Performance Analysis of Multi-GNSS Occultation Electron Density Profiles from the Tianmu-1 Constellation
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摘要: 天目一号是中国首个在轨实现北斗、GPS、Galileo和GLONASS四大系统兼容的掩星气象探测星座。利用天目一号掩星任务2025年3月份的电离层电子密度廓线，对其每日掩星数据数量及其全球分布特征进行分析。基于电离层垂测仪提供的F2层临界频率值（FoF2）和F2层峰值高度（HmF2）数据，以及国际GNSS服务组织（IGS）的事后全球电离层格网（GIM）产品提供的总电子含量（TEC）数据，对天目一号星座掩星反演的峰值电子密度（NmF2）、HmF2和TEC参数进行了质量分析。结果表明，天目一号星座反演的NmF2与垂测仪数据的相关系数为0.93，平均偏差为0，平均相对偏差为17.9%，均方根误差（RMSE）为0.27×10⁶ el/cm³；HmF2的相关系数为0.75，平均偏差为0，平均相对偏差为6.83%，RMSE为29.6 km。借助 NeQuick 模型将天目一号星座反演的 TEC 映射至地面到GNSS 卫星高度范围后，以 IGS GIM TEC 为参考，GPS、BDS、GLONASS 与 Galileo 四种系统的 TEC 反演精度相当，RMSE 依次为 9.64、9.52、9.75 和 9.56 TECu。相较于 IRI模型，NeQuick 归一化后的结果与 IGS GIM TEC 一致性更佳：平均偏差为 −1.87 TECu，RMSE 降至 9.62 TECu；而 IRI 模型对应的平均偏差为 −5.59 TECu，RMSE 为 10.69 TECu。
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关键词:
- 天目一号星座 /
- 掩星 /
- 电子密度廓线 /
- F2层电子密度 （NmF2） /
- F2层峰值高度（HmF2） /
- 总电子含量（TEC） /
- 垂测仪 /
- 全球电离层格网（GIM）
Abstract: Tianmu-1 is China’s first occultation meteorological constellation capable of on-orbit compatibility among BeiDou, GPS, Galileo and GLONASS. Using the ionospheric electron-density profiles retrieved by Tianmu-1 occultations in March 2025, we analyzed the daily number of occultations and their global distribution. The quality of the peak electron density (NmF2), F2-layer peak height (HmF2) and total electron content (TEC) derived from Tianmu-1 was assessed against F2-layer critical frequency (foF2) and peak height (hmF2) measured by ionosondes, and against the post-processed Global Ionospheric Map (GIM) TEC provided by the International GNSS Service (IGS). The results show that Tianmu-1-derived NmF2 correlates with ionosonde data at 0.93, with zero mean bias, 17.9 % mean relative bias and an RMSE of 0.27 × 10⁶ el cm⁻³. For HmF2, the correlation is 0.75, the mean bias is also zero, the mean relative bias is 6.83 %, and the RMSE is 29.6 km. After mapping Tianmu-1 TEC to the ground-to-GNSS-satellite altitude range with the NeQuick model, the TEC accuracies for GPS, BDS, GLONASS and Galileo are comparable when referenced to IGS GIM TEC, yielding RMSEs of 9.64, 9.52, 9.75 and 9.56 TECu, respectively. Compared with the IRI 2020 model, the NeQuick-normalized results exhibit better agreement with IGS GIM TEC: the mean bias is only −1.87 TECu and the RMSE is reduced to 9.62 TECu, whereas the IRI model produces a mean bias of −5.59 TECu and an RMSE of 10.69 TECu. -
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