That's SBAS/WAAS! another cool thing This is trying to measure ionosphere disturbances which affect signal propagation rates via ground reference stations. The

That's SBAS/WAAS! another cool thing This is trying to measure ionosphere disturbances which affect signal propagation rates via ground reference stations. The real-time model is then calculated and distributed using ground stations and geostationary satellites. GPS is way, way cool, and it's a pity the extent of its engineering is not better known.