O.C. Rodríguez and S.M. Jesus
orodrig@ualg.pt and sjesus@ualg.pt
SiPLAB-FCT, Universidade do Algarve
Faro, Portugal
Comments: download pdf file .
Ref.: Proc. ECUA 2002, (ISBN 83-907591-8-7),
p.515-520, Gdansk (Poland), June 2002.
Abstract : Ocean Acoustic Tomography is an important method
developed in the context of Underwater Acoustics, oriented to the
monitoring of ocean environments. The method intends to estimate the
variations of the physical properties of an ocean waveguide as, for
instance, temperature and sound speed, by taking advantage of the
sensitivity of acoustic signals to those variations. A particular way
to accomplish that estimation (known as "travel time inversion")
consists in introducing a system of linear equations, relating an apriori known vector of delays in
travel time, to an unknown vector of perturbations in sound speed,
through the so-called "observation matrix". Inverting the system allows
to estimate the perturbations in sound speed. Travel time inversion is
reviewed in this paper by introducing a plane-wave representation of
the sound speed field, expanded on a set of hydrostatic orthogonal
modes, which can be accurately estimated from temperature. The
representation allows to develope a range-dependent regularization of
the system of equations, which can be extended in a natural way in
order to handle multiple hydrophones. The reliability of the method is
tested through its corresponding application to acoustic data acquired
during the INTIMATE'96 experiment, whose environmental scenario was
strongly affected by the propagation of internal tides. Inversion
results, which took into account the effects of both barotropic and
baroclinic tides on signal propagation, reveal an accurate agreement
between expected and actual data, when compared with temperature and
sound speed measurements acquired simultaneously near the acoustic
source and the system of hydrophones. The results also indicate the
method's ability in achieving a high degree of range dependent
tomographic resolution when applied to shallow water short-range
scenarios of acoustic propagation.
ACKNOWLEDGMENT: this work was partially supported by projects INTIMATE and ATOMS from FCT (Portugal).