应用天文研究组知识库

Satellite Based Augmentation Systems (SBASs) improve the positioning accuracy and integrity by broadcasting to the civil aviation community the corrections and integrity parameters. A snapshot algorithm based on the minimum variance estimation is investigated in this study to calculate the satellite clock and orbit corrections. A chi-square test is performed on the remaining errors in the corrected ephemeris to guarantee the integrity. User Differential Range Error (UDRE) and scaling matrix contained in Message Type 28 are derived using the covariance information based on the assumption that one of the reference stations failed. A software package is developed and applied in the real data collected at 26 stations. International GNSS (Global Navigation Satellite System) Service (IGS) precise clock and orbit products are taken as the references to assess the accuracy of corrections. For both Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS), the range accuracy of 0.10 m can be achieved with the employment of the derived corrections. No obvious performance difference between GPS and BDS is found. UDREs for all visible satellites are generated with the maximum index of 12 and minimum index of 3. The geometric range differences calculated with IGS precise products and broadcast ephemeris are employed to assess the integrity of UDRE. It is found that the UDRE is able to bound the residuals with 99.9% confidence which meet the requirement of aviation users. With ionospheric delay corrected by Global Ionosphere Map (GIM), the positioning accuracy of 0.98 m with GPS corrections and 0.80 m with multi-constellation augmentation can be achieved which indicates a significant improvement of GPS standalone results.