Mitigating Receiver Code Bias in Wideband Low-Elevation TEC Retrievals from GNSS Ground Stations

This study explores the use of wideband GNSS receiver pseudorange data to improve absolute slant total electron content (sTEC) retrievals from low-elevation signals to expand ionospheric measurement capabilities, particularly in high-latitude regions with sparse observational coverage. This technique utilizes modernized wideband GNSS signals, such as GPS L5 and Galileo E5, which offer enhanced precision. Expanding low-elevation GNSS measurements could increase TEC data availability, improving space weather forecasting and navigation accuracy.
Ionospheric disturbances disrupt navigation, communications, and power grids, making continuous monitoring essential. However, GNSS-based TEC observations are spatially limited, especially in polar regions where receiver coverage is sparse and satellite geometry restricts high-elevation visibility. Global ionospheric models (GIMs) rely on interpolation in these regions, reducing accuracy, particularly during high solar activity. Incorporating low-elevation GNSS signals can enhance navigation and space weather resilience.
TEC estimation typically relies on dual-frequency GNSS measurements, where pseudorange provides unbiased but noisy estimates, and carrier-phase data offers high precision but contains ambiguities. Low-elevation signals introduce uncertainty from multipath and low signal-to-noise ratio (SNR), leading most GNSS ground stations to use elevation masks (15°–30°), discarding valuable data. Wideband GNSS signals have higher code chipping rates, reducing uncertainties and making them well-suited for low-elevation TEC retrievals.
This study uses GNSS receiver data from high-latitude stations (above 60°) sourced from the International GNSS Service (IGS). GPS L1 C/A, L2 C, and L5 pseudorange measurements, combined with precise orbit and tropospheric delay models, provide single-frequency wideband relative TEC estimates. To obtain absolute TEC, satellite and receiver code biases (CBs) must be corrected. Satellite CBs are addressed using public bias correction products, while receiver CBs are estimated from high-elevation dual-frequency measurements, leveraging TEC spatial gradients. Once determined, the receiver-wideband CB enables absolute sTEC retrieval for low-elevation signals.
Preliminary results analyze TEC uncertainty levels using wideband GNSS signals compared to conventional methods. Results also validate code bias and TEC retrieval accuracy via comparison to electron density profiles from the Poker Flat ISR (PFISR). By improving low-elevation TEC retrievals, this approach enhances ionospheric data availability, supports GNSS reflectometry applications, and advances space weather forecasting and navigation resilience. Expanding low-elevation GNSS signal usage through wideband pseudorange measurements is a critical step toward mitigating ionospheric data gaps and improving global ionospheric models.