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Two people provided answers to my previous questions:

And they referred me to Appendix G. "Explanatory Notes on BTO and BFO Analysis".

Now I have questions about Appendix G.

  1. The report (Appendix G) says that the Doppler shift from the satellite (down-link) to GES depends on the satellite movement with respect to GES, since the satellite is not exactly stationary. But in Table 6. the Down-link Doppler frequency varies, from the satellite to GES depending on the aircraft Latitude. Why should the Aircraft Latitude affect the DeltaFdown Doppler frequency shift?

  2. And another question is about the Down-link doppler-shifts, from the Satellite to GES, given in Table 5. The listed Doppler-shift in frequency is -75.1 Hz for UTC time 17:07. However, I can only derive this frequency using the satellite velocity for UTC time 16:55:00? The calculated frequency differs slightly from the one in the report.

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    $\begingroup$ While I share your interest in this subject, I worry these questions are getting to the point where they don't have a lot to do with normal aviation. More attention to spelling MH370 etc correctly, providing links to info you mention and formatting would probably go down well with the audience here. Just my 0.02 worth. I'll fix that for you on this question. $\endgroup$ – RedGrittyBrick Jul 28 '14 at 21:04
  • $\begingroup$ Your reply does not answer the question I asked. You include the aircraft velocity and heading as viewed from the satellite's location as a possible explaination. But the DeltaFdown is suppose to only apply to the satellite movement wiith respect to GES. The Aircraft velocity should not affect the the DeltaFdown value. The same goes for the Aircraft Latitude. I now understand that Mr. Duncan Steel asked the same question about the aircraft Latitude several days ago. Getting answers as to how the Log- Data was derived may help in locating Flt370. Reasonable questions should be encouraged. $\endgroup$ – John Mauch Jul 29 '14 at 23:39
  • $\begingroup$ For 16:55 UTC, I calculate a doppler frequency of -74.5 Hz for DelFdown. For 17:05 UTC, I calculate a Doppler frequency of -71.2 Hz for DelFdown. These calculations are based upon the relative movement of the satellite with respect to GES. If there are other variables that contribute to DelFdown then the report should state so. $\endgroup$ – John Mauch Jul 30 '14 at 1:55
  • $\begingroup$ 1) Being reasonable is a necessary but insufficient condition for questions here. Questions should also be on-topic and it appears that many people feel this question does not meet that condition. 2) It is better that comments on answers are attached to the answer not to the question. I'd delete my answer but it contains some links and info that may be useful to future readers. $\endgroup$ – RedGrittyBrick Jul 30 '14 at 9:34
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1. Why should the Aircraft Latitude affect the Doppler frequency shift?

It seems to me that table 6 is a check to test whether the equation on page 55 can reliably be used to predict the possible locations of an aircraft from a measured BFO. It does this by using the equation to predict what the BFO should be for a given set of inputs and comparing that with the measured BFO. To see how reliable this is they vary one of the parameters, latitude in this example, to show that the predicted BFO is considerably different for different latitudes and that the best match of predicted BFO to the measured BFO is for the known location of the aircraft. Therefore you know that the BFO is useful - it can be used to rule out some locations.

If you hold constant all the other factors and vary latitude why should that affect BFO?

I guess it's because for the same aircraft heading (with respect to true north), different latitudes but same headings mean different angles of flight with respect to the satellite. That means that there are different magnitudes of component of velocity that is parallel to the line from satellite to aircraft - those different magnitudes represent different speeds in a line directly away-from or directly towards the satellite. This affects doppler.

enter image description here

Note: The above doesn't explain why ΔFdown varies with aircraft latitude.


Other independent analyses of this data

I'm pretty sure Duncan Steele is smarter than me, so you may be on to something.


2. However, I can only derive this exact frequency using the satellite velocity for UTC time 16:55:00?

That's more of a statement than a question. I guess your question is:

why do my calculations give a different answer?

I see two possibilities

  • you made a mistake.
  • the ATSB made a mistake†.

In order for readers to help you with the first or confirm the second, you'd really have to share your calculations with us.


† And presumably Inmarsat, the NTSB, the AAIB and others.

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  • $\begingroup$ And for checking any calculations, there is probably more people who can help with math over at physics.stackexchange.com. $\endgroup$ – Jan Hudec Jul 29 '14 at 8:23
  • $\begingroup$ I withddraw my comments about a possible error in Table 5 of Appendix G regarding the -75.1 Hz. DelFdown doppler shift. $\endgroup$ – John Mauch Jul 30 '14 at 14:56

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