How British satellite company Inmarsat tracked down MH370

http://www.telegraph.co.uk/technology/news/10719304/How-British-satellite-company-Inmarsat-tracked-down-MH370.html

by pedrocr • 12 years ago

164 86 12 years ago

telegraph.co.uk

zaroth• 12 years ago

  engineers were able to narrow the location of the plane down
  with an initial analysis of the Doppler effect on the signal
  from the flight’s pings and the plane’s approximate altitude.

How and why would they have a record of this to be able to study it?

Serow2253• 12 years ago

I'm curious about that too, it seems very unlikely that the actual digitized RF waveform was available for analysis. My guess, based on working with somewhat similar systems in the past, is that the ping packet content was also tagged by the satellite with the measured carrier frequency (or offset from nominal) and this value had enough precision that it let them calculate the Doppler effect. The reason I would say this is because I've done similar things in the past for telemetry applications, it can be really handy for debugging when things aren't working right.

sliverstorm• 12 years ago

Or, what if they studied the time dilation between pings? The pings are probably on a precise, known schedule.

waterlesscloud5• 12 years ago

So the idea is that there's a shift on the intra-ping timescale? So there are numerous packets and each packet would have the frequency of that particular packet attached to it? Obviously I have no clue what the protocol for the ping looks like, just trying to understand how it would work.

Also curious how they matched it to planes flying the southern route, since I wouldn't have guessed there were any other planes flying on the southern route (which goes...nowhere).

rz2k4• 12 years ago

What is a likely way for that to work with something launched in 1996? If the plane was going 50 MPH away or toward satellite, that's ~7e-8 * c. If I remember, the frequency would be shifted by a factor of the square root of (1 - 7e-8)/(1 + 7e-8), or its inverse.

Would the satellite always relaying that level of precision to the ground? If it is, why would they have prioritized that over what would have presumably be a dramatic increase in capability if it were discarded instead? Could they have designed it to store that much precision in rotating logs available on request? And furthermore, how is a relativistic Doppler shift on those magnitudes discernible from the frequency shift naturally occurring from the plane's transmitter?

I suppose my point is that while it's easy to understand the idea of a train whistle changing pitch as it passes by, how they would do it in practice sounds like magic, being unfamiliar with the capabilities and the equipment that geostationary satellites generally carry.

chronomex• 12 years ago

Inmarsat is a "bent pipe" system, meaning that the satellite just amplifies and sends down to the base station everything that it receives. So the operator's RF fanciness is limited only by the noise factor in the satellite's amplifiers.

wallflower• 12 years ago

A pretty detailed explanation from Reddit user XenonOfArcticus.

http://www.reddit.com/r/MH370/comments/218i36/how_the_satell...

waterlesscloud5• 12 years ago

Ah! Now I get it. Thanks for the link. :-)

ynniv• 12 years ago

A better one: http://www.reddit.com/r/MH370/comments/218i36/how_the_satell...

cynwoody3• 12 years ago

The Doppler stuff is new (as of the 24th).

What I had understood before was that the airplane carried an Inmarsat satellite transceiver which remained active, even though certain subsystems that use it (notably ACARS) were disabled. While active, the transceiver communicates with the satellite once an hour (the "pings" at 11 minutes past), even if it has no traffic to send. Failing to disable the transceiver in addition to the other systems would have been an oversight on the part of the plane's hijackers, assuming it was hijacked.

Apparently, Inmarsat had available accurate ping timing data. Combined with knowledge of turnaround delays, this would enable them to calculate the plane's distance from the satellite during each ping. That defines an imaginary sphere in space, which intersects with the earth's surface to form a circular locus of where the plane could have been at the time. Presumably, there were eight such ping interactions, ending with the one at 0811 Kuala Lumpur time. There was no 0911 ping, meaning the plane had either crashed or landed and powered off before that time.

And so we had the northern and southern arcs. These were obtained by cropping the circle based on factors such as how far the plane could have flown in the available time, whether or not military radars, if any, had detected the plane, etc.

Now comes the Doppler data. Apparently, Inmarsat also has an accurate read of the plane's transmit frequency. The extent to which this frequency differs from the nominal frequency would indicate the plane's velocity towards or away from the satellite at the time of the ping.

Today, Chris McLaughlin revealed that Inmarsat had studied the Doppler patterns of normal flights in the same region and concluded that the Doppler data for MH370 indicated that the southern arc was the right one. Hopefully, Inmarsat has it right, and the black boxes will be found before their beacon batteries run out.

brador• 12 years ago

Is the data on the black boxes dependent on continual power? That seems strange.

bteitelb• 12 years ago

The data is persistent, but the beacons only transmit for 30 days or so.

spc476• 12 years ago

I don't think so, but having the beacon on will make finding the black box easier.

khuey• 12 years ago

No. Persistence of the data does not require continuous power. But the black box has a battery-powered "pinger" that produces sound to make it easier to find. The batteries for that is only required to last for 30 days.

Shivetya• 12 years ago

the second biggest issue with the data is that it will have written over some of the information that would have occurred at the time the flight deviated from the assigned course.

