auv-ee;
Many thanks for the path loss calculations. I am in agreement with what you say, the only additional problem in deep water searches is the salinity inversion layers - one at 250 - 350m and if deep enough another near 4,500m.
I suspect, and it would appear to be the BEA's position, that the upper inversion layer was the barrier to the Emeraude recovering something useful above the S/N. Whatever technique has been used to to extract viable data, probably had to make use of some analogue techniques to mix something out of the noise. As I mentioned in a previous post, playing with digital analysis in a playpen of noise, is a bit of a no go area.
You might like to share your ideas on what form the Thales analysis probably took. On the otherhand, as the data was obtained by the military, we will probably never know what was actually done!
mm43