trawling or optics. Work is progressing in 

 all of these fields but this Straza unit is 

 apparently the only sea-going Doppler unit 

 under investigation. Soundness of its con- 

 tinued use on surface targets is questionable. 

 Experience suggests that the direction of the 

 research be changed. The difficulties caused 

 by sea return suggest that the sonar should 

 concentrate on deeper targets. Since body- 

 motion Doppler effect is aspect-dependent, 

 that is, it is strong only on the horizontal 

 plane, the transducer array must be mounted 

 on a subsurface vehicle so that it can operate 

 at the same depth as the target. The problems 

 arising from trying to maintain contact with 

 rapidly moving surface schools may not be as 

 great with deep targets since some studies 

 show that these targets generally are nearly 

 stationary. It is most likely, however, that 

 these deep targets are snnall organisms-- 

 which means that work on the big scombroids, 

 the original goal of these experiments, will 

 have to be deemphasized. In addition we should 

 have a combination of laboratory studies of 

 fish locomotion along with the future Doppler 

 work. 



3. The at-sea experiments showed that 

 under certain conditions, Doppler information 

 could be obtained fronn near-surface fish 

 schools. This information was not successfully 

 used in target classification, however. The 

 major difficulties with the at-sea phase were 

 caused by sea return and the erratic behavior 

 of near-surface schools. Recommendations for 

 further studies are aimed at overcoming these 

 difficulties. The recommendations include 

 mounting the sonar transducers on an under- 

 water vehicle and working with deeper, slow- 

 moving targets. 



ACKNOWLEDGMENTS 



The editor acknowledges the cooperation of 

 the U.S. Navy for the loan and subsequent 

 transfer of our sonar boat, the engineering 

 staffs of the contractors for their outstanding 

 performance and reports, and the Direccion 

 General de Pesca e Industrias Conexas, De- 

 partmento de Estudios Biologicos Pesqueros, 

 for permission to enter and work in the 

 territorial waters of Mexico, 



SUMMARY 



Three phases in the development of a Doppler 

 target classification sonar are reported: 



1. Target strengths of subject species were 

 determined to permit the estimation of target- 

 classification sonar equipment: frequency, 

 source level, hydrophone and receiver sensi- 

 tivity, and scan rate, 



2. Feasibility studies were made to deter- 

 mine whether or not Doppler effects from fish 

 body-motion could be detected. These studies 

 were sufficiently promising that a shipboard 

 CTFM/Doppler sonar was constructed. 



LITERATURE CITED 



HESTER, FRANK J, 



1967, Identification of biological sonar tar- 

 gets from body-motion Doppler shifts. 

 In Wm. N. Tavolga (editor). Marine 

 bio-acoustics, pp. 59-74. Pergannon 

 Press, Oxford and N.Y. 

 INTER -AMERICAN TROPICAL TUNA COM- 

 MISSION. 



1960. Annual reportfor the year 1960. Inter- 

 Amer. Trop. Tuna Comm. 183 pp. 



1961. Annual report for the year 1961. Inter- 

 Amer. Trop. Tuna Comm. 171 pp. 



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