In last two decades, many researchers have been involved in
acoustic tomography applications. Recently, few algorithms have
been dedicated to the passive acoustic tomography applications in
a single input single output channel. Unfortunately, most of these
algorithms can not be applied  in a real situation when we have a
Multi-Input Multi-Output channel. In this paper, we propose at
first a realistic model of an underwater acoustic channel, then a
general structure to separate acoustic signals crossing  an
underwater channel is proposed. Concerning ICA algorithms, many
algorithms have been implemented and tested but only two
algorithms give us good results. The latter algorithms minimize
two different second order statistic criteria in the frequency
domain. Finally, some simulations have been presented and
discussed.

KEY WORD: Underwater acoustic applications, passive acoustic
Tomography, second order statistics in frequency domain, multipath
channel, sparseness or non-stationary signals.