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(Malaysian Insider)   Doppler Shift. That's how Inmarsat traced MH370 to the Southern Indian Ocean   (themalaysianinsider.com) divider line 47
    More: Interesting, Doppler shift, Inmarsat, Indian Ocean, physics, Prime Minister of Malaysia, Kuala Lumpur to Beijing, Air Accidents Investigation Branch, satellites  
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2318 clicks; posted to Geek » on 25 Mar 2014 at 7:50 AM (17 weeks ago)   |  Favorite    |   share:  Share on Twitter share via Email Share on Facebook   more»



47 Comments   (+0 »)
   
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2014-03-25 07:33:56 AM
oooooooooooooooooooOOOOOOOooooooooooooooooo    shiat!!!!      *splish*
 
2014-03-25 07:36:59 AM
It's a tiny piece of data, but it doesn't really help all that much except to confirm what we already know:  The aircraft went down in the southern Indian Ocean.

Doppler shift can be used to get a very accurate location, if both the receiver *AND* transmitter have very accurate frequency tolerances.  And while I am prepared to believe than an INMARSAT satellite receiver may have a very accurate receiver, I'm less inclined to believe the ACARS transmitter(s) on the Boeing 777 are that accurate, because they don't need to be all that accurate.

Without knowing the precise frequency the transmitter on MH370 was operating on (and also what precise frequency the satellite was listening to), it's impossible to get any kind of a very accurate doppler location.

Oh, and complicating this is that the plane could have been flying for up to half an hour from the time of the last "ping" until it crashed.  At the typical cruising speed of 490 knots, that's a potential search area of 245 nautical miles in length, minimum.
 
2014-03-25 07:58:07 AM
media-cache-ak0.pinimg.com

I'm not quite as well versed as dittybopper. here's my contribution.
 
2014-03-25 08:22:39 AM
www.graffitiwithpunctuation.net
Well, let's not start sucking each other's dicks quite yet. You still haven't found the plane, you found a HUGE area where you think it is.
 
2014-03-25 08:26:00 AM
Now the Doppler shift has really hit the fan?
 
2014-03-25 08:28:29 AM

YodaBlues: [www.graffitiwithpunctuation.net image 317x417]
Well, let's not start sucking each other's dicks quite yet. You still haven't found the plane, you found a HUGE area where you think it is.


^^^ yaaa......  THIS   ^^^^^^

I'm still treating the Malaysian announement as if it came from Bagdad Bob....
 
2014-03-25 08:31:39 AM

dittybopper: It's a tiny piece of data, but it doesn't really help all that much except to confirm what we already know:  The aircraft went down in the southern Indian Ocean.

Doppler shift can be used to get a very accurate location, if both the receiver *AND* transmitter have very accurate frequency tolerances.  And while I am prepared to believe than an INMARSAT satellite receiver may have a very accurate receiver, I'm less inclined to believe the ACARS transmitter(s) on the Boeing 777 are that accurate, because they don't need to be all that accurate.


Without knowing the precise frequency the transmitter on MH370 was operating on (and also what precise frequency the satellite was listening to), it's impossible to get any kind of a very accurate doppler location.

Oh, and complicating this is that the plane could have been flying for up to half an hour from the time of the last "ping" until it crashed.  At the typical cruising speed of 490 knots, that's a potential search area of 245 nautical miles in length, minimum.


That's what I love about the Internet: there's always That Guy who thinks he knows more than an entire team of engineers and scientists from the company THAT BUILT THE FRIKKIN' SATELLITE and developed a model that's (reportedly) never been done before because reasons. Hey, Radio Ham Guy, do you think maybe its possible that Inmarsat, ATC, and Boeing do actually know the precise frequencies they were operating on? Or that they don't actually care what you are "prepared to believe"?

Oh, and apparently That Guy was the THE ONLY PERSON ON THE PLANET who already knew where the plane was. Perhaps he could have let the people searching know, who apparently only knew that it was probably somewhere along two arcs, one north and one south?
 
2014-03-25 08:38:04 AM

czetie: That's what I love about the Internet: there's always That Guy who thinks he knows more than an entire team of engineers and scientists from the company THAT BUILT THE FRIKKIN' SATELLITE and developed a model that's (reportedly) never been done before because reasons. Hey, Radio Ham Guy, do you think maybe its possible that Inmarsat, ATC, and Boeing do actually know the precise frequencies they were operating on? Or that they don't actually care what you are "prepared to believe"?


Damn!  Beat me to it.
 
2014-03-25 08:50:40 AM

czetie: dittybopper: It's a tiny piece of data, but it doesn't really help all that much except to confirm what we already know:  The aircraft went down in the southern Indian Ocean.

Doppler shift can be used to get a very accurate location, if both the receiver *AND* transmitter have very accurate frequency tolerances.  And while I am prepared to believe than an INMARSAT satellite receiver may have a very accurate receiver, I'm less inclined to believe the ACARS transmitter(s) on the Boeing 777 are that accurate, because they don't need to be all that accurate.

