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-   -   Malaysian Airlines MH370 contact lost (http://www.pprune.org/rumours-news/535538-malaysian-airlines-mh370-contact-lost.html)

Hunter58 22nd Mar 2014 18:27

Quote:

Primary radar can be used to compute distance as it would be proportional to the transit time taken by a pulse of energy to travel to the object and back again. As they have azimuth, they may be also have SOME elevation resolution.
Military Primary Radar is 3D since the 1960. They beam both in azimuth as well as vertical. The altutude capturing capability is usually quite good, but it needs to be calibrated from time to time. Also it shows geographical altitude, not barometric, which in older systems could be a pain in the backside when trying to correlate own primary targets with civilian secondaries. Software changes later life was good again...

BOAC 22nd Mar 2014 18:30

Quote:

that to me says you think they searched there because of the arc.
- er, no. The Inmarsat data was not known at that time. You need to revisit the timeline.
Quote:

You also still seem to think it flew all along one of these arcs it did not.
- this is difficult! A massive search effort is being expended ON THE 40 DEGREE ARC at supposed fuel exhaustion point. Inmarsat tell us the pings were 'all' at 40 degree elevations. Since we know where the first ping was transmitted (roughly), please explain how it got to the SIS, pinging at the same elevation all 7 times without tracking along the arc?
Quote:

It was seen on malay and Thai mil primary radar and the Malayasia track was confirmed later
- you obviously believe the reported radar data. Confirmed???? By whom? I have not seen these statements stand questioning.
Quote:

If you think mil radar will not pick up unidentified planes please explain why they have them!
- read the posts in this thread and you will see. Half+ the mil probably asleep at the wheel at the time. Oh, do ask the Russians who popped a Badger up in the Firth of Forth a few years back....................... :-)

nh1200c 22nd Mar 2014 18:32

Current military primary surveillance radar DOES provide altitude
 
For all who think that primary radar cannot indicate altitude, please look up the SPS-48 - which entered service in the U.S. Navy over 50 YEARS ago and is just a typical example of a long range 3-D radar type.

Phased array 3-D surveillance radars are common in military air defense service as we really don't like to just have interceptors go wandering around trying to determine if the bogey target is at 10K or FL450.

Now, the fair point here is that the height accuracy is definitely affected by the target range, but less than ~4K foot altitude error at 200 nm range is definitely common.

(Lonewolf50 - I was on the design team for the NTU many, many years ago. It's good to see it spoken of well.)

MountainBear 22nd Mar 2014 18:35

Quote:

Originally Posted by BOAC http://www.pprune.org/images/buttons/viewpost.gif
-

Yes, everyone, I do understand the margins of error (as yet unknown) on this '40 degree arc', but I still reckon that the odds of the a/c tracking ACROSS the arcs and at least one ping being at some other angle would be high.


A very valid point, why would anyone navigate along a route exactly the same distance (elevation) from a satellite?
The 40 degree arc is based upon the altitude of the plane at the LKP. That's why the satellite polling the device terminal has to contain altitude data. The physical radius of the radio waves (the band) is limited. So if the polling has the wrong altitude the signal will miss the plane entirely and the connection is going to be dropped. So a difference in the arc implies a difference in the altitude of the plane and nothing more. Moreover, since the polling take place only once an hour it only tells us something about the altitude of the plane at that precise moment in time, not what happened in between.

BOAC 22nd Mar 2014 18:38

Quote:

Originally Posted by MB
The 40 degree arc is based upon the altitude of the plane at the LKP.

- no. Little to do with aircraft altitude. Forget altitude. Covered in depth in previous posts. You need to compare geo-stat orbit distance with 6 nm to see.

Anna's Dad 22nd Mar 2014 18:38

Re Satellite imagery
 
Just watching a BBC News interview with David Mearns (Blue Water Recoveries Ltd), expert in marine recovery. He was describing where the search may be directed now, assuming drift, and comparisons with the locations of the Australian and Chinese imagery. Also using current information to work backwards to calculate a predicted area for any original ditching.

When asked that all this assumes the material photographed is positively identified as part(s) of MH370, he implied the Australians and Chinese would not be chasing things likely to have another obvious origin.

