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#268545 - 03/25/14 08:48 PM Re: Lost Malaysian Plane [Re: unimogbert]
RNewcomb Offline
Member

Registered: 04/19/12
Posts: 170
Loc: Iowa
Originally Posted By: unimogbert
In the thread about PLBs in slot canyons I wrote-

"US Navy NAVSAT of the 1970's used observed doppler shift to provide location information to vessels. The rate shape of the frequency shift curve (it would be an S from high to low like listening to a locomotive horn going past you) reveals the distance from the observer to the ground track of the satellite. (still have to choose which side you are on from it)"

This is the principle that INMARSAT folks applied to the flight tracking. Only in this case the satellite was "stationary" and the airplane beacon was moving.

This is quite a feat of measurement considering that the airplane is mostly flying ACROSS the line of sight (from 22,500 miles EVERYTHING is across the LOS!) and the doppler effect only applies to the component of velocity IN the line of sight.

Found an online calculator- assuming 400kt aircraft speed the biggest doppler shift would be 0.27Hz. That's quite a measurement feat!



Yes.. yes it is. I am amazed by how creative we can get when we really want to solve a problem. I just hope they change guidelines a little to help track incidents like this. Putting the family and friends of the passengers on this plane through two weeks of not knowing, and still.. just really, really good educated calculations and no other evidence to refute it... I find kind of unacceptable with the technology we have available now.

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#268549 - 03/25/14 10:19 PM Re: Lost Malaysian Plane [Re: RNewcomb]
Russ Online   content
Carpal Tunnel

Registered: 06/02/06
Posts: 4821
Loc: SOCAL
This incident had a shakey start with sending the search assets to the wrong body of water when they should have known better. Then the credibility of everyone including the Malaysian PM went downhill. At a certain point incomplete and inaccurate reporting leads one to not believe anything they say no matter how hard they try to get it right.

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#268767 - 04/01/14 07:29 PM Re: Lost Malaysian Plane [Re: Ian]
ireckon Offline
Pooh-Bah

Registered: 04/01/10
Posts: 1626
Loc: Northern California
I guess the ratings are still going strong. CNN is still providing expert after expert of interesting but useless information.
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#268770 - 04/01/14 08:22 PM Re: Lost Malaysian Plane [Re: ireckon]
Russ Online   content
Carpal Tunnel

Registered: 06/02/06
Posts: 4821
Loc: SOCAL
... Interesting but useless SPECULATION.

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#268774 - 04/01/14 11:58 PM Re: Lost Malaysian Plane [Re: Ian]
JerryFountain Offline
Addict

Registered: 12/06/07
Posts: 418
Loc: St. Petersburg, Florida
unimogbert,

I think you will find they did not use doppler, but time delay from the outgoing signal to the incoming signal. Gives you distance toward or away from the satellite. Longer interval = further away. That is why they were not able to initially tell the northern from the southern route.

Respectfully,

Jerry

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#268780 - 04/02/14 07:56 AM Re: Lost Malaysian Plane [Re: Ian]
Phaedrus Offline
Pooh-Bah

Registered: 04/28/10
Posts: 2120
Loc: Great Plains
Starting to look like they're not going to find it. Maybe in 20 years it will turn up while they're looking for something else.
_________________________
“You can tell whether a man is clever by his answers. You can tell whether a man is wise by his questions.” Naguib Mahfouz

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#268784 - 04/02/14 01:19 PM Re: Lost Malaysian Plane [Re: JerryFountain]
unimogbert Offline
Old Hand

Registered: 08/10/06
Posts: 854
Loc: Colorado
Originally Posted By: JerryFountain
unimogbert,

I think you will find they did not use doppler, but time delay from the outgoing signal to the incoming signal. Gives you distance toward or away from the satellite. Longer interval = further away. That is why they were not able to initially tell the northern from the southern route.

Respectfully,

Jerry


Hmmm. Probably right. Interesting problem since the transmitted signal may not be to Cesium standards in its timing. But all you'd really need is 2 or more satellites timing the same ping and working out the differences in delay/geometry/satellite location.

Thanks.

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#268786 - 04/02/14 05:33 PM Re: Lost Malaysian Plane [Re: JerryFountain]
Arney Offline
Pooh-Bah

Registered: 09/15/05
Posts: 2485
Loc: California
Originally Posted By: JerryFountain
I think you will find they did not use doppler, but time delay from the outgoing signal to the incoming signal.

I was under the impression that measuring the time delay of the signal was how the Inmarsat folks initially tried to locate the plane's position, which resulted in widely diverging flight paths, but that the "novel" method they used to later to focus the search towards the south was some sort of doppler analysis that gave them a direction vector.

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#268790 - 04/02/14 06:17 PM Re: Lost Malaysian Plane [Re: Ian]
Arney Offline
Pooh-Bah

Registered: 09/15/05
Posts: 2485
Loc: California
Was just reading that the first submarine has joined the search, the British Royal Navy's HMS Tireless. Another British Royal Navy ship should arrive shortly.

There's mention of an Australian naval vessel outfitted with a "black box detector" supplied by the US. It's not stated explicitly in the article, but the implication seems to be that it took this long for this "black box detector" to be brought into this search. Granted, this is a remote search area to reach, but still, it's almost the end of the 30 day battery on the black box pinger!

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#268791 - 04/02/14 08:08 PM Re: Lost Malaysian Plane [Re: Arney]
Russ Online   content
Carpal Tunnel

Registered: 06/02/06
Posts: 4821
Loc: SOCAL
Arney - The "Black Box" is that little device they tow to detect the aircraft black box ping. It needs to be close to the actual aircraft location because the black box ping is a low power signal. IMO the search area is still way too big for this to be effective..

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