Implementation of an Effective Ionospheric Gradient Detection Technique for GBAS Applications at Low-Latitudes

Ground-Based Augmentation Systems (GBAS) are essential for ensuring the accuracy and integrity of satellite-based navigation for aircraft precision landings. However, severe ionospheric gradients can affect the integrity of GBAS systems. Very limited work has been done on the aspect of ionospheric gradient detection and alert mechanism. This paper focuses on the implementation of a simple approach to detect ionospheric gradients over low-latitude Indian stations, known for severe ionospheric variations. Time-step method is used to calculate the gradients from Slant Total Electron Content (STEC) data. The gradients are computed using 30-second intervals, and an alerting framework is implemented based on three predefined threshold values (Alert Threshold (AT), Recovery Threshold (RT) and Time to Recover (TR)). Results indicate that the threshold combination (AT = 300 mm/km, RT = 100 mm/km, TR = 5 minutes) effectively detects high gradients, triggers alerts when necessary, and maintains them until conditions return to a safe level, while minimizing false alarms. The results obtained are encouraging and will be helpful for effective implementation of GBAS at low-latitude stations.