基于附加方位角参数的投影函数研究GNSS电离层TEC多层建模

随着GNSS高精度位置服务需求的日益旺盛，对电离层延迟误差影响要求已经从趋势修正走向高精细化修正。针对当前影响与制约GNSS TEC建模精度的“电离层薄层假说”和“电离层变化各向同性假说”，考虑电离层TEC在南北方向的倾斜投影误差大的实际变化规律，本项目在参考椭球坐标框架下导出附加卫星方位角参数的电离层投影函数（AMF），理论上经典的三角投影函数是AMF函数在一定条件下的退化特例；在此基础上，充分利用GNSS/LEO异构星座具备的不同层电离层观测的独特优势，提出分步式约束优化的TEC多层建模思路，实现利用地基GNSS实测数据建立LEO虚拟观测信息并通过迭代优化估计不同层TEC之间合理比例约束，有望突破制约现有TEC建模的技术瓶颈，（特别是在低纬度提高）提高TEC建模精度和可靠性。

With the increasing demand of GNSS high-precision positioning services, the requirements of the impacts of ionospheric delay error correction has been shifted from trend correction to high-precision correction. This project aims at minimizing the impacts the “ionosphere thin layer hypothesis” and “ionospheric isotropy hypothesis” on the accuracy of GNSS TEC modeling. A mapping function with azimuth parameter (AMF) derived under the ellipsoidal coordinate frame is proposed considering that the ionospheric TEC mapping errors are largest in the north-south direction than those from other directions. In theory, the classic triangular mapping function for sTEC (line-of-sight TEC) to vTEC (vertical TEC) conversion is a special case of the AMF function in certain conditions. With the help of the AMF function and the GNSS/LEO unique heterogeneous constellations, a multi-layer TEC modeling algorithm of step-by-step constraint is proposed to reconstruct the LEO virtual observation using ground-based GNSS data, and the reasonable proportion constraints between TEC values from the thin shells at different ionospheric height layers are estimated through iterative processing. It is expected that the new algorithm can break through the bottleneck of TEC modeling, and to improve the accuracy and reliability of TEC modeling especially at low latitudes.