Without knowing the precise frequency the transmitter on MH370 was operating on (and also what precise frequency the satellite was listening to), it's impossible to get any kind of a very accurate doppler location.

Oh, and complicating this is that the plane could have been flying for up to half an hour from the time of the last "ping" until it crashed.  At the typical cruising speed of 490 knots, that's a potential search area of 245 nautical miles in length, minimum.

That's what I love about the Internet: there's always That Guy who thinks he knows more than an entire team of engineers and scientists from the company THAT BUILT THE FRIKKIN' SATELLITE and developed a model that's (reportedly) never been done before because reasons. Hey, Radio Ham Guy, do you think maybe its possible that Inmarsat, ATC, and Boeing do actually know the precise frequencies they were operating on? Or that they don't actually care what you are "prepared to believe"?

Oh, and apparently That Guy was the THE ONLY PERSON ON THE PLANET who already knew where the plane was. Perhaps he could have let the people searching know, who apparently only knew that it was probably somewhere along two arcs, one north and one south?


Beautiful.
 
2014-03-25 09:00:57 AM

czetie: dittybopper: It's a tiny piece of data, but it doesn't really help all that much except to confirm what we already know:  The aircraft went down in the southern Indian Ocean.

Doppler shift can be used to get a very accurate location, if both the receiver *AND* transmitter have very accurate frequency tolerances.  And while I am prepared to believe than an INMARSAT satellite receiver may have a very accurate receiver, I'm less inclined to believe the ACARS transmitter(s) on the Boeing 777 are that accurate, because they don't need to be all that accurate.

Without knowing the precise frequency the transmitter on MH370 was operating on (and also what precise frequency the satellite was listening to), it's impossible to get any kind of a very accurate doppler location.

Oh, and complicating this is that the plane could have been flying for up to half an hour from the time of the last "ping" until it crashed.  At the typical cruising speed of 490 knots, that's a potential search area of 245 nautical miles in length, minimum.

That's what I love about the Internet: there's always That Guy who thinks he knows more than an entire team of engineers and scientists from the company THAT BUILT THE FRIKKIN' SATELLITE and developed a model that's (reportedly) never been done before because reasons. Hey, Radio Ham Guy, do you think maybe its possible that Inmarsat, ATC, and Boeing do actually know the precise frequencies they were operating on? Or that they don't actually care what you are "prepared to believe"?

Oh, and apparently That Guy was the THE ONLY PERSON ON THE PLANET who already knew where the plane was. Perhaps he could have let the people searching know, who apparently only knew that it was probably somewhere along two arcs, one north and one south?


You win the internet!  This made my morning.
 
2014-03-25 10:00:33 AM
I'm glad I'm not THAT GUY. I'm just the other guy.
 
2014-03-25 10:07:21 AM

czetie: ey, Radio Ham Guy, do you think maybe its possible that Inmarsat, ATC, and Boeing do actually know the precise frequencies they were operating on?


Nope, and neither do they, because there is natural variation in the manufacture of transmitters due to the tolerances of the various parts that make them up unless you build into them very precise controls on the frequency.  Controls that cost money.

And there is no point in doing that for a transmitter that is going to be used solely to transmit a relatively wide-band data burst.  Does your FM broadcast receiver need to be precise to within a single kilohertz?  Obviously not.  Does a transmitter that is sending a 10 KHz wide signal need to be precise down to the 10 Hz level?  Nope.

But since you asked so nicely, I'll do the farkin' math for you.

A 406 MHz ELT beacon transmits a signal that is accurate to 2 parts per *BILLION*, which means that the signal (if precisely at 406 MHz) will vary from 459,999,999.999 MHz to 406,000,000.001 MHz.  This allows for a doppler accuracy of 2 kilometers radius, which is pretty damned good.

A typical ACARS transmitter will be transmitting at 130 MHz.  Because of the nature of the data transmission, the transmitter doesn't need to be anywhere near as accurately controlled.

In fact, the FCC regulates the tolerance, and it can be 2 parts per million for G1D and G7D data transmissions on VHF aeronautical frequencies*, which is a thousand times looser than the standard for a location beacon specifically built to be doppler-located.

Right there, you've introduced a much, much bigger search area even under optimum conditions.

Not to mention tolerances of the satellite, but I'm going to assume they know precisely the frequency of the received signal.

And as I said, even *IF* you could accurate locate that final ping, because they don't know how long the aircraft flew after that last ping (could be as much as half an hour at 560 MPH), or even in what direction, you're still looking at a search area of about 3.14*2302 = ~246,000 square miles.

That's an area just a little bit smaller than the state of Texas (269,000 mi2)

You know, I can do the simple math.  I have to assume the engineers can also.

*And I assume other countries have the same standards, because it's by international agreement, but even if they didn't, most likely the US-made Boeing-777 would use equipment that's type accepted in the United States.
 
