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sci.geo.satellite-nav (Global Satellite Navigation) (sci.geo.satellite-nav) Discussion of global navigation satellite systems (GNSS). Topics include the technical aspects of GNSS operation, user experiences in the use of GNSS, information regarding GNSS products and discussion of GNSS policy (such as GPS selective availability).

MH 370



 
 
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  #21  
Old March 22nd 14, 01:24 PM posted to sci.geo.satellite-nav
Alan Browne
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Posts: 1,339
Default MH 370

On 2014.03.22, 06:46 , Jeff wrote:

From what I was told it's quite consistent and even. That said, the
chain of errors mentioned adds up to +/- 300 km. ie: the errors aren't
horrendous - but they are there. Like GPS, the particular INMARSAT
bands are chosen to be least affected by atmospheric conditions - at
least wrt power. (They are very close to GPS frequencies).



Well a very quick calculation shows that the change in slant range, in


What calculation?

the area in question, to the satellite (and hence the free space path
loss) only changes by about 50km in a total path of about 36,000km for a
500km change in surface radius position.
The consequent change in free-space path loss is about 0.01dB for that
change in surface radius of 500km.

A change of 3000km in position only results in about 0.1dB path loss
change.

Of course that does not take into account the change in the satellites
antenna polar diagram, which almost certainly will make those figures
larger.

So the other potential changes in the link budget seem to totally
overwhelm any accuracy that may be obtained by signal strength
calculations alone. A 0.1db error could put you 3000km out!!

I suppose that if you accurately know the antennas polar diagram it
might be possible from the strength of signals from last known position
to deduce things a little closer, but the margin for error still looks
way too high with sub 0.1dB changes giving you very large positional
errors.


As I said earlier, I'll defer to the expert I know a lot about.

I've been discussing another possibility with him, but it depends on too
many "depends". (That where the beam elevation angle from the
transmitter (aircraft) is communicated to the satellite and then that is
used to determine the arc position. This has a lot of unknowns and
potential for more variance (lobe shape - you can't point the lobe all
that accurately) so not a good candidate. He's also re-opened the
possibility that there may be some useful timing information but he's
not sure about the implementation).

--
Privacy has become an essential personal chore that most
people are not trained to perform.
- Jaron Lanier, Scientific American, 2013.11.

  #22  
Old March 22nd 14, 02:48 PM posted to sci.geo.satellite-nav
Happy Trails
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Posts: 341
Default MH 370

On Sat, 22 Mar 2014 09:46:46 +0000, Jeff wrote:
If you had bothered to read my posts fully you would know the answer to
that!!


We'll take that as a "no" then.

  #23  
Old March 22nd 14, 11:17 PM posted to sci.geo.satellite-nav
Gilbert Smith[_2_]
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Posts: 5
Default MH 370

Alan Browne wrote:

On 2014.03.21, 20:53 , David Chamberlain wrote:

Sorry. My first attempt at this post went to the sender, not the
newsgroup. Stupid news client...

http://www.slate.com/blogs/future_te..._langkawi.html


A fire.
A decompression.
A hijacking (botched or other).

Are all plausible (and not the sole possibilities). Until the FDR
is found speculation of any kind is silly. Articles attacking other
articles are silliest.

I suspect the CVR will be useless as they only record the last 30
minutes of cockpit sound. So the events at the critical time will have
been written over many times. (The FDR, OTOH runs 16+ hours).


Does the CVR continue if all power is lost ?

They can get the turnaround time for the ping from similar equipment,
and/or use the response delay from a point where the range was known.
  #24  
Old March 23rd 14, 01:22 AM posted to sci.geo.satellite-nav
Alan Browne
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Posts: 1,339
Default MH 370

On 2014.03.22, 19:17 , Gilbert Smith wrote:
Alan Browne wrote:

On 2014.03.21, 20:53 , David Chamberlain wrote:

Sorry. My first attempt at this post went to the sender, not the
newsgroup. Stupid news client...

http://www.slate.com/blogs/future_te..._langkawi.html


A fire.
A decompression.
A hijacking (botched or other).

Are all plausible (and not the sole possibilities). Until the FDR
is found speculation of any kind is silly. Articles attacking other
articles are silliest.

I suspect the CVR will be useless as they only record the last 30
minutes of cockpit sound. So the events at the critical time will have
been written over many times. (The FDR, OTOH runs 16+ hours).


Does the CVR continue if all power is lost ?


It's not, itself, a critical system (it can fail in any possible manner
w/o affecting the airplane in any way; and if it's not powered up, there
is nothing to prevent the a/c from operating).

