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Other uses for 37.5khz?
From the NPR report on the Xinhua story:
We'll caution that the signal hasn't yet been investigated, and it's too early to draw a connection to the missing flight MH370. The signal's frequency is 37.5 kHz, according to Xinhua. That's the frequency underwater locator beacons use to transmit their location; it's also reportedly used by other systems. |
The ULB batteries are 30 days @4c . Does any one know the sea bed temp at pinger location. I understand the unit is powered by lithium ion batteries, how are these affected by temp.
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Deep ocean water is uniformly somewhat below 4 C, usually 1-3 C.
So the battery life expectancy was set to reflect expected conditions. Afaik, lithium batteries drop their power pretty steeply once past their rated duty service, so there is not much time left to pick up the pinger. |
If the Chinese actually have picked up the pinger off the black boxes, my guess is that they were led to them by some sort of high tech military technology they don't want the rest of us to know they have. Whether that is satellite imaging, submarines or something else... Hard to believe they just accidentally stumbled upon the scene.
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what happens if this is the FDR/CVR and the Chinese get hold of it - who then undertakes the data/tape play back and investigation?? It was widely reported that this was directed at the Chinese without specifically saying so. Reading between the lines, Certainly under currents within / in the SAR effort regardless of the smiles from the air side. But it would also be good if they left the release of information, verified or otherwise, to the lead investigating authority. I'd then feel a little more convinced that it's less about PR and more about finding the aircraft. - from what I can gather - Chinese ship - to China - Chinese news releases information - someone from the SAR Effort comments. 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. |
If the signals are from MH370's boxes and the source can triangulated, surely it doesn't matter if the batteries run out before they can be retrieved. If AF447's black boxes could be retrieved two years after the accident, surely these boxes and the wreckage will be found too? Or am I missing something?
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Originally Posted by Chronus
(Post 8420439)
The ULB batteries are 30 days @4c . Does any one know the sea bed temp at pinger location. I understand the unit is powered by lithium ion batteries, how are these affected by temp.
Lithium-based Batteries Information - Battery University Choices of Primary Batteries - Battery University |
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. |
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. |
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 :O Luckily Angus Houston is the type of person with the knowledge of the people involved who should be able to keep things "in check". |
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. |
Originally Posted by etudiant
(Post 8420450)
Deep ocean water is uniformly around 4 C, which also happens to be the highest density temperature for water.
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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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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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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, JORN’s peacetime use is focused on searching for those objects that the system has been designed to detect, thus ensuring efficient peacetime use of JORN’s fiscal and staff resources From https://www.airforce.gov.au/docs/JORN_FAQS.pdf |
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. |
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. 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. 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. |
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. |
Originally Posted by highland
(Post 8420599)
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.
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. |
The following by auv-ee explains in laymans language the affect of water temperature on acoustic channelling.
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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