2014-03-25 10:15:23 AM

dittybopper: That's an area just a little bit smaller than the state of Texas (269,000 mi2)


Well, a week ago they were searching an area ten times that size. A week before that they had no farking clue where the jet went. I'd say that's progress.
 
2014-03-25 10:25:04 AM

dittybopper: czetie: ey, Radio Ham Guy, do you think maybe its possible that Inmarsat, ATC, and Boeing do actually know the precise frequencies they were operating on?

Nope, and neither do they, because there is natural variation in the manufacture of transmitters due to the tolerances of the various parts that make them up unless you build into them very precise controls on the frequency.  Controls that cost money.

And there is no point in doing that for a transmitter that is going to be used solely to transmit a relatively wide-band data burst.  Does your FM broadcast receiver need to be precise to within a single kilohertz?  Obviously not.  Does a transmitter that is sending a 10 KHz wide signal need to be precise down to the 10 Hz level?  Nope.

But since you asked so nicely, I'll do the farkin' math for you.

A 406 MHz ELT beacon transmits a signal that is accurate to 2 parts per *BILLION*, which means that the signal (if precisely at 406 MHz) will vary from 459,999,999.999 MHz to 406,000,000.001 MHz.  This allows for a doppler accuracy of 2 kilometers radius, which is pretty damned good.

A typical ACARS transmitter will be transmitting at 130 MHz.  Because of the nature of the data transmission, the transmitter doesn't need to be anywhere near as accurately controlled.

In fact, the FCC regulates the tolerance, and it can be 2 parts per million for G1D and G7D data transmissions on VHF aeronautical frequencies*, which is a thousand times looser than the standard for a location beacon specifically built to be doppler-located.

Right there, you've introduced a much, much bigger search area even under optimum conditions.

Not to mention tolerances of the satellite, but I'm going to assume they know precisely the frequency of the received signal.

And as I said, even *IF* you could accurate locate that final ping, because they don't know how long the aircraft flew after that last ping (could be as much as half an hour at 560 MPH), or even in what direction, you're still loo ...


And you'd be right except for this case - ACARS wasn't using VHF, it was using SATCOM.
 
2014-03-25 10:26:33 AM

dittybopper: A 406 MHz ELT beacon transmits a signal that is accurate to 2 parts per *BILLION*, which means that the signal (if precisely at 406 MHz) will vary from 459,999,999.999 MHz to 406,000,000.001 MHz.


I farked this up.  Should be:

405,999,999.594 Hz
to
406,000,000.406 Hz.

at 2 parts per billion.

The corresponding numbers for a VHF ACARS transmission, as allowed by FCC regulations at 2 parts per million, would be:

129,999,870 Hz
to
130,000,130 Hz

That's a difference of  260 Hz.

Do you know what the doppler shift is for an aircraft traveling at 560 MPH is, at 130 MHz?

This doppler shift calculator says maximum doppler shift at 40 degrees (INMARSAT angle) for an aircraft travelling that speed is about 166 Hz.

So maybe they can use it to resolve the ambiguity of which arc, but the actual doppler shift would be within the legal tolerance of the transmitter, so you aren't going to obtain an accurate location.
 
2014-03-25 10:34:13 AM

dittybopper: dittybopper: A 406 MHz ELT beacon transmits a signal that is accurate to 2 parts per *BILLION*, which means that the signal (if precisely at 406 MHz) will vary from 459,999,999.999 MHz to 406,000,000.001 MHz.

I farked this up.  Should be:

405,999,999.594 Hz
to
406,000,000.406 Hz.

at 2 parts per billion.

The corresponding numbers for a VHF ACARS transmission, as allowed by FCC regulations at 2 parts per million, would be:

129,999,870 Hz
to
130,000,130 Hz

That's a difference of  260 Hz.

Do you know what the doppler shift is for an aircraft traveling at 560 MPH is, at 130 MHz?

This doppler shift calculator says maximum doppler shift at 40 degrees (INMARSAT angle) for an aircraft travelling that speed is about 166 Hz.

So maybe they can use it to resolve the ambiguity of which arc, but the actual doppler shift would be within the legal tolerance of the transmitter, so you aren't going to obtain an accurate location.


Again,  in the case of MH370 the ACARS transmission was done through an Inmarsat SATCOM link, not VHF.
 
2014-03-25 10:37:03 AM

joness0154: And you'd be right except for this case - ACARS wasn't using VHF, it was using SATCOM.


Even worse.  SATCOM allowable variation is 20 parts per million.
 
2014-03-25 10:43:26 AM

joness0154: Again,  in the case of MH370 the ACARS transmission was done through an Inmarsat SATCOM link, not VHF.


Even worse.  SATCOM allowable variation is 20 parts per million.
 
2014-03-25 10:45:13 AM

dittybopper: joness0154: And you'd be right except for this case - ACARS wasn't using VHF, it was using SATCOM.

Even worse.  SATCOM allowable variation is 20 parts per million.


http://tmfassociates.com/blog/2014/03/

This guy seems to think that the SATCOM timing is pretty darn accurate.  Maybe you should tell him he's wrong?
 