So while desired to work, it's not a safety issue if it doesn't. IIRC
the CVR has two sources of DC (28V) power. If they both are absent, it
stops. (perhaps some work DC (28 VDC) and AC (115/400Hz) and either is
sufficient ... but I don't recall seeing anything like that...).

What it does do:

- record cockpit sounds from several microphones
- for 30 minutes
- on getting wet - it emits an audible tone for about 30 days. (Or
rather, a device attached to it does the audible (under water) pinging.)

I seem to recall seeing a call for the battery endurance to be increased
from 30 to 90 minutes. Not sure if that has been enacted or what the
compliance period is if enacted. (Which would be a country by country
policy IAC).

They can get the turnaround time for the ping from similar equipment,
and/or use the response delay from a point where the range was known.


Maybe it's the wine I had with supper, but I haven't got a clue what you
mean by that. Please elaborate.

--
Those who have reduced our privacy, whether they are state
or commercial actors, prefer that we do not reduce theirs.
- Jaron Lanier, Scientific American, 2013.11.


  #25  
Old March 23rd 14, 12:11 PM posted to sci.geo.satellite-nav
Gilbert Smith[_2_]
external usenet poster
 
Posts: 5
Default MH 370

Alan Browne wrote:

On 2014.03.22, 19:17 , Gilbert Smith wrote:
Alan Browne wrote:

On 2014.03.21, 20:53 , David Chamberlain wrote:

Sorry. My first attempt at this post went to the sender, not the
newsgroup. Stupid news client...

http://www.slate.com/blogs/future_te..._langkawi.html

A fire.
A decompression.
A hijacking (botched or other).

Are all plausible (and not the sole possibilities). Until the FDR
is found speculation of any kind is silly. Articles attacking other
articles are silliest.

I suspect the CVR will be useless as they only record the last 30
minutes of cockpit sound. So the events at the critical time will have
been written over many times. (The FDR, OTOH runs 16+ hours).


Does the CVR continue if all power is lost ?


It's not, itself, a critical system (it can fail in any possible manner
w/o affecting the airplane in any way; and if it's not powered up, there
is nothing to prevent the a/c from operating).

So while desired to work, it's not a safety issue if it doesn't. IIRC
the CVR has two sources of DC (28V) power. If they both are absent, it
stops. (perhaps some work DC (28 VDC) and AC (115/400Hz) and either is
sufficient ... but I don't recall seeing anything like that...).

What it does do:

- record cockpit sounds from several microphones
- for 30 minutes
- on getting wet - it emits an audible tone for about 30 days. (Or
rather, a device attached to it does the audible (under water) pinging.)

I seem to recall seeing a call for the battery endurance to be increased
from 30 to 90 minutes. Not sure if that has been enacted or what the
compliance period is if enacted. (Which would be a country by country
policy IAC).

They can get the turnaround time for the ping from similar equipment,
and/or use the response delay from a point where the range was known.


Maybe it's the wine I had with supper, but I haven't got a clue what you
mean by that. Please elaborate.


There has been a lot of discussion about the range measuring
capabilites of the satelite, with huge discrepancies possible if you
don't know the time taken for the equipment to respond to a ping. I
was suggesting that they already have this figure.
  #26  
Old March 23rd 14, 04:28 PM posted to sci.geo.satellite-nav
Peter H. Coffin
external usenet poster
 
Posts: 53
Default MH 370

On Fri, 21 Mar 2014 12:33:09 +0000, Jeff wrote:

On 20/03/2014 20:06, Happy Trails wrote:

In actual fact, the degree of timing synchronization required to do
any position determination based on a time difference is far more
precise than you will ever get from hardware and software that is not
designed specifically to provide this, like gps.


Strange then that they manage to do just that on mobile phone networks
(without GPS)_!!!


GPS triangulation is starting from a much smaller range, and is using
differential strengths to account for differences in strength of
returned signal broadcast. That is, it doesn't matter much how loud
the cell phone's broadcasting because the relative loudness at each of
three towers is important, not how loud one reception is. That's really
different from a single satellite reception. And the cellphone version
is STILL only good down to maybe a couple hundred meters in an urban
area with multiple tower coverage.

--
People who are willing to rely on the government to keep them safe are
pretty much standing on Darwin's mat, pounding on the door, screaming,
'Take me, take me!'
-- Carl Jacobs in the Monastery
  #27  
Old March 23rd 14, 05:12 PM posted to sci.geo.satellite-nav
Alan Browne
external usenet poster
 
Posts: 1,339
Default MH 370

On 2014.03.23, 12:28 , Peter H. Coffin wrote:
On Fri, 21 Mar 2014 12:33:09 +0000, Jeff wrote:

On 20/03/2014 20:06, Happy Trails wrote:

In actual fact, the degree of timing synchronization required to do
any position determination based on a time difference is far more
precise than you will ever get from hardware and software that is not
designed specifically to provide this, like gps.


