ABSTRACT 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.

Abstract: The ionosphere may not only degrade the accuracy of the GNSS positioning but also reduce its availability because there is a high dependence between signal losses and ionospheric irregularities. Irregularities in the Earth’s ionosphere may produce rapid fluctuations in phase and amplitude. These rapid fluctuations are called ionospheric scintillation. Thus, loss of signal can occur due to the effects of diffraction and refraction, which cause a weakening in the signal received by the GNSS receivers. In this way, this paper aims to evaluate the magnitude of ionospheric scintillation in Brazil and the performance of the positioning under its influence in the period of high solar activity in the current cycle (24), through the Spearman correlation analysis and the Wavelet periodogram. For that, three-year time series (2012 to 2014) of the S4 index and 3D MSE (Mean Squared Error) of three Brazilian stations with different ionospheric conditions were considered, PALM (near the Geomagnetic Equator) PRU2 (Equatorial region and Anomalies) and POAL (Mid-latitude region). Thus, it was possible to evaluate the correlation between the accuracy of the precise point positioning using only the C/A code of the GPS satellite and the S4 index. As a result, there was a correlation of 53% and 51%, using the Spearman method, for the PALM and PRU2 series, respectively. In addition, considering the analysis of space-frequency in relation to time by the Wavelet coherence method, a correlation of more than 70% is noted in the period of greatest 3D MSE concerning the spring and autumn equinox months.

O estado da arte na modelagem da ionosfera está em desenvolver e/ou aprimorar métodos capazes de fornecer aos usuários do GNSS correções ionosféricas confiáveis, em tempo real e utilizando estruturas simples de transmissão de dados. Dentro desta necessidade e com o surgimento dos sistemas de apoio à navegação, tal como os SBASs (Satellite Based Augmentation Systems), esforços estão voltados em fornecer informações de correções do erro sistemático da ionosfera utilizando uma estrutura de grade regular de pontos. Além disto, esforços também vêm sendo direcionados para corrigir a limitação na performance dos atuais métodos de geração de grade ionosférica em regiões equatoriais. Neste contexto, num trabalho pioneiro no Brasil, foi proposto um método para a geração da Grade Ionosférica (GI) e seu nível de confiança (GIVE - Grid Ionospheric Vertical Error) a fim de melhorar a acurácia de posicionamento e navegação pelo GNSS, além de fornecer uma ferramenta que possa ser utilizada na área de estudos da ionosfera. Este trabalho apresenta uma análise para definir a resolução espacial mais viável para a GI e para o GIVE, bem como o impacto da distribuição das estações de referência na definição de tal resolução.

The state-of-the-art of ionosphere modeling is to develop and to improve methods to provide reliable ionospheric corrections in real time to GNSS users using simple structures for data broadcast. Considering this requirement and support systems for navigation, such as SBAS (Satellite Based Augmentation Systems), efforts are made to provide information to the corrections of the ionospheric systematic error using a regular grid of points. In addition, efforts are also being directed to improve the performance of current methods used to generate ionosphere grid in equatorial regions. In this context, a pioneering work in Brazil was proposed a method for the generation of Ionospheric Grid (GI) and the level of confidence (GIVE - Grid Ionospheric Vertical Error) to improve the accuracy of GNSS positioning and navigation, as well as provide a tool can be used in the research on the ionosphere. This paper presents an analysis for setting the spatial resolution most viable for GI and GIVE, as well as the impact of the distribution of reference stations.