用全球等离子体模型分析月球导航信号延迟，提升定位精度
Ionospheric and Plasmaspheric Delay Characterization for Lunar Terrestrial GNSS Receivers with Global Core Plasma Model
- 基于全球等离子体模型与射线追踪算法，模拟信号传播延迟
- 低轨信号延迟可达100米以上，太阳活动高时影响显著
- 为月球轨道和南极的卫星定位提供关键误差校正依据
近年来，月球定位、导航与授时（PNT）技术表明，可利用地基GNSS信号（包括弱侧瓣信号）实现月球航天器的定位与授时。尽管基于GNSS的月球导航已得到验证，但未建模的电离层和等离子体层延迟仍是主要误差来源，尤其在独特信号几何与长传播路径条件下。本文采用全球核心等离子体模型（GCPM）和自研低成本射线追踪算法，迭代求解弯曲信号路径，模拟了在不同太阳与地磁条件下，月球轨道及月球南极接收的GNSS信号的一阶、二阶和三阶群延迟，以及由射线弯曲导致的额外路径长度。结果表明，平均群延迟通常在1米量级，但在高太阳活动期，低轨路径延迟可超过100米；弯曲延迟整体较小，但对低轨路径仍不可忽略。同时量化了信号频率、地磁Kp指数和太阳R12指数的影响。这些发现为利用地基GNSS信号设计鲁棒的定位与授时算法提供了重要支持。
原文摘要 · Abstract (English)
Recent advancements in lunar positioning, navigation, and timing (PNT) have demonstrated that terrestrial GNSS signals, including weak sidelobe transmissions, can be exploited for lunar spacecraft positioning and timing. While GNSS-based navigation at the Moon has been validated recently, unmodeled ionospheric and plasmaspheric delays remain a significant error source, particularly given the unique signal geometry and extended propagation paths. This paper characterizes these delays using the Global Core Plasma Model (GCPM) and a custom low-cost ray-tracing algorithm that iteratively solves for bent signal paths. We simulate first-, second-, and third-order group delays, as well as excess path length from ray bending, for GNSS signals received at both lunar orbit and the lunar south pole under varying solar and geomagnetic conditions. Results show that mean group delays are typically on the order of 1 m, but can exceed 100 m for low-altitude ray paths during high solar activity, while bending delays are generally smaller but non-negligible for low-altitude ray paths. We also quantify the influence of signal frequency, geomagnetic $K_p$ index, and solar R12 index. These findings inform the design of robust positioning and timing algorithms that utilize terrestrial GNSS signals.
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