Overbounding of Near Real-Time Estimated Ionospheric Gradient Slope in Low-Latitude Regions

This paper addresses the potential threats posed by large ionospheric gradients acting between ground-based augmentation system (GBAS) reference stations and aircraft during approach. Current GBAS stations rely on conservative threat models to mitigate ionospheric gradient threats, limiting system availability and continuity. To solve these issues, previous research has introduced a methodology for real-time detection and estimation of ionospheric gradients using a network of dual-frequency, multi-constellation global navigation satellite system monitoring stations. This paper proposes to expand this approach by including the derivation of an uncertainty model for the estimated gradient slope, allowing the threat model to be substituted with the near real-time estimated and overbounded gradient slope in current GBAS algorithms. Evaluations with simulated and real anomalous gradients produced by equatorial plasma bubbles demonstrate the efficacy of this methodology, indicating its potential to enhance GBASs by dynamically detecting, estimating, and overbounding the estimated anomalous gradients instead of relying solely on worst-case models, thus improving system availability and continuity.