MountainBear 22nd Mar 2014 18:41

Quote:

Inmarsat tell us the pings were 'all' at 40 degree elevations. Since we know where the first ping was transmitted (roughly), please explain how it got to the SIS, pinging at the same elevation all 7 times without tracking along the arc?
If I understand the complaint correctly, the complaint is based upon a fundamental error. The 40 degree arc that is plotted on a map is a two dimensional representation of a three dimensional reality. There is no claim that the plane moved along the 40 degree arc in two dimensional space, only that it moved along the arc in three dimensional space. If every ping happened along the 40 degree arc all the means is that the plane held to the same altitude for 7 hours, nothing more.

Either that or I do not understand the criticism.

jimjim1 22nd Mar 2014 18:43

Few possible routes - given several Inmarsat arcs
 
@awblain
Quote:

the number of possible routes likely isn't very large.
RichardC10 has posted that he has used computer simulation to determine that if a set of several Inmarsat arcs is available then if a constant course is assumed then two unique track can be obtained - one for each hemisphere.

http://www.pprune.org/rumours-news/5...ml#post8386704

says:
Quote:

The result is that there is only one constant heading course from the last recorded radar position that matches the example set of ping arcs, that is the destination is uniquely defined by the interim and final ping arcs (if interim arcs exist). There is a (rough) mirror course in the southern hemisphere which may be hard to distinguish as the last recorded radar position was close to the equator.
I have the impression that Mr RichardC10 is cluefull.

In my view the whole post is worth a careful read.

oldoberon 22nd Mar 2014 18:44

BOAC
Quote:

- read the posts in this thread and you will see. Half+ the mil probably asleep at the wheel at the time. Oh, do ask the Russians who popped a Badger up in the Firth of Forth a few years back....................... :-)
they had a track but were not certain it was 370, they tracked it to the straits of malacca until losing contact.

The fact that it was 370 was confirmed at a mid week conference by the minister based on a variety of data, so your sleepy byes argument is like most of your argument -rubbish

Karel_x 22nd Mar 2014 18:44

Quote:

Primary radar can be used to compute distance as it would be proportional to the transit time taken by a pulse of energy to travel to the object and back again. As they have azimuth, they may be also have SOME elevation resolution.
It is not easy to measure altitude of plane by radar. If I remember times of my military service, the main lobe of parabolic antenna is not narrow enough to measure altitude with good accuracy. To increase accuracy, vertical orange peel antenna was used, but I can remember that a precision was not usually better then +/- 3000 ft. Sometime worse, it depends on distance between plane and radar, clouds, surface objects, size of plane etc.

http://upload.wikimedia.org/wikipedi...a/Mps-16-1.jpg

To track position of plane like T7 at FL 300+ and distance about 200nm was very easy. Blips were clear and you could see them in a second on the screen.

sky9 22nd Mar 2014 18:45

Inmarsat

I understand that the arcs are based on the time difference between TX and RX of the signal from the satellite. Would such a signal frequency experience doppler shift if the aircraft was travelling towards or away from the satellite?

The other inference of the aircraft ACARS responding to the satellite is that there must have been power on that particular bus.

davidre 22nd Mar 2014 18:45

Confused?
 
BOAC:
Quote:

A massive search effort is being expended ON THE 40 DEGREE ARC at supposed fuel exhaustion point. Inmarsat tell us the pings were 'all' at 40 degree elevations. Since we know where the first ping was transmitted (roughly), please explain how it got to the SIS, pinging at the same elevation all 7 times without tracking along the arc?
What is the basis of your assertion concerning what Inmarsat has said? I don't believe I've seen any such statement. Have I missed something?

Mr Optimistic 22nd Mar 2014 18:45

MB, Its the intersection of two spherical surfaces. One being the earths surface the other being the locus of all points a certain distance from the satellite based on signal travel time.

BOAC 22nd Mar 2014 18:46

MB - I don't think you understand the 40 degree elevation actually. Work out please (someone did it way back here) what difference a 6nm change in altitude would make in angular terms over a distance of 22000nm +? Un-measurable, I suggest. Altitude has very little to do with it. The 'red arcs' are probably drawn as ground position but would be near as dammit the same at 40,000' - a 3-D 'corridor' if you like.

