Measurements of sound propagation in a littoral environment using a vertical synthetic array

Abstract

Shallow-water propagation experiments were carried out in St. Andrews Bay, Florida. These investigations used a vertical one-dimensional synthetic array measurement system where two hydrophones incrementally mapped the acoustic pressure from 2m below through 2m above the sand-water interface. A broadband (1 to 12kHz) chirp was used to insonify the water channel. The source to receiver distance was varied and included measurements at 20, 30, 50, 70, and 90m. These measurements quantified the acoustic pressure above and below a sandy bottom and the results are presented along with frequency analysis, temporal impulse analysis, and wave number analysis. To obtain a better understanding of the results, the measurements are compared to two numerical models. The first model is a temporal ray path prediction of sound propagation in the water channel. The second model, range-dependent acoustic model (RAM), based on a parabolic equation, predicts the sound propagating in a water channel with a sandy bottom. The experimental results agreed well with both numerical predictions in the water column. However, the measured acoustic energy in the sandy bottom was different from the prediction by RAM, which assumed a smooth air-water and water-bottom interface and a point source.