auv-ee wrote:-
I'm not sure what conditions have to exist for sound from a deep water source to enter a duct. It seems like the angle of incidence would have to be far from vertical, which would increase the path length (slant range) making for an already weak signal at entry. I was assuming previously that useful ducting was unlikely on that basis, but who knows.
My assumption was based on the angle of incidence having changed when transitioning a deepwater inversion (4,000m) and subsequently becoming entrapped on encountering another layer in the 300 - 500m range. If that was the case, it would explain the apparently low signal/noise levels that have been recorded.
As you say, we don't know at what depth the sub was operating, though on examination of some bathymetry I believe she obtained, I'd make a guess and say in the 150 - 200m range.
mm43