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Old 5th Apr 2014, 19:45   #9221 (permalink)
 
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Considering the nationalities of the passengers, I don't think the Chinese are behaving significantly more different than any other country might.

Put another way, if the pax manifest was predominately American, what communications channels would the USA use? That's not me being critical, I just think it is a fact of life and not necessarily an unreasonable thing to do.
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Old 5th Apr 2014, 19:45   #9222 (permalink)
 
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I think this is China playing to domestic and making sure it is seen to be active, for the same reasons I have said before, previous tardy response to emergencies.
...not to mention the international audience, especially in trying to highlight Malaysian incompetence.
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Old 5th Apr 2014, 19:47   #9223 (permalink)

 
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Breezy

Yes, you can add that as well, plus probably a few other things, like they find it and not the Japanese etc.


The "back channel" communications would be interesting to say the least
Luckily Angus Houston is the type of person with the knowledge of the people involved who should be able to keep things "in check".
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Old 5th Apr 2014, 19:57   #9224 (permalink)
 
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Echo sounding - Wikipedia, the free encyclopedia

Most hydrographic operations use a 200 kHz transducer, which is suitable for inshore work up to 100 metres in depth. Deeper water requires a lower frequency transducer as the acoustic signal of lower frequencies is less susceptible to attenuation in the water column. Commonly used frequencies for deep water sounding are 33 kHz and 24 kHz.
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Old 5th Apr 2014, 20:22   #9225 (permalink)
 
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Originally Posted by etudiant View Post
Deep ocean water is uniformly around 4 C, which also happens to be the highest density temperature for water.
That's not coincidental...
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Old 5th Apr 2014, 21:00   #9226 (permalink)
 
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The lack of any recording of that " regular, once-a-second rate" that would have been so useful alongside the 37.5khz frequency is most disturbing.
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Old 5th Apr 2014, 21:05   #9227 (permalink)
 
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What disturbs me is that China being deeply engaged in the search, when the reported pinger was detected they were so "surprised" that they did not record it??? Surely they had enough info as to know the frequency of the pinger so they could detect it. I still think something is not right...
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Old 5th Apr 2014, 21:05   #9228 (permalink)
 
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Looks to not be operating 24/7.

. JORN was designed and acquired for the defence of Australia. In the context of the defence of Australia and peacetime military operations, JORN is not resourced or tasked to conduct surveillance operations 24-hours-a-day 7-days-a-week. To this end, JORNís peacetime use is focused on searching for those objects that the system has been designed to detect, thus ensuring efficient peacetime use of JORNís fiscal and staff resources

From https://www.airforce.gov.au/docs/JORN_FAQS.pdf
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Old 5th Apr 2014, 21:16   #9229 (permalink)
 
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atr-drivr, perhaps the Chinese are as susceptible to being taken by surprise as all us normal humans?

And I haven't read anywhere that the 90-second or 15-minute pings were NOT one-a-second. Like most on here I am hopeful that their find is authentic, regardless of the geopolitics.

Edit: I hardly think that, in the context of such a multi-national effort, China would be playing by their own rules, i.e. going it alone. If the find turns out to be authentic they'll have more than enough international kudos.

Last edited by broadreach; 5th Apr 2014 at 21:23. Reason: to add a bit of optimistic opinion
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Old 5th Apr 2014, 21:16   #9230 (permalink)
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Convergence Zone

Reading up on underwater acoustics Underwater acoustics - Wikipedia, the free encyclopedia reminded me about convergence zone propagation.

Essentially radiated sound is reflecting between bottom and near the surface and down again. It may near the surface at some distance from the source in a narrow range like an annulus. It can then re-emerge at twice the distance and so on.

The short 90 seconds detection reported in characteristic of a convergence zone detection where the hydrophone has passed through the emitted sound. Sailing a cloverleaf will not work.

It needs to relocate the convergence zone. The shortest the time between signal gain and signal loss will give you a bearing the to source. This is an ambiguous bearing.

The zones could be typically at 30, 60, 90 miles etc depending on bathythermal conditions and power of the source.

Quote:
Another phenomenon in the deep sea is the formation of sound focusing areas, known as Convergence Zones. In this case sound is refracted downward from a near-surface source and then back up again. The horizontal distance from the source at which this occurs depends on the positive and negative sound speed gradients. A surface duct can also occur in both deep and moderately shallow water when there is upward refraction, for example due to cold surface temperatures. Propagation is by repeated sound bounces off the surface.
I then found this link http://en.wikipedia.org/wiki/SOFAR_channel which has an animated graphic that demonstrates the deep sound channel and convergence zone.

Quote:
Acoustic pulses travel great distances in the ocean because they are trapped in an acoustic "wave guide". This means that as acoustic pulses approach the surface they are turned back towards the bottom, and as they approach the ocean bottom they are turned back towards the surface. The ocean conducts sound very efficiently, particularly sound at low frequencies, i.e., less than a few hundred Hz.

Last edited by Pontius Navigator; 5th Apr 2014 at 21:49.
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Old 5th Apr 2014, 21:39   #9231 (permalink)

 
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Highland

Firstly, how would the Aussies know unless someone told them ?
- which is entirely possible.

"It could have been heading towards Oz, they must have been prepared for that scenario after 9/11."

Apart from Perth and Darwin and a few other smaller towns and cities, the rest of Aus is one GAFA - Great Australia F All,
1000's of Kms of sand and desert and a long way to get to another big city.
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Old 5th Apr 2014, 21:40   #9232 (permalink)
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Originally Posted by highland View Post
Even if JORN doesn't operate 24/7, surely it must have occurred to someone it may be a good idea to switch it on with a large passenger jet "disappearing" within its range?? It could have been heading towards Oz, they must have been prepared for that scenario after 9/11.
Highland, first off if JORN was not scheduled to be on and there was no threat it follows that everyone would have been asleep with the weekend ahead of them.

