To: samim anbarcioglu who wrote (27324 ) 10/1/2002 9:46:53 AM From: RalphCramden Read Replies (1) | Respond to I believe I wrote down in the description that you would use your knowledge of the relative positions of the base station, ground station, and geosynch sat. position to take out, to first order, the differences in path length. But even doing that, you still get degraded accuracy as you move away from the original ground station. The reason for this is that the speed of light in air and in the top of the atmosphere especially varies a little bit from hour to hour and day to day. This is because that speed depends in detail on the density of the air, and in the high atmosphere, the ionosphere, on the density of free electrons. Especially the ionosphere varies quite a bit, with a peak electron density typically at ~2 PM every day (raised by the sunlight) but with the variation being not completely repeatable day to day. In the scheme I proposed, all variations are calibrated out by the round trip measurement the ground station does, but that applies exactly only right at the ground station. As you move away from the ground station, that calibrated out amount becomes less and less exactly accurate, and that is a major part of why accuracy would decrease.
