UK satellite operator used the Doppler effect to locate MH370 | Hacker News Reader

UK satellite operator used the Doppler effect to locate MH370

themalaysianinsider.com

33 pointsdcx6 comments

Here's some intuition about how the Doppler effect can be used to find location of a transmitter given a single receiver: objects (transmitters) moving in a straight line that are far away from the receiver will have less of a shift in frequency when they "pass" the receiver than objects that are close to the receiver.

What's more, you don't actually have to wait for the transmitter to pass the receiver: the radial velocity is what's important, and if you measure that at several points, you can fit a curve. That will tell you how far the transmitter is from the receiver.

Do this several times, and you can make a constellation of possible locations, and then fit those points to a line.

Globalstar does this with its satellite phones. Their situation is easier than with Inmarsat, because Globalstar uses fast-moving (relative to points on Earth) LEO satellites rather than geostationary satellites. Given a single LEO satellite on a known orbit and assuming that the phone on the ground is stationary, a fix on position can be made relatively quickly using the Doppler effect.

Here's a paper about how Globalstar does it: http://www.eng.tau.ac.il/~nadav/pdf-files/Instant_active_pos...

We should all take a page from this book - data storage is incredibly cheap, and you can't predict what potential value you might get from it. Store any data you can get your hands on, timing information, raw packets, everything. It's easy to throw away later, but impossible to recreate if you never had it in the first place.

I think this is exactly how the NSA works:)

More on topic this is pretty cool use of limited data to solve a problem - now lets hope they can find the black box.

This is really interesting and I appreciate knowing the technique that went into coming up with this conclusion, but I find it kind of weird to see the article mention that the plane crashed and killed all passengers so factually. People need closure on this, but it seems kind of cold to speak this way about the fate of the passengers considering we have no physical proof.

It's kind of like when having a funeral without a body. Which is done in some extraordinary situations.

Statistically speaking, assuming the plane's final destination was somewhere in the Southern Indian Ocean, there are no more survivors. If the plane had somehow landed in the Southern Indian Ocean (roiling seas, 20 to 40 foot waves [1], pitch black - remember moonless night) and there were survivors, there would be no more survivors two weeks later (hypothermia due to wind chill, lack of fresh water). Also, the emergency locators in the life rafts would have most likely sent out the distress signals upon contact with water.

The mystery of MH370 is that in most all previous cases of onboard fires, there was some successful attempt to make a form of emergency radio contact. Even when the ceiling was literally melting [2]. There was none with MH370.

[1] http://www.seos-project.eu/modules/oceancurrents/oceancurren... http://en.wikipedia.org/wiki/Roaring_Forties

[2] http://en.wikipedia.org/wiki/Swissair_Flight_111

Minor correction: by the time the plane must have come down in the ocean, it was after 8am, which I think is well after sunrise at that date and location.

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