The second generic class of techniques employs only 

 passive acoustic receivers, usually hydrophone arrays, to detect and 

 process acoustic energy emitted by objects in the ocean surrounding 

 the receivers. 



Both kinds of techniques have been widely employed in 

 military systems for submarine and antisubmarine warfare and in both 

 military and commercial systems for navigation, communications, position 

 fixing, oceanographic exploration, and a variety of scientific purposes. 



The performance of both active and passive acoustic 

 systems can be enhanced by the use of acoustic beacons mounted on 

 objects to be detected. In addition to assisting in position fixing, 

 beacons can be coded to provide a wide variety of status and intention 

 data in the same way as for radar beacons. 



With the exception of the possibilities described in 

 Volume Two of this report, acoustic techniques were found to have little 

 potential to support enforcement of the 200-nmi fishing zone. Qualita- 

 tive reasons for the lack of potential are given below. 



b. Performance Potential 



Feasible approaches for using acoustic techniques in the 

 detection and classification of fishing activity include active devices 

 mounted on patrol vessels or installed on fixed platforms at various 

 depths from the surface to the bottom of the ocean and passive devices 

 mounted similarly. In addition, both active and passive devices can 

 be towed by patrol vessels to better isolate them from noise generated 

 by the patrol vessel. Each of these categories is briefly examined 

 below. 



89 



