O.C. Rodriguez orodrig@ualg.pt
S.M. Jesus sjesus@ualg.pt
UCEH - Universidade do Algarve, Faro, Portugal
M.B. Porter porter@mpl.ucsd.edu
Dep. of Applied Mathematics, New Jersey Institute of Technology, NJ, USA
Y. Stephan stephan@shom.fr X. Demoulin demoulin@shom.fr
Centre Militaire Oceanographique - SHOM, Brest, France
E. Coelho oceanografia@hidrografico.pt
Instituto Hidrografico, Lisboa, Portugal
Comments: download pdf
file .
Ref.: in Experimental Acoustics
Inversion Methods for Exploration of the Shallow Water Environment,
Caiti, Hermand, Jesus and Porter (eds.), KLUWER, (ISBN 0-7923-6305-1)
pp. 1-18, March 1999.
Abstract : Experimental observations of acoustic propagation
through
a Soliton Wave Packet (SWP) show an abnormally large attenuation over
some
frequencies, that was found to be significantly time-dependent and
anisotropic.
Nevertheless, by considering the problem of signal attenuation, the
approach
used in most of the studies can be considered as ``static'' since no
additional
effects were taken into account as a SWP evolves in range and time.
Hydrographic
and acoustic data from the INTIMATE'96 experiment clearly exhibit
traces
of the presence of soliton packets, but in contrast with known
observations
of attenuation, its frequency response also reveals a sudden
increase
of signal amplitude, which may be due to a focusing effect. This signal
increase
coincides with a significant peak found in current and temperature
records.
However, the correlation of both acoustic and hydrographic features is
difficult
to support due to the different time scales between the rate of
hydrographic
data sampling and the rate of signal transmissions. To study the
possibility
that a SWP could be responsible for the observed signal increase, the
INTIMATE'96
hydrographic data was used to generate physically consistent
distributions
of ``soliton-like'' fields of temperature and sound velocity, which
were
used as input for a range-dependent normal-mode model; it was found
that
for a particular soliton field, the set of ``dynamic'' (i.e.,
range-dependent
and time-dependent) acoustic simulations reveals an acoustic signature
similar
to that observed in the data. These results contribute to a better
understanding
of underwater propagation in shallow-water coastal environments and
therefore
provide a potential basis for range-dependent temperature and
sound-speed
inversions.
ACKNOWLEDGMENT: this work was partially supported by project
INTIMATE from FCT.