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Old 3rd Jun 2009, 22:21
  #771 (permalink)  
Join Date: Aug 2005
Location: fairly close to the colonial capitol
Age: 51
Posts: 1,687
Buoys might have limited value in this search.

The pingers can nominally be heard for about 2 miles (10,000 ft) The depth of the ocean in this area appears to be about 10,000 feet, but varies between about 8,000 feet and 12,000 feet. It would be pure luck to drop a monitoring buoy in a position where it heard a pinger, given the depth in the area, and the fact that at the surface, the radius of success is substantially smaller than 2 miles..

The distance the pinger can be heard will also be affected by any thermal layers in the ocean, and the terrain where the wreckage came to rest, both reducing the range..

The search won't begin to be effective until towed sensors that work below the surface are deployed. I suspect they are being flown in as we discuss this.
The type of sonobuoy that the P-3 carries is an improved version of the type that has allowed us to track Soviet boomers around the world using only the passive-type sonar, that is listening only.

Generally, these are laid out in a pattern-grid field for SAR use. An Orion can typically carry over 4 dozen of these things or more for that purpose. They don't just plop one in the water in a random fashion.

As Bubbers correctly pointed out earlier, for effective active sonar searches, a side-scan array is the best option as would be for finding a DFDR/CVR using passive hydrophones. The aforementioned sonobuoys are most often used for SAR operations for temporarily marking a location at sea.

As an aside:
At the frequency of the DFDR/CVR pinger (37.5khz) the average absorption rate in sea water is between 6-10 dB/km. This does not take into account thermal layers. The relationship between absorption and frequency is more on a log scale rather than linear. Lower frequencies can travel further than higher ones, not unlike the audio range in air.

Last edited by vapilot2004; 3rd Jun 2009 at 22:37.
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