"Seabed Worker" & "Anne Candies" - 28 April positions
The "Seabed Worker" at 28/1411z was berthed at Port Suape [8°23'47"S 34°57'32"W].
The "Anne Candies" at 28/0338z was at 4°32'22"S 3°02'14"W, 199°T/8.5KT,
and should berth at either Suape or Recife tommorow.
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Hydrophone detection of explosions in the sea, is the normal practice when undertaking offshore oil exploration. The seismic survey vessel tows a long streamer (up to 1.5NM in length) fitted with in the range of 100 hydrophone detectors. The same vessel also tows about 100 meters from its stern, an array of air guns.
The sensitivity of this system is such that geophysical structures over 5,000m below the the seabed can be detected. Higher resolutions can be had when two vessels work in tandem, and the differential signal is also recorded.
So in short, the sound travels well in the water, penetrates terra firma and echoes back through the same path. All very well and good for what it is designed to do.
Seismometers on the other-hand are designed to detect the vibrations caused by terra firma shifting. The energy generated even by a small tectonic plate shift is normally far greater than a non nuclear explosion on the sea surface, and a force 1 Richter quake would probably be detected a few hundred miles from its source. So, in the case of AF447, if the Atlantic had been ringed by sensitive hydrophones and the best noise cancelling techniques were used, I suspect that with the distances involved the chances of triangulating an aircraft crash by this means would be remote.
I live 25km from an active though currently dormant volcano which has a number of seismometers embedded on its slopes, as detection of activity is difficult from any great distance.
mm43