Originally Posted by
scr33d
Earth's geoid is both non-symmetrical and well-mapped (GRACE and GOCE), Inmarsat may have done a relativistic gravitation Doppler analysis on the transmission to rule out the north arc. Will see if this is true as they give more details.
This would be an extremely weak effect. Even the baseline for GR time dilation between Earth's surface and the satellite in a geosynchronous orbit is ~50 microseconds/day (5*10^-10), equivalent to frequency shift of just 1 Hz in the microwave band. Fluctuations in the geoid aren't going to be visible without sophisticated equipment.