ChristiaanJ
If your "3000m range" figures are roughly in the right ballpark, we're still knee-deep in the soft brown matter.
Agreed, except as has been pointed out previously, ducting is also possible due to inversions caused by salinity/temperature. Hence the call for the lower pinger frequency to mitigate some of the potential signal loss.
The BEA report,
The results of these tests identified new settings to increase the detection capabilities of the "Emeraude" interceptors sensing distance of 2 000 meters during 10 to 30 June, and extended to about 3 200 meters for 1 to 10 July.
When it comes to the directional characteristics of the acoustic detection system, I would be surprised if an x/y axial scanning method was not employed by the sub. Would leave it rather vulnerable, if that wasn't the case.
I don't think that a fuselage containing lots of composites within it is going to go to the bottom at such a speed that it is going to dig a hole and bury itself. No, more likely a very gentle bottom landing.
What is missing, is where the fuselage or parts of it landed on the surface before commencing their passage to the bottom!
mm43