The above discussion deals with the most general aspects of 

 propagation of sound in the ocean. In practice, sound propagation in any 

 given situation depends on a yery complex set of parameters, including water 

 depth, source depth, water temperature and salinity, surface roughness, 

 surface cover (e.g., ice), bottom type, bottom profile, etc. Although sound 

 propagation can be predicted roughly by employing the general concepts of 

 spreading and absorption presented in the section above, accurate prediction 

 is virtually impossible without specific knowledge of each of the above listed 

 factors. Continental shelf operations pose a particularly difficult problem 

 because of the fact that they generally occur in shallow water (depth less 

 than 100 fathoms) for which the bottom plays an important role, and the water 

 structure is often quite variable. Discussing shallow v/ater propagation, 

 Urick (1975) states, "Because of these complexities, the transmission loss to 

 be expected at a shallow water location may be said to be, for many purposes, 

 unpredictable. Resource to direct measurements is necessary." 



In view of this complexity, it is beyond the scope of this report to 

 attempt to predict the propagation at specific OCS sites. Instead, the basic 

 equations of spreading loss and absorption loss (expressions (1) and (2) above 

 will be used to provide general estimates of propagation of OCS-related noise. 



G-17 