Your second supposition didn't occur until many hours later. Recall it "crashed in the South China Sea" for several hours before they found it had "flown to the west north west" what, a day later? And a couple of days later that it might have been in the southern ocean or Kazakhstan? And days later that it might have been south west of Australia.
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Old 5th Apr 2014, 21:50   #9233 (permalink)
 
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The following by auv-ee explains in laymans language the affect of water temperature on acoustic channelling.
Quote:
For horizontal isotherms (temperature changes with depth but not laterally; the usual case considered), there is no bending of the straight-down ray. As the angle of incidence increases away from the vertical, bending will occur, either toward or away from the vertical.

Surface waters vary around the world, but are warm in the tropics. Thus, near the top of the water column, sound speed is elevated, due to increased temperature, and at great depth (1000s of meters) the temperature is uniformly cold, but the sound speed increases with depth due to increasing pressure. In the mid water (1000-2000m) the sound speed is minimum. This effect creates the deep sound channel, where near-horizontally directed sound is trapped and guided.

The critical angles vary with the particular profile of sound velocity vs. depth at any given place and time, but generally, sound can be exchanged between two points that are shallow and deep over a cone exceeding 45deg from the vertical. If this were not so, transponder navigation of surface vessels and acoustic communication with deep systems would not be possible. In fact sound leaving either a surface or deep source in tropical water will both be deflected toward the vertical as it approaches the mid-water channel. Things are different in the polar regions where the surface water is so cold that channelling occurs at the surface, rather than deep.
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Old 5th Apr 2014, 22:02   #9234 (permalink)
 
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Am I reading this right? Are the hugely knowledgeable (and most welcome) posters saying that the subsurface pinger signal may be subject to range extending effects just as HF radio waves are bounced/skipped off the ionosphere?
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Old 5th Apr 2014, 22:06   #9235 (permalink)
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CGB, yes, but that is the start of a new problem.

IMHO the Chinese ship may have gained a convergence zone contact and may well not have recognised it as such. It is the sudden signal loss which is a clue.

If they held it for 15 minutes the first time, as 2 nm, then they may have been crossing the annulus. The 90 second contact may have been just clipping it.

I did post about the deep sound channel a few days ago but it was modded out.
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Old 5th Apr 2014, 22:19   #9236 (permalink)
 
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Am I reading this right? Are the hugely knowledgeable (and most welcome) posters saying that the subsurface pinger signal may be subject to range extending effects just as HF radio waves are bounced/skipped off the ionosphere?
Basically yes. Differences in the properties of a material, be it something as simple as a glass fiber or as complex as the atmosphere or the ocean can cause signals (acoustic, electromagnetic, or optical (a special case of EM)) to be bend. If the conditions are correct, the bending tends to refocus the energy of the wave in a channel so that the loss in energy becomes linear in distance rather than the normal quadratic (1/r^2). For those old enough to remember early microwave (not oven), the medium becomes a natural wave guide.

Physics may not find MH370 but the laws it provides still do provide rational explanations for all manner of natural phenomenon which have come up as a result. Sadly the "laws" of human nature don't.

Last edited by jmmilner; 5th Apr 2014 at 22:23. Reason: Add comment
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Old 5th Apr 2014, 22:33   #9237 (permalink)
 
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It's interesting that the Chinese are always the first...

It's interesting that the Chinese are always the first to "find" something with regards to this aircraft.....first to spot floating "items" on their satellites photos now the first to "hear" the ping but did not record what they heard.
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Old 5th Apr 2014, 22:41   #9238 (permalink)
 
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Quote:
Am I reading this right? Are the hugely knowledgeable (and most welcome) posters saying that the subsurface pinger signal may be subject to range extending effects just as HF radio waves are bounced/skipped off the ionosphere?
No. At the high ultrasonic frequency used by the pinger, attenuation with distance is very significant, so the signal at detectable levels just doesn't go very far.

At much lower frequencies, where passive sonar is used for submarine detection and tracking, signals can travel hundreds or even thousands of miles. They are refracted by the thermocline (an area of rapid vertical temperature change) a few hundred feet below the surface. In that sense, it is similar to tropospheric ducting of radio waves and perhaps a little analogous to HF ionospheric "skip" propagation.
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Old 5th Apr 2014, 22:46   #9239 (permalink)
 
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Quote:
Originally Posted by Robin Clark

... which means that either the speed of the aircraft was changing , or it was turning fairly slowly left from its southerly heading.
The increasing westerly magnetic variation would provide the direction change you are suggesting, provided the a/c was in HDG mode of say 180įM from west of Banda Aceh.
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Old 5th Apr 2014, 23:00   #9240 (permalink)
 
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To summarise, the 37KHz pings heard near the surface (if true) indicate that wreckage is on the bottom somewhere nearby.

It is not, however, a simple job to narrow the search and determine an exact location because the signal could have bounced around in an underwater mountain range and been deflected by temperature and salinity layers.

The next part of the job, therefore, is to get listening devices as deep as possible whilst avoiding collision with the mountains. This requires specialist kit and is not easy.

This is going to take time and the batteries are nearing their end. It is therfore likely that a deep water sidescan survey will be required, the good bit is that the search area is now much smaller.

When wreckage is eventually located it will still take months rather than weeks to recover anything using UAVs
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