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Malaysian Airlines MH370 contact lost

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Malaysian Airlines MH370 contact lost

Old 9th Apr 2014, 19:14
  #9601 (permalink)  
 
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Ocean Shield reels the TPL in to to a shallower depth when turning and then lowers it again.
They MAY do this if they want to make a tighter turn, but you really try to avoid this when towing, as you lose all the time turning and not searching.
Typically you run a racetrack type of search pattern to optimize the depth and the search area.
While it is called mowing the lawn, it is not efficient to directly overlap paths, you just keep moving the entire racetrack over...

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Old 9th Apr 2014, 19:30
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"Analysis by the British satellite company Inmarsat and the UK's Air Accidents Investigation Branch (AAIB) was cited on Monday by the Malaysian prime minister as the source of information that has narrowed the location where the Malaysia Airlines flight MH370 may have crashed into the southern Indian Ocean to a corridor a couple of hundred miles wide."

The new method "gives the approximate direction of travel, plus or minus about 100 miles, to a track line", Chris McLaughlin, senior vice-president for external affairs at Inmarsat, told Sky News"

For AF 447, BEA used the sat data to narrow the search area when it was found by Swire Seabed...it was found long after the pingers stopped working.
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Old 9th Apr 2014, 19:36
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why is there no TPL ROVs yet?
a "towed pinger locator remotely operated vehicle" doesn't make any sense. Neither does an ROV for locating pingers. Any ROV has a huge disadvantage: propulsion noise. I can't think of any advantages, it would still need to be tethered to a mother ship. So why exactly would you want an ROV for that?
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Old 9th Apr 2014, 19:36
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why is there no TPL ROVs yet
The Blufin 21 platform can be equipped with a PL, no problem. There is at least one from the US Navy on Ocean Shield.

Currently, it can be also be outfitted with sidescan, magnetometer, and video...it is completely autonomous...

EDIT: You program the path of the fish, and to surface at intervals to charge and send data. You can program it to surface at contact as well.
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Old 9th Apr 2014, 19:46
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Originally Posted by island_airphoto
Also it is possible a classified asset heard it first and a hint was dropped to get everyone in range of the pinger
That is certainly a possibility and has been used before.

«look here» to a trusted ally then take it overtly from there.
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Old 9th Apr 2014, 19:55
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RS, I am quite certain it is not the Capt driving the search pattern parameters. Why would I mention your name?

Coding course paths for surface and subsurface vessels is much the same as a coded flightpath for an aircraft.

When mapping, a surface vessel is typically on a coded course. When towing an array, the coded turns must take into account the towfish depth and dynamic properties. The fish must stay at depth for proper mapping overlap.

Look at the search pattern that I provided, and you will see that it is much more efficient.

I have been providing mapping patterns for autonomous underwater platforms for telecommunications cable laying for several years, so commercially, we understand how to map effectively. When one is paying for fuel, one learns to be efficient.

EDIT: I would also take note of the TPL shown in the image above. (post 9682) IF that is the actual configuration, it is not correct, which is likely why they have to tow it so slowly. A higher speed tow would involve a towfish depressor weighted wing in front of the array. The wing would keep it at depth with far higher speeds, about 7kts instead of 2...

Last edited by underfire; 9th Apr 2014 at 20:12.
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Old 9th Apr 2014, 20:00
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Originally Posted by silvertate




Not so. The final ping-ring gives a multitude of fuel-burn rates and speeds, all of which can reach somewhere along that long arc. Remember that the track-length between ping-rings varies, depending on whether you fly south or fly east - and that will greatly effect the fuel-burn/speed profile of the flight.

So you can have a low-burn/high-speed flight - and end up south and west of Australia. (Yellow track.)
Or you can have a high-burn/low-speed flight - and end up north and west of Australia. (Purple track.)

The first of these options must be a high level flight. (Yellow track.)
The second of these options must be a low level flight. (Purple track.)

But how low?
You misunderstand.


We know (or at least assume we know) the initial track of the aircraft to loss of radar contact
We know the fuel load the aircraft carried and the last miss-ping gives us the out-of-fuel time therefore we know the burn rate.
That burn rate can be achieved in a limited number of ways - assume it is relatively constant from loss of radar contact.

