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<p>The topside ionosphere plays a critical role in space weather applications. Accurate topside ionospheric observations are essential for driving and refining topside ionospheric models. This paper presents a method that uses an un-differenced and uncombined (UDUC) Precise Point Positioning (PPP) ambiguity-fixing technique to estimate the total electron content (TEC) of the topside ionosphere based on LEO onboard GPS observations. Spaceborne GPS observations from seven LEO satellites in 2022, including GRACE-FO, Sentinel-3, and Swarm missions, were used to validate the proposed method. Comparisons with official topside TEC products and Swarm Langmuir probe measurements show strong external consistency and geophysical consistency of the retrieved slant TEC (STEC). The ambiguity fixing rate ranges from 80 to 90%, with an average time-to-first-fix (TTFF) of less than 16&#xa0;min, indicating robust and efficient retrieval performance. Comparisons with precise science orbits show centimeter-level orbit consistency, providing an indirect consistency reference for the retrieved TEC under the adopted observation model. In addition, an SF-PPP experiment is used as a self-consistency check to further assess the internal coherence of the retrieved topside TEC.</p>

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Accurate topside ionospheric TEC estimation using LEO satellites with onboard GPS observations

  • 期刊论文

  • 发表日期：

    2026年6月23日

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  • Xiaodong Ren,
  • Jianfeng Wu,
  • Xuan Le,
  • Yuhang Yang,
  • Haochen Yang,
  • Linghuo Jian,
  • Xiaohong Zhang

摘要

The topside ionosphere plays a critical role in space weather applications. Accurate topside ionospheric observations are essential for driving and refining topside ionospheric models. This paper presents a method that uses an un-differenced and uncombined (UDUC) Precise Point Positioning (PPP) ambiguity-fixing technique to estimate the total electron content (TEC) of the topside ionosphere based on LEO onboard GPS observations. Spaceborne GPS observations from seven LEO satellites in 2022, including GRACE-FO, Sentinel-3, and Swarm missions, were used to validate the proposed method. Comparisons with official topside TEC products and Swarm Langmuir probe measurements show strong external consistency and geophysical consistency of the retrieved slant TEC (STEC). The ambiguity fixing rate ranges from 80 to 90%, with an average time-to-first-fix (TTFF) of less than 16 min, indicating robust and efficient retrieval performance. Comparisons with precise science orbits show centimeter-level orbit consistency, providing an indirect consistency reference for the retrieved TEC under the adopted observation model. In addition, an SF-PPP experiment is used as a self-consistency check to further assess the internal coherence of the retrieved topside TEC.