title: Deterministic forward scatter from surface gravity waves.
abstract: Deterministic structures in sound reflected by gravity waves, such as focused arrivals and Doppler shifts, have implications for underwater acoustics and sonar, and the performance of underwater acoustic communications systems. A stationary phase analysis of the Helmholtz-Kirchhoff scattering integral yields the trajectory of focused arrivals and their relationship to the curvature of the surface wave field. Deterministic effects along paths up to 70 water depths long are observed in shallow water measurements of surface-scattered sound at the Martha's Vineyard Coastal Observatory. The arrival time and amplitude of surface-scattered pulses are reconciled with model calculations using measurements of surface waves made with an upward-looking sonar mounted mid-way along the propagation path. The root mean square difference between the modeled and observed pulse arrival amplitude and delay, respectively, normalized by the maximum range of amplitudes and delays, is found to be 0.2 or less for the observation periods analyzed. Cross-correlation coefficients for modeled and observed pulse arrival delays varied from 0.83 to 0.16 depending on surface conditions. Cross-correlation coefficients for normalized pulse energy for the same conditions were small and varied from 0.16 to 0.06. In contrast, the modeled and observed pulse arrival delay and amplitude statistics were in good agreement.
authors.affiliation: Scripps Institution of Oceanography, University of California-San Diego, La Jolla, California 92093-0238, USA. gdeane@ucsd.edu
authors.forename: Grant B
authors.initials: GB
authors.lastname: Deane
authors.forename: James C
authors.initials: JC
authors.lastname: Preisig
authors.forename: Chris T
authors.initials: CT
authors.lastname: Tindle
authors.forename: Andone
authors.initials: A
authors.lastname: Lavery
authors.forename: M Dale
authors.initials: MD
authors.lastname: Stokes
mesh_terms: D000162:Acoustics / Q000295:instrumentation; D006112:Gravitation; D008962:Models, Theoretical; D009038:Motion; D009792:Oceans and Seas; D012542:Scattering, Radiation; D012815:Signal Processing, Computer-Assisted; D013016:Sound; D013018:Sound Spectrography; D013499:Surface Properties; D013997:Time Factors; D014159:Transducers; D014867:Water; D014872:Water Movements; D014919:Wind
chemical_list: D014867:Water