wwrrw^swf^Fwmmm^msmwm^w^^mww^M'^maamm 



NATURAL SOUNDS 



REFLECTION 

 Transmitted and Reflected 



Sound; Useful for Detection 

 Scattered Sound; Usually Obscures Submarine 



Echoes & Degrades System Performance 



A significant problem in acoustic detection is the result of sound scattering and 

 reverberation. 



these paths through experiments at sea and computer simulations. 



Because sonar systems must detect their target signal against a 

 background of sea noise, it is important that the noise field be as well 

 understood as transmission phenomena. Present investigations are 

 concerned with identifying the possible sources of the noise, 

 measuring their strength, and statistically describing their 

 fluctuations in time. In addition, measurements of ambient noise as a 

 function of depth and of horizontal and vertical directionality are 

 important aspects of this program. Major experiments have recently 

 been conducted in the North Atlantic, North Pacific, and Caribbean 

 Sea to measure transmission loss, ambient noise, biological 

 reverberation, currents, and other characteristics. 



Computer models (simulations] enable the Navy to predict 

 environmental effects on system performance throughout the oceans 

 by suitable manipulations of computer input parameters. With the 

 cost of going to sea increasing rapidly, model development has 

 become a key part of the Navy's ocean science R&D program. 



The Navy's contract research program, carried out primarily 

 through academic and nonprofit institutions, continues to achieve 

 goals that enhance naval operations. Among recent 

 accomplishments in physical oceanography are improved models to 



84 



