Abstract
Ionospheric delay is one of the largest and most variable sources of error for Ground-Based Augmentation System (GBAS) users because inospheric activity is unpredictable. Under normal conditions, GBAS eliminates ionospheric delays, but during extreme ionospheric storms, GBAS users and GBAS ground facilities may experience different ionospheric delays, leading to considerable differential errors and threatening the safety of users. Therefore, ionospheric monitoring and assessment are important parts of GBAS integrity monitoring. To study the effects of the ionosphere on the GBAS of Guangdong Province, China, GPS data collected from 65 reference stations were processed using the improved “Simple Truth” algorithm. In addition, the ionospheric characteristics of Guangdong Province were calculated and an ionospheric threat model was established. Finally, we evaluated the influence of the standard deviation and maximum ionospheric gradient on GBAS. The results show that, under normal ionospheric conditions, the vertical protection level of GBAS was increased by 0.8 m for the largest over bound (sigma of vertical ionospheric gradient), and in the case of the maximum ionospheric gradient conditions, the differential correction error may reach 5 m. From an airworthiness perspective, when the satellite is at a low elevation, this interference does not cause airworthiness risks, but when the satellite is at a high elevation, this interference can cause airworthiness risks.
Highlights
Ground-Based Augmentation System (GBAS) is a type of regional satellite augmentation system used for precision positioning [1]
GBAS have extremely high accuracies and availabilities, which are necessary for Category I (CAT I) approaches, and in the future, GBAS will support CAT II/III precision approaches [4,5]
During the last solar maximum (2000–2004), the ionospheric anomaly threat model for the local area augmentation systems in the Conterminous United States (CONUS) was developed based on the extreme ionospheric gradients observed in the United States [9]
Summary
Ground-Based Augmentation System (GBAS) is a type of regional satellite augmentation system used for precision positioning [1]. During the last solar maximum (2000–2004), the ionospheric anomaly threat model for the local area augmentation systems in the Conterminous United States (CONUS) was developed based on the extreme ionospheric gradients observed in the United States [9]. In Brazil, the largest gradient is approximately 850 mm/km, which is almost twice as large as the maximum gradient observed in the CONUS [11] These models cannot be directly applied in China because ionospheric behavior varies significantly between locations with different solar radiation and geomagnetic environments. By simulating the ionosphere wave fronts at both aircraft and GBAS, we studied the max ionospheric gradient and its influence on GBAS, including the vertical protection level (VPL), Svert (projection of the vertical component and the translation of the along track errors in the vertical direction, as stated in Equation (15)) and maximum differential correction error.
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