EGNOS

EGNOS, the European Geostationary Navigation Overlay Service, is Europe’s satellite-based augmentation system, the regional counterpart of the US WAAS. It improves GPS over Europe by broadcasting wide-area differential corrections and integrity data from geostationary satellites on the GPS L1 frequency, so a standard GPS or SBAS receiver reads them without extra hardware. Reference stations across Europe compute corrections for satellite clock, ephemeris, and ionospheric delay, which a central facility uplinks to the GEO satellites. EGNOS tightens horizontal accuracy to about 1 to 3 m and, more importantly, flags faulty satellites within seconds, the integrity function that bare GPS lacks.