Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF447 wreckage found

Tech Log The very best in practical technical discussion on the web

AF447 wreckage found

Old 6th Apr 2011, 08:50
  #61 (permalink)  
 
Join Date: Jan 2008
Location: Cotswolds
Age: 63
Posts: 1,259
Except that on the other thread RELEVANT discussion takes place, where here, it is (rightly) RUMOURS only.

I Think till this thread shows signs of maturity, Mods will refrain from merging the two out of respect for mm43 and his fellows.

Respect to the Mods!
vanHorck is offline  
Old 6th Apr 2011, 08:53
  #62 (permalink)  
 
Join Date: Apr 2002
Location: FUBAR
Posts: 3,347
I think it is best the Mods DON'T merge the threads, leave the other one well & good, and keep this one to deposit all the drivel and nonsense.

Why corrupt a perfectly good thread whilst you can just let this one fester here
captplaystation is online now  
Old 6th Apr 2011, 09:18
  #63 (permalink)  
 
Join Date: Mar 2009
Location: Perth Western Australia
Age: 52
Posts: 809
I think people should stop mentioning the other thread least it gets corrupted.
rh200 is offline  
Old 6th Apr 2011, 09:31
  #64 (permalink)  
 
Join Date: Mar 2009
Location: melb
Posts: 58
The sidescan radar image is amazing, wings, mid section, clear as a bell. Looks like there may even be a part of the tail and the engines detached and forward of the wings.
mickk is offline  
Old 6th Apr 2011, 09:48
  #65 (permalink)  
 
Join Date: Aug 2009
Location: Germany
Age: 62
Posts: 1,809
Cool

Hi,

I think it is best the Mods DON'T merge the threads, leave the other one well & good, and keep this one to deposit all the drivel and nonsense.

Why corrupt a perfectly good thread whilst you can just let this one fester here
Seem's this thread deserve a place in the Jetblast forum
jcjeant is offline  
Old 6th Apr 2011, 10:36
  #66 (permalink)  
 
Join Date: Mar 2005
Location: Europe
Posts: 91
The 'clear' images are not side scan images, they are from an ROV (remote operated vehicle). You can clearly see the bright light from the ROV and the black and white camera.

If you look at the BEA website you will see the side scan image at the bottom (the dark image). You will see reference to 'AUV' in the title box, this is an 'Autonomous Underwater Vehicle'. A 'side scan' is normally incorporated into a 'towed fish', and the deeper the water the longer the umbilical and the difficulty in controlling the fish, and knowing the exact location of the fish. The 'AUV' is the latest and greatest, an 'untethered vehicle', think of it as an underwater 'tomahawk missile' with a side scan fitted, you programme it where you want it to go, and off it goes and then pops up to the surface when it is finished.

So the Side Scan gives you an acoustic return, and they can be hard to interpret. The ROV gives you a real image, and is much clearer.

So I presume they mapped the seabed with the AUV, then pin pointed the location and then used the ROV to take the still images.
Langball is offline  
Old 6th Apr 2011, 10:41
  #67 (permalink)  
 
Join Date: Jun 2007
Location: london
Posts: 9
So let's review then....a brazillian search plane spots an oil slick more or less right over this newly discovered debris zone (correct). A french submarine is sent to investigate and finds nothing. Said submarine can find another sub in the worlds oceans, but can't find a data recorder (that wants to be found, due to emitting a signal on a specific bandwidth) that is more or less right next to it. Thermoclines and other known sonar deficiencies aside, for which sub sonar crews are trained, this one has more questions than answers.