Then use the different levels and speeds that give that burn rate and see which fit the ping rings.

We may of course be having a noisy agreement - but the burn rate is simple - time of flight and known fuel upload adjusted for initial tracked flight. Assumption necessary is that the aircraft maintained a steady cruise.
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Old 9th Apr 2014, 20:02
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While it is called mowing the lawn, it is not efficient to directly overlap paths, you just keep moving the entire racetrack over..
Agreed, but AIS data I have just seen from Ocean Shield indicates they are more focused around 21°06'S 103°54'E, and the latest positions indicate the vessel is crabbing its way to the north again on 293°/113°T tracks.



The latest position at 10/04:50 UTC is 21°08.5'S 104°10.2'E and heading 113°T. The speed is currently 1.7 KTS.

Last edited by mm43; 10th Apr 2014 at 05:31. Reason: changed image 0450
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Old 9th Apr 2014, 20:19
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I am curious why OS continues all by herself?
The other search area has 6 search vessels..

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Old 9th Apr 2014, 20:22
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Suspect Ocean Shield searches by herself to minimize noise disturbance for her ping detector.
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Old 9th Apr 2014, 20:35
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Originally Posted by silvertate
Not so. The final ping-ring gives a multitude of fuel-burn rates and speeds, all of which can reach somewhere along that long arc. Remember that the track-length between ping-rings varies, depending on whether you fly south or fly east - and that will greatly effect the fuel-burn/speed profile of the flight.

So you can have a low-burn/high-speed flight - and end up south and west of Australia. (Yellow track.)
Or you can have a high-burn/low-speed flight - and end up north and west of Australia. (Purple track.)
Right.

Now let's say that you can narrow down the burn rate and speed to the point where you're certain that it's not yellow track, and it's closer to purple to red. (After all, fuel burn and speed are continuous variables). On your map, the distance between red and purple tracks is ~1000 km. So you need to search the strip running 500 km to either side of the purple track.

You know the partial ping arc with precision of, say, +/-100 km. The aircraft may have glided 100 km after it ran out of fuel. That makes your strip 1000 km long x 300 km wide.

This is all very good fine tuning (you cut down the search area to less than 10% of what you started with).

That's still roughly the size of Germany.

Now you have to search Germany on foot (Ocean Shield's speed while searching, ~2 kts, is comparable to walking speed) while carrying a device that can detect a hidden transmitter if you are within 2 km of its location.
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Old 9th Apr 2014, 20:37
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TPL search

Marine Traffic gives the course data for Ocean Shield
They are only achieving 2-3 transects per day so following 023/203 course on the 6th & 7th, they are now following 113/293.
It appears they take parallel transects with some 2nm separation, initial then a track either side.

The cable length can be up to 18,000m which complicates position of the actual TPL but the later detections (by time) seem to be around 103.90; -21.135.

I have been unable to completely reconcile the chart locations issued with the AIS track for those times provided in the briefing; in particular #3 and #4 seem to be be reversed.

The good news is that the depth in that particular area is less than 4,500m (4,050m - 4,200m according to GE) although #1 & #2 detections are in an area where depth could be up to 4,800m.

edit -mm43 - they appear to slow (1.2-1.6KTS) when detecting - (also at the end of a pass while reeling in the cable; conversely speed up at the beginning of a pass while reeling out)

The TPL appears to be approaching an interesting area in about 1-2 hours time so hopefully we might have more information at tomorrows brief.

AIS also shows ECHO approaching with an ETA in the search area in about 15hrs

Last edited by BillS; 9th Apr 2014 at 20:44. Reason: just seen mm43 post
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Old 9th Apr 2014, 20:42
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The Ocean Shield has in the past couple of hours dropped her towing speed to 1.6 KTS, most likely in an effort to minimize any background noise.

My latest graphic has been updated with the 09/23:00 UTC position.

Last edited by mm43; 10th Apr 2014 at 01:42. Reason: altered latest position time
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Old 9th Apr 2014, 20:49
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If you plot a straight great circle line from NILAM to the magnetic south-pole you get extremely close to the search site of Ocean Shield* (last satellite ping not shown but passes over search site).

