Acoustical Search
Acoustical Search
(OP)
Let's have a little discussion on the hunt for the Flight 370 black boxes.
There's now a map out of the week's detected pings.
AP Article
Acoustical
What's happening is that as they drag the small skate-shaped microphone platform around they hear the recorder pings for a couple of seconds to over a couple of hours. Once they lose the the signal they turn and weave and try to pick up the signal again, always failing.
From their statments they are trying to "triangulate" the pings to figure out where the black boxes (BB) are.
My two questions:
1) How can they possibly hope to triangulate on the BBs with such sparse data containing NO directional information.
and
2) Why do they not have two, or three, or four microphones on the drag platform so they can instantly get a direction vector from ANY and EVERY ping detected? I'm baffled by this obvious lack of sophistication.
There's now a map out of the week's detected pings.
AP Article
Acoustical
What's happening is that as they drag the small skate-shaped microphone platform around they hear the recorder pings for a couple of seconds to over a couple of hours. Once they lose the the signal they turn and weave and try to pick up the signal again, always failing.
From their statments they are trying to "triangulate" the pings to figure out where the black boxes (BB) are.
My two questions:
1) How can they possibly hope to triangulate on the BBs with such sparse data containing NO directional information.
and
2) Why do they not have two, or three, or four microphones on the drag platform so they can instantly get a direction vector from ANY and EVERY ping detected? I'm baffled by this obvious lack of sophistication.
Keith Cress
kcress - http://www.flaminsystems.com





RE: Acoustical Search
As for location, I'm guess, given the size, is that it's doing it solely based on signal strength, and building up a signal strength map, which would show the direction of maximum signal. I'm surprised someone isn't using submarine towed arrays, which ought to be able to do direction finding within a single pass.
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RE: Acoustical Search
We used low-frequency microphones to locate enemy gun locations when I did my military service around years ago. An array with microphones (we used large loudspeakers as microphones) spread out along a 200 - 300 m long baseline, a fast recorder (used UV at that time) and some trigonometry located any gun or haubits to within 20 - 50 meters. Depending on weather and distance to enemy.
Surely, a similar technique is available today? With a lot more precision - even if speed of sound in water is a lot faster than in air.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Acoustical Search
RE: Acoustical Search
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Some wag on the Internet has processed an audio sample from the MHG370 search coverage and he believed he could detect a change in the period indicating increasing range. Perhaps it's a future search technique.
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These UABs will be good for 90 days, not just 30, in future versions. The transition to the new standard is just starting.
RE: Acoustical Search
We are obviously discussing deeper waters here. Some 3000 - 4000 m. So, it should be possible to get below the upper layers and get useful readings.
I admit that I am out on deep waters here. Never done that myself. But the fact that there may be a few problems to solve shouldn't discourage us nerd engineers - should it?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Acoustical Search
{
It won't help now, but it should be possible, and relatively simple, for future pingers to just identify themselves directly, by encoding a unique serial number in the burst by suppressing individual clicks in a pattern.
}
The self-imposed requirement to dredge up some identifiable wreckage before committing the UAVS to do side-scan sonar sweeps is sort of self-contradictory, because you need an ROV to grab stuff off the ocean floor, and you're sending it down blind without the side scan map to tell you where to drop it.
OTOH, the side-scan will presumably deafen the TPLs, so I can understand running TPLs as quietly as possible until the pingers die. ... which seems to be happening about now.
Identifiable flotsam would be nice. Either there is no flotsam, or it has blown into a gigantic gyre of garbage, or ... the wreckage is actually on a mountainside in Kazakhstan.
Yeah, I saw the analysis showing better correlation for a straight course intersecting the 'southern arc', but I couldn't help wondering if a curved course would correlate to the northern arc. I'm troubled that that decision to abandon half of a huge search space was based on five-ish inferred data points and the assumption of a straight line course.
Mike Halloran
Pembroke Pines, FL, USA
RE: Acoustical Search
CODE
-------*-- * * * * * ----*--------------- * BBA sub makes soOOO much sense. I bet they have crazy good direction abilities. If it was an American flight they'd probably jump right to it.
VE1BLL; Don't leave us hanging!! How'd the L-shaped array and your filters work out?
