindrical spreading from 

 then on with attenuation along the range. We plot this to get a 

 linear fit for the attenuation. 



Figure 3 illustrates the type of fit that we get from our data. 

 We have used a very simple spreading model, what you might call a 

 crude fit to the data. Naturally, when any more sophisticated methods 

 come along, we are the first to try to see if this will improve upon 

 things . 



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