Evaluation for BDSABS Ionospheric Grid Augmented by LEO Constellations

The utilization of onboard GNSS receivers and the potential broadcasting of dual-frequency navigation signals for low earth orbit (LEO) satellites represent effective means for improving ionospheric modeling performance in the future. Regional ionospheric corrections can be provided by the single-frequency (SF) service of Satellite-Based Augmentation System (SBAS), and further improvement relies on effective utilizations of LEO-related observations, which travel only a portion of the ionosphere. In addressing this challenge, the ionosphere is simplified as multiple thin layers, and bottom-side LEO-related observations are compensated by the established topside ionospheric grid. Subsequently, observations from GPS and LEO are integrated, and the entire ionospheric grid of SBAS is estimated using Kriging. The performance improvement of the BeiDou SBAS (BDSBAS) ionospheric grid is evaluated in a simulated environment based on the NeQuick-2 model. The evaluation involves the GPS constellation and a LEO constellation comprising 192 satellites. The results indicate that the better performance is achieved when the bottom-side observations from LEO satellites are first compensated and then mapped to vertical delays. Accordingly, the optimal cut-off elevation angle for these observations is determined to be 15°. Under these conditions, the root mean square (RMS) of the vertical delay estimation errors for 117 ionospheric grid points (IGPs) decreases by an average of 16.47% throughout the day, with a maximum reduction of up to 38.39% compared to using only GPS observations. Additionally, it is observed that the inclusion of LEO-related observations has the most significant improvement on the southern edge IGPs of BDSBAS during periods of high solar activity throughout the day.