Enhancements of Long Term Ionospheric Anomaly Monitoring for the Ground-Based Augmentation System

Extremely large ionospheric gradients can pose a potential integrity threat to the users of ground-based augmentation systems (GBAS). A better understanding of the ionospheric behavior (not limited to that during extreme ionospheric activity) is important in the design and operation of GBAS to meet its integrity and availability requirements. A tool for long-term ionosphere monitoring was developed to build an ionosphere threat model, evaluate its validity over the system operation, monitor ionospheric behavior continuously, and update it when necessary. This paper presents the enhanced algorithms of long-term ionospheric anomaly monitoring and evaluates its performance using data from a ionospheric storm day, 20 November 2003, and a nominal day, 9 November 2004. The automation of data processing enables us to more accurately categorize ionospheric behavior under both nominal and anomalous conditions. This paper also demonstrates that the automated procedure of enhanced long-term ionosphere monitoring not only identifies gradients large enough to threaten GBAS users but periodically generates reliable statistics of ionospheric gradients under all conditions.