应用天文研究组知识库

星基增强系统（satellite based augmentation system,SBAS）通过地球同步轨道卫星实时播发导航卫星星历改正数和完好性参数,以提升用户定位精度和完好性。采用最小方差法解算GPS星历改正数,利用卡方统计进行改正数完好性检核,并依据星历改正数方差-协方差信息计算SBAS用户差分距离误差（user differential range error,UDRE）和信息类型28（message type 28, MT28）等完好性参数。利用中国区域27个监测站的实测数据,首先以国际GNSS服务组织的精密轨道和钟差产品为参考解算星历改正数,结果表明,钟差改正精度优于0.1 m,轨道改正精度优于0.4 m;然后解算广播星历改正数,并生成UDRE和MT28参数,广播星历残余误差卡方检验值均小于告警门限,保证了改正数的完好性;最后利用生成的改正数进行SBAS定位解算,得到定位结果的水平精度优于0.7 m,垂直精度优于1.0 m,对比GPS单点定位,所提算法的水平和垂直方向精度分别提升了30%和40%。 

Satellite based augmentation system (SBAS) improves the accuracy and integrity of user positioning by broadcasting ephemeris corrections and associated integrity parameters through geostationary earth orbit satellites in real time. Minimum variance estimation method is proposed to derive the GPS ephemeris corrections and a Chi-square test is performed on the residual errors of corrected ephemeris to meet the integrity requirement. Satellite user differential range error (UDRE) and scaling matrix contained in message type 28 (MT28) are calculated based on the covariance information with the assumption that one of the reference stations failed. Actual data collected by 27 stations spread over China are applied to verify the proposed algorithm. International GNSS Service precise clock and orbit products are firstly taken as reference to assess the accuracy of ephemeris corrections. Results indicate that an accuracy of 0.1 m for clock and 0.4 m for orbit corrections can be obtained. Then, corrections of GPS broadcast ephemeris are estimated, the integrity parameters including UDRE and MT28 are generated. Chi-square test results of the ephemeris remaining errors show no exceeding of the threshold which reveals the integrity of corrections. A clear dependence of UDRE on satellite elevation is presented. On board clock failure and satellite maneuvering were simulated to evaluate the performance of the proposed algorithm. Measurement errors introduced by satellite abnormity can be effectively detected and compensated by the algorithm. With ionospheric delay corrected by Klobuchar model and ephemeris corrections generated in this contribution, SBAS positioning results achieve the accuracies of 0.7 m in horizontal direction and 1.0 m in vertical direction, which show an improvement of 30% in horizontal direction and 40% in vertical direction compared with the GPS single point positioning results.