Previous studies evaluated several characteristics of ionospheric fading events and amplitude scintillation. However, a detailed analysis on how the fading profiles and scintillation probabilities vary according to the dip latitude is still required. In this work, a statistical analysis of data from four ground-based scintillation monitors was performed to evaluate how the α coefficient (first parameter of the “α–μ” probability distribution model); the deepest fading occurrence; the number of fading events per minute; and the duration of fading events change according to the dip latitudes of the ionospheric pierce points (IPPs) of transionospheric propagation paths. The results reveal a nuanced spatial variation in amplitude scintillation, emphasizing an enhanced severity within the equatorial ionization anomaly (EIA) southern crest, resulting in a clear increase in the probability of severe fading events. An increasing trend in the α fading coefficient at more poleward dip latitudes was found, in comparison with results from equatorward locations, suggesting an asymmetry favoring more severe fading events within the former region. The average fading occurrences are significantly larger over the EIA peak region, especially for increasing scintillation levels. Complementary Cumulative Distribution Function (CCDF) curves demonstrate peak probabilities between dip latitudes from − 14.5° to − 10.5° for higher scintillation levels, also displaying an asymmetrical pattern around the EIA boundaries. This study provides important insights on the spatial dynamics of scintillation and fading profiles, enhancing the understanding of low-latitude ionospheric effects on global network satellite system (GNSS) signals.

AbstractSignals recorded by two stations in the Brazilian region: [Fortaleza (3.74°S, 38.57°W) and Inconfidentes (22.31°S, 46.32°W)], receiving L1 transmissions from different geostationary satellites, were used to evaluate the amplitude scintillation index S4 and several characteristics of scintillation events (continuous record with S4 > 0.2) during nighttime hours (18:00 LT–02:00 LT) in the years 2014–2016. The effects from solar activity, season, and local time on the number of scintillation events per night, maximum scintillation, scintillation event duration, and spacing between consecutive events will be discussed. The results indicate that: (a) scintillation occurs from September to March in both links; (b) the most likely numbers of observed scintillation events per night were two or three, particularly during the first 2 years; (c) on average, the first scintillation event usually had larger maximum S4 values when compared to those of the later ones along the night; (d) the first scintillation event had a longer mean duration than the succeeding ones in a given night; (e) the durations of scintillation events, regardless of their numbers per night and the location, decreased with local time; (f) the opposite dependence of spacings between consecutive events on local time was observed; (g) the cumulative distribution functions of the scintillation onset time indicated a strong dependence on the dip latitude of the station; and (h) early occurrences of onset times are directly related to the increased probability of the occurrence of multiple scintillation events.

Thereis a demand for the development of GNSS positioning processing techniques that are more tolerant to the effects of the low latitude ionosphere (in particular, scintillation). The possibility of simulating scintillating channels supports the development of more sophisticated test benches and receivers. This paper proposes a neural network-based simulator of ionospheric amplitude scintillation. This synthetic scintillation simulator uses autoencoders and generative adversarial networks (GANs) to generate time series that follow the statistical characteristics of the $\alpha-\mu$ fading model. A part of the proposed network tries to create a synthetic signal, similar to the field data. The proposed neural network was trained and validated with scintillation data acquired in Sao Jose dos Campos, Brazil, in February 2012 and November 2014. The results of the proposed method show that the simulator yields the correct values of the scintillation index, and the estimated fading coefficients are also close to the specified values. These aspects show that this kind of approach can be promising in the simulation of fading channels. Future improvements of the model are also be discussed.

Ground Based Augmentation Systems are designed to meet demanding requirements during airport approach and landing sections of aircraft routes. It computes corrected and smoothed differential corrections and other information. These messages are transmitted to aircraft, which may use the corrections to improve their position estimation. However, residual correction errors remain, due to ionospheric spatial and temporal gradients between Ground Based Augmentation System reference receivers and approaching aircraft. Large vertical ionospheric delay gradients detected during combinations of extreme geophysical environments indicate that there are problematic conditions for Ground Based Augmentation System operation over the Brazilian region. Motivated by the above conditions, data from Rede Brasileira de Monitoramento Contínuo, the Brazilian public network of dual-frequency global navigation satellite system receivers operated by Instituto Brasileiro de Geografia e Estatística were analyzed to estimate ionospheric vertical Total Electron Content (vTEC) gradients. The effects from different locations (represented by the dip latitude) and geophysical conditions (represented by solar activity, season, and local time) on variations of ionospheric vTEC gradients have been statistically quantified. The results from the present work provide information to more detailed performance assessments of Ground Based Augmentation System procedures under equatorial and low-latitude ionospheric regions, aimed at flexibly delimiting the conditions for feasible operation in such regions.

