电离层顶部电子含量对GNSS电离层层析的影响分析

卫星信号射线上的总电子含量(slant total electron content, STEC)是像素基全球卫星导航系统电离层层析(computerized ionospheric tomography, CIT)建模的必要数据来源，但电离层层析通常忽略1 000 km以上的顶部电子含量，为弄清这部分电子含量对层析结果的影响，利用NeQuick2模型计算站星视线上的STEC与其在电离层区域内的STEC比值来改正原始数据，并分别利用改正前后的STEC进行电离层层析。结果显示，电离层顶部电子含量占比约为10%，白天占比略大于黑夜，与测高仪站的数据相比，改正后的均方根值比改正前提高了20%以上；与Swarm卫星提供的电子剖面数据对比，改正后的层析结果精度较改正前提升了19.6%左右，且该方法受地磁扰动影响较为明显。总的来说，利用CIT进行小尺度电离层探测，可较直观地看出，顶部电子含量对层析结果的影响较大，需要采取相应手段予以剔除。

Effects of electron content on GNSS ionospheric tomography at the top of ionosphere

Slant total electron content(STEC) on satellite signals is a GNSS computerized ionospheric tomography(CIT) modeling source. However, ionization chromatography usually ignores the electron content at the top above 1 000 km. In order to clarify the influence of electron content on the chromatographic results, the NeQuick2 model is used to calculate the ratio of STEC at the star line of the station to STEC in the ionosphere region, and the STEC before and after correction is used for ionization chromatography. The results show that the electron content at the top of the ionosphere is about 10%, which is slightly larger in the day than in the night, and compared with the lonosonde station''s data, the root mean square error(RMSE) increases by more than 20% after correction. Compared with the electronic profile data provided by Swarm satellite, the accuracy of the corrected chromatographic results is improved by about 19.6%, and the method is significantly affected by geomagnetic disturbance. In general, when CIT is used for small-scale ionospheric detection, it can be seen intuitively that the top electron content has a great influence on the chromatographic results, so it is necessary to take corresponding measures to eliminate it.