Originally Posted by
IRpilot2006
I thought that the entire reason Immarsat was able to distinguish between the N arc and the S arc was because their satellite is not perfectly stationary above the earth but happens to move about a bit, which creates a second doppler shift which obviously varies according to which way the satellite happens to be moving.
Correct the INMARSAT satellite moves in an extended thin North South figure of 8 (geoloocated as opposed to geostationary ) This provides two levels of Doppler shift due to the aircraft and the satellite.