Ionospheric density irregularities embedded in Equatorial Plasma Bubbles (EPBs), with scale sizes varying from several hundred kilometers to several tens of meters, may cause amplitude and phase scintillation of transionospheric radio waves, degrading the performance and availability of space-based communication and navigation systems. A recent computer simulation study, based on ionospheric irregularities detected by the Planar Langmuir Probe (PLP) onboard the Communication/Navigation Outage Forecasting System (C/NOFS) satellite, analyzed the mitigation effects from space diversity on amplitude scintillation of transionospheric signals received on the ground. The present work, based on experimental data, will confirm and extend the previous results, indicating, in statistically quantitative terms, how space diversity, effective on uplink and downlink ground-satellite paths, particularly in the strong and saturated scintillation regimes, depends on Ionospheric Pierce Point (IPP) dip-latitude and distance intervals, as well as on a well-known amplitude scintillation index.

Equatorial Plasma Bubbles (EPBs) and their ionospheric density irregularities exhibit structures with scale sizes that can vary from several hundred kilometers to tens of meters. These random irregularities degrade both the performance and the availability of space-based communication and navigation systems in different ways. As examples of effects to be analyzed, wideband Ultra High Frequency (UHF) (360–380 MHz) transmissions received by Ascension Island (7.93 °S, 14.25 °W) monitors during an observational campaign in October 2016 displayed flat-fading and frequency-selective fading conditions. In this report, the ionospheric structures that are responsible for the harmful observed behavior (flat and frequency-selective fading) will initially be identified through the application of a discrete version of the single phase-screen formulation to low- and high-resolution in situ ion density data recorded by the Planar Langmuir Probe (PLP) onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. Next, the resulting hypothesis will be confirmed by the application of the continuous version of the same formulation to single-scale irregularities with different scale sizes. Finally, mitigation effects from space and frequency diversity on the observed behavior will be discussed with basis on the application of the initial formulation to the high-resolution C/NOFS PLP data.

Air navigation is increasingly dependent on the use of Global Navigation Satellite Systems (GNSS). It allows the determination of the aircraft’s position in all phases of the flight and brings many advantages. Although GNSS navigation results in gains, the radio signals from these systems are strongly influenced by the ionospheric environment. It introduces errors that can affect the accuracy, integrity, availability and continuity requirements established by the International Civil Aviation Organization (ICAO). The ionospheric layer has different behaviors depending on the latitude, time of day, season of the year, geomagnetic activity and solar cycle. Since Brazil is located in a region of low latitudes, it experiences a series of unique challenges when compared to regions of mid-latitudes. For this reason, the application of GNSS-based technologies in aviation over the Brazilian territory requires an in-depth assessment of the ionosphere effects. Therefore, the Instituto Nacional de Ciência e Tecnologia (INCT) named GNSS Technology for Supporting Air Navigation was formed in 2017 to better assess the ionosphere impacts and assist government agencies and companies in the development of safe air navigation procedures over Brazil in a near future. This paper presents the most relevant advances achieved so far within this multidisciplinary project that involves Brazilian research centers and universities.

The ionosphere affects the propagation of global positioning system signals. Due to their special features, the equatorial and low-latitude ionosphere may produce particularly severe effects on them. The ground-based augmentation system has been developed to meet the safety requirements of civil aviation. To evaluate the performance of such a system, a statistical simulation model of the global positioning system signal-in-space has been developed, considering several components. The present work will focus on: (1) the ionospheric delay, with basis on statistical distributions of vertical total electron content obtained by the combination of the International Reference Ionosphere with data from the Rede Brasileira de Monitoramento Contínuo, operated by Instituto Brasileiro de Geografia e Estatística; (2) cycle ambiguity, characterized through the processing of the same data set; (3) ionospheric amplitude scintillation, simulated with basis on proper indices and the α–μ probability distribution; and (4) ionospheric phase scintillation, generated according to its standard deviation. The statistical simulation model is based on a set of representative geophysical parameters and may be used to generate time series of pseudorange, carrier phase, and received signal power, to be applied as inputs to existing or future ground-based augmentation system testbeds. This provides an alternative to experimental data collection, which could be expensive and time-consuming. Additionally, such data may not be available for all regions and critical geophysical conditions of interest.

