SOUND PROPAGATION IN A RANDOM MEDIUM 



Robert H. Mellen 



New London Laboratory 



Naval Underwater Systems Center 



New London, Connecticut 



For more than a decade we have been trying to identify 

 and measure the various factors within the water column 

 that contribute to the low-frequency attenuation in sound 

 channels. Experiments have been carried out in a number of 

 bodies of water, including fresh-water lakes, to study ef- 

 fects of temperature, salinity, and other environmental 

 factors. The results show an anomalous attenuation in sea- 

 water below 1 kHz in excess of the magnesium- sulfate relax- 

 ation contribution. A new relaxation mechanism involving 

 boron has been identified by Fisher and Yaeger. A second 

 anomaly is frequency- independent over considerable ranges 

 and is thought to arise from scattering by random vari- 

 ations in refractive index. Comparison of the scatter loss 

 estimated from random variations in sound-speed profiles 

 shows order-of-magnitude agreement with a wide range of 

 experimental results. Effects of the random component 

 of sound speed on spatial and temporal coherence within 

 the channel are discussed. 



INTRODUCTION 



For more than a decade we have been trying to identify the 

 sources and behavior of the various components within the water column 

 that contribute to the attenuation of low-frequency sound in the sea. 

 In 1967 we began a series of experiments designed to study the dif- 

 ferences in various bodies of water, both fresh and saline, of 

 different temperatures and other environmental factors. The map 

 in Figure 1 shows the regions that were studied and I would like to 

 discuss the results of these experiments (Browning and Thorp, 1972). 



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