It used to be that voice recorders with 30 minute loops, I am not sure if that is still the case.

sigkill• 12 years ago

I don't know why I haven't seen this linked before here, but this is a very informative teardown of an FDR by Mike of MikesElectricStuff

https://www.youtube.com/watch?v=mQehX0rVYuY

Check out his other videos as well. He is really good at what he does, and his videos still retain the hackery feel.

hga2• 12 years ago

One minor correction, which I'd seen an indication of and had suspected from an architectural design point of view: the plane was getting pinged, it wasn't producing the pings. Per The Aviation Herald, which has lots of details today (and isn't behind a pay wall who's visits per month I used up yesterday): http://avherald.com/h?article=4710c69b&opt=0

"During the flight the ground station logged the transmitted and received pulse frequencies at each handshake."

That's in the middle of a huge paragraph describing how they did it in quite some detail, e.g. compared data to other 777s flying that day.

sixQuarks• 12 years ago

Call me a conspiracy nut, but here's what I believe may have happened:

It's almost a certainty that the US government has spy satellites video recording the entire planet at all times, at a level good enough to distinguish individual aircraft. The US spy agencies probably knew where the plane was right away, but they can't just tell everybody or the jig is up.

So they may have just contacted this satellite company, told them where the plane is, and came up with a technical explanation of how it was located.

ewoodrich• 12 years ago

The US certainly has a bloated defense budget, but I strongly doubt that we have satellites constantly trained on the typically empty oceans that cover 70% of the Earth.

marshray2• 12 years ago

While I don't subscribe to GP's view that satellites have bandwidth for "video recording the entire planet at all times", it seems plausible that SIGINT satellites would have a relatively constant bandwidth available for observation. As a (non-geostationary) satellite passes over relatively unpopulated areas (e.g., the southern Indian Ocean), it will be "bored" and thus far more likely to notice a single low-power transmission.

On the other hand, if it is storage and downlink bandwidth that is limited, sats would probably be programmed to ignore or discard uninteresting signals. This seems likely to me.

So the question may be whether commercial airliner pings from the southern Indian Ocean area were considered 'interesting' at the time and, if not, did anyone realize there was a rogue 777 in time to re-task the satellites?

Regardless, I'd bet those signals are considered interesting going forward.

kanamekun• 12 years ago

The satellites need to be repositioned to provide eyes on coverage. Source: every episode of 24 ever.

danieltillett• 12 years ago

While I don't think this particular suggestion is likely given the shear amount of data that would need transmitted, it might be possible that there is more data being transmitted by these planes than has been admitted.

roel_v• 12 years ago

Why would they take the risk of telling anyone?

conformal• 12 years ago

based on the region where this occurred, you can rest assured that one, if not several, state intelligence services knows exactly what happened to the plane and has near continuous knowledge of its position. the area of asia where this occurred would likely be of interest to US, CN and RU.

the fact that none of these countries gave information about the whereabouts of the plane in a timely fashion suggests to me that they have a vested interest in not sharing what they know.

ansible• 12 years ago

Call me a conspiracy nut, but here's what I believe may have happened:

It's almost a certainty that the US government has spy satellites video recording the entire planet at all times, at a level good enough to distinguish individual aircraft. ...

You are a conspiracy nut. :-)

Spy satellite time is expensive. And they typically have a narrow field of view (the better to read the license plate number off of your car). Basically they are orbiting telescopes like the Hubble, except they are pointed down instead of up.

It is inconceivable to me that they'd waste time having a spy sat looking at empty stretches of the Indian Ocean for no good reason. Especially when there are more interesting things to look at (Afghanistan, Ukraine, North Korea, etc.).

topbanana• 12 years ago

As an interesting aside, Inmarsat are based on the Old Street roundabout in London. This is reputedly the centre of the startup scene.

awalton• 12 years ago

    ** is thought to have tracked down.

They still haven't actually found the plane, they've just got a very well reasoned assumption of the area the plane should be in.

sebcat• 12 years ago

What people write in the article's comment section is certainly an interesting read. Irrational at best.

Patient0• 12 years ago

In the actual video he seems to have misunderstood what the Doppler effect actually is. He gives the example of a train whistle "getting louder as it comes towards you and fainter as it moves away" but he should have said something along the lines of "the same way that a train whistle has a higher pitch as it moves towards you and a lower pitch as it moves away from you". The intensity of the signal is much harder to measure/calibrate than the frequency of the signal.

jacoplane• 12 years ago

Chris McLaughlin (the guy in the video) is a PR guy, not a scientist.

mkonecny• 12 years ago

We learned what the doppler effect was in Grade 11 physics - it's literally high school material.

Tloewald2• 12 years ago

...and by the way, we offer a service that only costs $1/h/plane and we'd like governments to force everyone to pay us. Now, I have no idea whether $1/h/plane is reasonable (is that to cover the satellite comms, or is that on top of them?) but it is kind of stunning that planes aren't tracked automatically and as a matter of course the way, say, most people with cell phones are.

How British satellite company Inmarsat tracked down MH370

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