Differential GNSS (DGNSS)

A code-phase augmentation that improves GNSS accuracy to roughly 1 to 3 meters by broadcasting pseudorange corrections from a reference station at a surveyed position. Maritime DGNSS uses IALA radiobeacons in the 285 to 325 kHz band, transmitting corrections in the RTCM SC-104 message format under ITU-R M.823. A receiver applies the corrections to remove correlated errors from satellite clock, ephemeris, and ionospheric delay. It differs from RTK, which resolves carrier-phase ambiguities for centimeter accuracy. Many national authorities operate DGNSS beacon networks as a PNT backup.