Initially the pings from Malaysian airlines flight MH370 could only determine the distance of the aircraft from the satelite based on round trip times of the pings sent at one hour intervals. Taking the fuel range and estimated speed of the aircraft into account this confined the possible location of the missing aircraft to two arcs, the so called North and South corridors. What is the physics behind the claim of the satellite company to have narrowed the location to the Southern corridor? Does anyone have any idea what mathematical analysis they used? I can see how a Doppler analysis of the pings would indicate whether the plane was going towards the satellite or away from it, but that still gives no indication of whether the aircraft was going North or South.