S.M. Jesussjesus@ualg.pt
O.C. Rodríguezorodrig@ualg.pt
Institute for Systems and Robotics, Universidade do Algarve,
Campus de Gambelas, PT-8005-139 Faro, Portugal.
Comments: download pdf file.
Ref.: Oceans'08, Quebec, Canada, September 2008.
Abstract
This paper proposes an experimental setup composed
of two interconnected vertical arrays: one transmit only
array (TOA) and a receive only array (ROA). It is shown that
using the time reversal principle, where the ocean is used as
a spatial matched filter, signal energy can be simultaneously
focused on each ROA hydrophone and thus obtain the detector
output by simple summation of the received energy over the
array. This setup effectively configures a multistatic system with
several transmitters and several receivers coherently processed
both in time and space. Simulations using a ray trace propagation
model combined with a naive scattering formulation show that
the obtained empirical detection probability is close to the
theoretical optimal bound derived assuming space - time white
Gaussian noise. This system was tested in a sea trial that
took place during September 2007 in the Hopav°agen Bay near
Trondheim, Norway. The actual setup was composed of a 2
sources TOA on a shallow area of 8 m depth near the shore
and a 16 receivers ROA approximately 100 m apart in a 8 to
25 m depth range dependent duct. The transmitted signals were
200 ms duration LFMs with 3 kHz bandwidths in two frequency
bands centered on 5 and 10 kHz. The results obtained in realistic
conditions show that a 1.7 m2 hard plate could be detected
when placed across the barrier. Several results are presented and
compared with the theoretical values. Although the system can be
significantely improved, in particular by using more populated
source and receiving arrays, it is believed that these results can
be reproduced at sea in harbor like conditions.
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