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In July and August of 1995, a large-scale shallow water experiment dubbed
SWARM was conducted off the coast of New Jersey near the continental shelfbreak
in the Mid-Atlantic Bight
region. It's purpose was to further our understanding of acoustic scattering by coastal
internal waves, including solitary internal waves (solitons).
Deep ocean acoustic scattering due to internal waves is relatively well-known,
but in shallow water regions, especially along the continental shelf,
acoustic scattering is not as well understood. As well as studying the acoustics
in this region, SWARM also investigated the
interesting oceanography of the solitons themselves.
Internal solitons tend to be generated in
groups or packets at the continental shelfbreak when the tide shifts from
ebb to flood. Each packet can contain six to twelve solitons that are large enough
to show effects at the surface. Solitons can be seen at the surface by
satellite imagery and
on-board with the ship's radar.
These internal wave packets move quickly and are closely spaced
together. A thermistor array shows
solitons passing by in 1 hour and for 2 days.
A CTD station yoyo also shows
temperature,
salinity, and
soundspeed of a packet of solitons passing by.
The solitons create significant scattering of the normal modes that
comprise an acoustic signal. This scattering appears as both amplitude and phase
(travel time). We are currently studying these effects intensively and will have
more to report on them soon!
Participants in this experiment included WHOI,
NPS,
NRL,
APL/JHU, and
Univ. of Delware.
Publications
"An overview of the 1995 SWARM shallow water internal acoustic scattering experiment", Apel, et el. IEEE J.Ocean. Eng., Vol 22, No. 3, July 1997.
"A Surface-Trapped Intrusion of Slope Water onto the Continental Shelf in the Middle Atlantic Bight", Gawarkiewicz, et. el., Geophys. Res. Let. 23(25), 3763-3766, 1996.
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