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Old 9th Apr 2014, 07:39   #9581 (permalink)
 
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what is really needed is another couple of boats to pick up the same signal at the same time to enable triangulation

at the moment it looks as if we're getting point detections - you sail towards the last one and listen and hope the next one comes from roughly the same direction
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Old 9th Apr 2014, 07:54   #9582 (permalink)
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Heathrow Harry,


Commodore Leavy said that P-3C Orions would drop sonar buoys in the water today around the area of the Ocean Shield search area. He was saying during the JACC news conference today the RAAF technicians had modified the sonar buoys to detect 37.5 KHZ signal. He described how when sonar buoys hit the water they drop on a 1000ft wire a hydrophone into the sea below.

They cant afford to have other vessels in the area as it contaminates the sound signature and introduces more background noises. The TPL-25 is towed a few Kilometres behind the vessel at around 2 knots. And all the Ocean shield unnecessary equipment is switched off.


So its a one ship job until the pinger is out of power and or they decide they have enough returns to calculate a reasonable search area.
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Old 9th Apr 2014, 08:08   #9583 (permalink)
 
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This could be the equipment for that task

Thanks "skadi" for that link.

World's only three Abyss submarines sent to Indian Ocean for plane search - Telegraph

It may explain why HMAS Toowoomba is making turns for her published maximum speed.
As shown on Marine Traffic she appears to be headed for Exmouth/Learmonth on Australia's North West Cape. Exmouth has a port and Learmonth is is a joint user facility with a runway (3,047m) suitable for large airplanes.

Live Ships Map - AIS - Vessel Traffic and Positions - AIS Marine Traffic
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Old 9th Apr 2014, 08:09   #9584 (permalink)
 
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Quote:
I think that calling it a "pinger" is a bit misleading.

It's a towed listening device - the sonar pings are produced by the main vessel

The reason it's towed is to keep it some kilometers from the ship noise so it has a wider area to listen to
innaflap,

Your reply is even more misleading!

The ADV Ocean Shield is NOT putting out any pings. The towed pinger locator is purely a passive device, listening for the 37.5 kHz ultrasound signal from the CVR and FDR pingers.

The reason the cable is very long (several thousand metres) is that it is the only way you can "fly" the towed pinger locator at its operational depth, when the Ocean Shield is moving at two or three knots. It is NOT to do with ship noise. The length of the cable is also the reason that turn arounds take so long. I read somewhere that much of the cable is reeled in before turning and then let out again.
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Old 9th Apr 2014, 08:10   #9585 (permalink)
 
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One should be prepared for the possibility that the DFDR and the CVR could have stopped recording early in the flight, with no CB tripping "snap" sound in the last second of CVR recording. Remember MI185.
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Old 9th Apr 2014, 08:15   #9586 (permalink)
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whats the deepest recovery of a CVR/FDR?

Anyone know? The pressure at these depths are very high. I 've found 20000 feet. But no other specs.

Last edited by Sheep Guts; 9th Apr 2014 at 08:32.
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Old 9th Apr 2014, 08:24   #9587 (permalink)
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They are trying to introduce the SAFE act again in Congress in response to MH370

Wikipedia quote
Quote:
Proposed requirements[edit]

In the United States, the "Safe Aviation Flight Enhancement (SAFE) Act of 2003" was introduced on June 26, 2003 by Congressman David Price (NC) and Congressman John Duncan (Tennessee) as a bipartisan effort to ensure investigators have access to information immediately following commercial accidents.[27] On July 19, 2005, a revised SAFE Act was introduced and referred to the Committee on Transportation and Infrastructure of the U.S. House of Representatives. The bill was referred to the House Subcommittee on Aviation during the 108th, 109th, and 110th congresses.[28][29][30] On March 12, 2014 in response to the missing Malaysia Airlines Flight 370, Congressman David Price re-introduced the concept in the House of Representatives.[31] The SAFE Act calls for implementing the NTSB 1999 recommendations. Under the NTSB's recommendations, operators would be required to install two sets of combination Cockpit Voice and Data Recorder (CVDR) systems (or "Black Boxes"). The SAFE Act calls for making the second CVDR set "deployable or ejectable". The "deployable" recorder combines the cockpit voice/flight data recorders and an emergency locator transmitter (ELT) in a single unit. The "deployable" unit would depart the aircraft milliseconds before impact, activated by sensors. The unit is designed to "eject" and "fly" away from the crash site, to survive the terminal velocity of fall, to float on water indefinitely, and would be equipped with satellite technology for immediate location of crash impact site. The "deployable" CVDR technology has been used by the U.S. Navy since 1993.[32] The recommendations would involve a massive retrofit program. However, government funding would negate cost objections from manufacturers and airlines. Operators would get both sets of recorders for free: they would not have to pay for the one set they are currently required by law to carry. The cost of the second "deployable/ejectable CVDR" (or "Black Box") was estimated at $30 million for installation in 500 new aircraft (about $60,000 per new commercial plane). The SAFE ACT legislation failed to pass in 2003 (H.R. 2632) or in 2005 (H.R. 3336) or in 2007 (H.R. 4336).[33]
Interesting lets hope it passes now.
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Old 9th Apr 2014, 09:09   #9588 (permalink)
 
