Advantages of Computing ROTI From Single-Frequency L1 Carrier-Phase Measurements of Geodetic Receivers Operating at 1 Hz

The customary procedure to compute the rate of total electron content index (ROTI) presents some limitations when using the geometry-free (GF) combination of global positioning system (GPS) L1 and L2 carriers tracked by geodetic receivers. First, the effect of the tracking strategy implemented by each receiver manufacturer to obtain the L2 carrier from codeless observations. Second, the impact of frequent cycle slips (CSs) on the L2 carrier. These limitations hinder the monitoring and characterization of ionospheric scintillation. To overcome them, the present study proposes the calculation of ROTI from the individual (uncombined) L1 carrier-phase, ROTIL1, using the geodetic detrending (GD) post-processing methodology, in contrast to the conventional GF combination, ROTIGF. The analysis of the entire year 2020 shows that those two aforementioned limitations produce inconsistent ROTIGF values measured by pairs of close receivers from different manufacturers. In contrast, the distribution of ROTIL1 values shows a full consistency between different receivers, being significantly less affected by CSs and allowing a valid and well-grounded identification of scintillation. The study concludes that ROTIL1, calculated using a 60-s window from geodetic receivers operating at 1 Hz, provides a robust tool to monitor and characterize ionospheric scintillation worldwide and regardless of the type of receiver. In particular, a ROTIL1 threshold of 1.8 TEC unit (TECU)/min is established as the minimum level of detectable scintillation in 2020, a year of low solar activity. The most intense scintillation periods in high-latitude regions are statistically characterized by the newly proposed ROTIL1.