TARGET IDENTIFICATION 



The varied fish population that 

 lives and feeds around the tower affords 

 an unusual opportunity to observe and 

 measure the sonar target characteristics 

 of individual species. Identification of 

 fish types by acoustic means has value 

 not only to the Navy but also to commer- 

 cial fishermen. 



One target identification study 

 was conducted by using a diver-held 

 sonar. Sonar reflections from the fish 

 were transmitted by wire to a tape re- 

 corder on the tower. The tapes were 

 analyzed for frequency and relative 

 intensity of echoes from individual 

 species and groups. Analysis of these 

 tapes revealed a variation in signal 

 pattern that depended upon the charac- 

 teristic shape and structure of the in- 

 dividual fish and other objects, the fre- 

 quency of the sound, and the range of the 

 sonar target. 



Studies of the identification of 

 biological organisms by underwater 

 sounds are not limited to the larger 

 animals. Schools of small fish and 

 masses of zooplankton organisms have 

 been observed to cause extensive acoustic 

 scattering. 



Divers train NEL-developed hand-held sonar 

 (AN/PQS-1B) on various species of fish to record 

 the characteristics of echoes produced. The spnar 

 sweeps from 85 to 55 kc/s in a linear, sawtoothed 

 manner. An air-filled aluminum sphere is suspended 

 in the water and used as a reference target. 



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