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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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  #1  
Old March 18th 14, 08:07 PM posted to sci.geo.satellite-nav
Happy Trails
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Posts: 341
Default MH 370

Does anyone still read msgs here?

  #2  
Old March 18th 14, 09:03 PM posted to sci.geo.satellite-nav
Mike Coon[_3_]
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Posts: 14
Default MH 370

"Happy Trails" wrote in message
...
Does anyone still read msgs here?


Does anyone say anything interesting?

Mike.

  #3  
Old March 18th 14, 09:27 PM posted to sci.geo.satellite-nav
Alan Browne
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Posts: 1,339
Default MH 370

On 2014.03.18, 17:07 , Happy Trails wrote:
Does anyone still read msgs here?


Yes.


--
... it may be that "in the cloud" really isn't the best term
for the services these companies offer. What they really
want is to have us "on the leash."
-David Pogue, Scientific American, 2014.02
  #4  
Old March 18th 14, 09:27 PM posted to sci.geo.satellite-nav
Alan Browne
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Posts: 1,339
Default MH 370

On 2014.03.18, 18:03 , Mike Coon wrote:
"Happy Trails" wrote in message
...
Does anyone still read msgs here?


Does anyone say anything interesting?


Not often enough.

--
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.

  #5  
Old March 18th 14, 10:32 PM posted to sci.geo.satellite-nav
Happy Trails
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Posts: 341
Default MH 370

Is it just me, or are the potential locations suggested by the
Malaysian authorities for the missing aircraft way off base?

They seem to be estimating a line of positions based on an arc from an
Inmarsat satellite, which I don't think is possible.

I believe they should be looing at mirror image arcs way out to the
west of where the news channels are showing in that goofy graphic.

Arcs which define the maximum range possible away from Malaysia with
the given load of fuel.

Am I wrong or am I the only guy on the planet that sees it this way?

I can't believe that the US & Australian navies would search in
entirely the wrong places just on some Malaysian officials say so, but
it appears that is what is happening.

Tell me I'm wrong!

  #6  
Old March 18th 14, 11:09 PM posted to sci.geo.satellite-nav
Alan Browne
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Posts: 1,339
Default MH 370

On 2014.03.18, 19:32 , Happy Trails wrote:
Is it just me, or are the potential locations suggested by the
Malaysian authorities for the missing aircraft way off base?

They seem to be estimating a line of positions based on an arc from an
Inmarsat satellite, which I don't think is possible.


I "spoke" with a satellite antenna system designer via e-mail (as I
didn't understand how they came up with those arcs).

Simplistically: the INMARSAT satellite reports the power level of
received messages and from that the 'arc' was developed ... a line of
"equal" power received from the surface by that satellite. (I guess they
ignore a/c altitude... or maybe not)

The errors in power level, as well as the pointing accuracy of the space
based antenna, it's actual lobe shape, attenuation at different points
in the chain (transmitter power, cables, antenna) add up to those arcs
being roughly +/- 156 km laterally from the nice clean arc in the Malay
presentation, by his estimation.

His caveat there is that the antennas may be twice as bad in platform
pointing stability ... so over +/- 300 km from the arc....

I believe they should be looing at mirror image arcs way out to the
west of where the news channels are showing in that goofy graphic.

Arcs which define the maximum range possible away from Malaysia with
the given load of fuel.

Am I wrong or am I the only guy on the planet that sees it this way?

I can't believe that the US & Australian navies would search in
entirely the wrong places just on some Malaysian officials say so, but
it appears that is what is happening.

Tell me I'm wrong!


There has been so much wrong to date in this affair that anything you
think wrong has just as much chance being right.

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

  #7  
Old March 19th 14, 07:16 AM posted to sci.geo.satellite-nav
Hans-Georg Michna
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Posts: 764
Default MH 370

On Tue, 18 Mar 2014 17:07:31 -0400, Happy Trails wrote:

Does anyone still read msgs here?


Yes. Some more information:

Infographic by Bloomberg:
http://www.bloomberg.com/infographic...ince-1948.html

A Startlingly Simple Theory About the Missing Malaysia Airlines
Jet - wired.com
http://www.wired.com/autopia/2014/03...ectrical-fire/

Sounds very convincing to me.

Hans-Georg
  #8  
Old March 19th 14, 07:44 PM posted to sci.geo.satellite-nav
Alan Browne
external usenet poster
 
Posts: 1,339
Default MH 370

On 2014.03.19, 03:39 , Jeff wrote:
On 19/03/2014 00:09, Alan Browne wrote:
On 2014.03.18, 19:32 , Happy Trails wrote:
Is it just me, or are the potential locations suggested by the
Malaysian authorities for the missing aircraft way off base?

They seem to be estimating a line of positions based on an arc from an
Inmarsat satellite, which I don't think is possible.


I "spoke" with a satellite antenna system designer via e-mail (as I
didn't understand how they came up with those arcs).

Simplistically: the INMARSAT satellite reports the power level of
received messages and from that the 'arc' was developed ... a line of
"equal" power received from the surface by that satellite. (I guess they
ignore a/c altitude... or maybe not)

The errors in power level, as well as the pointing accuracy of the space
based antenna, it's actual lobe shape, attenuation at different points
in the chain (transmitter power, cables, antenna) add up to those arcs
being roughly +/- 156 km laterally from the nice clean arc in the Malay
presentation, by his estimation.