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Quote:
Originally Posted by Sheep Guts
Commodore Leavy said that P-3C Orions would drop sonar buoys in the water today around the area of the Ocean Shield search area. He was saying during the JACC news conference today the RAAF technicians had modified the sonar buoys to detect 37.5 KHZ signal. He described how when sonar buoys hit the water they drop on a 1000ft wire a hydrophone into the sea below.
The buoys could be inoperative if tuned to 37.5 kHz.
Angus Houston has reported that the signals detected by Ocean Shield pinger locator are on 33.331 kHz.
Could that frequency drift of -11% be caused by hydrostatic pressure ?
I understand that a pressure of 50 MPa is compatible with a +/- 10^5 ppm drift.
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Old 9th Apr 2014, 09:10   #9589 (permalink)
 
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Press conference 9 April

Link to the JACC 9 April full press conference (including Q&A) - Press Conference by JACC on MH370 - (11.00am, 9/4/2014) | Astro Awani.
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Old 9th Apr 2014, 09:22   #9590 (permalink)
 
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The locations at which pinging was detected shown in the map in post 9647 are around 26 km apart. Wikipedia states
Quote:
A 37.5 kHz (160.5 dB re 1 μPa) pinger can be detectable 12 kilometres (0.621.24 mi) from the surface in normal conditions and 45 kilometres (2.53.1 mi) in good conditions. A 37.5 kHz (180 dB re 1 μPa) transponder pinger can be detected 45 kilometres (2.53.1 mi) in normal conditions and 67 kilometres (3.74.3 mi) in good conditions
There have been numerous posts about convergence,ducting etc that could result in longer ranges and, I presume, that is how these pings are being detected so far apart. However it shows what a big area of uncertainty there must still be about the location of the pingers. I seem to recall that when the first announcements of hearing the pingers were made at the press conference a few days ago, Angus Houston said they were searching a 3 mile square area to narrow down the source - it now looks quite a bit bigger than that.
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Old 9th Apr 2014, 09:37   #9591 (permalink)
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Luc Lion,

I miss quoted the Commodore he said that the Aircraft equipment had been modified and not the sonar buoys themselves to receive the 37.5 khz. I believe they have taken into consideration the frequency drift that has occurred since the 1st acquisition on the weekend.

Last edited by Sheep Guts; 9th Apr 2014 at 10:18.
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Old 9th Apr 2014, 09:37   #9592 (permalink)
 
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Hightflyer40

Quote:
just thought of something, the unions would probably scupper the whole thing as they would object to live CVR being transmitted in flight!
It would be interesting to see a debate between those unions and the relatives of the 239 missing people on MH370. Perhaps the time has come for something more constructive than worrying about unethical management oversight.
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Old 9th Apr 2014, 09:46   #9593 (permalink)
 
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ADV "Ocean Shield" - Current Position

The Ocean Shield is working its way to the south crossing at a right angle the tracks previously taken. The graphic below updates a previous one, and the latest position is noted in Orange. These are the ship's position and the TPL can be over a 1000 meters astern or even out to one side, depending on the effective "drift" component existing between the TPL and the towing vessel.



Bear in mind that the signal strength received at the TPL can vary considerably due to the effects of deep water sound channel ducting, but will show the least phase distortion and largest signal etc.. normally when the TPL is directly above the ULB.
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Old 9th Apr 2014, 09:58   #9594 (permalink)
 
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Quote:
Link to the JACC 9 April full press conference (including Q&A) - Press Conference by JACC on MH370 - (11.00am,
9/4/2014) | Astro Awani
.
I've just watched the whole news conference. Very informative and I have to say I'm very impressed by Angus Houston. I know senior officers have media training, but he comes across as if he'd had years of experience of doing this and I would never have guessed that he was such a distinguished RAAF officer, if I hadn't known.

