The Earth's ionosphere is greatly influenced by geomagnetic activities, especially geomagnetic storms. During a geomagnetic storm, the ionosphere suffers many perturbations, leading to a spatial gradient that are neglected during geomagnetically quiet periods. An ionospheric gradient generates potential hazards for a ground-based argumentation system (GBAS) by enlarging the errors in the delay corrections between ground monitor stations and users. To address this problem, this work investigates the characteristics of the ionospheric gradient under geomagnetic storms. Global Navigation Satellite System (GNSS) observations from the continuously operating reference station (CORS) network were used to analyze the ionospheric gradients during the geomagnetic storm on 8 September 2017. The statistical behavior of the ionospheric gradient was further discussed. Experiments show that strong geomagnetic perturbations lead to large ionospheric gradients, and the gradients also vary with the geomagnetic location.
Keywords: geomagnetic storm; ground-based augmentation system; ionospheric gradient; satellite navigation; sigma bound.