Dynamics of acoustic propagation through a soliton wave packet: observations from the INTIMATE'96 experiment.

O.C. Rodriguez orodrig@ualg.pt S.M. Jesus sjesus@ualg.pt
UCEH - Universidade do Algarve, Faro, Portugal
M.B. Porter porter@mpl.ucsd.edu
Dep. of Applied Mathematics, New Jersey Institute of Technology, NJ, USA
Y. Stephan stephan@shom.fr  X. Demoulin demoulin@shom.fr
Centre Militaire Oceanographique - SHOM, Brest, France
E. Coelho oceanografia@hidrografico.pt
Instituto Hidrografico, Lisboa, Portugal

Comments: download pdf file .
Ref.: in Experimental Acoustics Inversion Methods for Exploration of the Shallow Water Environment, Caiti, Hermand, Jesus and Porter (eds.), KLUWER, (ISBN 0-7923-6305-1) pp. 1-18, March 1999.

Abstract : Experimental observations of acoustic propagation through a Soliton Wave Packet (SWP) show an abnormally large attenuation over some frequencies, that was found to be significantly time-dependent and anisotropic. Nevertheless, by considering the problem of signal attenuation, the approach used in most of the studies can be considered as ``static'' since no additional effects were taken into account as a SWP evolves in range and time. Hydrographic and acoustic data from the INTIMATE'96 experiment clearly exhibit traces of the presence of soliton packets, but in contrast with known observations of attenuation,  its frequency response also reveals a sudden increase of signal amplitude, which may be due to a focusing effect. This signal increase coincides with a significant peak found in current and temperature records. However, the correlation of both acoustic and hydrographic features is difficult to support due to the different time scales between the rate of hydrographic data sampling and the rate of signal transmissions.  To study the possibility that a SWP could be responsible for the observed signal increase, the INTIMATE'96 hydrographic data was used to generate physically consistent distributions of ``soliton-like'' fields of temperature and sound velocity, which were used as input for a range-dependent normal-mode model; it was found that for a particular soliton field, the set of ``dynamic'' (i.e., range-dependent and time-dependent) acoustic simulations reveals an acoustic signature similar to that observed in the data. These results contribute to a better understanding of underwater propagation in shallow-water coastal environments and therefore provide a potential basis for range-dependent temperature and sound-speed inversions.

ACKNOWLEDGMENT: this work was partially supported by project INTIMATE from FCT.