Also, on the tech thread there are sonar pics of the debris field overlaid with the original search pattern and newly discovered debris field. They are so close that they were on the edge of this new find during the original search. The time taken for this new search to find the debris field was very short given the size of the search area, guess they were just lucky eh ! ......ummm !
memyself is offline  
Old 6th Apr 2011, 10:54
  #68 (permalink)  
 
Join Date: Jun 2009
Location: paradise,bc
Age: 77
Posts: 22
If I recall correctly, the AUVs had to be retrofitted with better sonar and other systems before being deployed on this latest mission. It seems plausible that it was this upgrade that allowed the relatively speedy location of the debris field to be established. Remember, this isn't necessarily a walk in the park.
cribbagepeg is offline  
Old 6th Apr 2011, 12:37
  #69 (permalink)  
 
Join Date: Jun 2009
Location: VA, USA
Age: 53
Posts: 555
A french submarine is sent to investigate and finds nothing. Said submarine can find another sub in the worlds oceans, but can't find a data recorder (that wants to be found, due to emitting a signal on a specific bandwidth) that is more or less right next to it
So it's that easy then?

If you have any kind of search abilities using Google, you will be very capable of finding a report where two of the latest, highly instrumented, sonar overloaded submarines (one British, one French) HIT EACH OTHER in the middle of the Ocean.

Both submarines were equipped with state-of-the-art sonar technology, but xxxxx said it was possible that neither was aware of the close proximity of the other vessel.
So, your implied assertion that it is simple to find an audio signal (which incidentally we do NOT know was functional) using a sub is perhaps a little off. If two submarines can get close enough to HIT EACH OTHER, with all this fine sonar technology, which is specifically intended to detect other submarines, and not even know the other was there rather clearly confirms that acoustic detection at best is a hit or miss affair.

The search area was, what, 3,200 square miles... with depths that exceed the hull crushing depth of most submarines.

Modern nuclear attack submarines like the American Seawolf class are estimated to have a test depth of 490 m (1,600 ft),[which would imply (see above) a collapse depth of 730 m (2,400 ft).
[Wiki]

That leaves a LOT of water and many thermoclines between any sub and the bottom of the Ocean in this area.

'Nuff said?
GarageYears is offline  
Old 6th Apr 2011, 13:42
  #70 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 60
Posts: 5,340
Having spent a few years in the ASW community (though it's some years ago), I would like to comment on sonar search optimization in the military sense, and the impression Hollywood and Tom Clancy have given of magical sound detection capability in military submarines using sensors optimized for military use.

The whole point of tuning your gear, and positioning it in the water column when you are using a towed array, is to
1) put it in a good direct path posture for some missions
2) take advantage of various sound channels, sound layers, or convergence zones in other missions.

This sensor positioning is predicated on searching for "things" between the surface of the ocean and about 3000 feet, things which try to hide in the "shadow zones" between various water layers in a given area. I use 3000 feet since it is well beyond crush depth for every submarine I can think of in all navies, and roughly where the main thermocline is over come by the isothermal layer.

Thanks to physics, this depth range represents the zone where sound velocity undergoes a series of changes for a variety of reasons. Deeper than that, the velocity gradient takes on a predictable profile.

http://usna.edu/Users/physics/ejtuchol/Chapter5.pdf

See page 5-10 for a nice picture of the whole ball of wax for very deep oecan.

As the ocean gets deeper, the influence on sound propagation with basically constant temperature at some point around 3000 feet is water density. The other factors (like salinity) tend to have reached a constant by then.

This "roughly homogenous" medium (water, cold, deep) removes the various exotic sound channel features like the deep sound channel and the convergence zone, which take advantage of the changes in sound velocity from shallower water to deeper water.

With the pinger at depths in excess of 5000 feet, the long range signal reception enjoyed against manned submerged "things" most likely cannot be taken advantage of. (Caveat .... depending on what the CZ and sound channels are doing in that locale on that day ... it can vary a bit).

With the source well below the main thermocline, my back of the napkin estimates are that you are stuck with a direct path propagation ... IF you can get your sensor below some of the last sound channels at depth (and thus a possible difractive layer). If the sub is trailing a towed array at, say, 500 or 700 feet, he's not going to be able to trail it at 3000 feet ...