2014-03-25 10:48:46 AM

joness0154: dittybopper: dittybopper: A 406 MHz ELT beacon transmits a signal that is accurate to 2 parts per *BILLION*, which means that the signal (if precisely at 406 MHz) will vary from 459,999,999.999 MHz to 406,000,000.001 MHz.

I farked this up.  Should be:

405,999,999.594 Hz
to
406,000,000.406 Hz.

at 2 parts per billion.

The corresponding numbers for a VHF ACARS transmission, as allowed by FCC regulations at 2 parts per million, would be:

129,999,870 Hz
to
130,000,130 Hz

That's a difference of  260 Hz.

Do you know what the doppler shift is for an aircraft traveling at 560 MPH is, at 130 MHz?

This doppler shift calculator says maximum doppler shift at 40 degrees (INMARSAT angle) for an aircraft travelling that speed is about 166 Hz.

So maybe they can use it to resolve the ambiguity of which arc, but the actual doppler shift would be within the legal tolerance of the transmitter, so you aren't going to obtain an accurate location.

Again,  in the case of MH370 the ACARS transmission was done through an Inmarsat SATCOM link, not VHF.


Apparently it was accurate enough for several teams of engineers to say "South Indian Ocean" with enough confidence to tell the leaders of nations they were confident in it.

You can also probably cut the search area down on the quoted 246,000 square miles by half. The jet probably didn't do a magical 180 degree turn after the last ping.
 
2014-03-25 10:51:14 AM

joness0154: dittybopper: joness0154: And you'd be right except for this case - ACARS wasn't using VHF, it was using SATCOM.

Even worse.  SATCOM allowable variation is 20 parts per million.

http://tmfassociates.com/blog/2014/03/

This guy seems to think that the SATCOM timing is pretty darn accurate.  Maybe you should tell him he's wrong?


RTFA.  Specifically, this part:

Inmarsat was able to use the fact that the satellite was moving relative to the aircraft to calculate the resulting Doppler effect that shifted the frequency of the ping as measured at the satellite. If the satellite was moving towards the south, then the frequency of pings from airplanes flying in the southern hemisphere would be shifted up in frequency, while the frequency of pings from airplanes in the northern hemisphere would be shifted slightly down in frequency.

Last week Inmarsat performed an analysis of pings received from other aircraft flying in the Indian Ocean region to confirm that this effect is consistent across all of these planes and therefore concluded that MH370 must have been to the south of the satellite at the time of the last ping, not to its north. This led up to today's announcement that the plane must have crashed in the Southern Ocean.


The *ONLY* thing that the doppler shift analysis did for them was resolve the North-South ambiguity of the arcs.

It didn't generate a position.  It's not accurate enough to do that.
 
2014-03-25 11:01:10 AM

dittybopper: joness0154: dittybopper: joness0154: And you'd be right except for this case - ACARS wasn't using VHF, it was using SATCOM.

Even worse.  SATCOM allowable variation is 20 parts per million.

http://tmfassociates.com/blog/2014/03/

This guy seems to think that the SATCOM timing is pretty darn accurate.  Maybe you should tell him he's wrong?

RTFA.  Specifically, this part:

Inmarsat was able to use the fact that the satellite was moving relative to the aircraft to calculate the resulting Doppler effect that shifted the frequency of the ping as measured at the satellite. If the satellite was moving towards the south, then the frequency of pings from airplanes flying in the southern hemisphere would be shifted up in frequency, while the frequency of pings from airplanes in the northern hemisphere would be shifted slightly down in frequency.

Last week Inmarsat performed an analysis of pings received from other aircraft flying in the Indian Ocean region to confirm that this effect is consistent across all of these planes and therefore concluded that MH370 must have been to the south of the satellite at the time of the last ping, not to its north. This led up to today's announcement that the plane must have crashed in the Southern Ocean.

The *ONLY* thing that the doppler shift analysis did for them was resolve the North-South ambiguity of the arcs.

It didn't generate a position.  It's not accurate enough to do that.


No one was stating otherwise.

But they can narrow down the position to a much smaller area enough using multiple ping locations and assuming a constant speed.
 
2014-03-25 11:06:03 AM
OMG, it's a nerd fight!!!!
 
2014-03-25 11:06:44 AM

MadMattressMack: Apparently it was accurate enough for several teams of engineers to say "South Indian Ocean" with enough confidence to tell the leaders of nations they were confident in it.


All they did was resolve the ambiguity of whether the aircraft went north or south.

You can also probably cut the search area down on the quoted 246,000 square miles by half. The jet probably didn't do a magical 180 degree turn after the last ping.

But they don't have anything resembling an accurate location for that ping.  All they know is that it lies upon an arc.  So in theory, they have a huge corridor to search.

You are probably right about it not doing a magical 180 turn right after the last ping, but balancing that is the fact that we don't know precisely how fast it was going, so you are going to end up with an enlarged search area.

