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AF 447 Search to resume

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AF 447 Search to resume

Old 3rd May 2010, 14:23
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For those not familiar with the concept of frequency sweeping to enhance spatial resolution, the following is a good example of the CHIRP technique:-

STARFISH CHIRP SIGNAL PROCESSING

CHIRP (Compressed High Intensity Radar Pulse) techniques have been used for a number of years above the water in many commercial and military RADAR systems. The techniques used to create an electromagnetic CHIRP pulse have now been modified and adapted for acoustic imaging sonar systems. StarFish uses CHIRP techniques at the core of its acoustic engine.

To understand the benefits of using CHIRP acoustic techniques, we need to analyse the limitations using conventional single frequency (monotonic) techniques.

An acoustic pulse consists of an on / off switch modulating the amplitude of a single carrier frequency. The figure below shows how this relationship exists between the transmitted signal and the output produced by the receiver circuitry in the sonar. It can be seen that the receiver does not decode each cycle of the transmitted pulse, but instead produces the 'envelope' of its overall amplitude...



The ability of monotonic acoustic systems to resolve targets is better if the pulse duration is short; this, however, has its drawbacks. Ideally, we need long transmit pulses to get enough acoustic energy into the water for good identification of the furthermost targets, but due to the velocity of sound (VOS) through water (typically around 1500 metres / second), each pulse will occupy an equivalent 'distance' related to its pulse duration - this is referred to as 'range resolution', and can be given by the following equation...

Range Resolution = (Pulse Duration x Velocity of Sound) / 2

EXAMPLE...

In conventional monotonic side scan sonar systems the pulse duration is typically 100 micro seconds, and combining this with the typical VOS of 1500 metres / second, a range resolution of 75mm is obtained.



The 'range resolution' effectively determines the ability of the sonar to identify separate targets; so, using the example above, if two targets are less than 75mm apart then they cannot be distinguished from each other. The net effect is that the system will display a single large 'combined' target, rather than multiple smaller targets, and any fine sonar detail is lost.

CHIRP SIGNAL PROCESSING OVERCOMES THESE LIMITATIONS!

Instead of using a pulse of a single carrier frequency, the frequency within the burst is changed (swept) through the duration of the transmission, from one frequency to another. For example, at the start of the transmission the sonar may operate at 100KHz, and at the end, it may have reached 150KHz - the difference between the starting and ending frequency is known as the 'Bandwidth' of the transmission, and typically the centre frequency of the transmission is used to identify the sonar (in this case it would be a 125KHz sonar).

By constantly changing its frequency over time, this 'chirped' transmission can be thought of as having a unique acoustic signature, and so if two pulses now overlap (as the targets are closer than the range resolution), we can use the known 'frequency versus time' information to tell them apart.

With modern high-speed digital-signal-processing (DSP) techniques, the StarFish sonar receiver contains a 'pattern-matching' circuit that looks for its transmitted 'CHIRP' being echoed back from targets, and its receiver now produces a sharp 'spike' when a good match is found (whereas the monotonic sonar produces an output the same duration as its transmit pulse)...



This means that the critical factor in determining range resolution is no longer the pulse duration, but the bandwidth of the CHIRP, so the range resolution can be found by...

Range Resolution = (Velocity of Sound) / (Bandwidth x 2)

EXAMPLE...

The bandwidth of the StarFish CHIRP system is typically 40kHz, and using the same VOS of 1500 metres / second, our new range resolution is 18.75mm... a theoretical improvement by a factor of 4 over the monotonic example above!



The figure above shows that on a chirped sonar, when two acoustic echoes overlap, the CHIRP pulses do not merge into a single acoustic return (as their frequency is different from each other at the overlapping points), and the sonar is able to resolve and display the two targets independently.

Therefore, we now can have longer transmissions (and see targets further away) without a loss in resolution; and additionally, CHIRP signal processing techniques offer improvements in background noise rejection (as the side scan sonar is only looking for a swept frequency echoes, removing random noise or out-of-band noise).
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The above data in its original form is at:-

CHIRP Signal Processing - StarFish Seabed Imaging System - Side Scan Sonar Acoustics

mm43
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Old 3rd May 2010, 15:22
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Anne Candies?