Granted, it's been a few years since I had to chart sound velocity profiles from at BT trace. That said, I cannot recall any military tactical hydrophone optimized for detecting "things" below 2000 feet, even though sounds of many sorts would follow varying paths from various depths to reach the hydrophones.

I am pretty sure that SOSUS (if it's still in operation) would not be listening in the proper layer of water to hear the pinger. I think the pinger's sonic waves were likely "bent away" from a hydrophone array at tactical depth. The best one could hope for is the pinger being in a zone of "half channel," but I don't recall if there is a depth limitation to that phenomenon. I seem to remember the limit being less than 10,000 feet, and half channel being somewhat available in the Med during some seasons ... but it's been a few years.

For those more current in acoustic sensing, I'll accept corrections to my recollection on how all of that sonar detection fits together.

It amazed me to learn that post mission acoustic analysis of the tapes from the submarine showed that a pinger signal had been detected. I suspect that "which direction was it from us at the time?" was very difficult to confirm. Had they verified a detection 'in situ' during the mission, the captain might have been able to use some simple tactical maneuvring to arrive at an AOP and expedite the search and location while the pinging was in progress.

EDIT: the more I think of it, the less likely it is for half channel to have been in operation, as I think that requires a surface layer temp roughly equal to bottom layer temp, little to no mixing layer and a few other things that memory does not serve up.

This crash was in June, so half channel not likely in the tropics.

Last edited by Lonewolf_50; 6th Apr 2011 at 14:02.
Lonewolf_50 is offline  
Old 6th Apr 2011, 15:35
  #71 (permalink)  
 
Join Date: Jun 2007
Location: london
Posts: 9
Lonewolf 50 - what an informative post,

I didn't realize that the French sub had actually picked-up the pinger from the data recorder, but could not define the position. What a pity that was not identified while on-position.

I am not a military specialist, (so question to those who are ?)but wouldn't aircraft such as the P3 Orian, or some military helicopters have onomoly detectors that could have investigated the oil slick over the debris site ? If they can find submarines coated in rubber and all kinds of other anti-detection materials, that are also hiding in thermoclines then could they theoretically have found the debris site. Notwithstanding it's a 3,000ft !!
memyself is offline  
Old 6th Apr 2011, 15:47
  #72 (permalink)  
Per Ardua ad Astraeus
 
Join Date: Mar 2000
Location: UK
Posts: 18,584
"have found the debris site. Notwithstanding it's a 3,000ft !" wrong - try 3900'
BOAC is offline  
Old 6th Apr 2011, 15:50
  #73 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 60
Posts: 5,340
1) The pinger/wreck is a bit deeper than 3000 feet.

2) In the time it takes to get to the oil slick, it will have drifted and over time spread and dispersed. As I understand the history, there were in fact patrol planes and aircraft that did take a look at the oil slick, but the Tech Log thread has waaaaaaay more info on that.

3) P-3 dropping some LOFAR or VLAD passive buoys ... might that have detected a ping? Not sure. Maybe, maybe not. Not sure if it was requested, or such missions flown. I assumed that Brazil has maritime patrol aircraft like the P-3. If they wanted US help, they'd have asked for it. I'll try and find out from a few old Navy friends if any US P-3's did acoustic search ... may not be able to come up with anything.

4) Time to datum. In any search mission, you first have to get to datum (or last known position) and then come up with a scheme.

