Measurements of sea surface effects on the low-frequency acoustic propagation in shallow water

Abstract

In shallow water, spatial and temporal variability of the water column often restricts accurate estimations of bottom properties from low-frequency acoustic data, especially under highly active oceanographic conditions during the summer. These effects are reduced under winter conditions having a more uniform sound-speed profile. However, during the RAGS03 winter experiment, significant low-frequency (200–500 Hz) acoustic signal degradations have been observed on the New Jersey Shelf, especially in the presence of frequently occurring winter storms. Both in-plane and out-of-plane propagation effects were observed on three moored VLAs and one bottom-moored HLA. These effects were further analyzed using 3-D PE simulations with inputs from a 3-D time-evolving surface gravity wave model. It is shown that higher-order acoustic modes are highly scattered at high sea states and out-of-plane propagation effects become important when surface-wave fronts are parallel to the acoustic propagation track. In addition, 3-D propagation effects on the source localization and geoacoustic inversions are investigated using the VLA data with/without the presence of winter storms. [Work supported by ONR.]