Ionospheric delay gradient model for GBAS in the Asia-Pacific region

We investigated characteristics of anomalous spatial gradients in ionospheric delay on GNSS signals in the Asia-Pacific (APAC) low-magnetic latitude region in the context of the ground-based augmentation system (GBAS). The ionospheric studies task force established under the Communications, Navigation, and Surveillance subgroup of International Civil Aviation Organization (ICAO) Asia-Pacific Air Navigation Planning and Implementation Regional Group, analyzed GNSS observation data from the Asia-Pacific region to establish a regionally specified ionospheric threat model for GBAS. The largest ionospheric delay gradient value in the analyzed data was 518 mm/km at the L1 frequency (1.57542 GHz), observed at Ishigaki, Japan in April 2008. The upper bound on the ionospheric delay gradient for a common ionospheric threat model for GBAS in the ICAO APAC region was determined to be 600 mm/km, irrespective of satellite elevation angle.