A difference in just 30 MPH ground speed over the course of the 6 hours between the last radar contact and the last ACARS ping translates to over 180 miles linear distance to be added to the search, so I actually stand by my original estimate of a search area roughly the size of Texas, if not actually bigger.

And that would be if we had a clue where that last ping originated, and we really don't.  If there had been two INMARSATs in view, both listening, you could have looked at the intersection of the two coverage arcs, and gotten some idea that way.
 
2014-03-25 11:12:15 AM

dittybopper: MadMattressMack: Apparently it was accurate enough for several teams of engineers to say "South Indian Ocean" with enough confidence to tell the leaders of nations they were confident in it.

All they did was resolve the ambiguity of whether the aircraft went north or south.

You can also probably cut the search area down on the quoted 246,000 square miles by half. The jet probably didn't do a magical 180 degree turn after the last ping.

But they don't have anything resembling an accurate location for that ping.  All they know is that it lies upon an arc.  So in theory, they have a huge corridor to search.

You are probably right about it not doing a magical 180 turn right after the last ping, but balancing that is the fact that we don't know precisely how fast it was going, so you are going to end up with an enlarged search area.

A difference in just 30 MPH ground speed over the course of the 6 hours between the last radar contact and the last ACARS ping translates to over 180 miles linear distance to be added to the search, so I actually stand by my original estimate of a search area roughly the size of Texas, if not actually bigger.

And that would be if we had a clue where that last ping originated, and we really don't.  If there had been two INMARSATs in view, both listening, you could have looked at the intersection of the two coverage arcs, and gotten some idea that way.


Granted, and if you had 2 in view you'd still have 2 intersections unless you got lucky enough that the edge of the arcs were right at each other. Either way, it doesn't look like this technique came up with a very small search area. It was just enough to say "plane gone".
 
2014-03-25 11:12:33 AM

dittybopper: MadMattressMack: Apparently it was accurate enough for several teams of engineers to say "South Indian Ocean" with enough confidence to tell the leaders of nations they were confident in it.

All they did was resolve the ambiguity of whether the aircraft went north or south.

You can also probably cut the search area down on the quoted 246,000 square miles by half. The jet probably didn't do a magical 180 degree turn after the last ping.

But they don't have anything resembling an accurate location for that ping.  All they know is that it lies upon an arc.  So in theory, they have a huge corridor to search.

You are probably right about it not doing a magical 180 turn right after the last ping, but balancing that is the fact that we don't know precisely how fast it was going, so you are going to end up with an enlarged search area.

A difference in just 30 MPH ground speed over the course of the 6 hours between the last radar contact and the last ACARS ping translates to over 180 miles linear distance to be added to the search, so I actually stand by my original estimate of a search area roughly the size of Texas, if not actually bigger.

And that would be if we had a clue where that last ping originated, and we really don't.  If there had been two INMARSATs in view, both listening, you could have looked at the intersection of the two coverage arcs, and gotten some idea that way.


There were hourly pings to the Inmarsat bird, giving them a more accurate estimate of where it may have been.

"Inmarsat measured the arc positions each hour from 2.11am to 8.11am and the possible routes taken by MH370 can be estimated by assuming that the plane was flying at a constant cruise speed, and then noting that the distance between the points at which the plane crossed each successive arc is equal to the distance the plane traveled in one hour. That led to the NTSB's two potential tracks for the southern route, which included two different assumptions for the speed at which the plane was flying. "

Isn't math great?
 
2014-03-25 11:19:20 AM

joness0154: But they can narrow down the position to a much smaller area enough using multiple ping locations and assuming a constant speed.


You can come up with a bit of a guess, and a decent one given the information available, but it's still just a guess.

For all we know right now, the plane flew in lazy circles in a generally southern area, and went down much farther to the north-east than we are currently searching, and the debris sighted in the current search area is unrelated.

Of course, that could all change with new information.  I'm just trying to say that we shouldn't pin our hopes on something that's relatively thin.  We don't have, and likely won't ever have, a good location for the plane when it went into the drink.  Unless, of course, we manage to find it.

And if we do find it, it'll likely be because of a long-dead Presbyterian minister.
 
2014-03-25 11:28:51 AM

joness0154: There were hourly pings to the Inmarsat bird, giving them a more accurate estimate of where it may have been.

"Inmarsat measured the arc positions each hour from 2.11am to 8.11am and the possible routes taken by MH370 can be estimated by assuming that the plane was flying at a constant cruise speed, and then noting that the distance between the points at which the plane crossed each successive arc is equal to the distance the plane traveled in one hour. That led to the NTSB's two potential tracks for the southern route, which included two different assumptions for the speed at which the plane was flying. "

Isn't math great?


So you have 2 semi circles, slightly offset, the radius of which are centered on the last ping and include up to 1 hour of flight time at cruising speed. This is still a huge area to search.