NILAM (western tip of Indonesia) is at the upper left of the image. Search site is small yellow thumbnail west of northern Australia. Magnetic south-pole is in lower right corner of image.

[180 degree magnetic heading from western tip of indonesia]



Edit: *

Last edited by alph2z; 9th Apr 2014 at 23:07.
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Old 9th Apr 2014, 20:52
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Suspect Ocean Shield searches by herself to minimize noise disturbance for her ping detector.
that is another reason why they are delaying any AUV activity and told other ships to keep away.

Last edited by James7; 9th Apr 2014 at 20:53. Reason: typo
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Old 9th Apr 2014, 20:53
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It's possible that they don't want a higher tow speed due to increased noise from the TPL passing through the water.
Another reason for the wing, it isolates the towfish from the towcable. Harmonics from the cable has a significant effect.

Hydrodynamic drag increases as a square function of velocity, so isolation of the towfish connections is also very important.

If the towfish is isolated, I would expect 5 to 7kts without issue...you can tell pretty quickly.

Again, commercially, time is money, and given that pinger locators are seldom used, I would expect that the technology, and the logistics of using them, may not be the most current.
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Old 9th Apr 2014, 20:58
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The Sea Floor

BBC News - Missing Malaysia plane: Search 'regains recorder signal'

"Other key points made by ACM Houston:
- Searchers have no idea what the sea bed looks like in the search area. They think it may be silty
- Silt is bad news. It can be thick and can hide things in a way that rock does not"

A second opinion:

http://iod.ucsd.edu/~amanda/Files/De...he%20World.pdf

"Owing to strong geostrophic currents and consequent scouring of the sediments, the Wharton Basin, the southern Mascarene Basin, and parts of the Southwest Indian and Australian–Antarctic Basins have little or no sediment (Kennett, 1982). Sediment in these areas, when present, is mostly brown clay."

"There are strong bottom currents, with speeds approaching 10–20 cm s−1, in the Wharton Basin and the southern Mascarene Basin, and in parts of the Southwest Indian Basin and Australian–Antarctic Basins, resulting in minimal sediment deposition (Kennett, 1982; Gage and Tyler, 1991)."

Kennett, J.P., 1982. Marine Geology. Prentice-Hall, Englewood Cliffs, NJ, 813 pp.

Same author claims that the average depth, both in the Indian Ocean and world-wide, is nearly 4 km:

"The Indian Ocean, including adjacent seas (e.g., the Arabian Sea, the Bay of Bengal, and the Southern Ocean), covers 73 426 000 km2, roughly one-fifth of the total world oceanic area. It has an average depth of 3890 m, which is approximately equivalent to the average world-ocean depth."
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Old 9th Apr 2014, 21:03
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The cable length can be up to 18,000m which complicates position of the actual TPL
It is very important for the operator to know exactly where the towfish is in relation to the surface vessel. The computer system onboard calcs the towspeed, cable length, catenary arc in the cable, and data from the towfish so they pretty much know exactly where the fish is.
Many actually actively ping the surface ship to coordinate surface ship coordinates with their offset and IRU.
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Old 9th Apr 2014, 23:20
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Bill S,

AIS also shows ECHO approaching with an ETA in the search area in about 15hrs

My guess is they will use HMS Echo to do a sonar map of the search area. Whilst HMAS Ocean Shield will prepare the Blue Fin 21. So maybe on the weekend will be the Blue Fins turn finally. Of course then it still takes a long time. They will search grid patterns and retrieve the Blue Fin 21 maybe every 12-20 hrs to download its sonar mapped data and exchange fresh batteries. There is a long road ahead. They may not positive ID the wreckage for another week or 2.

Last edited by Sheep Guts; 10th Apr 2014 at 00:20.
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Old 9th Apr 2014, 23:59
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Does anyone know if the black box pingers stay phase stable? Its been mentioned before about folding data to get a better signal to noise. Its a common pulsar technique.

So I'm wondering as the battery weakens and the amplitude gets less, if they can just go to folding the signal on the pulse period. Of course if the phase is drifting significantly then thats not an option.

I presume if they are recording every thing then they would do that any way to bring out the pulse in the areas to produce some kind of spatial map of intensity.

Any one with an understanding of the acoustics side of things care to enlighten me?
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