Blind Ocean Acoustic Tomography with Source Spectrum Estimation

S.M. Jesus and C. Soares and
SiPLAB-FCT, Universidade do Algarve
Faro, Portugal

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Ref.: Proc. Int. Conf. on Theoretical and Computational Acoustics, p.211-220, Honolulu, USA,2003.

Abstract : One of the most stringent impairments in the development and widespread of ocean tomography are the enormous equipment requirement to obtain a useful spatial coverage and resolution. In particular the need to have a perfect control both on the source and receiver sides over large areas and during long periods of time is seen as a major obstacle. Passive tomography has been proposed under various forms to take advantage of natural sound sources to simplify the tomographic process while producing meaningful inversion results for environmental parameters. Most of the results found in the literature make use of ambient noise, and sea surface wind generated noise, to invert bottom parameters in shallow water regions. Recently, another approach used unknown deterministic signals and ship noise as illuminating sources to invert for water column parameters [Jesus et al., ECUA, Gdansk (Poland), June 2002, and Conference on Acoustic Variability, Lerici (Italy), September 2002]. In that work, a focalization process was used to simultaneous invert known geometrical and unknown environmental parameters. In particular it was shown that geometrical parameters such as source range and depth, and receiving array geometry, could be used as focus and out of focus indicators. During the focus periods, estimated water column parameters favorably compared to independently measured values. This was particularly true for the unknown deterministic signals, while for the ship noise the low received power and the difficulty to determine enough stable frequencies destroyed the result during several portions of the run.

In the present work, the received signal is used to deconvolve the source power, and thus obtain a full-spectrum weighting function for optimum frequency combination during the focalization process. Results obtained in the same ship noise data set have shown a significant improvement where a stable localization and inversion could be seen throughout the run.

ACKNOWLEDGMENT: this work was partially supported by LOCAPASS and ATOMS projects (FCT).