Any wreckage you find won't do much to help pinpoint the site and will only confirm what you already know - "plane gone". Air France 447 was flying a known route, had wreckage found within 2 days, and still took 2 years to locate.
 
2014-03-25 11:53:38 AM

joness0154: There were hourly pings to the Inmarsat bird, giving them a more accurate estimate of where it may have been.

"Inmarsat measured the arc positions each hour from 2.11am to 8.11am and the possible routes taken by MH370 can be estimated by assuming that the plane was flying at a constant cruise speed, and then noting that the distance between the points at which the plane crossed each successive arc is equal to the distance the plane traveled in one hour. That led to the NTSB's two potential tracks for the southern route, which included two different assumptions for the speed at which the plane was flying. "

Isn't math great?


Do you see how big that area is?  It's not just two tracks, it's *ALL* the area in between and a bit to the side.

Also, I'm kind of curious just how accurate the INMARSAT angular resolution is.

Apparently they have a 12 meter antenna, and operate on the L-band.  Assuming a frequency of 2 GHz (upper end of the L-Band), which is about 0.15 meters wavelength, the antenna will have a beamwidth of about 2(0.15)/12 = 0.0249 radians * 180/3.14 =  1.4 degree beamwidth for that antenna.

At 22,200 miles, 1.4 degrees equates to an ambiguity of roughly 540 miles.  Actual location could be anywhere within 280 miles to either side of that line.


*Actually, that's just under the sub satellite point, and it would increase as the angle increases, but this is just a back of the envelope calculation.
 
2014-03-25 11:55:31 AM

dittybopper: Actual location could be anywhere within 280 270 miles to either side of that line.


Why do I keep making stupid mistakes like that this morning?

/Probably because I'm also trying to get something else done.
 
2014-03-25 12:16:38 PM
dittybopper: ...

He just can't stop, can he?
 
2014-03-25 12:59:01 PM

dittybopper: but the actual doppler shift would be within the legal tolerance of the transmitter


Without seeing the data I can't come to any conclusions obviously, but the legal tolerance or manufacturing tolerance doesn't necessarily translate to ping-to-ping difference in transmission frequencies. Maybe they'd be able to assume that all the pings coming from one flight are well within this legal window, that is, if the instrument doesn't have much drift to it.
 
2014-03-25 01:00:19 PM
The main problem is right there in the headline: 19th century physics. The Doppler shift was fine for grandpa, but us folks in the modern world deserve something new and better. Something with a few LEDs on it so it looks rilly kewl and with a camera for those vitally important moments when girls in short skirts bend over and maybe can play MP3s so I can listen to my tunes while I search for . . . whoa, check out the front porch of that betty in the tube top.

How do you work this thing? This is bullshiat.
 
2014-03-25 01:16:23 PM

sgh46: dittybopper: but the actual doppler shift would be within the legal tolerance of the transmitter

Without seeing the data I can't come to any conclusions obviously, but the legal tolerance or manufacturing tolerance doesn't necessarily translate to ping-to-ping difference in transmission frequencies. Maybe they'd be able to assume that all the pings coming from one flight are well within this legal window, that is, if the instrument doesn't have much drift to it.


The problem is that over the course of a 7 hour flight, you might get some drift.  Changes in temperature, pressure, etc. can cause it.

Even if it didn't, and the transmitter was rock-solid, all it did was resolve something we already pretty much had guessed at:  The plane flew into the southern Indian Ocean.
 
2014-03-25 01:26:16 PM

dittybopper: sgh46: dittybopper: but the actual doppler shift would be within the legal tolerance of the transmitter

Without seeing the data I can't come to any conclusions obviously, but the legal tolerance or manufacturing tolerance doesn't necessarily translate to ping-to-ping difference in transmission frequencies. Maybe they'd be able to assume that all the pings coming from one flight are well within this legal window, that is, if the instrument doesn't have much drift to it.

The problem is that over the course of a 7 hour flight, you might get some drift.  Changes in temperature, pressure, etc. can cause it.

Even if it didn't, and the transmitter was rock-solid, all it did was resolve something we already pretty much had guessed at:  The plane flew into the southern Indian Ocean.



If the transmitter were rock-solid, then they may be able to use slight changes in the doppler shift as the plane changes it's incidence angle to the satellite to get a location, if they assume that the true speed of the aircraft was maintained during the flight.
 
2014-03-25 02:09:52 PM
Will you please stop comparing the search area to Texas. We don't have the freak in' plane.

Still getting blamed forGWB, about to elect an imported Bush from Bush The Next Generation back into state government and now this.

Don't you see we can't take anymore.

We were invaded by hordes of plague infested Yankees in the 70's and 80's. Now Guv Good hair goes around recruiting them.

You've dumped Glenn Beck and the Huge on us. My God please have some humanity.
 
2014-03-25 02:14:02 PM

Chigroe Please: Will you please stop comparing the search area to Texas. We don't have the freak in' plane.

Still getting blamed forGWB, about to elect an imported Bush from Bush The Next Generation back into state government and now this.

