Modélisation de la propagation acoustique par la théorie des modes : application à la tomographie océanique

Abstract
Acoustic tomography monitors mesoscale fluctuations of ocean characteristics using prediction of rays travel times between sources and receivers. Unfortunately this method falls down near the channel axis because crowded rays cannot then be time resolved. We here first describe an implementation of a range-independant normal modes model to simulate acoustic propagation. Using the fact that crowded part of the time response can be described using only a small number of modes we then expose some results on modal filtering in the frequency domain applied to the analysis of this powerful ray-unresolved part of the response. We show that contribution of each mode to response can be pointed out using an approximate sound speed profile. We also compare results on the modal filtering with classical beamforming, showing the complementarity of these two array processings.