Abstract:

One of the primary objectives of the 1996 Shelfbreak Primer Experiment, located in the Mid-Atlantic Bight south of Nanucket Shoals, was to investigate the effects of the shelfbreak front on the propagation of acoustic signals. The acoustic component of the experiment consisted of two 16-element vertical hydrophone arrays (VLAs) along the northern edge of the region (inshore of the shelfbreak), and three sources (one 224 Hz and two 400 Hz) along the southern edge (seaward of the shelfbreak). Source-to-receiver path lengths ranged from 40--60 km. The high-quality oceanographic data collected, including SeaSoar sections and numerous thermistor records, are critical to modeling and interpreting the acoustics. From a modal perspective, there is strong coupling from not only the front, but also from the sloping bathymetry and from scattering by solitons. The receptions at the northeast VLA coinciding with a 6-day period of SeaSoar deployment are considered here. Fluctuations in the signal arrivals are consistent with the picture provided by the measured oceanography. Results from coupled-mode propagation modeling are also discussed. [Work supported by ONR.]