Don't you see we can't take anymore.

We were invaded by hordes of plague infested Yankees in the 70's and 80's. Now Guv Good hair goes around recruiting them.

You've dumped Glenn Beck and the Huge on us. My God please have some humanity.


Nuge. Not huge.
/huge steam in pile in his shorts
 
2014-03-25 02:50:56 PM

Chigroe Please: Will you please stop comparing the search area to Texas. We don't have the freak in' plane.


I picked Texas because it's approximately the right size, and people are familiar with it from look at maps, and such as.
 
2014-03-25 02:56:06 PM

dittybopper: Chigroe Please: Will you please stop comparing the search area to Texas. We don't have the freak in' plane.

I picked Texas because it's approximately the right size, and people are familiar with it from look at maps, and such as.


AP is saying the size of Texas AND Oklahoma!
 
2014-03-25 03:09:17 PM

sgh46: If the transmitter were rock-solid, then they may be able to use slight changes in the doppler shift as the plane changes it's incidence angle to the satellite to get a location, if they assume that the true speed of the aircraft was maintained during the flight.


You *COULD* do this, in theory.  It would be most accurate if the aircraft were heading straight at the SSP, but it could also be of use so long as there were some measurable change in doppler.

I just don't think they can measure the doppler shift that accurately, given the limitations of equipment not designed for that sort of thing.

Interestingly enough, if this were from an LEO or MEO satellite instead of a GEO one, you could use the satellite's coverage area, combined with the measured doppler from the motion of the satellite on the signal, to get a reasonable estimation of the area.

I once wrote a bit of software, based upon the formulas in "The Satellite Experimenter's Handbook" to do just that.  As I recall, the major problem I had in locating people using RS-10/11 was the lack of precision of my receiver:  I was using a Kenwood TS-520 with a 500 Hz CW filter, but I had to use the wider SSB setting, and since this was before the explosion of sound-card based FFT programs with fancy waterfall displays, actually measuring the received frequency was problematic.  Not to mention that if I didn't calibrate the receiver accurately, all bets were off.  Still, I usually managed to get in the approximately correct region, until I got bored with it.
 
2014-03-25 03:11:21 PM

dittybopper: Chigroe Please: Will you please stop comparing the search area to Texas. We don't have the freak in' plane.

I picked Texas because it's approximately the right size, and people are familiar with it from look at maps, and such as.


Um, I realized that. It was supposed to be humor.

And BTW, your explanation was well presented. Thanks
 
2014-03-25 03:13:09 PM

MadMattressMack: dittybopper: Chigroe Please: Will you please stop comparing the search area to Texas. We don't have the freak in' plane.

I picked Texas because it's approximately the right size, and people are familiar with it from look at maps, and such as.

AP is saying the size of Texas AND Oklahoma!


But I was just talking about this:

And as I said, even *IF* you could accurate locate that final ping, because they don't know how long the aircraft flew after that last ping (could be as much as half an hour at 560 MPH), or even in what direction, you're still looking at a search area of about 3.14*2302 = ~246,000 square miles.

That's an area just a little bit smaller than the state of Texas (269,000 mi2)


In other words*, even if you could get an accurate location of that last ping, which you can't, you're still looking at an area roughly the size of the state that shall not be named.

*Actually, pretty  much the same words.
 
2014-03-25 03:30:31 PM
My impression from the article is they didn't use doppler shift to locate the aircraft, they used doppler shift to differentiate between two potential solutions: northern arc vs. southern arc. And they didn't do that by using the doppler shift of the transmissions of the aircraft by itself, they did that by comparing the doppler shift of the transmissions of the aircraft to the doppler shifts of other aircrafts that have flown along the southern arc (and presumably as well to other aircraft that have flown along the northern arc.)
 
2014-03-25 03:52:05 PM

RoyBatty: My impression from the article is they didn't use doppler shift to locate the aircraft, they used doppler shift to differentiate between two potential solutions: northern arc vs. southern arc. And they didn't do that by using the doppler shift of the transmissions of the aircraft by itself, they did that by comparing the doppler shift of the transmissions of the aircraft to the doppler shifts of other aircrafts that have flown along the southern arc (and presumably as well to other aircraft that have flown along the northern arc.)


Precisely.
 
2014-03-25 04:34:50 PM

dittybopper: sgh46: If the transmitter were rock-solid, then they may be able to use slight changes in the doppler shift as the plane changes it's incidence angle to the satellite to get a location, if they assume that the true speed of the aircraft was maintained during the flight.

You *COULD* do this, in theory.  It would be most accurate if the aircraft were heading straight at the SSP, but it could also be of use so long as there were some measurable change in doppler.

I just don't think they can measure the doppler shift that accurately, given the limitations of equipment not designed for that sort of thing.

Interestingly enough, if this were from an LEO or MEO satellite instead of a GEO one, you could use the satellite's coverage area, combined with the measured doppler from the motion of the satellite on the signal, to get a reasonable estimation of the area.