Strange then that they manage to do just that on mobile phone networks
(without GPS)_!!!


GPS triangulation is starting from a much smaller range, and is using


1. GPS does not "triangulate", it trilaterates. (ranges, not angles).

2. The ranges involved are over 20 million meters from sat to receiver
on the ground.

differential strengths to account for differences in strength of
returned signal broadcast. That is, it doesn't matter much how loud
the cell phone's broadcasting because the relative loudness at each of


Cell tower based positioning is also trilateration, not triangulation.

three towers is important, not how loud one reception is. That's really
different from a single satellite reception. And the cellphone version
is STILL only good down to maybe a couple hundred meters in an urban
area with multiple tower coverage.


In both cell phone trilateration and that of GPS, a strong enough signal
is needed; 'loudness' does not = accuracy unless the signal is very weak
in which case the accuracy will be less.

(number of sources and geometry are more important).

--
Privacy has become an essential personal chore that most
people are not trained to perform.
- Jaron Lanier, Scientific American, 2013.11.

  #28  
Old March 25th 14, 12:42 AM posted to sci.geo.satellite-nav
Alan Browne
external usenet poster
 
Posts: 1,339
Default MH 370

On 2014.03.23, 08:11 , Gilbert Smith wrote:
Alan Browne wrote:

On 2014.03.22, 19:17 , Gilbert Smith wrote:
Alan Browne wrote:

On 2014.03.21, 20:53 , David Chamberlain wrote:

Sorry. My first attempt at this post went to the sender, not the
newsgroup. Stupid news client...

http://www.slate.com/blogs/future_te..._langkawi.html

A fire.
A decompression.
A hijacking (botched or other).

Are all plausible (and not the sole possibilities). Until the FDR
is found speculation of any kind is silly. Articles attacking other
articles are silliest.

I suspect the CVR will be useless as they only record the last 30
minutes of cockpit sound. So the events at the critical time will have
been written over many times. (The FDR, OTOH runs 16+ hours).

Does the CVR continue if all power is lost ?


It's not, itself, a critical system (it can fail in any possible manner
w/o affecting the airplane in any way; and if it's not powered up, there
is nothing to prevent the a/c from operating).

So while desired to work, it's not a safety issue if it doesn't. IIRC
the CVR has two sources of DC (28V) power. If they both are absent, it
stops. (perhaps some work DC (28 VDC) and AC (115/400Hz) and either is
sufficient ... but I don't recall seeing anything like that...).

What it does do:

- record cockpit sounds from several microphones
- for 30 minutes
- on getting wet - it emits an audible tone for about 30 days. (Or
rather, a device attached to it does the audible (under water) pinging.)

I seem to recall seeing a call for the battery endurance to be increased
from 30 to 90 minutes. Not sure if that has been enacted or what the
compliance period is if enacted. (Which would be a country by country
policy IAC).

They can get the turnaround time for the ping from similar equipment,
and/or use the response delay from a point where the range was known.


Maybe it's the wine I had with supper, but I haven't got a clue what you
mean by that. Please elaborate.


There has been a lot of discussion about the range measuring
capabilites of the satelite, with huge discrepancies possible if you
don't know the time taken for the equipment to respond to a ping. I
was suggesting that they already have this figure.


I've yet to find anything solid based on timing wrt INMARSAT.

As discussed, you either need synchronized timestamping so the prop time
is known, or two stations receiving the message and them both
timestamping (and then the means to measure the difference in their time
stamping systems if they are not sharing a timebase).

--
Privacy has become an essential personal chore that most
people are not trained to perform.
- Jaron Lanier, Scientific American, 2013.11.

  #29  
Old March 25th 14, 08:53 AM posted to sci.geo.satellite-nav
Mike Coon[_3_]
external usenet poster
 
Posts: 14
Default MH 370

"Alan Browne" wrote in message
...

I've yet to find anything solid based on timing wrt INMARSAT.


Unfortunately the INMARSAT chap interviewed on UK TV last night didn't go
into detail about how they contributed. He did say the transmission from the
plane they examined was hourly. I haven't looked to see if they have a news
flash on their web site...

Mike.

  #30  
Old March 25th 14, 09:02 AM posted to sci.geo.satellite-nav
Mike Coon[_3_]
external usenet poster
 
Posts: 14
Default MH 370

"Mike Coon" wrote in message
...
Unfortunately the INMARSAT chap interviewed on UK TV last night didn't go
into detail about how they contributed.


I've just remembered he did say they used Doppler.

He did say the transmission from the plane they examined was hourly.


That much is available from their web site.

Mike.

 




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