Effects of Wind Speed on Shallow-Water Broadband Acoustic Transmission

Applications such as underwater acoustic communication and acoustical oceanography in very shallow water regions, such as estuaries, depend critically on understanding broadband acoustic transmissions. Since underwater acoustic channels in these regions can he drastically affected by wind-wave dynamics, this study aims to investigate how wind-driven surface waves affects the variability of low- to high-frequency broadband (0.1-20 kHz) acoustic channels. Concurrent oceanographic and acoustic data of one week were collected inside Delaware Bay where the water depth is 15 m. Combined modeling of surface hydrodynamics and underwater acoustic propagation was performed using a shallow-water wind-wave spectral method and a 2-D rough-surface parabolic equation model. Modeling results agree with field data analyses, and together they reveal a strong correlation between wind speeds and pressure amplitudes of acoustic waves reflected from the ocean surface, indicating that increased wind-driven surface roughness is the primary factor for the weakening of surface-reflected paths. These findings lead to a new empirical method for prediction of surface-reflected acoustic pressure amplitudes under wind-generated sea surface waves. Our combined model applies well for time-varying surface conditions, but more accurate acoustic modeling needs to consider 3-D, bubble, and Doppler effects.