Would mm43 or anyone else know why is the Anne Candies apparently leaving the search efforts?

Heading towards the Gulf of Mexico?
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Old 3rd May 2010, 15:40
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Anne Candies

She is pretty unique - perhaps assisting with the oil slick?
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Old 3rd May 2010, 16:00
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Anne Candies

The following Radio Nav Warning to Shipping was issued by the Brazilian Navy on 01 May 2010:-
0098/10
NORTHWEST OF ARQUIPELAGO SAO PEDRO E SAO PAULO
CARTA 10(INT. 216)
VESSEL SEABED WORKER - BLUE HULL AND WHITE SUPERSTRUCTURE
SEARCHED THE WREKAGE AR PERIOD: 01/MAY TO 28/MAY
AREA INTERDICTED TO NAVIGATION AMONG PARALELS: 03-53.17N 02-39.40N AND MERIDIANS:
030-17.00W 031-14.22W
CAUTION ADVISED.
CANCEL THIS WARNING 290000 UTC MAY 2010
The "Anne Candies" is no longer part of the extended Phase 3 search, and I expect the BEA will confirm that in their press release tomorrow - 04 May.

mm43
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Old 3rd May 2010, 18:13
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Specialist ROV's needed elsewhere cappin that well is priority I guess
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Old 4th May 2010, 17:33
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Another 3m going into the search fund

Air France and Airbus to fund extended search for AF447
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Old 4th May 2010, 17:53
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Only one vessel and 1.5 mln for Airbus and AF? This is only to keep the families happy . Otherwise there would have been many vessels in the area to find every bits and pieces.
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Old 4th May 2010, 18:36
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Originally Posted by wingview View Post
... This is only to keep the families happy ...
That's a bit too cynical, in my view.
In that case, the money could have been spent directly on the families....
Everybody concerned still has an interest in finding at least something, even if the chances don't look all that good.

CJ
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Old 4th May 2010, 18:39
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I fear, though, that some have a vested interest in finding nothing. And especially not the boxes.

I hope I'm wrong.
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Old 4th May 2010, 20:30
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Extended Phase 3 Search

The BEA's priorities in the extended search, are to search the Zones 1, 2 and 3 in that order. Their graphic released today follows:-



I have roughly overlaid and merged a graphic of the southwest corner which indicates where I believe the chances of finding debris is good. The positions and area marked are nothing new, and have been published in this forum since September 2009.



The last position for the "Seabed Worker" was on 03 May 2010 13:56z at 318'N 3108'W and probably in the process of launching her 2 AUVs.

mm43

Last edited by mm43; 4th May 2010 at 20:54.
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Old 4th May 2010, 21:44
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Fingers crossed MM43, can we just nudge that yellow area 1 south a bit.
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Old 4th May 2010, 23:26
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Wingview and RGBrock,

Families happy? One thing those families know is that relatives or friends are not going to reappear so "happy" hardly applies, don't you think?

I had my doubts nine/ten months ago as to the diligence that would be put into this search, and as to the possible benefit to Airbus and AF of a superficial search finding nothing. No longer; it seems preposterous to think the people on those ships were there just to pretend to be looking or that BEA/AF/AB would prefer the accident forgotten, nothing to be learned from it.
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Old 5th May 2010, 12:59
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Update: "Seabed Worker" 04 May positions

Here are a couple of positions for the "Seabed Worker":-

04 May 2010 12:14z 315'57"N 3108'30"W Track 265.5T Spd 00.6KT
04 May 2010 11:07z 306'44"N 3106'26"W Track 346.8T Spd 10.4KT

She appears to be working in the northwest corner of Zone 1.

mm43
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Old 5th May 2010, 19:34
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Has anything whats so ever been reported as any search having located anything. One would think with as many repeated sweeps, multible activity and/or new tracks, something would have triggered acute interest. I continue to read with great interest the posting every day in hopes that some new fact might be stated. How frustrating to all.
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Old 6th May 2010, 05:49
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Tough Terrain