Gunnar; It's interesting that they're hearing the pings even though it seems they're greatly exceeding the reported distance limits they were saying earlier. It's probably why the hearing is so erratic. Pipes of clear conduction stretching the distance considerably when things are lined up.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Acoustical Search
If it could be modulated, then it might be better to encode a Barker code or similar SNR improving waveform than an ID. They're unfortunately short range and rarely used, so there's not too much business case for an ID.
RE: Acoustical Search
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RE: Acoustical Search
RE: Acoustical Search
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RE: Acoustical Search
They're acting like there could be an infinity of pinger-type devices active at any given time in that desolate ocean; I'm having a hard time with that.
Okay, if the piezo is part of the oscillator, gating individual cycles gets harder. It's still possible to modulate the oscillator gate duration to encode numbers; add or subtract a little time, etc.
Mike Halloran
Pembroke Pines, FL, USA
RE: Acoustical Search
So when they first talked about the pinging they said they had to be within three miles. Later the reports talked about picking up signals 100 miles away. Then I remembered the experiment. At great depths there are very few dissolved gases.
Might be the reason for extended travel. Also the reason they want to drop the microphones down to pick up.
RE: Acoustical Search
Could it not just send the aircraft callsign in Morse code? (If anyone can still read it!)
H
www.tynevalleyplastics.co.uk
It's ok to soar like an eagle, but weasels don't get sucked into jet engines.
RE: Acoustical Search
If the pinger had its own globally unique serial number, not unlike the MAC address of each and every network adapter, then the a/c could be identified by searching paper-ish records, after picking a number out of an audio recording or scope trace, where say a 9ms burst was a binary 0, and a 15 ms burst was a binary 1, and taking it from there.
If you wanted to get fancy, you could move the trailing edge of the burst around in 1ms increments to encode more than one bit per burst, but there's something to be said for not requiring anything more special than an oscilloscope or laptop screen, and given the demonstrated capture times of whatever they've found, the data rate is not terribly important.
Mike Halloran
Pembroke Pines, FL, USA
RE: Acoustical Search
That would make it substantially more complicated than it is, which is currently and oscillator, a gating circuit, and a water pressure activated switch. In order to send anything else, there would need to be a programming interface, flash memory, etc.
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RE: Acoustical Search
RE: Acoustical Search
Any chance a Doppler shift could be detected based on a 10knot tow speed that would give directional info?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Acoustical Search
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RE: Acoustical Search
RE: Acoustical Search
The ship mows-the-lawn in a series of parallel lines. At the end of each line, the process of turning 180 degrees and running the next line with a platform on the end of a long cable may require several hours to perform. Additionally IRstuff points out the slow speed required to keep noise down (from waterflow over the sensor platform). So the process of doing the search is tedious and takes time.
Some of the encouraging news is that on some single lines, pinger noise would be heard continuously, fade away, and heard again about a km apart. This could be due to propagation through the water (temperature inversion, path effects, etc) or could represent hearing the pinger from one of the two data recorders, and then the other.
Some discouraging news is that the recorders could be under a meter of silt if seperated from aircraft structure. So, if the pingers are dead by the time they get a ROV down, finding them may be impossible.
News articles quoting information from the pinger manufacturers have reported the lower frequency of the signals could come from a combination of the water depth (high pressure), water temperature (it's cold down there), and low pinger battery voltage (nearly gone).
RE: Acoustical Search
IR: I had no idea they towed that slowly. That's hideous. It's probably hard to even point the ship at that speed.
Buried in the silt?! Oh, that's a horrid possibility.
A plane dropped hydrophone buoy has heard a ping. If they could get a couple of them to hear the same ping they'd have it in the bag.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Acoustical Search
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RE: Acoustical Search
RE: Acoustical Search
Interesting, the maritime traffic site from above doesn't show any of the US warships, for good reason, no doubt, but it makes it very unclear where they are, and where they're searching. The search map shown on the site has shrunk somewhat; it showed a large rectangular area that encompassed both of the two rectangular regions to the west, but the Ocean Shield has pretty much been glued to the tiny rectangle closer to Aus. since Saturday. The track history for Ocean Shield shows a portion of a raster pattern.
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RE: Acoustical Search
Keith Cress
kcress - http://www.flaminsystems.com
RE: Acoustical Search