title: Surface gravity waves and their acoustic signatures, 1-30 Hz, on the mid-Pacific sea floor.
abstract: In 1999, Duennebier et al. deployed a hydrophone and geophone below the conjugate depth in the abyssal Pacific, midway between Hawaii and California. Real time data were transmitted for 3 yr over an abandoned ATT cable. These data have been analyzed in the frequency band 1 to 30 Hz. Between 1 and 6 Hz, the bottom data are interpreted as acoustic radiation from surface gravity waves, an extension to higher frequencies of a non-linear mechanism proposed by Longuet-Higgins in 1950 to explain microseisms. The inferred surface wave spectrum for wave lengths between 6 m and 17 cm is saturated (wind-independent) and roughly consistent with the traditional Phillips κ(-4) wave number spectrum. Shorter ocean waves have a strong wind dependence and a less steep wave number dependence. Similar features are found in the bottom record between 6 and 30 Hz. But this leads to an enigma: The derived surface spectrum inferred from the Longuet-Higgins mechanism with conventional assumptions for the dispersion relation is associated with mean square slopes that greatly exceed those derived from glitter. Regardless of the generation mechanism, the measured bottom intensities between 10 and 30 Hz are well below minimum noise standards reported in the literature.
authors.affiliation: 13765 Durango Drive, Del Mar, California 92014.
authors.forename: W E
authors.initials: WE
authors.lastname: Farrell
authors.forename: Walter
authors.initials: W
authors.lastname: Munk
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D004867:Equipment Design; D019015:Geologic Sediments; D006112:Gravitation; D009038:Motion; D017711:Nonlinear Dynamics; D009791:Oceanography / Q000295:instrumentation / Q000379:methods*; D010140:Pacific Ocean; D011312:Pressure; D012623:Seawater; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013499:Surface Properties; D013997:Time Factors; D014159:Transducers; D014872:Water Movements; D014919:Wind