Thanks for the opening of this thread!
I have some problem understanding the BTO values published in the "Raw data" PDF (
http://www.dca.gov.my/mainpage/MH370...ion%20Logs.pdf)
Perhaps there is a big thing I don't see, but I am looking at those values for a moment without a clue...
On page 1, we can read (bold from me):
Understanding the Burst Timing Offset (BTO) values:
- The round trip time for a message is a combination of:
1.) Time from the ground station ? satellite ? aircraft ? satellite ? ground station
2.) Processing time within the ground station, satellite and aircraft terminal, which are constant
- The BTO is a value (in microseconds) relative to a terminal at a nominal fixed location. Only R-Channel messages are used.
- The BTO therefore allows the determination of the distance between the satellite and the aircraft. It does not provide the actual aircraft location.
All this seems perfectly clear, and I understand that the BTO is the sum of the round trip of the message (at light speed) and some delay from processing times in the different units.
And because of these processing times, the BTO have to be longer than the time (at light speed) from Perth (ground Inmarsat station) to Inmarsat 3F1 (the satellite) then to the aircraft and all the way back.
How long is this travel? It has to be longer than four times the height of 3F1, which is around 36000 km above the equator, that is about 144000 km, say 150,000 km, which is the distance the light travels in half a second (some maths gives ~159,100 km at 16:00 UTC when the aircraft was on the ground in Kuala Lumpur, so a ~0.5307 second travel time).
But all the BTO values given (for the "R" channel) in the PDF are between 14740 and 14920 microseconds (that is repeated on each page in the column title) when the aircraft was on the ground in KL between 16:00 and 16:30 UTC. Between these times 3F1 moved slightly away from KL : from ~37294 to ~37296 km, that is, in time at light speed, 124399 to 124406 microseconds. For this segment only, the travel time is thus near ten times the given BFO (and ~35 times for the round trip).
So, which distance are those microseconds values given in the "raw data" related to?
Could it be in relation with the distance between a point at sea level under 3F1? At 16:00 UTC, the point at sea level under 3F1 is 13560 microseconds away from KL airport in straight line and ~13790 microseconds along Earth surface. So in the same magnitude order of the "raw data" BTO (14820). But which magic brand could give this kind of "raw data"? Is some unit in the system making this computation, and only this result is filed?
Or I misunderstand all this stuff?
PS: From deleted post of the "main" thread, a "sub"question is: what is the "
terminal at a nominal fixed location" (last line of "Raw data" page 1), question which came along with the post of a Canadian whose pseudo is something like ??23 (sorry for forgetting). I supposed it was the ground station near Perth, or, may be, the theoretical position of 3F1, but this obviously erroneous from the published BTO.