I once wrote a bit of software, based upon the formulas in "The Satellite Experimenter's Handbook" to do just that.  As I recall, the major problem I had in locating people using RS-10/11 was the lack of precision of my receiver:  I was using a Kenwood TS-520 with a 500 Hz CW filter, but I had to use the wider SSB setting, and since this was before the explosion of sound-card based FFT programs with fancy waterfall displays, actually measuring the received frequency was problematic.  Not to mention that if I didn't calibrate the receiver accurately, all bets were off.  Still, I usually managed to get in the approximately correct region, until I got bored with it.


This is all gibberish people don't listen to him this is a long-running troll and nobody has called him out but this entire post is gibberish; Kenwood isn't a company, FFT programs for SoundBlaster 16 were always crap, and there's no way to "calibrate" a "receiver" or "approximate" a "region", it's a bunch of Hackers/CSI Lord Nikon DaVinci virus Penn Gillette flu-shot bullshiat

We're all going to die
 
2014-03-25 06:50:06 PM

ransack.: dittybopper: sgh46: If the transmitter were rock-solid, then they may be able to use slight changes in the doppler shift as the plane changes it's incidence angle to the satellite to get a location, if they assume that the true speed of the aircraft was maintained during the flight.

You *COULD* do this, in theory.  It would be most accurate if the aircraft were heading straight at the SSP, but it could also be of use so long as there were some measurable change in doppler.

I just don't think they can measure the doppler shift that accurately, given the limitations of equipment not designed for that sort of thing.

Interestingly enough, if this were from an LEO or MEO satellite instead of a GEO one, you could use the satellite's coverage area, combined with the measured doppler from the motion of the satellite on the signal, to get a reasonable estimation of the area.

I once wrote a bit of software, based upon the formulas in "The Satellite Experimenter's Handbook" to do just that.  As I recall, the major problem I had in locating people using RS-10/11 was the lack of precision of my receiver:  I was using a Kenwood TS-520 with a 500 Hz CW filter, but I had to use the wider SSB setting, and since this was before the explosion of sound-card based FFT programs with fancy waterfall displays, actually measuring the received frequency was problematic.  Not to mention that if I didn't calibrate the receiver accurately, all bets were off.  Still, I usually managed to get in the approximately correct region, until I got bored with it.

This is all gibberish people don't listen to him this is a long-running troll and nobody has called him out but this entire post is gibberish; Kenwood isn't a company, FFT programs for SoundBlaster 16 were always crap, and there's no way to "calibrate" a "receiver" or "approximate" a "region", it's a bunch of Hackers/CSI Lord Nikon DaVinci virus Penn Gillette flu-shot bullshiat

We're all going to die


So you're getting a kick out of his replies?
 
2014-03-25 09:09:32 PM

CigaretteSmokingMan: ransack.: dittybopper: sgh46: If the transmitter were rock-solid, then they may be able to use slight changes in the doppler shift as the plane changes it's incidence angle to the satellite to get a location, if they assume that the true speed of the aircraft was maintained during the flight.

You *COULD* do this, in theory.  It would be most accurate if the aircraft were heading straight at the SSP, but it could also be of use so long as there were some measurable change in doppler.

I just don't think they can measure the doppler shift that accurately, given the limitations of equipment not designed for that sort of thing.

Interestingly enough, if this were from an LEO or MEO satellite instead of a GEO one, you could use the satellite's coverage area, combined with the measured doppler from the motion of the satellite on the signal, to get a reasonable estimation of the area.

I once wrote a bit of software, based upon the formulas in "The Satellite Experimenter's Handbook" to do just that.  As I recall, the major problem I had in locating people using RS-10/11 was the lack of precision of my receiver:  I was using a Kenwood TS-520 with a 500 Hz CW filter, but I had to use the wider SSB setting, and since this was before the explosion of sound-card based FFT programs with fancy waterfall displays, actually measuring the received frequency was problematic.  Not to mention that if I didn't calibrate the receiver accurately, all bets were off.  Still, I usually managed to get in the approximately correct region, until I got bored with it.

This is all gibberish people don't listen to him this is a long-running troll and nobody has called him out but this entire post is gibberish; Kenwood isn't a company, FFT programs for SoundBlaster 16 were always crap, and there's no way to "calibrate" a "receiver" or "approximate" a "region", it's a bunch of Hackers/CSI Lord Nikon DaVinci virus Penn Gillette flu-shot bullshiat

We're all going to die

So you're getting a kick ou ...


Must be he is, because here is my Kenwood:

img.fark.net

Actually, that's my non-existent Kenwood TS-520 on the bottom, and a non-existent Kenwood TS-700S in the middle, and of course a non-existent Yaesu FC-301 antenna tuner on top of that.  Because who would name a company "Yaesu".

Though I've temporarily replaced the non-existent TS-700S with a non-existent TR-7500 because the non-existent transmit/receive relay is sticking in the non-existent TS-700S.
 
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