Originally Posted by
arlev
That SATCOM (the 1:11 to 8:11 pings) does not initiate pings would mean that this cannot be the system that's used.
I don't quite get this bit. Why do you think SATCOM could not have initiated the partial ping / communication? My reading was along the lines of:
- SATCOM initiates connection on power up, like a laptop's WiFi connection to an access point;
- In normal ops on-board avionics kit sends info over that connection, which keeps it alive, but normal kit was turned off so these never happened;
- Periodically the 'access point' pinged back to say 'You're very quiet today, do you want to stay connected?' and these were detected;
- At some point something on the plane that hadn't been transmitting decided it would after all. Maybe this was the low-level SATCOM wanting to re-establish a link during power loss / recovery, maybe it was a bit of kit that recovered power or went into special mode that forced transmission.
Originally Posted by
arlev
And that was my problem - if the crash site is as assumed (or as calculated), then, if the last ping at 8:19 was VHF (and it can't be SATCOM) then the 'line of sight' becomes a problem.
And just to make sure I'm following again...
Because VHF would only have a range of a few hundred miles at best - typically 200ish for a airplane height?
Originally Posted by
arlev
If the Doppler analysis is accurate, of course. I actually trust the Inmarsat people quite a bit - being British myself
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Quite
!
Originally Posted by
arlev
However, as far as I understand the relevance of the Doppler analysis, it means something like how you interpret the data based on the shift in signal between receipt by MH370 and transmission - that is, the distance travelled which will have had the effect of causing the plane to be at two different distances between the two events.
This is perhaps where our understanding of the significance of the Doppler analysis varies. I think the thing they can tell from the measurements is how fast the plane was flying directly away from the satellite. But since it was not on a directly away path this will only have been one part of the velocity vector. I've tried to show what I mean here:
The green and blue diagonals show a distance covered in a fixed period of time, so as they are different lengths they represent different speeds. But if you were travelling along the brown line (which is the direct away from satellite path for the initial positions) and keeping the plane at right angles to you then you would cover the same distance for both the green and blue 'targets', and it is effectively your speed along the brown line that the Doppler effect is measuring (I'm ignoring the fact that the 'direct away from satellite' path sweeps around as time progresses, but I think that is what causes the upwards slope on the Doppler graphs from Inmarsat).
Originally Posted by
arlev
Two observations:
1. That would still work if the aircraft circled (but I'm not suggesting that it *did* - I am simply pointing out that such an event would throw the crash site further north).
If the target flew in a circle you'd go forwards an backwards on the brown line, and the Doppler measurements wouldn't be linear(ish). So I think they can infer that the plane took a straight-ish course (maybe the earth curvature bit starts to come in as well) south rather than anything northern or circular.
I agree there could have been a circular bit at the end. Can the plane be put in hold over a point where someone wants it to comedown after fuel exhaustion? But why do that unless the 'deepest point in the ocean' theory is valid?
Originally Posted by
arlev
2. Haven't they just disregarded the Doppler work of the initial route by shifting the debris site hundreds of miles from its initial location? That is, assumed a crash site further north based on more fuel burnt rather than on a reassessment of the Doppler maths?
I don't think so. If a lower speed 'diagonal' is now assumed then you end up with something more like the green path than the blue one - which takes you NW-ish. The Doppler measurements gave them the 'along the brown line' bit and that stays the same, so they haven't disregarded or changed it. I think we agreed above that you get a similar effect just by considering the path across the arcs at different speeds. My brain starts to hurt when trying to think about how combining speed across arcs with Doppler shift vectors gives you a better combined result than just one of the methods, but presumably someone's didn't!
As ever, very happy for others to correct / expand on this. I think discussing it helps us all understand what may or may not have happened and to debunk ill-formed theories.