Originally Posted by
VinRouge
Doppler from multiple geostationary sats would give you derived heading, speed and possibly location. It's how the Americans tracked Sputnik.
Doppler is no use in this case.
For a start Sputnik was moving about 7km/sec relative the ground and because it was in low-earth orbit the motion relative to a ground observer was very high.
A Geostationary satellite has no motion relative to a fixed point on earth, and the only motion relative to the aircraft is the component of its velocity moving toward or away from the satellite. If the a/c is moving at say 290m/s parallel to the satellite which is 35,786,000 meters away and the earth curves at about 12 cm per km, then the motion relative to the satellite directly overhead is about 3.5cm/sec. Of course at the far end of the satellite's range the relative motion will higher, but only a couple of m/s at the maximum edge of the satellite footprint. To measure a speed that small using doppler is very difficult and I doubt very much that Inmarsat is set up for that.