Abstract
A calm sea state, low‐frequency sound transmission experiment was conducted in shallow water on the New Jersey continental shelf in the vicinity of the AMCOR 6010 borehole [L. Maiocco, W. Carey, E. Parssinen, and J. Doutt, J. Acoust. Soc. Am. Suppl. 1 86, S8 (1989)], where bottom topology and composition have been previously characterized. A source towed at 12‐ and 34‐channel depth was used to transmit cw (two families of four tones, frequency range 50–600 Hz) and pulsed (Gaussian, LFM) signals to a 24‐element vertical hydrophone array deployed in 73 m of water. Measurements were obtained along a constant depth radial at tow speeds of 5 kn, 2 kn, and adrift, and at 5 kn along a varying‐depth radial course. An internally consistent description of normal mode propagation was sought at 50 and 75 Hz from a combination of (a) horizontal wave‐number spectra obtained from the Hankel transform inversion [G. Frisk and J. Lynch, J. Acoust. Soc. Am. 76, 205–216 (1984)] of the complex pressure field at 24 separate depths, (b) the vertical wave‐number spectrum determined as a function of range from the spatial transform of complex pressure over the real aperture formed by the vertical array, and (c) the normal mode shapes and amplitudes constructed from the depth dependence of pole peak amplitude in the wave‐number domain and of pulsed transmission amplitude in the time domain. A unique feature of the analysis is the successful generation of well‐resolved wavenumber spectra from the sound field projected by a moving source in the presence of multiple receivers. These spectra have been filtered and inverted to yield noise‐free estimates of signal level and transmission loss.
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