S.M. Jesus and C. Soares sjesus@ualg.pt
csoares@ualg.pt
SiPLAB - FCT, Universidade do Algarve,
Campus de Gambelas,
PT-8005-139 Faro, Portugal.
E. Coelho coelho@saclantc.nato.int
NATO Undersea Research Centre
Viale San Bartolomeo
I-19138 La Spezia, Italy.
P. Picco picco@estosf.santateresa.enea.it
ENEA, Marine Environment Research Centre
P.O. Box 224
I-19100 La Spezia, Italy.
Comments: download pdf
file.
Ref.: Journal of the Acoustical Society of America, 119(3),
pp. 1420-1431, March 2006.
Abstract
Ocean Acoustic Tomography (OAT) was proposed more than 30 years ago but
its routine usage is still not a reality today. Despite the advantages
clearly demonstrated by OAT when compared to other ocean monitoring
techniques, it suffers from several technical-related drawbacks. One is
the requirement for rather expensive equipment to be maintained and
operated at several locations in order to obtain sufficient source -
receiver propagation paths to cover a given ocean volume. In relation
with this issue, classic OAT is known to be very sensitive to the
precise knowledge of source - receiver relative locations at all times,
which imposes severe constraints on the systems to be deployed. This
paper presents the preliminary feasibility tests of a new concept that
uses ships of opportunity as sound sources for OAT. This concept,
sometimes called passive acoustic tomography (PAT), assumes that the
acoustic source illuminating the field is emitting an unknown signal,
possibly of random nature, at an undetermined location. The approach
adopted in this paper views the tomographic problem as a global
inversion that includes determining both the emitted signal and the
environmental parameters, which is a similar problem to that seen in
blind channel identification and was therefore termed Blind Ocean
Acoustic Tomography (BOAT). BOAT was tested on a data set acquired in
October 2000 in a shallow water area off the west coast of Portugal,
including both active and passive (ship noise) data. Successful results
show that BOAT is able to estimate detailed water column temperature
profiles coherent with independent measurements in intervals where the
uncontrolled (ship noise) source signal presents a sufficient bandwidth
and signal to noise ratio, which clearly define the limitations of the
presented method.
Acknowledgement: this work was supported under projects ATOMS from FCT (Portugal) and TOMPACO, under contract from DUNE, CNR (Italy).