No abstract

Measurements from the Global Navigation Satellite System (GNSS) have become a leading data source for ionospheric studies. Different technologies are used to monitor the ionospheric layer. It is possible to carry out this monitoring using GNSS networks through the indices of ionospheric irregularities, as well as through ionosondes and imagers. It has therefore become essential to correlate these forms of monitoring, presenting their advantages and disadvantages. With this in mind, the aim of this work was to perform an analysis of the behavior of the ionosphere in the Brazilian region through the ionospheric irregularity indices, along with ionosonde information and all-sky optical imagers, for a day of high solar activity (1 March 2014) and a day of low activity (12 April 2015). The results of each monitoring technique were compatible for the different scenarios, showing a moderate and positive correlation between the irregularity indices (FP) and ionosonde parameter. The imagers perform measures of greater spatial extent, however, they need favorable meteorological conditions. The ionosondes present a greater diagnostic capacity of the ionosphere but they are fewer in number than the imagers. The GNSS networks become ionosphere monitoring stations through the irregularity indices, enabling an increase in spatial resolution and a better understanding of ionospheric phenomena in the Brazilian territory.

The Earth's atmosphere is known to have great influence on the propagation of radio wave signals from Global Navigation Satellite Systems (GNSS). The ionospheric layer, which comprises the partially ionized portion of the Earth's atmosphere between about 60-1,000 km height, contains an appreciably dense plasma capable of modifying the amplitude, phase and polarization of GNSS signals. Moreover, the presence of inhomogeneities in the electron density distribution of the ionospheric plasma can also provoke severe amplitude and phase fluctuations of a satellite power signal received on the ground. Such inhomogeneities in the ionosphere are called plasma bubble irregularities. These bubbles are in fact plasma-depleted density irregularity structures developed in the equatorial ionosphere shortly after sunset. There is a consensus in the literature that the primary mechanism responsible for the generation of the equatorial plasma bubble (EPB) irregularities is the gravitational Rayleigh-Taylor plasma instability (

The ionospheric scintillation associated to small-scale irregularities in the ionospheric layer can lead to performance degradation of Global Navigation Satellite Systems (GNSS) signals, and the reduction of positioning accuracy. The influence of the ionospheric layer on the GNSS systems is expected to be different for each signal since it is transmitted on different carrier frequencies. This paper presents the results of a quantitative analysis of the scintillation amplitude of GPS (Global Positioning System) signals at L1, L2 and L5 frequencies, aiming to evaluate the impact of the ionospheric scintillation effects on the GPS frequencies. As the ionospheric scintillation may impact positioning accuracy, we also present an assessment of GPS point positioning using those frequencies. The GPS sample data were collected for 30 days between November and December 2014 at SJCE station located in São José dos Campos (SP), Brazil. Such a region is subjected to the equatorial anomaly effects being characterized by the occurrence of strong ionosphere scintillation. Considering the quantitative analysis, during the different levels of ionospheric scintillation presented a similar behavior, the magnitude of scintillations is small for the L1 signal and larger for L5. In general, the results confirmed that lower frequencies (L2 and L5) suffer more impact from intense scintillation than L1. Regarding the positioning assessment, the multi-frequency positioning was more accurate than single frequency. Considering dual-frequency positioning, results with L1-L2 were more accurate than those with L1-L5 signals. With single-frequency positioning, the L1 signal was more accurate compared to the L2 frequency.

<p>Global Navigation Satellite Systems (GNSS) has been widely used in aviation applications, nonetheless its accuracy and reliability are degraded under ionospheric scintillation. This effect on the radio wave signals causes a rapid fluctuation on both amplitude and phase of the signals, which may even lead to loss of lock in the worst case. The (Ground Based Augmentation Systems) GBAS based on GNSS signals is used for positioning improvement of aircraft landing. For safety-of-life applications, augmentation systems are necessary once reliability under all conditions is of great importance. Therefore, the evaluation of GNSS performance under amplitude and phase ionospheric scintillation is an important task when introducing a new safety-of-life technology such as GBAS. In this context, we present a quantitative analysis of the ionospheric amplitude and phase scintillation impact on the GPS and Galileo frequencies. Analysis considered S<sub>4</sub> and σ_moraeφ60 behavior for the same frequencies between both systems (L1 = E1 and L5 = E5a signals). The data used in this study were measured by a station located in a region characterized by the occurrence of strong scintillations, station SJCU (23.1°S, 45.8°W). The analyzed data were collected from November 12 to December 12, 2014, a period with moderate to strong solar activity. S4 and σ<sub>φ </sub>indices were estimated for satellites with elevation angle higher than 20° and indices values classified above 0.2 and 0.08, respectively. Considering GPS, amplitude and phase scintillation, the L5 signal had the greatest ionospheric impact in 91.7% and 98.4% of the epochs, respectively. Considering Galileo, for amplitude and phase scintillation, the E5a signal had the greatest ionospheric impact in 96.4% and 99.4% of the epochs, respectively. Those results indicate that lower frequencies are most affected under ionospheric scintillation. Similar behavior could be observed considering the same frequencies with GPS and Galileo, specially taking into account phase scintillation for L5 and E5 frequencies.</p>