Análise da integração GPS/GLONASS para posicionamento sob efeito de cintilação ionosférica
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Data
2017-03-17
Autores
Jerez, Gabriel Oliveira [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Com o desenvolvimento dos sistemas globais de navegação por satélite as atividades que envolvem posicionamento passaram por uma revolução. Os pioneiros, GLONASS (GLObal NAvigation Satellite System) e GPS (Global Positioning System), são atualmente os principais sistemas, e únicos com constelação completa. A utilização combinada de dados GPS e GLONASS passou por uma perda de interesse no final da década de noventa devido à rápida degradação que o GLONASS sofreu. Porém, em 2001 teve início um plano de restabelecimento do sistema que em 2011 voltou a contar com constelação completa de 24 satélites e cobertura global. O GLONASS passa ainda por um processo de modernização, com novas gerações de satélites sendo desenvolvidas, refinamentos dos sistemas de tempo e referência e novas estações de controle sendo instaladas. Além do uso de dados combinados, outros fatores que influenciam a qualidade do posicionamento são os métodos empregados e os erros aos quais os sinais transmitidos estão sujeitos. Nas metodologias de integração devem constar as diferenças de estrutura dos sistemas, sendo as principais, para este caso, os sistemas de referência, sistemas de tempo e a tecnologia relacionada às frequências. Em relação aos erros, a ionosfera é uma importante fonte, principalmente para usuários de receptores de apenas uma frequência. Ela exige atenção especial, pois além de degradar a acurácia do posicionamento há uma grande dependência entre perdas do sinal e irregularidades ionosféricas, como a cintilação ionosférica. Na presente pesquisa buscou-se analisar as melhorias apresentadas no posicionamento utilizando dados combinados GPS/GLONASS sob efeito de cintilação ionosférica, avaliar a influência da cintilação nos sinais GLONASS e realizar um estudo da estrutura do sistema. Foram realizados três experimentos, relacionados à aplicação do PPP (Posicionamento por Ponto Preciso), do posicionamento relativo estático e do posicionamento em redes (especificamente no conceito de VRS – Virtual Reference Station). Para possibilitar o posicionamento em redes foi adaptada a ferramenta VRS-UNESP, para permitir a geração de bases virtuais com dados GLONASS ou GPS/GLONASS. Para as três metodologias foram selecionadas estações em três regiões do Brasil com comportamentos ionosféricos distintos visando possibilitar também a análise do efeito da cintilação. Para isso foram escolhidas regiões próximas ao equador geomagnético, próximas a área afetada pelo efeito fonte e ao sul do país, onde se tem menor influência da ionosfera. Para o PPP considerando-se todos os casos, independente da configuração, houve melhoria em 92,28% dos dias com o uso de dados GPS e GLONASS. Para o posicionamento relativo os resultados obtidos foram mais irregulares que para o PPP, sendo que a melhoria ocorreu em 69,18% dos casos. Os dados virtuais foram processados de maneira análoga ao experimento com PPP, obtendo melhoria em 100% os casos analisados ao se utilizar dados GPS e GLONASS.
With the development of the Global Navigation Satellite Systems (GNSS) the activities involving positioning passed by a great revolution. Currently, the pioneers, GLONASS (GLObal NAvigation Satellite System) and GPS (Global Positioning System), are the main systems with full constellation. The interest in the combined use of GPS and GLONASS data had a great fall in the late nineties due to the fast degradation of GLONASS. However, in 2001 a restoration plan of the system began and in 2011 GLONASS recovered the full constellation of 24 satellites with global coverage. Furthermore GLONASS is going through a modernization process, with the development of new satellite generations, time and reference systems refinements and new control stations. Besides the use of combined data, other factors that influence the positioning quality are the applied methods and the errors that can affect the transmitted signals. The integration methodologies must consider the differences in the systems structures, the main differences, for this case, are reference and time systems and the technology related to the frequencies. About the errors, the ionosphere is an important source, mainly for users of single frequency receivers. It requires special attention, because besides of degrading the positioning accuracy there is a great dependency between the loss of signal and ionospheric irregularities, as ionospheric scintillation. In this research it was intended to analyze the improvement of the combined use of GPS/GLONASS data at positioning under ionospheric scintillation effect, evaluate the influence of scintillation at GLONASS signals and perform a study about the structure of the system. Three experiments were performed, the first one is related to the application of PPP (Precise Point Positioning), the second one is about static relative positioning and the third one is about network based positioning (specifically in the Virtual Reference Station concept).To enable the network based positioning the software VRS-UNESP was adapted, in order to allow the generation of virtual stations with GLONASS or GPS/GLONASS data. In the three methodologies were selected three regions of Brazil with distinct ionospheric behavior, in order to evaluate the scintillation effect in the positioning. It was selected regions near to the geomagnetic equator, regions near the fountain effect and in the south of the country, where the ionosphere effect is less intense. For the PPP, considering all the configurations adopted, there was improvement with the use of GPS and GLONASS combined data in 92,28% of the days analyzed. For the relative positioning the results obtained were more irregulars than the ones from PPP. In such case it was achieved improvement in 69,18% of the cases with the use of combined data. The virtual data were processed in a procedure similar to the one used in the PPP experiment. It was achieved improvement in 100% of the cases that were used GPS and GLONASS data.
With the development of the Global Navigation Satellite Systems (GNSS) the activities involving positioning passed by a great revolution. Currently, the pioneers, GLONASS (GLObal NAvigation Satellite System) and GPS (Global Positioning System), are the main systems with full constellation. The interest in the combined use of GPS and GLONASS data had a great fall in the late nineties due to the fast degradation of GLONASS. However, in 2001 a restoration plan of the system began and in 2011 GLONASS recovered the full constellation of 24 satellites with global coverage. Furthermore GLONASS is going through a modernization process, with the development of new satellite generations, time and reference systems refinements and new control stations. Besides the use of combined data, other factors that influence the positioning quality are the applied methods and the errors that can affect the transmitted signals. The integration methodologies must consider the differences in the systems structures, the main differences, for this case, are reference and time systems and the technology related to the frequencies. About the errors, the ionosphere is an important source, mainly for users of single frequency receivers. It requires special attention, because besides of degrading the positioning accuracy there is a great dependency between the loss of signal and ionospheric irregularities, as ionospheric scintillation. In this research it was intended to analyze the improvement of the combined use of GPS/GLONASS data at positioning under ionospheric scintillation effect, evaluate the influence of scintillation at GLONASS signals and perform a study about the structure of the system. Three experiments were performed, the first one is related to the application of PPP (Precise Point Positioning), the second one is about static relative positioning and the third one is about network based positioning (specifically in the Virtual Reference Station concept).To enable the network based positioning the software VRS-UNESP was adapted, in order to allow the generation of virtual stations with GLONASS or GPS/GLONASS data. In the three methodologies were selected three regions of Brazil with distinct ionospheric behavior, in order to evaluate the scintillation effect in the positioning. It was selected regions near to the geomagnetic equator, regions near the fountain effect and in the south of the country, where the ionosphere effect is less intense. For the PPP, considering all the configurations adopted, there was improvement with the use of GPS and GLONASS combined data in 92,28% of the days analyzed. For the relative positioning the results obtained were more irregulars than the ones from PPP. In such case it was achieved improvement in 69,18% of the cases with the use of combined data. The virtual data were processed in a procedure similar to the one used in the PPP experiment. It was achieved improvement in 100% of the cases that were used GPS and GLONASS data.
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Palavras-chave
Posicionamento, GPS/GLONASS, Cintilação ionosférica, Positioning, Ionospheric scintillation