Three dimensional parabolic equation modeling of acoustic intensity fluctuations due to internal wave phenomena.

Abstract

During the Shallow Water 2006 (SW06) experiment, a J-15 acoustic source deployed from the Research Vessel Sharp transmitted broadband (50–450 Hz) chirp signals 15 km away from a vertical line array. The array was intentionally positioned near the shelf-break front and in an area where internal waves are known to occur. During the same time an internal wave, labeled event 44, passed through the sound field such that the internal wave front was near parallel to the acoustic transmission path. Measured data show substantial intensity fluctuations that vary over time and space due to complex multimode and multipath (both two and three dimensional) interference patterns. This presentation compares three dimensional modeling results using the experimental geometry, acoustic signal parameters, and a simulated oceanographic environment based on environmental moorings and ship-born sensors to mimic the measured internal wave event. A modified version of the three dimensional Monterey–Miami parabolic equation (MMPE) code, which incorporates a user-defined sound speed field, is used. Measured and modeled intensity fluctuations are compared during dominating horizontal regimes such as refraction, focusing, and defocusing. Modal-dependent time-arrival analysis during the different horizontal regimes is examined. A sensitivity study of different sea-bottom properties is explored. [Work sponsored by the Office of Naval Research.]