The future saturation of the electromagnetic spectrum currently allocated for mobile communications has led the scientific and technical communities to consider the use of the vast millimeter-wave frequency band. However, there are technical obstacles limiting the immediate use of this band. In the radio propagation area, there is a research effort to characterize the outdoor urban channel. The developed model described here uses a 2.5 D ray-tracing algorithm based on geometrical optics and uniform theory of diffraction concepts in outdoor environments. The model implements several techniques that could be considered by a future standard of fifth-generation mobile communications for the transmission of ultrawideband signals through line-of-sight (LOS) and non-LOS channels with a high density of scatterers, such as trees, poles, and diffuse scattering by rough building walls. In addition, simulations and comparisons are performed in environments where measurement campaigns were carried out, considering the following metrics: received power, mean delay, root mean square delay spread, and cross-polar discrimination. The comparison between simulation and experimental results shows a good agreement. Possible model impairments are also discussed.

Abstract Data from the planar Langmuir probe onboard the Communication/Navigation Outage Forecasting System has been processed, with focus on the: (1) identification of Equatorial Plasma Bubbles located within the eclipse sections of the satellite orbits; (2) subdivision of each Equatorial Plasma Bubble into three sections (West Wall, Center, and East Wall); and (3) statistical analyses of the standard deviations and gradients of ion density data for each section. The statistical distributions resulted from the application of the above processing to structures identified during the years October 1, 2008 to September 30, 2009 (solar minimum conditions) and June 5, 2012 to June 4, 2013 (close to maximum conditions of solar cycle 24). The statistical distributions have also been classified considering all longitudes or three 60° longitude sectors in South America, Africa, India‐Asia, as well as all altitudes of the C/NOFS satellite or the limited range from 650 to 800 km. It will be shown that all the parameters (Equatorial Plasma Bubble sections, solar activity, longitude sector, and altitude range) affect the resulting statistical distributions. Additionally, the probability density functions (pdfs) of ion density gradients for the EPB West Walls, Centers, and East Walls and the South American longitude sector, detected during 2012 and estimated with different resolutions will be compared. While the pdfs based on 1‐Hz low‐resolution data (sampling large‐scale structures) display east‐west asymmetries, those based on the original 512‐Hz high‐resolution data (sampling small‐scale structures), created by secondary plasma instabilities, are essentially symmetric around the reference 0 mm/km gradient.

Amplitude and phase variations of Global Navigation Satellite Systems (GNSS) radio signals used by the aeronautic community occur due to ionospheric irregularities (ionospheric scintillation), which may cause the degradation of service availability and performance, raising safety issues. This is particularly true in the Appleton Anomaly region, where the occurrence of ionospheric irregularities is known to be frequent. In this work, the results from an analysis of the impact of ionospheric irregularities on the single point positioning performance of GPS is presented and discussed. The results show that the developed model has a good positioning measurements and few discrepancies. However, in the presence of ionospheric scintillation, degradations of positioning quality are observed. These promising results can be applied to data from other stations and positioning system, with the objective of directly characterizing ionospheric scintillation effects.

Over the last 15 years, the satellite constellation of the global positioning system (GPS) has been modernized for more precise applications, with the introduction of the L2C and L5 signals. However, among other effects, they are susceptible to severe ionospheric effects, particularly in the equatorial and low-latitude regions. Equatorial plasma bubbles, resulting from the combination of the ionospheric electrodynamics with plasma instability mechanisms and thermospheric coupling, may generate irregularity structures with scale sizes ranging from hundreds of kilometers to a few meters (or less). Ionospheric irregularities may cause deep amplitude fades and phase shifts to transionospheric signals. That is, they are responsible for amplitude and phase scintillation, which degrade receiver operations and may cause failures and unavailability to positioning and navigation services under extreme conditions. The objective of the present work is to analyze ionospheric scintillation effects on the L2C and L5 GPS signals, to compare their vulnerabilities with those of the L1 signal. The data used in this analysis were collected between November 2014 and March 2015, during the maximum solar activity of cycle 24 (a period of great scintillation incidence), by scintillation monitors deployed at four different sites in the Brazilian territory: Fortaleza, Presidente Prudente, São José dos Campos, and Porto Alegre. Intensity fades will be analyzed, considering different thresholds, to reveal their empirical probability distributions of scintillation occurrence, average fading occurrences and durations. The results will show that greater probabilities of strong scintillation occurrences are present in the modernized signals, reaching up to five times more events in the L5 signal in comparison with those in the legacy L1 signal. It will be shown that the L5 average fade duration is distinctly longer than the corresponding ones for the other frequencies, considering the same site, threshold, and L1 amplitude scintillation level. The results will also show that the average fade duration decreases according to the average ratio 0.6 s/3 dB within the threshold range from − 6 to − 15 dB, considering the same amplitude scintillation level and location.