The potential errors in a received power based calculation seem to be
huge, are you sue that your source has it correct? A much more accurate


He has a 30+ year career in communications (and other) satellite
antennas for a major satellite designer and operator. I would defer to him.

Further the error he came up with was not the +/- 156 km above but over
+/- 300 km (as you snipped from my post). A 600 km wide swath that is
thousands of km long.

way would seem to be based on the timings of the replies, much in the
same way as it is possible to find the range of a phone from the tower.


To do so means you have to have an accurate timestamp for transmission
from the a/c and for reception at the satellite AND the satellite has to
have the same time base (GPS) in order to compute the difference (or
perhaps on the ground end but that means a lot more error).

No requirement for that in INMARSAT that I can find.

It would require GPS integration to supply both timestamp and a sync (1
PPS) to the INMARSAT antenna controller on the aircraft. It does not
get such (as I recall). Instead the FMS computes the direction and
elevation that the antenna should point its beam and relays that to the
INMARSAT system on board.

(Mind you, it's conceivable that the INMARSAT system receives position,
heading and attitude from the FMS in order to compute the position of
the satellite relative to the a/c and then compute the beam steering - I
just don't recall it as being such on HGA INMARSAT systems. I'm even
less sure about MGA (which is probably what the a/c in question had if
indeed it wasn't an LGA which does not point at all).


Regarding the 'mirror' arcs; it appears to me that it would be
impossible for the aircraft to have flown that far west to be on one of
those arcs.


That is another poster who put that out, not me.


What does not appear to have been made public is the possible positions
for the satellite 'pings' before the last known one which the arcs are
based on.


That's the point - you only know it's at about that range, not the angle
to the distance. You could extrapolate using last known radar positions
and guesstimate fuel and ground speed as well (and that is surely being
done).

Further, of course, the 4 or 5 hourly pings they received would only
have fallen on the same arc by a huge coincidence ... but I assume they
are working that into their basket of choices as well. In effect a set
of arcs. Add the error bounds outside that.

I'd further assume they are developing a Bayesian search - if the
appropriate experts are brought in and given access to all the
information and get input from everyone with info great or small. This
could reduce the search area considerably.

I see that the Aussies have constrained their search to a relatively
small patch of water ... maybe there will be news soon. Or not.

--
... it may be that "in the cloud" really isn't the best term
for the services these companies offer. What they really
want is to have us "on the leash."
-David Pogue, Scientific American, 2014.02
  #9  
Old March 19th 14, 08:04 PM posted to sci.geo.satellite-nav
Alan Browne
external usenet poster
 
Posts: 1,339
Default MH 370

On 2014.03.19, 04:16 , Hans-Georg Michna wrote:
On Tue, 18 Mar 2014 17:07:31 -0400, Happy Trails wrote:

Does anyone still read msgs here?


Yes. Some more information:

Infographic by Bloomberg:
http://www.bloomberg.com/infographic...ince-1948.html

A Startlingly Simple Theory About the Missing Malaysia Airlines
Jet - wired.com
http://www.wired.com/autopia/2014/03...ectrical-fire/

Sounds very convincing to me.


It's a possibility. As is decompression/hypoxia; as is a hijacking
(botched or otherwise).

There have been B-777 fires - but I'm not sure if they have been
resolved in terms of identifying cause and preventative action (design
change and retrofit).

Example:
http://www.aaib.gov.uk/publications/...22__n786ua.cfm

DL the pdf for the details.

I haven't found anything on the web showing that this has been
cause-ID'd and corrected.

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

  #10  
Old March 19th 14, 11:19 PM posted to sci.geo.satellite-nav
Happy Trails
external usenet poster
 
Posts: 341
Default MH 370

On Tue, 18 Mar 2014 20:09:08 -0400, Alan Browne
wrote:


the INMARSAT satellite reports the power level of
received messages and from that the 'arc' was developed ... a line of
"equal" power received from the surface by that satellite. (I guess they
ignore a/c altitude... or maybe not)

The errors in power level, as well as the pointing accuracy of the space
based antenna, it's actual lobe shape, attenuation at different points
in the chain (transmitter power, cables, antenna) add up to those arcs
being roughly +/- 156 km laterally from the nice clean arc in the Malay
presentation, by his estimation.

His caveat there is that the antennas may be twice as bad in platform
pointing stability ... so over +/- 300 km from the arc....


Thanks for the Inmarsat info - I only know gps, so I was not aware
there could be any position inference whatsoever from Inmarsat.

The scenario posed in the link from Michna seems very plausible, and I
would not trust to any degree of accuracy at all any line of position
from Inmarsat. There are too many factors that could reduce the power
level of a signal received at the Inmarsat satellite - the position
assumes full power available at the transmitter and a properly aimed
antenna on the transmitter, both of which are dubious in these
circumstances.

I have said all along they will find the plane/crash site on an
autopilot-maintained line west of Malaysia in the Indian Ocean about
6-7 hrs flying time to the west. That is what I originally meant by
"mirror-imaged" arcs - not exactly, and not centered on the Inmarsat
satellite, but way west of where they are looking and curved the other
way from the news articles.

You read it here first.

 




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