S.M. Jesus and C. Soares sjesus@ualg.pt and csoares@ualg.pt
SiPLAB-FCT, Universidade do Algarve
Faro, Portugal
Comments: download pdf file .
Ref.: Proc. Int. Conf. on Theoretical and
Computational
Acoustics, p.211-220, Honolulu, USA,2003.
Abstract : One of the most stringent impairments in the
development
and widespread of ocean tomography are the enormous equipment
requirement
to obtain a useful spatial coverage and resolution. In particular the
need
to have a perfect control both on the source and receiver sides over
large
areas and during long periods of time is seen as a major obstacle.
Passive
tomography has been proposed under various forms to take advantage of
natural
sound sources to simplify the tomographic process while producing
meaningful
inversion results for environmental parameters. Most of the results
found
in the literature make use of ambient noise, and sea surface wind
generated
noise, to invert bottom parameters in shallow water regions. Recently,
another
approach used unknown deterministic signals and ship noise as
illuminating
sources to invert for water column parameters [Jesus et al., ECUA,
Gdansk
(Poland), June 2002, and Conference on Acoustic Variability, Lerici
(Italy),
September 2002]. In that work, a focalization process was used to
simultaneous
invert known geometrical and unknown environmental parameters. In
particular
it was shown that geometrical parameters such as source range and
depth,
and receiving array geometry, could be used as focus and out of focus
indicators.
During the focus periods, estimated water column parameters favorably
compared
to independently measured values. This was particularly true for the
unknown
deterministic signals, while for the ship noise the low received power
and
the difficulty to determine enough stable frequencies destroyed the
result
during several portions of the run.
In the present work, the received signal is used to deconvolve the
source
power, and thus obtain a full-spectrum weighting function for optimum
frequency
combination during the focalization process. Results obtained in the
same
ship noise data set have shown a significant improvement where a stable
localization
and inversion could be seen throughout the run.
ACKNOWLEDGMENT: this work was partially supported by LOCAPASS and ATOMS projects (FCT).