Zorin_75 22nd Mar 2014 18:51

Quote:

Originally Posted by BOAC
Inmarsat tell us the pings were 'all' at 40 degree elevations

No! Only the final 8:11 ping came from a position somewhere on that arc, that's all.

BOAC 22nd Mar 2014 18:52

Quote:

Originally Posted by oldb
was confirmed at a mid week conference by the minister based on a variety of data

- ah - confirmed??? That's alright then. That would probably be the same minister who has changed tack just a few times?

I remain totally unconvinced so far of any 'stated facts' - except LKP and the 'essence' of the Inmarsat man's words. Everything else is 'subject to'. You, of course, are entiltled to believe all statements from Malaysia.

rabidstoat 22nd Mar 2014 18:54

Quote:

Apart from hypoxia, are there any other scenarios that would account for the crew and passengers being incapacitated AND the plane being able to fly for another 5-7 hours?
Surely there are. Off the top of my head, hijacker(s) with threat or use of force.

MG23 22nd Mar 2014 18:55

Quote:

Originally Posted by sky9 (Post 8394662)
Would such a signal frequency experience doppler shift if the aircraft was travelling towards or away from the satellite?

The terminal probably has to correct for doppler shift, because low bit-rate channels are very narrow; doesn't take much of a frequency shift to end up transmitting on or listening to an adjacent channel. There's a lot more flexibility in timing, which presumably explains why it doesn't try to correct for that.

Msunduzi 22nd Mar 2014 18:55

Quote:

Originally Posted by MountainBear (Post 8394655)
If I understand the complaint correctly, the complaint is based upon a fundamental error. The 40 degree arc that is plotted on a map is a two dimensional representation of a three dimensional reality. There is no claim that the plane moved along the 40 degree arc in two dimensional space, only that it moved along the arc in three dimensional space. If every ping happened along the 40 degree arc all the means is that the plane held to the same altitude for 7 hours, nothing more.

Either that or I do not understand the criticism.


The 40 degree "arc" has nothing to do with the plane's altitude.

If you plot a great circle map centered on the sub-satellite point, the 40 degree "arc" will be a circle.

Anywhere along that circle, the satellite will be 40deg elevation.

As the satellite is just under 35800 miles above the earths surface, the altitude of the plane will make a small difference to the elevation angle, and the effective circle under the plane on the surface would be marginally smaller than the 40deg circle on the ground.

Another way to look at the "arc" or circle, if you draw an imaginaru line from the sub-satellite point, through the satellite, and out into space, then positioned your self on that line far out past the satellite, then looked back at the earth with the satellite in the middle, the 40 degree "arc" would appear to be a circle, and the circles would get smaller until at 90deg, it is just a point.

inchman254 22nd Mar 2014 19:04

Quote:

There is no claim that the plane moved along the 40 degree arc in two dimensional space, only that it moved along the arc in three dimensional space. If every ping happened along the 40 degree arc all the means is that the plane held to the same altitude for 7 hours, nothing more.
Let's get something straight. The arc that we are presented with has nothing to do with 40 degrees except it happens to be a 40 degree arc. And it has nothing to do with the path of the aircraft.

The arc is simply a line that marks the potential range of positions of the aircraft at a single, specific moment in time, based on a single ping from the satellite. It is the distance from the satellite computed based on the length of time from the time at which the satellite sends the ping until it receives the response. The aircraft's altitude would have very little effect on the position of the line... perhaps a couple of miles, but there is enough potential error that the altitude makes very little difference

The Inmarsat satellite does not have any azimuth information. The data that we are being presented with is simply a distance from the satellite at the moment of the last single ping. A radar works sort of the same way... the time it takes for the signal to return to the radar head determines the distance. The difference between radar and this type of information is that radar provides the azimuth (direction) of the signal based on the direction the radar antenna is facing at the moment the signal is received. RADAR stands for RAdio Direction And Ranging. All this satellite can provide is RANGE and that's all the arc represents.

Thank goodness they didn't present the arcs from the other pings. It would have been even more confusing.


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