The propagation paths of signals through equatorial ionospheric irregularities are analyzed by evaluating their effects on Global Navigation Satellite System (GNSS) positioning and availability Based on observations during 32 days by a scintillation monitor at Sao Jose dos Campos, Brazil, it was noted that there is a dominance of enhanced scintillation events for Global Positioning System (GPS) ray paths aligned with the azimuth angle of 345° (geographic northwest) This azimuth corresponds to the magnetic meridian that has a large westward declination angle in the region (214oW) Such results suggest that the enhanced scintillation events were associated with GPS signals that propagated through plasma bubbles aligned along the direction of the magnetic field It will be shown that, under this alignment condition, the longer propagation path length through plasma bubbles can result in more severe scintillation cases and more losses of signal lock, as supported by proposed statistics of bit error probability and mean time between cycle slips Additionally, large precise positioning errors are also related to these events, as demonstrated by precise point positioning experiments

/pdf/gps-availability-and-positioning-issues-when-the-signal-9wwdqhxcl6.pdf

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

A noise reduction method based on adaptive weighted symplectic geometry decomposition and its application in early gear fault diagnosis

. In this study the climatology of ionospheric scintillations and the zonal drift velocities of scintillation-producing irregularities are depicted for a station located under the southern crest of the equatorial ionization anomaly. Then, the α − μ ionospheric fading model is used for the first- and second-order statistical characterization of amplitude scintillations. In the statistical analyzes, data are used from single-frequency GPS receivers acquired during ∼ 17 years (September 1997–November 2014) at Cachoeira Paulista (22.4° S; 45.0° W), Brazil. The results reveal that the nocturnal occurrence of scintillations follows the seasonal distribution of plasma bubble irregularities observed in the longitudinal sector of eastern South America. In addition to the solar cycle dependence, the results suggest that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of Cachoeira Paulista, since the maximum occurrence of scintillations during the peak of solar cycle 24 was ∼ 20 % lower than that observed during the maximum of solar cycle 23. The dynamics of the irregularities throughout a solar cycle, as investigated from the estimates of the mean zonal drift velocities, presented a good correlation with the EUV and F10.7 cm solar fluxes. Meanwhile, the seasonal behavior showed that the magnitude of the zonal drift velocities is larger during the December solstice months than during the equinoxes. In terms of modeling, the results for the α − μ distribution fit quite well with the experimental data and with the temporal characteristics of fading events independently of the solar activity level.

/pdf/climatology-and-modeling-of-ionospheric-scintillations-and-2y0g9ohox8.pdf

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

Two widely used scintillation indexes $$ S_{4} $$ and $$ \sigma_{\varphi } $$ are generated by dedicated ionospheric scintillation monitoring receivers (ISMRs), which typically have 50-Hz temporal resolution and thus require substantial memory capabilities. Taking into consideration the huge number of common Global Navigation Satellite System (GNSS) receivers, the derivation of a GNSS receiver-based scintillation index as a supplement to the ISMR indexes is expected to improve the study of ionospheric scintillation. We developed an amplitude scintillation index, $$ S_{{4{\text{c}}}} $$, which is derived from the carrier-to-noise density ratio ($$ C/N_{0} $$) data released by common geodetic GNSS receivers operating at 1-Hz. The reliability of the $$ S_{{4{\text{c}}}} $$ index is compared with the typical scintillation index $$ S_{4} $$ of three ISMRs located in Hong Kong and Brazil. The statistics indicate that during scintillation activity, the correlation coefficient between $$ S_{{4{\text{c}}}} $$ (derived from common receivers) and $$ S_{4} $$ (generated by ISMRs) is generally higher than 0.9. The reliability of $$ S_{{4{\text{c}}}} $$ was also verified based on 1-year observations from two adjacent stations in Hong Kong, which are equipped with Leica GR50 and Septentrio PolaRxS Pro receivers, respectively. Long-term scintillation occurrence ($$ S_{{4{\text{c}}}} $$ > 0.2 vs. $$ S_{4} $$ > 0.2) rates show good agreement between $$ S_{{4{\text{c}}}} $$ and $$ S_{4} $$. In addition, two-dimensional $$ S_{{4{\text{c}}}} $$ maps (1° × 1°) generated by GPS L1 and BDS B1 signals data collected at 117 continuous operation tracking stations in China clearly show post-sunset super plasma bubbles as the source of ionospheric scintillation during the main phase of the intense storm that occurred on September 8, 2017. These results demonstrate the feasibility of using the $$ S_{{4{\text{c}}}} $$ index derived from the large volume of GNSS observations recorded by non-scintillation GNSS receivers for the study and monitoring of ionospheric scintillation.

Amplitude scintillation index derived from C / N 0 measurements released by common geodetic GNSS receivers operating at 1 Hz

Scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation This phenomenon appears when the radio signal passes through ionospheric irregularities These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudesFor low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by σ ϕ ) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditionsFor high-latitude receivers the situation differs In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s) Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large σ ϕ ), but with a moderate fade in the amplitude (moderate S4) Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions

/pdf/feasibility-of-precise-navigation-in-high-and-low-latitude-2z2zuzs9x9.pdf

Feasibility of precise navigation in high and low latitude regions under scintillation conditions

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016RS006165

The variability of low-latitude ionospheric amplitude and phase scintillation detected by a triple-frequency GPS receiver

The - model has become widely used in statistical analyses of radio channels, due to the flexibility provided by its two degrees of freedom. Among several applications, it has been used in the characterization of low-latitude amplitude scintillation, which frequently occurs during the nighttime of particular seasons of high solar flux years, affecting radio signals that propagate through the ionosphere. Depending on temporal and spatial distributions, ionospheric scintillation may cause availability and precision problems to users of global navigation satellite systems. The present work initially stresses the importance of the flexibility provided by - model in comparison with the limitations of a single-parameter distribution for the representation of first-order statistics of amplitude scintillation. Next, it focuses on the statistical evaluation of the power spectral density of ionospheric amplitude scintillation. The formulation based on the - model is developed and validated using experimental data obtained in Sao Jose dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, located near the southern crest of the ionospheric equatorial ionization anomaly. These data were collected between December 2001 and January 2002, a period of high solar flux conditions. The results show that the proposed model fits power spectral densities estimated from field data quite well.

/pdf/validation-of-the-model-of-the-power-spectral-density-of-gps-21x0izh97l.pdf

Kelias Oliveira

Papers

The variability of low-latitude ionospheric amplitude and phase scintillation detected by a triple-frequency GPS receiver

Validation of the - Model of the Power Spectral Density of GPS Ionospheric Amplitude Scintillation

On the field validation of α-μ fading coefficients estimator based on the autocorrelation function for ionospheric amplitude scintillation