S.M. Jesus sjesus@ualg.pt
UCEH - Universidade do Algarve
PT-8000, Faro, Portugal
Comments: download pdf file .
Ref.: Full field Inversion Methods in
Ocean and Seismo-Acoustics, O. Diachock, A. Caiti, P. Gerstoft and
H. Schmidt (eds.), Kluwer (ISBN 0-7923-3459-0), Dordrecht, pp.
103-108, 1994.
Abstract: Inversion of acoustic data for estimating bottom acoustic
parameters
has been the subject of a considerable number of studies.
Usually,
signals are received on vertical arrays of sensors and transmitted from
sound
sources being towed away from the array location in order to form a
syntethic
aperture array. That configuration is greatly dependent on the
knowledge
of the source-receiver distance which is, in practice, relatively
difficult
to measure with the required precision. Also, since the vertical array
is
generally moored, or slowly drifting, the area that can be surveyed
with
such a method is limited to a tenth of a mile in shallow water.
Changing
area requires the recover and redeployement of the whole system. This
paper
explores the possibility of using an horizontal array and a sound
source
simultaneously towed by a single ship where the source-receiver
distance
is constant. It has been shown that sensitivity to sound speed
variations
is higher on the first bottom layers and it increases with array
length.
Density and attenuation (both compressional and shear) have in general
small
influence on the acoustic field structure and are therefore difficult
to
estimate. Increasing the signal frequency bandwidth by incoherent
module
averaging has no significant influence on sensitivity. Mismatch cases,
mainly
those related to array/source relative position, showed that deviations
of
more than lambda/2 in range and lambda/5 in depth may give erroneous
extremum
location and therefore biased final estimates.
ACKNOWLEDGMENT: this work was partially supported by the EU project MAS2-CT920022.