Shallow-water sound transmission measurements taken on the New Jersey continental shelf

Abstract

Calibrated acoustic measurements were made under calm sea state conditions on the New Jersey shelf near the AMCOR 6010 borehole, a surveyed area with known geophysical properties. The experiment was conducted in 73 m water with supporting measurements of salinity, temperature, and sound speed. These measurements were obtained with a vertical array of 24 equally spaced hydrophones at 2.5 m; one of which was on the bottom. A source towed at either 1/2- or 3/4- water depth transmitted one of two sets of four tones spaced between 50 and 600 Hz for each run to ranges of 4 and 26 km. The data were processed with both a Hankel transform and a high resolution Doppler technique to yield horizontal wave-number spectrum at several depths. Results were obtained along both a constant and gradually varying depth radial. Similar modal interference patterns were observed at the lower frequencies. The constant depth radial results were compared to calculations performed with several shallow water acoustic models using geoacoustic profiles derived from geophysical parameters and shear wave inversion methods. Calculated and measured sound transmission results were found to agree when scattering within the sediment and between sedimentary layers was included. Range dependent radials were found to have effects consistent with sub-sediment acoustic features.