An Airborne Ionospheric Correction Approach for Single-Frequency BDSBAS

The single-frequency (SF) BeiDou satellite-based augmentation system (BDSBAS) has been broadcasting small ionospheric residual uncertainties and grid ionospheric vertical errors (GIVEs), which may cause events of ionospheric integrity or system integrity. The system availability at high latitudes over Chinese territory is also constrained by the conventional interpolation algorithm within the ionosphere map surrounded by ionospheric grid points (IGPs). In this article, we proposed an airborne ionospheric correction approach based on the combination of a residual uncertainty model, a GIVE inflation strategy, and a global interpolation algorithm, and developed and verified with data from January 2021 to June 2022. The uncertainty model was rebuilt using the broadcast information from BDSBAS and the global ionosphere map (GIM) from the Center for Orbit Determination in Europe (CODE). From this model and historical residual data, we obtained the inflated GIVE that increased the average envelope probability of ionospheric residual errors from 94.08% to 99.99% for 117 BDSBAS IGPs. The biharmonic spline method (BSM) based on Green functions was introduced to extend the original ionosphere map to the north by 10° to enable more augmented signals. BSM increased the interpolation accuracy of the user ionospheric vertical delay (UIVD) by about 63%. The results from the regional test proved that our proposed approach could obtain an average minimum ionospheric safety index of 6.27 within the extended ionosphere map and increase the average coverage rate in the Chinese mainland from 95.15% to 99.07%. In the static station tests and the dynamic flight tests, positioning accuracies increased or remained the same, while misleading information (MI) events could be avoided.