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 L2C, denoted as ROTIL2C, and from L2 P(Y), denoted as ROTIL2P, through the analysis of 3 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 existing 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 0.5-1.1 TECu/min; for the Javad receiver, ROTIL2C is smaller than ROTIL2P by 0.3-0.5 TECu/min. A significant inconsistency of ROTIL2C (also ROTIL2P) is also found from the cross-comparison between receivers deployed at zero/short baselines. In addition, we find that large discrepancy of ROTI is observed for satellites with low maximum elevation angle. The correlation coefficients between ROTIL2C and S (4) are on average in the range of 0.4-0.8, comparable to those of ROTIL2P with S (4). But, a 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 3-9, larger than those between ROTIL2P and S (4). This study suggests that cautions be taken when the ROTI index, either ROTIL2P or ROTIL2C, derived from different types of GNSS receivers is used to characterize ionospheric irregularities and associated scintillations.