FRIDAY MORNING, 20 MAY 2005 REGENCY E, 8:30 A.M. TO 12:00 ...

esults, the feasibility of performing real-time adaptive environmental assesment
using AREA under realistic ocean conditions will be discussed.
Work supported by ONR.
2:30
5pUW5. Optimizing multistatic sonobuoy placement. Donald R.
DelBalzo, Erik R. Rike, and David N. McNeal Neptune Sci. Div. of
Planning Systems, Inc., 40201 Hwy 190 E, Slidell, LA 70461,
delbalzo@neptunesci.com
Sonobuoy patterns for monostatic sensors were developed during the
Cold War for deep, uniform underwater environments, where a simple
median detection range defined a fixed inter-buoy spacing usually along
staggered lines. Oceanographic and acoustic conditions in littoral environments
are so complex and dynamic that spatial and temporal variability
of low-frequency signal and noise fields destroys the basic homogeneous
assumption associated with standard tactical search concepts. Genetic Algorithms
GAs have been applied to this problem to produce nearoptimal,
non-standard search tracks for monostatic mobile sensors that
maximize probability of detection in such inhomogeneous environments.
The present work describes a new capability, SCOUT Sensor Coordination
for Optimal Utilization and Tactics, to simulate multistatic
distributed-sensor geometries and to optimize the locations of multistatic
active sonobuoys in a complex, littoral environment. This presentation
reviews the GA approach, discusses the new chromosome structure, and
introduces a new target-centric geometry. The results show that a standard
patterns are not optimal even for a homogeneous environment, b
small distributed sensor clusters are preferred, and c standard patterns
are grossly ineffective in inhomogeneous environments where 20% improvements
in detection are achieved with SCOUT. Work supported by
NAVAIR.
2:45
5pUW6. Acoustic particle velocity and intensity calculations from
tri-axial pressure gradient measurements. Melanie E. Austin and Alex
O. MacGillivray JASCO Res. Ltd., 2101-4464 Markham St., Victoria,
BC, Canada V8Z 7X8, melanie@jasco.com
In July 2004 Fisheries and Oceans Canada supported a study to investigate
effects of seismic airgun signals on hearing organs of freshwater fish
in the Mackenzie River at Inuvik, NWT Canada. The study required particle
velocity measurements for correlation with observed biological effects.
JASCO Research built a pressure gradient measurement apparatus
consisting of four hydrophones mounted at the vertices of a triangularpyramid
frame. The system was used to measure differential pressure from
the airgun events simultaneously in three perpendicular axial directions.
An attached depth-compass sensor monitored the depth and orientation of
the system. Hydrophone separations were chosen to be small relative to
the acoustic wavelength so that measured differential pressures correctly
approximated the pressure gradients along each axis. Particle accelerations
were computed directly from pressure gradients following Euler’s linearized
momentum equation, and particle velocities were computed by integrating
particle accelerations. Acoustic intensity was computed from the
product of acoustic pressure and particle velocity. The hydrophone precision
imposed a limit on accuracy of particle velocity measurements at low
frequencies. Likewise the fixed hydrophone spacings defined an upper
frequency limit for applicability of this method.
3:00
5pUW7. Macroscopic sonic crystals in a wave guide. Dalcio K. Dacol,
Gregory J. Orris, and David C. Calvo Acoust. Div. Naval Res. Lab.,
Washington, DC 20375-5350
Periodical arrays of long, parallel cylinders have been shown in the
published literature to exhibit acoustical properties which are analogous to
the electronic properties of certain crystalline solids. Thus there are frequency
bands for which no acoustic propagation through the array is allowed,
with those band gaps being directionally dependent. The properties
of such arrays in wave guides are examined in this work. Particular emphasis
is put in investigating the properties of those arrays in wave guides
that are idealized models of shallow water oceanic wave guides. The effects
of those arrays on the propagation of normal modes is investigated in
detail. The possibility of using such arrays in the construction of large
scale underwater devices such as filters and lenses is also discussed. Work
supported by ONR.
2625 J. Acoust. Soc. Am., Vol. 117, No. 4, Pt. 2, April 2005 149th Meeting: Acoustical Society of America 2625
5p FRI. PM