Session B1: Atmospheric Effects, GNSS Remote Sensing, and Scientific Applications

Isolation of Ionospheric Events in GNSS Phase Scintillation Observations
S. S. Beeck, D. H. Olesen, DTU Space; C. N. Mitchell, University of Bath
Location: Beacon B

During space weather events, ionospherically induced fluctuation on the phase of GNSS signals can severely affect users of GNSS services, and users therefore must be aware of these impacts. This effort includes both the utilisation of scintillation models and real time alerts based on observations, where the features of the used data must be related to the effects of space weather. This can be a challenge for scintillation indices where other events can result in high phase scintillation values that are not space weather-related. Since extreme values can also arise from non-space-weather-related sources, e.g. local interference and oscillator issues, it is crucial in statistical studies of extreme events and input data for statistical models to ensure that extreme values are related to space weather. Therefore, an isolation of ionospheric events in GNSS phase scintillation observations is needed. In a database of a scintillation model, a distinction between the origin of extreme phase scintillation values could increase the integrity of the model. Similarly, for real-time space weather alerts to be valuable, identifying and removing high scintillation values caused by other processes is crucial before issuing space weather alerts, since a real-time event distinction could make the user aware of whether disturbances are space-weather-induced or not. In this work, two methods for separating data according to whether high scintillation values are space-weather induced are presented. The first method is for single frequency observations, which is especially relevant for analysis of historic data, while the second method utilises multiple frequencies.
The work presented is based on the sigma phi index, which is used as a measure of signal phase fluctuations in GNSS based space weather research. The collected data is based on GPS and Galileo signals received at four GNSS stations in Greenland equipped with Septentrio PolaRx5S scintillation receivers. The stations are in Kangerlussuaq, Illoqqortoormiut, Kulusuk, and Qaqortoq, providing a range of 64 to 71 degrees in magnetic latitude for the receiver locations.
To test our two methods for isolation of ionospheric events in sigma phi observations, a full year of data from 2022 was used. Large quantities of data is a requirement due to sigma-phi following a skewed distribution with few extreme values. This means that even large datasets will provide significantly less data for studies of extreme events, and these can therefore be underrepresented in statistical studies.
From the analysis on the four stations, it was found that the station in Kulusuk had 46.85% sigma-phi values, above 0.4, related to space-weather which was significantly lower than what was seen from the other three stations, where the corresponding sigma-phi values were in the range of 0.14-0.90%. Therefore, isolating ionospherically induced high sigma-phi values enables a significant reduction of misassigned sigma phi, which can improve both GNSS-based modelling and alert systems.
In summary this abstract presents algorithms to distinguish increases in sigma phi caused by interference, oscillator issues and ionospheric phase scintillation. The purpose of this work is to allow the correct distinction of genuine ionospheric events so that they can be used reliably in geophysical research studies, statistical modelling and operational systems.