Towed array plane and non-plane wave beamforming under ship's
maneuvering
P. Felisberto, S.M. Jesus pfelis@ualg.pt
and sjesus@ualg.pt
Universidade do Algarve
Campus de Gambelas
PT-8000 Faro, Portugal
Comments: download pdf file .
Ref.: in 3rd European Conf. Underwater
Acoustics (ISBN 960-85709-2-1), p.483-488, Heraklion, Greece, 1996.
Abstract: Towed hydrophone arrays are commonly used for
determining
the spatial characteristics of the underwater acoustic field. The
assumption
that the hydrophones lie in a straight and horizontal line is often
made
when beamforming the hydrophone outputs. However, due to tow vessel
motion,
ocean swells and currents the array adopts a nonlinear shape and the
beamformer
output is degraded. In order to estimate the positions of the
hydrophones,
an array was instrumented with a set of positioning sensors: compasses,
tiltmeters,
accelerometers and pressure gauges. This paper presents the array
deformations
recorded at sea when the tow vessel is turning and along straight line
tracks.
The influence of the observed deformations on the performance of the
conventional
beamformer output is discussed and illustrated with simulated and real
acoustic
data. In particular it is shown that the sensor positioning information
allows
for introducing the appropriate corrections on the plane-wave
beamformer
and obtain an unambigous localization of sound sources in the
360-degree
plane under heavy ship's maneuvering. Non-plane wave beamforming using
a
normal mode model shows that towed array deformations are also
extremely
important for source localization. In this case, the influence of towed
array's
deformation in the vertical plane is studied in particular, since this
deformation
is significant even when the array is being towed along straight line
tracks.
ACKNOWLEDGMENT: this work was partially supported by the EU
project
MAS2-CT920022.