More later.
Lonewolf_50 is offline  
Old 6th Apr 2011, 16:24
  #74 (permalink)  
 
Join Date: Nov 2010
Location: FR
Posts: 478
Originally Posted by memyself View Post
(...)A french submarine is sent to investigate and finds nothing. Said submarine can find another sub in the worlds oceans, but can't find a data recorder (that wants to be found, due to emitting a signal on a specific bandwidth) that is more or less right next to it(...)
On a side note : What if the emitter of the black boxes simply didn't work ?
Before being accused of too big "whatification", a little digression : 3 helicopters of the same type & operator were lost (crash) in the past years. Said 3 helicopters were equipped with a 406MHz emergency beacon. No beacon ever emitted, as they were separated from their battery in each of the 3 crashes.
I suppose some redesign is to be done to those emergency beacons, but so far...
AlphaZuluRomeo is offline  
Old 6th Apr 2011, 16:37
  #75 (permalink)  
 
Join Date: Jun 2009
Location: VA, USA
Age: 53
Posts: 555
memyself: Do some research perhaps?

Magnetic anomaly detection (MAD) is not some magic that just "finds" stuff. I presume that is what you are implying?

Any reasonable sized structure (including plastic boats believe it or not) moving through water will create a magnetic signature that can be detected - Russia built a class of subs from Titanium in the misplaced belief that MAD detectors would not "see" them - but it is the motion of the structure, through a conductive medium (sea water) that creates electronic currents on the surface of the structure that can be detected, in addition to any ferrous metals.

However, once such a non-ferrous structure stops moving, the magnetic signature does too. No more MAD detection.

The second problem of acoustic detection, is that these systems have been highly "tuned" to detect the targets of choice - i.e. submarines. LOFAR buoys and the system used to interpret the signals received, are adapted to focus on the low frequency range (where a subs noise signature differs most from the normal background), and not the 37.5kHz tone of the data recorders. In fact this is near the upper range of LOFAR reception, which is 40kHz.

VLAD is no good the audio range is limited to 2400Hz, way below the pinger frequency.

Basically, the problem is way harder than it might seem from behind the keyboard. I believe the French tried really hard and even had support from the Sonar system manufacturer in an attempt to reprogram the software, but the depth of the pinger was very different from those the system was intended to detect signals from. An R&D project in other words on a very, very short, 30-day schedule (based on battery life of the pinger).

I already posted proof that acoustic detection is difficult...
GarageYears is offline  
Old 6th Apr 2011, 17:33
  #76 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 60
Posts: 5,340
Ah, had forgotten VLAD limitations ... and am still trying to sort out what sound propagation path was available for exploitation.

All I come up with is Direct Path, based on source location.
Lonewolf_50 is offline  
Old 6th Apr 2011, 18:55
  #77 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 76
Posts: 1,331
Originally posted by Langball ...
So I presume they mapped the seabed with the AUV, then pin pointed the location and then used the ROV to take the still images.
An AUV has been used to do both operations. The REMUS 6000 AUVs have provision to carry either a sidescan sonar package, or a camera and illumination source. The photo will be one of a sequence taken during a pre-programed fly-by.
mm43 is offline  
Old 6th Apr 2011, 19:22
  #78 (permalink)  
 
Join Date: Nov 2010
Location: CLE
Posts: 30
Question Resolution of 120kHz sidescan

Nevermind.

Last edited by asc12; 7th Apr 2011 at 20:13. Reason: Posted question in more relevant thread.
asc12 is offline  
Old 6th Apr 2011, 19:40
  #79 (permalink)  
 
Join Date: Mar 2007
Location: under the sea
Posts: 2,229
I would be surprised if any recovered bodies are intact for very long once they surface unless special preparations are in place.
When the submarine HMS Thetis was lost on trials in Liverpool Bay in 1939 the bodies of those lost with her were eventually recovered.Initially when they were extracted from the submarine they looked normal but within thirty minutes of recovery they rapidly started decomposing and became unrecognisable.
I suppose that with modern forensic science this is less of a problem but if the corpses have any useful information for the investigators then some kind of refrigeration unit on site would be needed.
tubby linton is online now  
Old 6th Apr 2011, 20:40
  #80 (permalink)  
 
Join Date: Jan 2005
Location: France
Posts: 2,319
A bit ghoulish, tubby, but you're entirely right.
Let's hope the right precautions will be in place this time....
ChristiaanJ is offline  

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.