Ionospheric TEC Estimations Using Single-Frequency Wideband Low Elevation GNSS Signals

This study presents the use of wideband, low elevation satellite signals to retrieve ionospheric Total Electron Content (TEC) from ground station Global Navigation Satellite System (GNSS) receiver data. TEC is a valuable measurement for both space weather research as well as GNSS precision and accuracy purposes. As ionospheric conditions are one of the most unpredictable factors for GNSS positioning, ionospheric monitoring is imperative for measuring and predicting impacts on space- and ground-based systems during space weather events. Monitoring the ionosphere in polar regions is challenging due to the scarcity of ground stations and lack of high-elevation angle GNSS signals, which is a consequence of GNSS orbit inclination angles. Elevation masks are commonly employed to limit the use of data at elevation angles below approximately 20°, where multipath and narrowband pseudorange noise are highest. Consequently, global ionospheric models (GIMs), which primarily use GNSS-derived TEC estimates, have degraded performance in these vital regions. Utilizing low-elevation GNSS signals can almost double the amount of TEC measurements in specific latitude bands. This study presents a method to utilize wideband low elevation GNSS signals to obtain accurate TEC estimations and circumvent limiting factors to GNSS ionospheric monitoring. In this study, we use data collected from GNSS ground stations deployed by the University of Colorado in Haleakala, HI (20.71°N latitude) and Toolik Lake, AK (68.63°N latitude). GPS L1 C/A, L2 C, and L5 pseudorange data are analyzed as a case study for single-frequency wideband TEC estimates. We will present a methodology to utilize single-frequency wideband signals for TEC estimation as well as compare results with dual-frequency TEC estimations. This study includes analyses of one week of satellite passes from two receiver locations, comparing the average noise levels from TEC estimates, and their dependence on elevation angle. Results show that the noise levels of single-frequency wideband-derived TEC are reduced by a factor of ?3–7 at low elevation angles and ?3–5 at high elevation angles, compared to dual-frequency narrowband-derived TEC. Overall, this technique could enhance the impact of GNSS ground stations to extend their capabilities over poorly monitored regions. This is in effort toward improving the detection of ionospheric irregularities where low-elevation measurements are frequent and contributing to a heightened understanding of ionospheric dynamics.