Very high frequency noise sources in the littoral zone

Recent interest in very high frequency (VHF, here defined as > 300kHz) underwater acoustic communications has motived a study of VHF noise sources in the littoral zone. The Littoral is a special environment for underwater ambient noise. Nearshore bathymetry induces wave breaking and wave-sediment interactions, both of which generate underwater noise, and a variety of marine organisms can radiate noise across a broad acoustic spectrum. Two potential VHF noise sources, breaking waves and snapping shrimp, are considered here. Measurements of the noise radiated by breaking laboratory waves are presented, which show that wave noise can extend to at least 400 kHz. Model calculations of the pulse of sound radiated by a collapsing cavitation bubble generated by a snapping shrimp jet show the potential for significant spectral components up to 1 MHz. The implications for these noise sources on the temporal and spatial distribution of the VHF noise field are discussed.