Advanced Warning of Threatening Equatorial Plasma Bubbles to Support GBAS in Low Latitudes

In low-latitude regions such as Brazil, the single-frequency ground-based augmentation system (GBAS) is not yet fully operational due to the influence of ionospheric variability. The most critical issue for GBAS is the occurrence of ionospheric gradients large enough to compromise the system's integrity. This can result in unsafe operation because a single GBAS ground station cannot identify all threatening gradients in real time. This article develops and validates a strategy to detect and alert in advance the presence and effects of equatorial plasma bubbles (EPBs), which create the largest threat to GBAS operations in low latitudes. This alerting system uses surrounding stations in the vicinity of the GBAS facilities being supported to monitor the ionosphere state in real time and send alerts to the served GBAS facility when threatening conditions are detected on one or more tracked satellites. Time-step measurements of ionospheric gradients and data availability at these surrounding stations are used to generate these alerts when needed. An architecture is proposed for such a system along with a complete validation of the method. Validation uses a reliable dataset from the peak of ionospheric Solar Cycle 24 containing postprocessed station-pair gradients in time, amplitude scintillation indices, and ionospheric maps. All gradients from the dataset classified as threatening to GBAS operation were encompassed by the alerts issued by the real-time methodology within the adopted success criteria. Based on these results, an EPB alerting approach based on this method presented and validated in this article can significantly enhance single-frequency GBAS integrity and availability in low latitudes.