High-Frequency Acoustic Variability in the Arctic.
Fluctuations in acoustic intensity have been studied for two locations in the Arctic -- the Chukchi Sea (1974) and the Kane Basin (1979) -- using the same measurement and analysis techniques. A five-frequency transducer covering the range 10-75 kHz was moved continuously in the vertical direction fr...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
1984
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| Subjects: | |
| Online Access: | http://www.dtic.mil/docs/citations/ADA150550 http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA150550 |
| Summary: | Fluctuations in acoustic intensity have been studied for two locations in the Arctic -- the Chukchi Sea (1974) and the Kane Basin (1979) -- using the same measurement and analysis techniques. A five-frequency transducer covering the range 10-75 kHz was moved continuously in the vertical direction from 10 to 70 m. The results were used to determine the vertical correlation length and the coefficient of variation (rms variance) for the intensity at the five frequencies simultaneously. Conductivity and temperature vs depth were measured continuously before and after each set of acoustic runs. These profiles were used to construct sound ray diagrams and to compute the refractive index variance. For direct-path propagation in both locations, it was found that when the acoustic intensity variance at low spatial wavenumbers is filtered out the remaining variance depends on the first power of the frequency and approximately the square of the range. This internal-wave-like behavior is supported by additional evidence. The vertical correlation lengths observed for the direction-path intensity indicate that the scattering features have lifetimes longer than a few seconds and les than a few minutes. The study suggests that the scattering structures are related to anisotropic eddies that tend toward isotropy as they cascade to smaller size. Plots of a strength parameter vs a diffraction parameter show that after deterministic variations are removed from the measurements the remaining variations lie in the unsaturated direct-path region. |
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