Nonlinear Soliton Interaction with Acoustic Signals: Focusing Effects

O.C. Rodrí S.M. Jesus
UCEH - Universidade do Algarve, Campus de Gambelas,
PT-8000 Faro, Portugal.
Y. X.
CMO - Service Hidrographique et Oceanographique de la Marine,
F-29275 Brest Cedex, France.
M.B. Porter
Science Applications Int. Corp., SAIC
La Jolla, CA, USA.
E. Coelho
Instituto Hidrografico,  Rua das Trinas 49,
PT-1296 Lisboa Codex, Portugal.

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Ref.: Journal of Computational Acoustics, vol. 8, no.2, pp.347-363, 2000.

Abstract: the nonlinear interaction of solitary wave packets with acoustic signals has been intensively studied in recent years. A key goal is to explain the frequency response of shallow-water propagation which has been found to be strongly time-dependent, anisotropic, and sometimes exhibited unexpected attenuation vs. frequency. Much of the existing literature considers the problem of attenuation without considering additional effects arising from groups of solitons evolving both in range and time. Hydrographic and acoustic data from the INTIMATE'96 experiment clearly exhibit the effects of soliton packets. However, in contrast with known observations of attenuation, the frequency response shows a sort of enhancement leading to an increase of signal amplitude. This focussing is correlated with peaks in the current, temperature, and surface tide. To study this, hydrographic data was used to generate physically consistent distributions of "soliton-like" fields of temperature and sound velocity. These fields were then used as input for a range-dependent normal-mode model. The results strongly support the hypothesis that the soliton field causes the observed signal enhancement.

ACKNOWLEDGMENT: this work was partially supported by the EU project MAS2-CT920022.