BDS-3/BDS-2卫星联合精密定轨关键技术研究

Due to the restriction of sparse and uneven tracking stations distribution, and inaccurate geometric and physical models of BeiDou satellites, the accuracy and precision of BeiDou precise orbit determination are still far behind the matured navigation systems, such as GPS and GLONASS. Moreover, it is unable to meet the precision requirements of phase 3 of BeiDou development (IGSO/MEO<5cm), which imposes a great threat to the system performances and global competitiveness of BeiDou. Therefore, this project will make full use of the available information of in-orbit BeiDou-2 and extract the advantages of new technologies on BeiDou-3 to improve the accuracy and precision of combined BDS-3/BDS-2 precise orbit determination by the deep fusion and optimal utilization of multi-source observations. In this project, the studies focus on the follows: ① estimate and analyze the parameters of the inter-system biases (ISBs), inter-frequency biases (IFBs) and equipment delay precisely, to realize the deep fusion and interoperability of multi-source observations. ② study the estimation of Earth radiation pressure (ERP), the adaptive control of Solar radiation pressure (SRP) during the special environments, such as eclipse and yaw maneuvers, to acquire the precise radiation pressure for the whole orbit determination solution. ③ construct the combined orbit determination models with constraint conditions of the high-precise on-board atomic clock information and satellite-to-satellite cross-link observations, to realize the deep fusion and efficient utilization of the satellite-ground link and satellite-to-satellite cross-link observations. ④ propose an effective combined precise orbit determination algorithm, based on the reduction of inversion dimension, parameters and redundant observations. The results of this project are of great significance to solve the insufficient utilization of multi-source information, unreasonable parameters setting and inaccurate SRP models in combined BDS-3/BDS-2 precise orbit determination.

因受地面测站少、分布不均匀、卫星几何与物理模型不准确等因素影响，目前北斗卫星定轨精度与GPS等成熟系统仍有较大差距，无法满足系统第三阶段指标要求（IGSO/MEO<5cm），严重影响了北斗的整体性能与全球竞争力。对此项目将充分利用BDS-2现有资源，深入挖掘BDS-3新技术优势，通过数据深度融合与优化利用，提升联合定轨精度。重点解决：①系统偏差/频间偏差/硬件延迟偏差统一估计问题，实现观测数据的兼容互操作；②研究地表反照辐射改正及日影、制动等特殊条件下光压模型参数自适应调节方法，实现北斗卫星全弧段光压摄动精确估计；③构建附加高精度原子钟信息与星间观测约束的联合定轨模型，实现星地/星间信息的深度融合与高效利用；④从减少过程参数、剔除冗余观测、降低矩阵求逆维度等角度出发，建立联合定轨数据快速处理新方法。成果对解决目前北斗光压模型不准确，联合定轨信息使用不合理，提升北斗卫星定轨精度具有重要意义。

为解决新一代BDS-3卫星精密定轨关键技术，提升BDS-2/BDS-3卫星定轨精度，完善现有卫星精密定轨理论与方法，项目针对BDS-2/BDS-3联合定轨关键技术展开了研究，主要包括：1、从数据完整率、信噪比、多路径效应、电离层延迟变化率、周跳等方面对新信号的观测数据进行了全面分析，发现BDS-3的B1C/B2a数据质量与GPS、GALILEO兼容频率基本处于同一水平，在信噪比、电离层延迟变化率等方面甚至优于L1/L5、E1/E5a；2、针对不同频率的BDS-3观测值存在明显不同码偏差和多路径误差问题，提出了一种考虑BDS-2和BDS-3集成处理的一步策略来建模和消除码偏差和多径延迟，通过引入星间相关性，可以获得更稳定和准确的码偏差模型，最终定位结果表明，与E和N方向相比，U方向的精度有所提高，B1I的改善大于B3I；3、为了实现伪距偏差与其他误差的分离，提高定轨精度，提出一种BDS伪距标定方法，发现伪距偏差标定序列波动STD约为0.1m，不随时间明显变化，不同地点接收机测量的伪距偏差具有较好的一致性；4、针对BDS-2与BDS-3卫星间的差异性，构建了一种改进的BDS-2/BDS-3联合精密定轨系统偏差处理模型，利用该模型可分别改善BDS-2/BDS-3轨道18h重叠弧段精度0.4~1.0cm与0.8~4.1cm；5、对比分析BDS-2/BDS-3卫星原子钟的性能，发现BDS-3卫星钟稳定度相较于BDS-2卫星钟稳定度提高了65%~74%；6、针对BDS钟差预报产品无法满足高精度快速服务需求的现状，提出了一种基于BDS-2/BDS-3联合估计的超快速卫星钟差预报优化策略，通过引入星间相关性对随机模型进行精化，钟差序列一步建模可分别将BDS-2与BDS-3卫星钟差18h预报精度提升28.6%与27.2%；基于半变异函数建模的模型残差相关性提取,可实现BDS-2与BDS-3预报钟差精度8.0%与11.1%的提升；7、提出了一种基于精密卫星钟差信息辅助的BDS-2/BDS-3超快速轨道联合确定方法，当采用高精度的卫星钟差预报约束后BDS-2和BDS-3超快速轨道观测部分的估计精度可以分别提高9.2%和5.0%；8、针对BDS-3 PPP-B2b服务，提出了基于星间链路和区域测站观测数据的BDS轨道确定策略，星间链路测量对轨道倾角、升交点赤经等轨道定向参数不敏感。