Abstract The present work describes the use of a simulation model based on asymptotic methods (ray tracing) on the propagation of ultra-wideband radio signals in a densely-arborized urban channel. The model was previously validated and adjusted using data obtained from measurement campaigns in the millimeter-wave band in locations different from the one to be analyzed here. The simulation uses deterministic methods to predict the received power, cross-polar discrimination, root mean square delay spread, and mean delay in a channel with a high density of scatterers (trees, buildings, and poles). Simulated signals were transmitted in the vertical and horizontal polarizations, considering non-specular reflections caused by rough surfaces and the effect of the transmitter’s height variation in outdoor channels.

The present contribution applies a modified version of a well‐known weak‐scatter scintillation model to the propagation paths between an Earth station and two geostationary satellites, as they are affected by drifting ionospheric irregularities detected by the planar Langmuir probe onboard the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. This study considers one year of data from a limited altitude range, two longitude sectors and frequencies to analyze the mitigation effects from the angular distance between the geostationary satellites on the space diversity gain, considering the statistical distributions of the amplitude scintillation index S4. The results indicate that the space diversity gain increases with the angular distance between geostationary satellites. However, once the angular distance between the geostationary satellites reaches a certain limit (approximately 20°), the space diversity gain no longer increases. Additionally, these gains are high at the L1 frequency and less impressive at an Ultra High Frequency (UHF). It is shown that these observations are consistent with the South American and Indian‐Asian equatorial and low‐latitude ionospheric environments, also characterized through the same data and the scintillation formulation.

The ionosphere affects the propagation of GPS signals in the equatorial and low-latitude regions. Even auxiliary systems based on GPS such as the Ground Based Augmentation System (GBAS), are affected by ionospheric effects. This contribution will present analysis of position errors resulting from the simulation of GPS observables and GBAS using differential corrections during aircraft approach and landing operations.

The ionosphere over the Brazilian region has particular characteristics due to the large geomagnetic declination angle over most of the territory. Furthermore, the equatorial ionization anomaly southern crest is located over the Brazilian territory. In this region, plasma irregularities may arise in the post-sunset hours. These ionospheric irregularities develop in the form of magnetic field-aligned plasma depletions, known as equatorial plasma bubbles, which may seriously affect radio signals that propagate through them. These irregularity structures can cause amplitude and phase scintillation of the propagating signals, thereby compromising the availability, performance, and integrity of satellite-based communication and navigation systems. Additionally, the total electron content (TEC) introduces propagation delays that can contribute to range measurement errors for global positioning system (GPS) users. The ionospheric characteristics change significantly according to the time of day, season, as well as the solar and geomagnetic activities, among other factors. Indeed, the ionosphere is one of the most significant sources of errors in the positioning and navigation systems based on the GPS satellites. Due to these features, there is a strong interest by the scientific community in better understanding and characterizing the ionospheric behavior. In this context, the TEC analysis has wide applicability for space plasma studies and is a well-established tool for investigating the ionospheric behavior and its potential impact on space-based navigation systems. One of the goals of these studies is the generation of TEC maps for a geographic region based on GPS observations. In the present work, some electrodynamic processes of the low-latitude ionosphere are reviewed and the TEC estimation based on GPS measurements is revisited in detail. A methodology aimed at creating the TEC maps is presented and validated by comparison with results from other geophysical instruments, such as all-sky imagers and ionosondes. Finally, examples of the ionospheric behavior displayed by TEC maps during equatorial plasma bubble events and a geomagnetic storm are fully described and discussed.

The two-dimensional ray tracing method allows an easy and fast modeling of tropospheric propagation in the microwave frequency range. A version of this method that determines ray trajectories, amplitudes and delays of the electromagnetic field, as well as the propagation loss in a two-dimensional inhomogeneous environment will be described. The implemented algorithm may consider generalized maps of modified refractivity (or refractive modulus), including not only the vertical gradients, but also their horizontal variations along the path between transmitter and receiver. Next, the present paper will discuss the results from the application of a model of evaporation duct height to data from instruments installed in sea buoys located along the Brazilian coast. Finally, the results from the application of the ray-tracing model to evaporation ducts will be presented, to analyze the propagation of microwave signals in the maritime environment. These results will also be compared with corresponding ones from the software Advanced Refractive Effects Prediction System 3.6, based on the numerical solution of a parabolic equation.