Effect of Monomolecular Films on the Underlying Ambient-Noise Field. Part 2. Low Sea State and Laboratory Tests
Abstract
A series of low sea-state tests show that the reduction of surface- related ambient noise beneath monomolecular (slick-forming) films begins between 1 and 2 kHz and extends to at least 70 kHz. Although the amount of noise reduction varies between experiments, attenuations of up to 8 dB are not uncommon. Most of the experiments are conducted in the absence of whitecapping, where for wind speeds are greater than 2 m/s, the ambient noise spectra beneath the films generally resemble those of nonfilmed, lower sea-state conditions. Laboratory experiments conducted with these same films spread upon a reservoir of sea water show that the regular bubble entrainment associated with vertically falling drops can be dramatically suppressed, and the air entrainment accompanying plunging liquid jets is characterized by a conspicuous increase in the number of smaller bubbles. Preliminary studies providing simultaneous in situ acoustic and video monitoring of the ocean surface from a meter beneath it suggests that, in the absence of whitecapping, the ambient noise reduction beneath the slick results from a dramatic decreases of microbreaking events within it. The acoustic signatures of these microbreaking events are distinguished by individual oscillating bubbles.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1991
- Accession Number
- ADA236089
Entities
People
- J. J. Rohr
- R. M. Detsch