Characterizing ionospheric delay gradients for GNSS ground-based augmentation system

The global navigation satellite system (GNSS) is widely used for air navigation and considered as a main sensor. While dual-frequency GNSS has been standardized recently by International Civil Aviation Organization (ICAO), only single-frequency GNSS equipment are available and used. GNSS ground-based augmentation system (GBAS) is an air navigation system which supports precision approach and landing of aircraft. GBAS is based on the range-domain differential GNSS technique where GNSS reference stations on the ground observe GNSS signals and send correction and their integrity information to aircraft. Spatial decorrelation in the ionospheric delay (i.e. ionospheric delay gradient) is one of the major error sources. Results of ionospheric delay gradient observations in Vietnam and Indonesia are reported. Furthermore, ionospheric delay gradients associated with other ionospheric phenomena are reported.