Breaker and O'Neil 



Dr. C. F. Black (presently with RAND Corporation). The structure 

 function, Dj(r) was computed along horizontal lines at various depths 

 out to a range of 35000 meters using NEL thermistor-chain data. The 

 slopes of these horizontal structure functions, when plotted against 

 range on log-log scales, were generally just slightly in excess of 

 the 2/3 predicted by Eq. (1), indicating that ocean turbulence "looks" 

 nearly isotropic in the horizontal plane. With vertical temperature 

 data, however, obtained using a Bissett-Berman STD unit, the structure 

 functions had slopes of about 1.8 over scales from 50 to 500 meters. 

 Thus, ocean turbulence is significantly anisotropic at least for 

 scales greater than 50 meters but seems nearly isotropic to one 

 traveling in a horizontal line at least out to scales of 35000 meters. 

 (This work is reported in Ref. 5.) When one reflects that sonar-to- 

 target geometries are typically such that the energy is transmitted 

 very largely in the horizontal it seems likely that, anisotropy 

 notwithstanding, the fluctuations in signal level may actually follow 

 Eqs. (4) and (6) rather closely. 



Previous work has often attributed observed fluctuations to 

 such causes as motion of source and/or receiver, non-uniform beam 

 patterns, and variations in source level, etc. These effects may 

 well overshadow turbulence effects at the short ranges usually 

 employed. However, since turbulence effects are cumulative with 

 range, fluctuations arising from turbulence should control the 

 structure of fluctuations at longer ranges. 



PLANNING AND EXECUTION OF EXPERIMENT 



In October of 1966, the Naval Oceanographic Office conducted 

 an experiment to determine whether the turbulence-induced theory of 

 transmission- loss fluctuation was, in fact, valid for values of ^ XL 

 typical of those experienced in sonar operation. Bissett-Berman, 

 under contract to the Oceanographic Office, assisted in the planning 

 of the experiment and the reduction and analysis of the resulting 

 data. 



The geometry selected for the experiment is shown in 

 Figure 2. The receiving hydrophone was suspended from a moored 

 vessel while the transmitting projector was towed in a circle about 

 the receiving ship. The radius of the circle is L and v^j is one- 

 half of the transmitting ship's speed (if that is sufficiently large 

 that currents may be neglected by comparison). 



The experiment was conducted in the Tongue of the Ocean 

 during the period 11 to 15 October 1966. The R. V. PAUL LANGEVIN 

 served as the receiving vessel and the USS LITTLEHALES (AGSC-15) 

 towed the projector. 



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