PT  - JOURNAL ARTICLE
AU  - Sparks, Lawrence
AU  - Altshuler, Eric
AU  - Pandya, Nitin
AU  - Blanch,, Juan
AU  - Walter, Todd
TI  - WAAS and the Ionosphere – A Historical Perspective: Monitoring Storms
AID  - 10.33012/navi.503
DP  - 2022 Mar 20
TA  - NAVIGATION: Journal of the Institute of Navigation
PG  - navi.503
VI  - 69
IP  - 1
4099  - https://navi.ion.org/content/69/1/navi.503.short
4100  - https://navi.ion.org/content/69/1/navi.503.full
SO  - NAVIGATION2022 Mar 20; 69
AB  - Satellite-based augmentation systems ensure the accuracy and integrity of aircraft position estimates derived from radio signals broadcast by the Global Navigation Satellite System. The United States’ Wide Area Augmentation System (WAAS) protects users of the Global Positioning System from threats generated by ionospheric disturbances. The means by which WAAS mitigates these threats depends upon their magnitude. This paper addresses: a) how WAAS monitors the level of ionospheric perturbation over North America; b) how various availability and integrity concerns have influenced the implementation of WAAS’s extreme and moderate ionospheric storm detectors; c) how the algorithms governing these implementations have evolved since WAAS’s commissioning in 2003; and d) how the largest ionospheric storms of the past two solar cycles can be ranked according to their impact on WAAS. A subsequent companion paper will address the evolution of the WAAS methodology for protecting users from the adverse influence of more moderate ionospheric disturbances.