Influence of environmental parameters on mid-to-high frequency acoustic signal propagation in coastal regiona)

Abstract

Broadband mid-to-high frequency (0.6–18 kHz) acoustic wave propagation in shallow coastal waters (20 m) is influenced by a variety of oceanographic conditions. Physical parameters such as temperature and salinity as well as hydrodynamic parameters such as surface waves, tide, and current can influence amplitude and travel time of acoustic transmissions. While some of these physical parameters can be extracted from the acoustic wave propagation, understanding the forward model is vital to a fundamental understanding of the inverted parameters in shallow coastal waters. A unique set of simultaneous ocean and acoustic observations that reveal interesting temporal behavior of the acoustic signal and its correlation with environmental variability are presented. Some forward modeling using full-wave and ray-based methods is employed to investigate the time-frequency-angle characteristics of the measured acoustic field. Results of acoustic inversion for current, salinity, and sea-surface roughness, as well as the limitations of such inversions when using broadband signals in very shallow water regions, are also discussed. [Work supported by ONR and Sea Grant.] a)For Underwater Acoustics Best Student Paper Award.