title: Observationally constrained modeling of sound in curved ocean internal waves: examination of deep ducting and surface ducting at short range.
abstract: A study of 400 Hz sound focusing and ducting effects in a packet of curved nonlinear internal waves in shallow water is presented. Sound propagation roughly along the crests of the waves is simulated with a three-dimensional parabolic equation computational code, and the results are compared to measured propagation along fixed 3 and 6 km source/receiver paths. The measurements were made on the shelf of the South China Sea northeast of Tung-Sha Island. Construction of the time-varying three-dimensional sound-speed fields used in the modeling simulations was guided by environmental data collected concurrently with the acoustic data. Computed three-dimensional propagation results compare well with field observations. The simulations allow identification of time-dependent sound forward scattering and ducting processes within the curved internal gravity waves. Strong acoustic intensity enhancement was observed during passage of high-amplitude nonlinear waves over the source/receiver paths, and is replicated in the model. The waves were typical of the region (35 m vertical displacement). Two types of ducting are found in the model, which occur asynchronously. One type is three-dimensional modal trapping in deep ducts within the wave crests (shallow thermocline zones). The second type is surface ducting within the wave troughs (deep thermocline zones).
authors: Department of Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA. tduda@whoi.edu
authors: Timothy F
authors: TF
authors: Duda
authors: Ying-Tsong
authors: YT
authors: Lin
authors: D Benjamin
authors: DB
authors: Reeder
mesh_terms: D000162:Acoustics; D003198:Computer Simulation; D008962:Models, Theoretical; D009038:Motion; D017711:Nonlinear Dynamics; D009716:Numerical Analysis, Computer-Assisted; D009792:Oceans and Seas; D012542:Scattering, Radiation; D013016:Sound; D013018:Sound Spectrography; D013499:Surface Properties; D013997:Time Factors; D014867:Water; D014872:Water Movements
chemical_list: D014867:Water