Validation and Intercomparison of Ionospheric Electron Density Products From COSMIC‐2, FY‐3, and Tianmu‐1 Radio Occultation Missions

Abstract Multi‐source GNSS radio occultation (RO) data are important for space weather monitoring, but instrumental and orbital variations introduce inconsistencies. This study assesses ionospheric data quality across Tianmu‐1, FY‐3, and COSMIC‐2 using over 6.9 million RO events from DOY 122, 2024 to DOY 120, 2025. Validated against ionosondes, NmF2 and hmF2 from all constellations show significant linear correlations ( r > 0.8 and 0.6, respectively) with near‐normal error distributions; profile validity rates range from 79.88% to 82.94%, decreasing notably in the equatorial ionization anomaly region. In TEC validation against CODE GIMs, all missions exhibited systematic underestimation, with mean differences of −1.04 (FY‐3), −3.58 (Tianmu‐1), and −3.88 TECU (COSMIC‐2), and RMSEs of 8.33, 8.52, and 9.89 TECU, respectively. During this period, the three constellations demonstrate complementary sampling: Tianmu‐1 covers a broader spatial range with the highest profile yield, COSMIC‐2 offers dense low‐latitude observations, and FY‐3 extends reliable measurements to high latitudes. Under NeQuick topside normalization, retrieval accuracy depends on LEO orbital altitude, with higher‐altitude FY‐3 showing smaller TEC biases. These results indicate that orbital configuration, sampling distribution, and topside normalization should be jointly considered when integrating multi‐source RO data for global ionospheric monitoring.