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Published news reports indicate Inmarsat used something similar to 'doppler shift' to analyze pings from flight MH370, concluding the plane was traveling south not north.

Any normal radio receiver would loose minor frequency shift early on in the signal path. So how did Inmarsat do the analysis after the fact? I assume it involved minor arrival time differences between subsequent pings, and the presumed angles of the north and south flight tracks, but exactly what was the mechanism?

Chris McLauglin, a senior vice-president at Inmarsat, told Sky News: “What we did two weeks ago was say it could be north or it could be south, and what we’ve done is refined that with the signals we got from other aircraft.

Bryce
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  • Given they claim to have done "several years worth of research in a couple of weeks", I expect that a paper is in the offing. You're probably going to have to wait until they publish to learn how they did it. – markt Mar 27 '14 at 08:45
  • The quote makes it sound to me like the determined something in the data they had that seemed like it could to a degree correlate to the doppler shift of the uplink, and then they went and qualified that with data from a bunch of other flights either on similar known tracks or intentionally flown for purposes of data collection. – Chris Stratton Mar 27 '14 at 15:28

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I would not think arrival time. The sat has to work with ground stations that it is approaching and receding from, so it can work with the Doppler shifted frequencies and probably uses the shift to calibrate position and orbital elements.

Depending on satellite position and orbit, one of the paths will give a different shift than the other. Slant angles would be different and if the sat is in between the arcs, one would cause blue shifting the the other red. Probably pretty easy for the them to figure out.

The police Dopplers can easily measure a car speed within 1 MPH. Consider the effect from the speed of a 777.

C. Towne Springer
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  • The sat to ground station transmission, sure. But the mobile unit to sat transmission, Doppler shift is just noise. – Bryce Mar 27 '14 at 08:52
  • @Bryce Since the sat communicates with the ground, it can handle the freq shift, which is not trivial. It may also simply amplify the mobile signal and relay it, in which case the ground equipment could analyze it. – C. Towne Springer Mar 27 '14 at 08:58
  • Looks like it was doppler, now it's a bit further down the track this has been published if you felt like including any of the info in your answer: http://www.inmarsat.com/news/malaysian-government-publishes-mh370-details-uk-aaib/ – PeterJ Apr 26 '14 at 10:19