Originally Posted by
Gysbreght
Hi mm43,
no, sorry, I have not made that spreadsheet yet and I doubt that it would be worth the effort. My intent was to get a qualitative understanding of the mechanism. We do not have sufficient data to allow a quantitative analysis based on the published BFO values. Looking at the BFO while the airplane was stationary indicates that the AES frequency bias and the GES AFC could be quite significant.
I don't understand why the available data do not allow a quantitative analysis of the BFO.
Even if we don't know the AES specific frequency bias and how the GES compensates for the D3 doppler shifts, if you model the BFO as
BFO = D1 + D2 + D3 + D1_AES + D3_GES + FreqBias _AES
where D1_AES is the D1 doppler estimated using a stationnary 3F1 satellite (above 64.5°E-0°N), FreqBias_AES is constant throughout the flight (neglecting the oscillators frequency drifts).
... you can still analyse the time serie BFO - (D1+D1_AES + D2) versus D3 and it will appear that the varied data points (the varied handshakes) are more or less scattered along a line, suggesting a simple linear regression (of BFO - (D1+D1_AES + D2) versus D3) enables to estimate:
- the FreqBias _AES (around 160 Hz) and
- a constant, partial compensation of D3 as D3_GES ~ -0.7*D3 (70 % of D3 compensated by the Perth GES) will do the job (replicating Inmarsat's predicted BFOs for north and south trajectories).
https://drive.google.com/file/d/0B3s...it?usp=sharing (for a south terminal leg at 470 kts)
https://drive.google.com/file/d/0B3s...it?usp=sharing (for a south terminal leg at 350kts, one of the trajectories is a north one)
These are the 10 000 simulated flights of a MonteCarlo simulation, the green plot is the closest flight to the BFO data (red), the blue-grey enveloppe gathers all the simulated flights around a reference trajectory. It seems that higher terminal speeds (470 kts versus 350 kts) allow a tighter fit to the data.