BEA Interim Report n2 stated that "There are depth variations of between 700 metres and 4,300 metres over short distances." The 1991 UNESCO report of the Russian multibeam explorations along the Mid-Atlantic Ridge (thanks to Machaca for the reference in post #766) includes a contour map of the area covered by the vessel Strakhov: there are some amazing tall peaks and steep deep valleys in this part of the Atlantic. The black areas are where contour lines are so close they bleed together in the UNESCO printout. The BEA areas of interest for continuing Phase Three search (Areas 1, 2, and 3, in yellow in the image below) unfortunately lie a bit eastward of the Strakhov data. Paull had suggested that it's mathematically possible (using the "CUBE" algorithm) to overlay two terrain data sets and look for differences and that the technique is commonly employed to discover changes in features and terrain over time. Makes sense -- that's how the tax assessor already knows about your swimming pool. But using lat/long coordinates from mm43's #764 post to scale the current AF447 search effort (posted yesterday at the BEA site) onto the Strakhov chart, it seems there is not much overlap.



Click here for larger image.

It was the black areas of the Russian contour map that brought reality home: "Debris field" becomes an oxymoron when there are few fields among the steep slopes. In a flyby, one moment you are peering at the top of a mountain peak, next you are looking a couple of thousand meters into the abyss. The recent BEA video included shots of crew at work and the Fledermaus 3D visualizer was showing peaks, but there was a tremendous amount of "undefined" hazy blue down into those valleys:



Click here for larger image.

Hats off to the BEA and the French government for pursuing this incredible search! Hats off and cheers to the French experts and the WHOI multibeam team for their dogged persistence at sea. I'd chip in to establish a new explorer's prize for these guys, even if they don't get lucky. Both the reason for this search and the search itself are playing out at the very edge of our technical capabilities and knowledge.
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Old 6th May 2010, 07:17
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The French media ( radio) this morning reported that the French Navy have localized " within a few kilometers " the area where the recorders would be. It is based on a computer model using sonar and acoustic recordings made by some deep sea robots in the weeks after the accident. , More info later during the day .

Latest : the French Ministry of Defense confirmed this, a vessel with a deep sea robot is on its way to the location according to them.

Last edited by ATC Watcher; 6th May 2010 at 07:35.
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Old 6th May 2010, 08:11
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BBC News ticker reporting it has been located.
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Old 6th May 2010, 08:13
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From AFP via the ABC (Oz) website a few minutes ago ...

Black boxes of Rio-Paris air crash plane found

Posted 5 minutes ago

French accident investigators say they have located the black box flight recorders from an Air France jet that crashed in the Atlantic in June last year, killing 228 people.

They added, however, that they might not be able to retrieve them.

The crash of flight AF 447 was the worst in Air France's 75-year history.

On June 1, the Airbus A330 came down in the Atlantic as it was flying from Rio de Janeiro to Paris, resulting in the deaths of all passengers and crew on board.

The cause of the accident is still unknown, but investigators say malfunctioning airspeed probes on the aircraft were a factor.

The flight data and cockpit conversations recorded on the black boxes are crucial to determining the circumstances of the crash.

A three-month search last year by a French navy submarine and sonar-equipped ships failed to locate the devices.

A private memorial was held for the victims in Rio de Janeiro in November.

In the same month, relatives of eight of the victims filed lawsuits against Air France seeking damages.

The lawsuit filed in the US state of Illinios alleges negligence and products liability on the part of Airbus and the makers of various instruments used on the flight.

"As a direct and proximate result of the defendants' negligence, the subject aircraft crashed into the Atlantic Ocean on June 1, 2009, killing plaintiff's descendants, causing severe terror and pain prior to impact, and resulting in both personal and pecuniary injuries," the lawsuit said.

- AFP
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Old 6th May 2010, 08:38
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The flight recorders from an Air France plane which crashed in the Atlantic last year have been located to within a 5km zone, a French official has said.

But Gen Christian Baptiste told AFP that retrieving the boxes from the ocean floor might be impossible.
BBC at 0723 GMT
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Old 6th May 2010, 08:43
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Sounds like a narrower search area has been defined only. 5 kilometres, so they didn't exactly locate them yet. Good luck anyway.

Last edited by Less Hair; 6th May 2010 at 09:11.
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