RODTI: A Method for Extracting Ionospheric Scintillation-Related Index Based on DORIS Dual-Frequency Observations and Its Verification on a Global Scale

Abstract

The advent of the peak year of the 25th solar cycle has led to a notable intensification of ionospheric disturbances, resulting in frequent occurrences of ionospheric scintillation. Ionospheric scintillation has emerged as a critical factor compromising the stability of global navigation satellite system (GNSS) positioning services. Global monitoring of ionospheric scintillation is essential for mitigating its disruptive effects on GNSS. However, conventional scintillation monitoring relies mainly on ground-based GNSS observation networks, whose limited geographical distribution leads to substantial coverage gaps over oceans, polar regions, and remote inland areas. In contrast, Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), as a space-based observation system, offers a viable complement to ground-based GNSS scintillation monitoring. Yet, a longstanding limitation of DORIS has been the absence of dedicated observational metrics suitable for scintillation monitoring. Accordingly, this study proposes a cycle-slip detection method tailored for the DORIS system and develops an ionospheric scintillation-related index, termed the Rate of DORIS TEC Index (RODTI), from dual-frequency carrier-phase observations, where TEC stands for total electron content. Unlike classical scintillation indices such as S4 or ${\sigma }_{\varphi }$ , RODTI is defined as a space-based complementary scintillation-related index to the GNSS-derived rate of TEC index (ROTI) and is intended to extend the spatial coverage of existing ground-based GNSS scintillation monitoring. Furthermore, a 2-D GPS ROTI grid is constructed using Kriging interpolation, enabling the acquisition of spatiotemporally co-located RODTI and GPS ROTI data. A latitude-constrained support vector regression (SVR) approach is applied to normalize RODTI amplitudes, effectively addressing the discrepancy in magnitude between RODTI and GPS ROTI. Validation was conducted using matched data from day of year 210–306 in 2024, incorporating observations from 250 global GPS stations, to assess the accuracy and long-term reliability of RODTI. Results indicate that the normalized RODTI and ROTI maintain correlation coefficients above 0.75 both globally and within individual latitude zones. The daily root-mean-square error (RMSE) throughout the validation period remained between 0.04 and 0.05 TECU/min. Moreover, during intense geomagnetic storm events, RODTI, ROTI, and ${\sigma }_{\varphi }$ exhibited closely aligned temporal variations and response patterns, affirming their consistency in monitoring ionospheric scintillation. The DORIS-based ionospheric scintillation-related index developed in this work serves as a new data source toward establishing a more detailed and densely distributed global ionospheric scintillation monitoring network.