Posicionamento por Ponto multi-GNSS: análise dos sistemas, sinais e modelos ionosféricos
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Data
2019-03-13
Autores
Setti Júnior, Paulo de Tarso
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Os GNSS (Global Navigation Satellite Systems) têm sido cada vez mais empregado em atividades que necessitam de estimativas de posição. Além do difundido sistema norte-americano GPS (Global Positioning System), orbitam a Terra satélites de outros três sistemas similares: o GLONASS, desenvolvido pela antiga União Soviética e que se encontra com constelação completa, o europeu Galileo e o chinês BDS, os dois últimos em fase de implantação e com previsão de dispor de constelação completa em 2020. Nas mensagens de navegação, os sistemas GPS e Galileo enviam também parâmetros para correção do atraso ionosférico a nível global, os quais são utilizados nos modelos de Klobuchar e NeQuick G, respectivamente. A tendência é que esses quatro sistemas funcionem em conjunto a nível de usuário, melhorando a disponibilidade e acuracidade do posicionamento. Na presente pesquisa avaliou-se a acurácia do Posicionamento por Ponto com uso de pseudodistância e efemérides precisas considerando os sistemas e frequências de forma separada, bem como o seu uso integrado no posicionamento denominado multi-GNSS. Além disso, o desempenho dos modelos de Klobuchar e NeQuick G na região brasileira e a nível global foram analisados. Três experimentos foram realizados; no primeiro deles, verificou-se que o posicionamento multi-GNSS em relação ao posicionamento GPS pode apresentar uma melhoria de aproximadamente 11% em ambientes desobstruídos e de até 60% em ambientes com alto grau de obstrução. Verificou-se que a taxa de melhoria está diretamente ligada ao nível de multicaminho da estação (correlação de 0,74). Com base nos resultados obtidos no segundo e terceiro experimentos, que avaliaram o desempenho dos modelos de Klobuchar e NeQuick G, verificou-se que estes apresentam um erro relativo a nível global de aproximadamente 49 e 40%, respectivamente. O uso do modelo de Klobuchar é recomendado para períodos e regiões de alta atividade ionosférica, uma vez que o atraso ionosférico é normalmente superestimado. O modelo NeQuick G, por outro lado, é recomendado para regiões e períodos de baixa atividade ionosférica, uma vez que o atraso ionosférico é normalmente subestimado.
GNSS (Global Navigation Satellite Systems) have been increasingly employed in activities that require position estimates. In addition to the widespread North American GPS (Global Positioning System), satellites from three similar systems are currently orbiting the Earth: GLONASS, developed by the former Soviet Union, which has now a full constellation, and the European Galileo and Chinese BDS, both under implementation phase and with plans to reach full constellation by 2020. Through their navigation messages, GPS and Galileo send parameters for ionospheric delay correction at global level, which are used in the Klobuchar and NeQuick G models, respectively. The tendency is for these four systems to work together at the user level, improving the positioning availability and accuracy. In this research we aimed to evaluate the accuracy of the Point Positioning (with pseudoranges and precise ephemeris) using the different systems and frequencies separately, as well as their integration in the so-called multi-GNSS positioning. In addition, the performance of the Klobuchar and NeQuick G models in the Brazilian region and worldwide was analyzed. Three experiments were performed; in the first one, it was verified that the multi-GNSS positioning in relation to GPS positioning can show an improvement of approximately 11% in unobstructed environments and up to 60% in environments with a high degree of obstruction. It was verified that the improvement rate is directly linked to the multipath level of the station (correlation of 0.74). Based on the results obtained in the second and third experiments, which evaluated the performance of the Klobuchar and NeQuick G, the models showed an overall relative error of approximately 49 and 40%, respectively. The use of the Klobuchar model is recommended for periods and regions of high ionospheric activity, since the ionospheric delay is usually overestimated. The NeQuick G model, on the other hand, is recommended for regions and periods of low ionospheric activity, since the ionospheric delay is usually underestimated.
GNSS (Global Navigation Satellite Systems) have been increasingly employed in activities that require position estimates. In addition to the widespread North American GPS (Global Positioning System), satellites from three similar systems are currently orbiting the Earth: GLONASS, developed by the former Soviet Union, which has now a full constellation, and the European Galileo and Chinese BDS, both under implementation phase and with plans to reach full constellation by 2020. Through their navigation messages, GPS and Galileo send parameters for ionospheric delay correction at global level, which are used in the Klobuchar and NeQuick G models, respectively. The tendency is for these four systems to work together at the user level, improving the positioning availability and accuracy. In this research we aimed to evaluate the accuracy of the Point Positioning (with pseudoranges and precise ephemeris) using the different systems and frequencies separately, as well as their integration in the so-called multi-GNSS positioning. In addition, the performance of the Klobuchar and NeQuick G models in the Brazilian region and worldwide was analyzed. Three experiments were performed; in the first one, it was verified that the multi-GNSS positioning in relation to GPS positioning can show an improvement of approximately 11% in unobstructed environments and up to 60% in environments with a high degree of obstruction. It was verified that the improvement rate is directly linked to the multipath level of the station (correlation of 0.74). Based on the results obtained in the second and third experiments, which evaluated the performance of the Klobuchar and NeQuick G, the models showed an overall relative error of approximately 49 and 40%, respectively. The use of the Klobuchar model is recommended for periods and regions of high ionospheric activity, since the ionospheric delay is usually overestimated. The NeQuick G model, on the other hand, is recommended for regions and periods of low ionospheric activity, since the ionospheric delay is usually underestimated.
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Palavras-chave
Posicionamento por Ponto, Posicionamento multi-GNSS, NeQuick G, Klobuchar, Point Positioning, Multi-GNSS positioning