C. Soares, S.M. Jesus csoares@ualg.pt , sjesus@ualg.pt
SiPLAB-FCT, Universidade do Algarve
8005-139 Faro, Portugal
E. Coelho coelho@saclantc.nato.int
NATO Undersea Research Centre
Via San Bartolomeu, 400
19138 La Spezia, Italia
Comments: download pdf file
Ref.: in Acoustics
Inversion Methods and Experiments for Assessment of the Shallow Water
Environment, (Springer) Caiti, Chapman, Hermand and Jesus
(eds.), Ischia, Italy, June 2004.
Abstract : Ocean acoustic tomography was initially proposed for
deep water regions where the ray approximation was valid and sound
speed could be analytically linked to acoustic ray travel-time.
Travel-time based tomography turned out to be highly dependent on the
ability to separate closely spaced arrivals and on the precise
knowledge on the source-receiver relative position at all times.
Instead, matched-field tomography (MFT) is based on some sort of
correlation of the full pressure field to the signal received at an
array of sensors and only requires relative travel times to which an
approximate knowledge of the source-receiver position is sufficient. In
most operational shallow water scenarios, only MFT is applicable due to
the close arrivals from bottom and surface reflections and to a
perpetual source/sensor motion. In October 2000, SiPLAB and the
Instituto Hidrografico (IH - PN) conducted the INTIFANTE'00 sea trial
in an area off the Peninsula of Troia, approximately 50 km south from
Lisbon, in Portugal. The experiment itself and results obtained in part
of the data set have been reported during these last two years in
various occasions. This paper focuses on the data acquired during Event
2, where acoustic propagation path was approximately range independent
and the source ship was held on station at constant range of 5.5 km
from the vertical line array (VLA). Although these conditions look like
ideal for MFT, retrieval of water column and bottom parameters over an
14 hours long recording reveal itself extremely difficult. This paper
analyses in detail the characteristics of that data set and in
particular proposes a selection of the data snapshot, prior to
inversion, according to the variable source range (due to the source
ship drift), according to tidal point where the data was acquired and
to the phase correlation at each frequency. It is shown that this data
selection procedure provides a better understanding of the influence of
the environment and thus final inversion results that are highly
consistent with independent measurements.
ACKNOWLEDGMENT: this work was partially supported by ATOMS, FCT - Portugal.