In this paper, we present an approach to generating a global topside ionospheric map (GTIM) using dual-frequency global positioning system (GPS) data from multiple low Earth orbit (LEO) satellites at different orbital altitudes. NeQuick2 is employed to normalize LEO data to the same observation range, and 13 LEO satellites from 2015/01/01 to 2015/09/27 are used to generate GTIM-500 (with an ionospheric range from 500 km to 20,200 km) and GTIM-800 (with an ionospheric range from 800 km to 20,200 km). First, we use the coinciding pierce point technique to study the error induced by altitude normalization. The results show that the relative bias error is approximately 1%. Then, the performance and accuracy of the GTIMs as well as the differential code bias (DCB) of GPS receivers onboard LEO and GPS satellites are compared and analyzed. The statistical results of the differences between the official LEO-DCB products and the LEO-DCBs estimated by our different solutions show a RMS improvement of 23% and 41% for GTIM-500 and GTIM-800, respectively. The improvement in RMS of GPS-DCBs for the proposed method is approximately 20%. Finally, the accuracy of GTIM is evaluated by the dSTEC assessment method. The results show that the RMS of GTIM-500 is 0.50 TECU (total electron content unit) for both methods. In terms of GTIM-800 estimated by the proposed method, the RMS has an improvement of 24%.

中文翻译：

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绘制来自不同轨道高度的多颗 LEO 卫星的顶部电离层垂直电子含量

在本文中，我们提出了一种使用来自不同轨道高度的多颗低地球轨道 (LEO) 卫星的双频全球定位系统 (GPS) 数据生成全球上部电离层图 (GTIM) 的方法。NeQuick2用于将LEO数据归一化到相同的观测范围，并使用2015/01/01至2015/09/27的13颗LEO卫星生成GTIM-500（电离层范围为500 km至20,200 km）和GTIM -800（电离层范围从 800 公里到 20,200 公里）。首先，我们使用重合穿刺点技术来研究高度归一化引起的误差。结果表明，相对偏差误差约为 1%。然后，对 GTIM 的性能和精度以及 LEO 和 GPS 卫星上 GPS 接收器的差分码偏差 (DCB) 进行了比较和分析。官方LEO-DCB产品与我们不同方案估计的LEO-DCBs差异的统计结果显示，GTIM-500和GTIM-800的RMS分别提高了23%和41%。所提出方法的 GPS-DCB RMS 的改进约为 20%。最后，通过dSTEC评估方法对GTIM的准确性进行评估。结果表明，两种方法的 GTIM-500 的 RMS 均为 0.50 TECU（总电子含量单位）。就所提出的方法估计的 GTIM-800 而言，RMS 有 24% 的改进。GTIM 的准确性通过 dSTEC 评估方法进行评估。结果表明，两种方法的 GTIM-500 的 RMS 均为 0.50 TECU（总电子含量单位）。就所提出的方法估计的 GTIM-800 而言，RMS 有 24% 的改进。GTIM 的准确性通过 dSTEC 评估方法进行评估。结果表明，两种方法的 GTIM-500 的 RMS 均为 0.50 TECU（总电子含量单位）。就所提出的方法估计的 GTIM-800 而言，RMS 有 24% 的改进。