联合GNSS和LEO星群构建高精度高分辨率全球电离层模型的关键技术研究

The global ionosphere model with high precision and high resolution is important for many studies. The accurate ionosphere model can be used to improve the positioning accuracy as well as the detailed variations and structure of the ionosphere. Moreover, studies the relationship between the ionospheric disturbances and hazards, e.g. earthquakes, tsunamis, and typhoons. To date, it is worthy of indicating that a global ionospheric product with high-precision and high-resolution has an urgency. However, the accuracy of the global ionospheric model is limited by few ground-based global navigation satellite system (GNSS) monitoring stations over some areas such as the oceans region, and the uneven distribution of the stations in the worldwide. Recently, with the rapid development of GNSS and low earth orbit (LEO) satellites, the modeling of the ionosphere can have a high resolution and high accuracy around the world by a combination of the GNSS and LEO. On this basis, this project will study the key technologies of modeling the ionosphere with high precision and high resolution based on the rapid development of LEO constellation. The key technologies include the accurate total electron content (TEC) extraction from the direct and reflect signals from LEO space-based GNSS receivers, multi-source ionospheric TEC normalization, as well as estimation of different time system with multi-source ionospheric TEC and so on. The ionospheric model with the best fusion of multi-source, different satellites constellations, and variety accuracies will improve the accuracy and reliability of the ionospheric model. The study of modeling ionosphere with high precision and high resolution combining GNSS and LEO constellations is of great importance to enrich and improve the ionospheric modeling and methods. The studied results can be regarded as an important reference for ionospheric modeling with LEO constellations in the future.

高精度全球电离层模型对提高卫星导航系统定位精度、研究电离层精细变化及探寻电离层与相关自然灾害（如地震、海啸）间的响应关系等具有重要意义。本项目瞄准建立高精度高分辨率全球电离层模型的迫切需求，结合GNSS/LEO卫星的最新发展动态，致力于解决因GNSS地面跟踪站全球分布不均匀，导致模型在海洋等区域的精度和可靠性严重不足的问题。在大规模LEO星群蓬勃发展的大背景下，开展联合GNSS和LEO星群观测构建高精度高分辨率全球电离层模型的关键技术研究，解决LEO星载GNSS直射与反射信号的电离层TEC观测值精确提取、多源电离层TEC信息的“归一化”及时变系统性偏差的准确估计等若干关键难题，实现多源、异构、非等精度电离层TEC信息的最优融合，提高全球电离层模型的精度和可靠性。项目研究对于丰富和发展电离层建模理论与方法具有重要意义，研究成果可为未来LEO星群条件下构建高精度全球电离层模型提供重要参考。

项目瞄准高精度高分辨率全球电离层建模的迫切需求，结合GNSS/GNSS卫星星座的最新发展动态，开展联合 GNSS 和 LEO 星群构建全球电离层模型的关键技术研究，致力于解决因GNSS地面跟站全球分布不均匀，导致模型在海洋等区域的精度和可靠性严重不足的问题。主要包括 LEO 星载 GNSS 信号的电离层 TEC 观测值精确提取、多源电离层 TEC 观测信息最优融合等。针对传统相位平滑伪距法提取电离层TEC易受观测噪声、观测弧段长度、多路径效应等影响，提出了基于非差相位整数解的电离层TEC提取方法，TEC提取精度可提高一个数量级；针对海洋地区电离层观测覆盖不足的问题，提出了顾及对流层和顶部电离层的星载GNSS-R电离层TEC精确反演方法，可大幅改善海洋区域电离层监测能力与建模精度；建立了LEO导航增强电离层建模仿真平台，在国际上率先论证了LEO星群增强GNSS电离层建模的可行性及增益；提出了“单层归一化法”和“分层叠加法”的LEO星群增强GNSS融合建模方法，从模拟数据到实测数据详细论证新方法的建模效果，为未来海量低轨卫星观测数据条件下的电离层精细建模提供重要支撑。项目成果对于丰富和发展电离层建模理论与方法具有重要意义。