than radar or visual detection ranges. Moreover, no classification of 

 objects detected is possible. 



Magnetic techniques are evaluated as having neglegible 

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



7. Acoustic Techniques 



a. Description 



Under favorable conditions, acoustic energy can propagate 

 for relatively long distances in the atmosphere and in the ocean. More- 

 over, the technology for the generation, transmission, and reception of 

 acoustic energy is well established and the characteristics that affect 

 propagation in both the atmosphere and the oceans are well known. 

 Accordingly, detection and classification of fishing vessels by use of 

 acoustic techniques are possible and were examined in this survey. 



Techniques based on the propagation of acoustic energy 

 in the atmosphere were ruled out immediately since both the attenuation 

 of the energy and the variability and unpredictability of sound propaga- 

 tion paths in the atmosphere make these techniques usable over only 

 extremely short range and under extensively instrumented laboratory con- 

 ditions. 



Two generic kinds of techniques using acoustic energy 

 propagated in seawater exist. The first involves sonar devices in which 

 acoustic energy is transmitted, reflected from surrounding objects, and 

 the returned (reflected) energy is processed to obtain position location 

 and classification information. The process is almost completely analogous 

 to radar, except that the characteristics of the transmission medium 

 exert a much more profound influence on the transmission and reception 

 of the acoustic signals and the nature and variability of naturally 

 occurring background noise sources are quite different. 



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