Investigating the inconsistency of ionospheric ROTI indices derived from GPS modernized L2C and legacy L2 P(Y) signals at low-latitude regions

Abstract

The rate of change of total electron content (TEC) index (ROTI), an important parameter to characterize ionospheric irregularities and associated scintillation activities, can be calculated from both new Global Positioning System (GPS) civilian L2C and legacy GPS L2 P(Y) signals. We investigate the inconsistency of the ROTI indices derived from the L2C, denoted as ROTIL2C, and from the L2 P(Y), denoted as ROTIL2P, through the analysis of three months of GPS data collected by four types of GNSS receivers, i.e., Javad, Leica, Septentrio and Trimble, installed at five low-latitude stations. The results show that inconsistencies existent between the ROTIL2C and ROTIL2P may be related to the receiver configurations, such as tracking techniques. For both Leica and Trimble receivers, ROTIL2C and ROTIL2P are generally comparable; for the Septentrio receiver, ROTIL2C is larger than ROTIL2P by 0.5 to 1.1 TECu/min; for the Javad receiver, ROTIL2C is smaller than ROTIL2P by -0.5 to 0.3 TECu/min. A significant inconsistency of ROTIL2C (also ROTIL2P) is also found from the cross-comparison between the receivers deployed at zero/short baselines. In addition we find that large discrepancy of ROTI is observed for satellites with low maximum elevation angle. Correlation coefficients between ROTIL2C and 𝑆 4 are on average in the range of 0.4 to 0.8, comparable to those of ROTIL2P with 𝑆 4 . But low correlation coefficient is found for satellites with low maximum elevation angle. The ratios between ROTIL2C and 𝑆 4 are also calculated. They are in the range of 3 to 9, larger than those between ROTIL2P and 𝑆 4 . This study suggests that cautions be taken when ROTI index, either ROTIL2P or ROTIL2C, derived from different types of GNSS receivers is used to characterize ionospheric irregularities and associated scintillations.

On Inconsistent ROTI Derived From Multiconstellation GNSS Measurements of Globally Distributed GNSS Receivers for Ionospheric Irregularities Characterization

“…In regard to the Leica and Trimble receivers, the magnitudes of ROTIs show a comparable level in general. Those above findings were also revealed in Yang and Liu () for low‐latitude regions.…”

“…In regard to the Leica and Trimble receivers, the magnitudes of ROTIs show a comparable level in general. Those above findings were also revealed in Yang and Liu (2017) for low-latitude regions. Figure 11 summarizes the mean values of multi-GNSS ROTIs in different time periods (i.e., postsunset, postmidnight, and daytime hours) for all the Leica, Javad, Septentrio, and Trimble receivers, which illustrates an overall depiction of the inconsistency in the magnitude of ROTIs.…”

“…The variation of the amplitude scintillation S 4 corresponds well with that of multi‐GNSS ROTIs, as observed at the HKHT station shown in Figure . In our previous study, it has been shown that 1‐s ROTI has a high correlation with the amplitude scintillation S 4 of GPS L1 (Yang & Liu, , ). To demonstrate the correlation of ROTI with scintillation indices of multi‐GNSS signals (i.e., GPS L1, L2C, and L5 signals; GLONASS L1 signal; Galileo E1 signal; and BeiDou B1 signal), Figure displays the scatter plots of multi‐GNSS ROTIs and S 4 observed at HKHT on 16–17 March 2015.…”

“…The large discrepancy of ROTI observed among them is very likely related to the tracking techniques of the receiver. Previously, Yang and Liu (2017) have presented the inconsistency of ROTI derived from the GPS (L1 and L2C) and GPS (L1 and L2P) observations at low-latitude regions and discussed the possible reason, that is, the tracking loop design employed by various receivers. In the following, the effects of tracking loop designs on the level of the ROTI index will be elaborated.…”

“…However, the ROTI levels shown in Figures 5 to 7 exhibit different magnitudes between the GPS (L1 and L2P) and GPS (L1 and L2C) observations from the same receiver. Yang and Liu (2017) has discussed the inconsistency of ROTIs derived from them at low-latitude regions. In this study, there are 12 GNSS stations worldwide offering the GPS (L1 and L2P) and GPS (L1 and L2C) observations.…”