Comments: download pdf .
Ref.: Proc. 2nd International Conference on Exhibition on Underwater Acoustics (UA2014),
Rhodes (Greece), June 2014.
Abstract:
Acoustic passive methods to infer properties of the oceanic medium have been subject
of progressive emphasis in order to obtain low cost, environmental friendly, long time characterization of
the ocean. To this end a first step consists in the estimation of the frequency response of the medium or
its time domain counterpart, the impulse response. In this work we consider distant ship noise as an
opportunity source characterized by a few low frequency discrete tones. Therefore, the frequency
response of a shallow water acoustic channel is estimated at these discrete frequencies, between
two vertical line arrays (VLA's). The influence on the estimates of several factors of uncertainty such
as range, depth and tilt variations in the VLA's is investigated. For validation purposes, a phase
conjugation method is considered. In a preliminary approach towards passive ocean acoustic tomography
implementation the estimates obtained by the proposed method are applied in a matched field framework
to track sound speed profile variations. Simulations are conducted based on experimental set up and
environmental parameters gathered during the MREA07 sea trial that took place in the Tyrrhenian Sea,
near Elba Island in May 2007. The results show that, although shadowed, the obtained frequency response
estimates allows to obtain a permanent focus and enables the tracking of sound speed profile variations
in the water column.
Acknowledgements:
This work was funded by National Funds through FCT - Foundation for
Science and Technology under Strategic Project - LA 9 -
2013-2014 (Pest-OE/EEI/LA0009/2013)