Speaking of officers, why is it that the RAN officer (Commander Leavy?) is wearing a camouflaged uniform? Is that normal shore-rig these days?
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Old 9th Apr 2014, 10:09   #9595 (permalink)
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India 42,

Quote:
Speaking of officers, why is it that the RAN officer (Commander Leavy?) is wearing a camouflaged uniform? Is that normal shore-rig these days?
Commodore Leavy actually. Not Commander. Being a Commodore and the Commander of the Military aspect of the search. I would suggest he sets the dress and standards himself. After all it is an operation. Not a passing out parade!
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Old 9th Apr 2014, 12:50   #9596 (permalink)
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Quote:
The fact is that for a primary radar the range limit will be about equal to the horizon. Factoring in a target altitude and the radar antenna elevation this will work out to something like 200 miles, probably a little more in practice. (The limitation of a radar's range will not be transmit power or receiver sensitivity, as even late 20th century technology has provided ample capability there.)
The detection range of a primary radar is dictated by the pulse repetition frequency - although ground clutter and the physical horizon limit the range at low elevations. A typical PRF for weather radar for example is 400 hz, supporting ranges up to 300 miles or more.

A military radar would use a low PRF for scanning, but would need to switch to a higher PRF for target acquisition and launch that would limit the range to about 90 miles or even less. I expect that is the "implied threat" in Indonesia's claim of a radar range of only 90 miles.
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Old 9th Apr 2014, 12:52   #9597 (permalink)
 
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Insurance Payout

Not sure if this has been mentioned - Malaysia Airlines has already been handed $110 million (67 million) by insurers over the loss of its missing Boeing 777 on flight MH370.

Flight MH370: insurers make first pay out on missing Malaysia Airlines plane - Telegraph
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Old 9th Apr 2014, 12:57   #9598 (permalink)
 
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Sonobuoy

The Sonobuoys that will be dropped as listening devices in the larger search area are indeed broad spectrum passive listening devices. The modifications to the aircraft equipment might allow for a narrow frequency spectrum to be more closely monitored so that the returned signal will only scan the chosen frequency range around 37.5kHz.
Depending on the pattern of the sonobuoys and the contact gained on one or many of the buoys, he contact could serve to localise and triangulate a more refined position of the signal source. This technique has been in use for decades but probably not used to date because of the modifications required. The buoys can be monitored by one or several aircraft at altitude depending on the number of buoys deployed and the number of receiver channels on each aircraft.

The limited depth of the sonobuoy hydrophone (about 300m) could make detection through varying thermal layers less likely with weak signals. At least all resources are being employed to solve this mystery.
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Old 9th Apr 2014, 13:31   #9599 (permalink)
 
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They are trying to introduce the SAFE act again in Congress in response to MH370

Yes, very interesting, SheepGuts.

Are you prepared to finance the government-sponsored/mandated retrofit of the US fleet? Would that have helped the Malaysians? After all, they couldn't be bothered to purchase the upgraded ACARS maintenance package; what makes you think the United States Congress and its knee-jerk reaction (if any) would make a difference in either AF or MH?

It's always up to the Brits, Aussies, or Yanks, isn't it?
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Old 9th Apr 2014, 13:55   #9600 (permalink)
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The latest TV news briefing said that the frequency received was 33.331 kHz, which is very precise.

Back of the envelope calculations assuming speed of sound in sea water at 4 degrees C and 4000 metres is around 1500 m/s, and the ship is towing at around 1 m/s, gives me a maximum doppler shift to the signal of around 20 Hz, which is an order of magnitude greater than the resolution indicated by the news report.

This is best case and assumes movement directly towards or away from the source, that there aren't effects due to currents, and that I haven't got my maths and assumptions wrong. Also, with 10 ms pings and the small windows of acquisition, there aren't that many waves to measure. Further, the signal seemed quite broad on the waterfall on the news report, but I couldn't make out bandwidth.

But - is it possible or even plausible that some further geometric information about the pinger's location wrt the receiver could be obtained this way? Perhaps the thread readers with DSP/hydroacoustic experience could comment...
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