Determinations of the vertical ionospheric gradient standard deviation (σ vig ) in real time to each Global Positioning System (GPS) and Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) satellite available in Ground-Based Augmentation System (GBAS) of the Rio de Janeiro International Airport (SBGL) were used in the estimates of Horizontal and Vertical Protection Level (HPL/VPL). For this purpose two software were developed: MoR_Ion_RT (real time ionospheric threat assessment for GBAS in Brazil) and SBGL_PL (calculation of SBGL HPL/VPL), whose methods and equations are presented in this paper. Since such determinations transmit the real ionospheric condition at the time of an approaching aircraft, they also allow performing the screening of the data, based on the Conterminous United States (CONUS) Threat Model threshold. Experiments carried out indicate that it is possible to attend CAT-I during the autumn (most affected season) at SBGL using GPS or GLONASS satellites, provided that the restrictions established by a temporal ionospheric threat model developed for the region are applied (avoid satellites with elevations between 10° and 37°). It was also found that the use of GLONASS in conjunction with GPS satellites makes it possible to meet CAT-III Horizontal and Vertical Alert Limit (HAL/VAL), since it has a better geometric configuration.

RESUMOO objetivo deste artigo é analisar a influência de intensas tempestades geomagnéticas na ionosfera e no posicionamento por GNSS (GPS). Neste sentido, foram analisados os efeitos da intensa tempestade geomagnética de 20 de novembro de 2003 utilizando dados GPS de algumas estações da RBMC (Rede Brasileira de Monitoramento Contínuo), situadas em diferentes locais na região brasileira, e mapas globais da ionosfera. Analisando os resultados se observa um aumento na densidade de elétrons livres da ionosfera nas regiões mais próximas do equador geomagnético no período da tarde no dia da tempestade. No período após o pôr do Sol do dia da tempestade, verifica-se um aumento na densidade de elétrons livres e de irregularidades ionosféricas em regiões mais afastadas do equador geomagnético, em comparação com dias geomagneticamente calmos. Quando analisado o posicionamento por ponto, se observa maiores discrepâncias em planimetria e altimetria no posicionamento para os mesmos períodos em que ocorreram mudanças

This research shows the viability of using Global Navigation Satellite System (GNSS) stations from Brazilian active networks in monitoring the ionosphere. Various indexes of ionospheric irregularities and scintillation of GNSS signals, estimated in real-time and post-processed from GNSS data, are explored for this purpose. This way, an increase in the spatial resolution of ionospheric information is provided, allowing the generation of maps of scintillation and irregularities in observing the spatial and temporal behavior of the layer's activity cycle, since the number of ionosondes, imagers, and radars is insufficient for monitoring the irregularities in Brazil. Experiments to evaluate the estimates of the indexes are performed for periods of high and low variability of electrons. Three Brazilian networks are used: the Brazilian Network for Continuous Monitoring (RBMC), the GNSS Active Network of Sao Paulo State (GNSS-SP), and CIGALA/ CALIBRA. The results are compared with data from ionosondes and PolaRxS-PRO Septentrio receivers, proving compatible with moderate to high correlations. An analysis of the seasonal variation during the peak of solar cycle 24 is carried out. The maps allow identifying the displacement of ionospheric irregularities along the magnetic equator over Brazil, from northeast to southwest, starting at 7:00 pm and ending at 2:00 am local time. Realtime monitoring is carried out for the summer solstice in the southern hemisphere, and results are consistent with those from the post-processed mode. The indexes and maps can be applied to the analysis of GNSS positioning. Realtime ionospheric information can be used in important practical applications because the displacement monitoring of irregularities allows prior knowledge of whether there will be a deterioration of positioning accuracy in a certain region.

As observáveis GNSS (Global Navigation Satellite System) são afetadas por erros sistemáticos devido aos elétrons livres presentes na ionosfera. O erro associado à ionosfera depende do Conteúdo Total de Elétrons (TEC - Total Electron Content), que é influenciado por diversas variáveis: ciclo solar, época do ano, hora local, localização geográfica e atividade geomagnética. Os receptores GPS (Global Positioning System), GLONASS (Global Orbiting Navigation Satellite System) e Galileo de dupla frequência permitem calcular o erro que afeta as observáveis GNSS e o TEC. Com a taxa de variação do TEC (ROT - Rate of TEC) pode-se determinar índices que indicam irregularidades da ionosfera, permitindo assim fazer inferências sobre o comportamento da mesma. Atualmente é possível realizar estudos dessa natureza no Brasil, devido às diversas Redes Ativas disponíveis, tais como a RBMC/RIBaC (Rede Brasileira de Monitoramento Contínuo/Rede INCRA de Bases Comunitárias) e a Rede GNSS Ativa do Estado de São Paulo. A pesquisa proposta visou à estimativa e análise de índices de irregularidades da ionosfera, além de suprir as geociências de informações sobre o comportamento da ionosfera.