应用天文研究组知识库

分析星基增强系统（satellite based augmentation system,SBAS）地球同步轨道(geostationary Earth orbit,GEO)卫星用户测距误差（user range error,URE），研究GEO卫星测距对导航定位性能的影响，可为SBAS系统设计和民航应用提供有益参考。利用广域增强系统（wide area augmentation system,WAAS）、北斗星基增强系统（BeiDou SBAS,BDSBAS）、GPS辅助静地增强导航系统（GPS aided GEO augmented navigation, GAGAN）和多功能卫星增强系统（multi-functional satellite augmentation system,MSAS）的SBAS信息对GPS和GEO卫星星历、时钟和观测值进行改正，固定测站位置，根据改正数残差方差加权计算接收机钟差，得到GEO卫星测距误差；将GEO卫星观测值纳入SBAS定位解算，评估GEO卫星测距对定位结果的影响。通过实测数据分析可知，WAAS GEO卫星URE优于1.6 m;BDSBAS 3颗GEO卫星分别存在14.32 m、12.64 m和17.44 m的系统偏差，经系统性误差改正后，GEO卫星URE优于2.9 m;GAGAN和MSAS GEO卫星URE分别优于13.9 m和3.2 m。当GPS卫星数较少时，联合GEO卫星观测值进行SBAS解算能够有效减小定位保护级，提升系统可用性。 

Objectives: Satellite based augmentation system (SBAS) improves the positioning accuracy and integrity by broadcasting ephemeris corrections and associated integrity parameters through geostationary Earth orbit (GEO) satellites. SBAS GEO satellite can also be used as a ranging source together with GPS satellites to improve the system performance. User range error (URE) of the GEO satellite and their effect on positioning results are investigated. URE of SBAS GEO and GPS satellite is determined by weighting the observation residuals which are derived with fixed station coordinates. SBAS messages are applied to correct the orbit and clock errors contained in broadcast ephemeris and the ionosphere delay. Ranging data from GEO satellite is engaged in the SBAS positioning process to explore the impact on positioning accuracy, integrity and availability. Methods: SBAS messages broadcast by wide area augmentation system (WAAS), BeiDou SBAS (BDSBAS), GPS aided GEO augmented navigation (GAGAN) and multi-functional satellite augmentation system (MSAS) and real data from international GNSS service (IGS) stations are applied to perform the assessment. European geostationary navigation overlay service (EGNOS) and system for differential corrections and monitoring (SDCM) are not included because of the absence of the ranging capability. Results: WAAS GEO satellite has the best performance with ranging accuracy better than 1. 6 m. The 99. 9% error bound is less than 6. 8 m while the broadcast user differential range error (UDRE) for the GEO satellite is 7. 5 m, which meets the integrity requirement. The 3 GEO satellites of BDSBAS show ranging biases of 14. 32 m, 12. 64 m and 17. 44 m respectively, and the accuracy is better than 2. 9 m. After removing the bias, the related 99. 9% error bound is 8. 60 m, 7. 80 m and 11. 60 m which suggests an UDRE of 11-12. User range accuracy (URA) of 15 is broadcast in message type 9 for the BDSBAS GEO satellites. URE of the GAGAN GEO satellite is better than 13. 9 m and MSAS is better than 3. 2 m. The UDRE of GAGAN and MSAS is 14. URE of GPS satellite after augmented by SBAS is also calculated for comparison purpose. Ranging accuracy of GPS is 0. 60 m, 0. 53 m, 0. 21 m and 0. 34 m for WAAS, BDSBAS, GAGAN and MSAS respectively. WAAS GEO satellite is selected to perform the positioning analysis whose UDRE is less than 14 so that it can be weighted properly in the solution. Engagement of GEO satellite in SBAS positioning will lead to lower position dilution of precision (PDOP) and reduce the protection level especially for the blockage circumstance. The system availability of localizer performance with vertical guidance 200 (LPV200) service is improved from 99. 984% to 99. 997% with collaboration of 3 GEO satellites' observation. Conclusions: With sufficient GPS satellites, the combination of GEO satellites will decrease the positioning accuracy because of the relative larger range error, while with less available satellites, combining the GEO satellite data effectively reduces the protection level and improves the system availability. Results suggest that SBAS GEO ranging data should be included in the SBAS solution for aviation users.