Assessing 1‐Second ROTI for Ionospheric Perturbation Monitoring Using Real‐Time Multi‐GNSS Data in China

Abstract With the onset of solar activities of the 25th solar cycle, ionospheric perturbations have become increasingly frequent, posing significant challenges to various applications of Global Navigation Satellite Systems (GNSS). The Rate of Total Electron Content (TEC) Index (Rate of TEC Index (ROTI)), commonly derived from GNSS data sampled at 30‐s intervals, fails to detect ionospheric irregularities smaller than the first Fresnel scale due to its low temporal resolution. This study investigates the efficacy of using 1‐s sampling intervals of multi‐GNSS (GPS, GLONASS, Galileo and BDS) data for monitoring ionospheric perturbations, comparing it to the conventional 30‐s sampling approach. Using real‐time multi‐GNSS observations in China, we computed ROTI values at both 1‐s (1s‐ROTI) and 30‐s (30s‐ROTI) intervals. Results indicate that 1s‐ROTI demonstrates higher magnitude and larger inconsistency across different GNSS constellations compared to 30s‐ROTI, with peak 1s‐ROTI values reaching 10 TECU/min and a maximum discrepancy of 1.0 TECU/min between different GNSS constellations. The inconsistency in 1s‐ROTI was found to correlate with different receivers types (e.g., Septentrio, Unicore, Trimble and Leica). Additionally, 1s‐ROTI exhibits better consistency and higher correlation with scintillation indices from Ionospheric Scintillation Monitoring Receivers (ISMR), with overall correlation coefficient exceeding 0.85 for all systems except for GLONASS. To mitigate inconsistencies in 1s‐ROTI, we propose different GNSS‐ROTI indices, with ROTI mean and ROTI ele showing the best performance in terms of correlation with scintillation indices and reflecting GNSS positioning performance degradation. The potential of 1s‐ROTI is highlighted for improving small‐scale ionospheric irregularities monitoring and indicating the GNSS positioning performance, especially in regions lacking ISMR.