Real-time estimation of Ionospheric Hole parameters through GNSS variometry

In this work, a new method for real-time estimation of Ionospheric Hole parameters using dual-frequency GNSS (Global Navigation Satellite System) observations is presented. The methodology is designed to work in real-time; it can be applied to different types of ionospheric disturbances and is based on a technique called VARION (Variometric Approach for Real-Time Ionosphere Observation), along with a tracking algorithm for the ionospheric perturbation parameters. The VARION, designed and developed by "Sapienza Università di Roma", allows the calculation of TEC (Total Electron Content) variations using double-frequencies GNSS phase observations. Additionally, the implementation of a least-squares tracking algorithm enables the calculation of the origin position, the propagation velocity of the disturbance, and the event time. The main assumption for the methodology is that the perturbation is considered as an isotropic wavefront propagating inside a single ionospheric layer at about 300 km altitude. This method has been tested on a dataset collected from 42 GPS (Global Positioning System) ground stations during the Falcon 9 launch event on August 24, 2017, a particular case that favored the formation of an Ionospheric Hole due to the low payload mass. The results show that the method effectively reconstructs the spatial and temporal evolution of the disturbance and highlights its potential for real-time monitoring of the ionosphere and to mitigate the impact of ionospheric irregularities on satellite navigation and telecommunications.