Real-Time Ionospheric Threat Adaptation to Increase CAT-I GBAS Availability in Equatorial Regions

Abstract Current solutions to mitigate errors caused by undetected anomalous ionospheric gradients in ground-based augmentation systems (GBASs) rely on conservative threat models. While effective, these models limit system availability, particularly in regions with highly active ionospheric conditions. In this paper, we propose a methodology to replace the worst-case large values of existing conservative threat models with the magnitudes of real-time observed anomalous ionospheric gradients. This approach involves determining the maximum anomalous ionospheric gradients that could be affecting a specific GBAS station without being detected by a network of dual-frequency global navigation satellite system monitoring stations protecting it. Using simulations and real data from a monitoring network in Brazil, we demonstrate that this methodology significantly enhances category-I GBAS availability in regions with active ionospheric conditions. Moreover, the proposed approach is compatible with current algorithms and hardware, enabling its adaptation for certification when tailored to the specific characteristics of a given region.