Global navigation satellite systems (GNSS) provide a great data source about the ionosphere state. These data can be used for testing ionosphere models. We studied the performance of nine ionospheric models (Klobuchar, NeQuickG, BDGIM, GLONASS, IRI-2016, IRI-2012, IRI-Plas, NeQuick2, and GEMTEC) both in the total electron content (TEC) domain—i.e., how precise the models calculate TEC—and in the positioning error domain—i.e., how the models improve single frequency positioning. The whole data set covers 20 years (2000–2020) from 13 GNSS stations, but the main analysis involves data during 2014–2020 when calculations are available from all the models. We used single-frequency positioning without ionospheric correction and with correction via global ionospheric maps (IGSG) data as expected limits for errors. Improvements against noncorrected solution were as follows: GIM IGSG—22.0%, BDGIM—15.3%, NeQuick2—13.8%, GEMTEC, NeQuickG and IRI-2016—13.3%, Klobuchar—13.2%, IRI-2012—11.6%, IRI-Plas—8.0%, GLONASS—7.3%. TEC bias and mean absolute TEC errors for the models are as follows: GEMTEC—−0.3 and 2.4 TECU, BDGIM—−0.7 and 2.9 TECU, NeQuick2—−1.2 and 3.5 TECU, IRI-2012—−1.5 and 3.2 TECU, NeQuickG—−1.5 and 3.5 TECU, IRI-2016—−1.8 and 3.2 TECU, Klobuchar—1.2 and 4.9 TECU, GLONASS—−1.9 and 4.8 TECU, and IRI-Plas—3.1 and 4.2 TECU. While TEC and positioning domains differ, new-generation operational models (BDGIM and NeQuickG) could overperform or at least be at the same level as classical empirical models.

For decades, GNSS code measurements were much noisier than phase ones, limiting their applicability to ionospheric total electron content (TEC) studies. Ultra-wideband AltBOC signals changed the situation. This study revisits the Galileo E5 and BeiDou B2 AltBOC signals and their potential applications in TEC estimation. We found that TEC noises are comparable for the single-frequency AltBOC phase-code combination and those of the dual-frequency legacy BPSK/QPSK phase combination, while single-frequency BPSK/QPSK TEC noises are much higher. A two-week high-rate measurement campaign at the ACRG receiver revealed a mean 100 sec TEC RMS (used as the noise proxy) of 0.26 TECU, 0.15 TECU, and 0.09 TECU for the BeiDou B2(a+b) AltBOC signal and satellite elevations 0–30°, 30–60°, and 60–90°, correspondingly, and 0.22 TECU, 0.14 TECU, and 0.09 TECU for the legacy B1/B3 dual-frequency phase combination. The Galileo E5(a+b) AltBOC signal corresponding values were 0.25 TECU, 0.14 TECU, and 0.09 TECU; for the legacy signals’ phase combination, the values were 0.19 TECU, 0.13 TECU, and 0.08 TECU. The AltBOC (for both BeiDou and Galileo) SNR exceeds those of BPSK/QPSK by 7.5 dB-Hz in undisturbed conditions. Radio frequency interference (the 28 August 2022 and 9 May 2024 Solar Radio Burst events in our study) decreased the AltBOC SNR 5 dB-Hz more against QPSK SNR, but, due to the higher initial SNR, the threshold for the loss of the lock was never broken. Today, we have enough BeiDou and Galileo satellites that transmit AltBOC signals for a reliable single-frequency vTEC estimation. This study provides new insights and evidence for using Galileo and BeiDou AltBOC signals in high-precision ionospheric monitoring.

The article considers the features of ionospheric global electron content (GEC) estimation based on simple empirical models of Klobuchar, BDGIM and NeQuickG used in the global satellite navigation systems GPS, Beidou and Galileo. Using GNSS observational data for almost the entire 24th solar activity cycle and global ionospheric maps CODG, the statistics of deviations and spectral characteristics of GEC variations estimated in the models and observed experimentally are studied. It is shown that the average deviation and standard deviation of GEC estimates by the BDGIM and NeQuickG models from the CODG data are (-0.041GECu and 0.092GECu) and (-0.025GECu and 0.042GECu), respectively. Thus, the NeQuickG model can be used in applications requiring prompt GEC estimation. The BDGIM model gives comparable results, but the dispersion of deviations of the model GEC estimates from the experimentally observed ones is higher for it than for NeQuickG, especially during periods of maximum solar activity. The Klobuchar model gives significantly biased GEC estimates, both at the minimum (0.172GECu) and at the maximum of the 24th solar activity cycle (-0.243GECu) and cannot be recommended for estimating GEC. At the same time, the BDGIM model requires improvements in terms of reliable reproduction of the amplitudes of 27-day and semi-annual GEC variations, especially during periods of solar maximum, which in the future should also improve the accounting of the ionospheric delay in positioning tasks in the single-frequency mode.

Linear instability analysis is performed to investigate the influence of solar wind parameters on instabilities driven by a cool pickup ion beam distribution, which is believed to excite the proton cyclotron waves upstream of Mars. Our analysis reveals that both parallel and oblique waves are excited, with parallel waves showing right-hand polarization and oblique waves exhibiting quasi-perpendicular, quasi-electrostatic characteristics at higher solar wind velocities. The growth rates of both types of waves increase with solar wind velocity, while solar wind plasma beta primarily enhances oblique wave growth, leaving parallel waves unaffected. Quasi-linear theory indicates that both parallel and oblique waves induce pitch-angle scattering of pickup ions, facilitating their escape from Mars. These findings advance our understanding of wave–particle interactions and their role in atmospheric escape at Mars.