Acoustic Radiation Due to Wave-Breaking

While wave-breaking is continually occurring at the sea surface, it's transient and sporadic nature makes it difficult to measure. Experimental results are presented which show how acoustic methods can be used as a remote sensor of this fundamental process. Sea surface-generated acoustic radiation (40 to 4000 Hz) is directly related to a quantitative measure of the boundary dynamics; i.e., the Toba variable. The frequency spectrum of the radiation remains remarkably unchanged over a wide range of environmental conditions but the correlation between the sound pressure level and the Toba variable undergoes an abrupt change when spilling breakers start to occur. Results support the use of acoustics to remotely measure the rate of energy being dissipated by wave- breaking and the characteristic length of the wavebreak. Theoretical studies have related the field measurements to analytical and laboratory results cited in the literature indicating that remote monitoring of the rate of occurrence and size distribution of infant (freshly entrained) bubbles may be possible if splashes on the surface do not radiate significant sound. Presented at the Meeting of the Acoustical Society of America (123rd) held in Salt Lake City, UT on 11-15 May 1992. Sponsored by Office of Naval Research and Naval Undersea Warfare Center.