Sound Transmission to Long Ranges in the Ocean
Abstract
Recent use of half-second pulses at 7.4 kc for sound transmission measurements at ranges between 5 and 28 miles in the deep ocean has shown that sound can travel to such ranges by either or both of two paths. One path is by reflection from the bottom; the other is a channelled path lying within the near-surface wind-mixed layer and involving repeated reflections from the ocean surface. The bottom reflection provides the only effective path between a source and receiver lying below the mixed layer. For this path the data indicate an absorption coefficient at 7.4 kc of 0.6 db per kiloyard, a figure about 40 percent smaller than expected from other measurements at higher frequencies. The near-surface path is the result of sound trapping by the isothermal wind-mixed layer. That this trapping can be almost complete under some conditions is shown by evidence from the measurements that leakage out of the channel amounts to only 0.2 db per kiloyard. For a shallow source and receiver, mixed-layer sound channelling with the above value of attenuation coefficient accounts for a transmission excess of 30 db at 25 miles over what was anticipated on the basis of spherical spreading and the best available estimate of attenuation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 06, 1950
- Accession Number
- ADA453787
Entities
People
- R. J. Urick
Organizations
- United States Naval Research Laboratory