Performance of the L2C civil GPS signal under various ionospheric scintillation effects

Abstract

As GPS is modernizing, there are currently fourteen satellites transmitting L2C civil code and seven satellites transmitting L5 signal. While the GPS observables are subject to several sources of errors, the ionosphere is one of the largest error sources affecting GPS signals. Small irregularities in the electrons density along the GPS radio signal propagation path cause ionospheric scintillation that is characterized by rapid fluctuations in the signal amplitude and phase. The ionospheric scintillation effects are stronger in equatorial and high-latitude geomagnetic latitude regions and occur mainly due to equatorial anomaly and solar storms. Several researchers have analyzed the L2C signal quality since becoming available in December, 2005. We analyze the performance of L2C using GPS data from stations in the equatorial region of Brazil, which is subject of weak, moderate and strong ionospheric scintillation conditions. The GPS data were collected by Septentrio PolaRxS-PRO receivers as part of the CIGALA/CALIBRA network. The analysis was performed as a function of scintillations indexes S4 and Phi60, lock time (time interval in seconds that the carrier phase is tracked continuously without cycle slips), multipath RMS and position variation of precise point positioning solutions. The analysis shows that L2C code solutions are less affected by multipath effects than that of P2 when data are collected under weak ionospheric scintillation effects. In terms of analysis of positions, the kinematic PPP results using L2C instead P2 codes show accuracy improvements up to 33 % in periods of weak or strong ionospheric scintillation. When combining phase and code collected under weak scintillation effects, the results by applying L2C against P2 provide improvement in accuracy up to 59 %. However, for data under strong scintillation effects, the use of L2C for PPP with code and phase does not provide improvements in the positioning accuracy.

Mitigation of ionospheric scintillation effects on GNSS precise point positioning (PPP) at low latitudes

“…The PPP approach described in Zumberge et al (1997), as implemented in the so-called RT-PPP software (Marques et al 2016), was used for processing the data. This software was chosen because of its capability to read an external input file with tracking error variances for every epoch and satellite, thus allowing to test the scintillation mitigation approach.…”

“…Vani et al (2019) described a scintillation mitigation approach consisting of three steps, namely a new functional model to correct the effects of range errors in the observables, a new stochastic model that uses these corrections to assign different precisions for the observables and a strategy to attenuate the effects of losses of lock and consequent ambiguities re-initializations. The use of modernised GPS L2C measurements in GNSS positioning (Marques et al 2016) and using multi-constellation GNSS data (Marques et al 2018) to improve positioning accuracy under scintillation have also been attempted. Although these studies have provided encouraging results, the effectiveness of these approaches depends also on the severity of the scintillation conditions.…”

“…For example, using the approach proposed in Zhang et al (2014), the positioning accuracy reaches about 20-30 cm in the vertical direction during periods of strong scintillation after a short initialization period. Marques et al (2016) pointed out that the use of GPS L2C for PPP can provide improvement in accuracy only under weak scintillation conditions. Even by integrating GPS and GLONASS observations as presented in Marques et al (2018), the RMS of the 3D positioning accuracy under moderate to strong scintillation conditions can still be as poor as 36 cm.…”

GPS availability and positioning issues when the signal paths are aligned with ionospheric plasma bubbles

“…The PPP was applied with the standard configuration (that is, with corrections for tropospheric and first-order ionospheric refraction effects, but without any attempt to mitigate those from scintillation). Dual-frequency GPS data from the monitoring station were processed in the RT-PPP with a sampling rate of 1 s. The position parameters and receiver clock error were estimated at every epoch by the least-squares adjustment, while the phase ambiguities were estimated iteratively (Marques et al 2016). Typically, this procedure leads to a centimeter-level accuracy within 20 min, due to the convergence period of the phase ambiguity parameters (Gao and Shen 2002).…”

GPS Scintillations and Total Electron Content Climatology in the Southern American Sector

“…The ionospheric knowledge has been used to improve the GNSS positional accuracy, which can be strongly degraded under severe atmospheric disturbances because they can suddenly change the satellite geometry that is essential for geodetic position, in particular for kinematic precise point position (PPP), and are a limiting factor to achieve centimeter accuracy (e.g., [14][15][16]). The main atmospheric disturbances that affect the GNSS quality signals are the ionospheric steep density gradients, signatures of irregularities of the electron density distribution.…”