O sistema GPS como ferramenta para avaliação da refração ionosférica no Brasil.

Abstract

Since the US president decided to turn off the selective availability (SA) one of the biggest error in the GPS system has been the ionosphere refraction. The refraction effect on GPS signals are: delay for the code and an advance for the phase. In the equatorial region, where Brazil is, the refraction presents the biggest variations that are caused by the solar cycle, the time of the day, the season, the geomagnetic field and many others phenomena. In this case, the ionosphere refraction is a limitation because it increases the degradation of the position, specially if the user is using a single frequency receiver. To evaluate the ionospheric effects in Brazil, between January 1997 and December 2001, data from the Brazilian Continuous GPS Monitoring Network were used, provided by double frequency GPS receivers. All data were prepared and used by a scientific software to process the GPS observations. The volume of data was so big that it was necessary to write a software to manage the data integrity, to transform the precise ephemeris and the observations to scientific program format and to create batch files. Also, the program was used to process the data and to compute the total electron content automatically. At the end of the process, the software shows the TEC parameters. These parameters were used to create a historical series of the ionosphere refraction in Brazil. This series represents a period of minimal solar cycle, 1997, and a maximum period of the solar cycle, 2000 / 2001 in one of the most active regions of the planet. This series will improve the knowledge on the ionosphere and will allow to improve models or create new ones.

Avaliação Dos Efeitos Ionosféricos Nos Sinais GPS E Correlação Com Índices Ionosféricos E Geomagnéticos / Evaluation of Ionospheric Effects on GPS Signals and Correlation With Ionospheric and Geomagnetic Indices

“…Durante as quatro estações do ano, diferentes níveis de ionização são lançados à ionosfera. Nesse sentido, os máximos de densidade de elétrons são registrados em meses como Março/Abril e Setembro/Outubro, e os mínimos em Junho/Julho (FONSECA, 2002).…”

Resolução espacial da Grade Ionosférica e do Give

“…No Brasil, vários estudos vêm sendo realizados para entender o comportamento da ionosfera bem como as limitações dos modelos analíticos nesta região, dentre os quais pode-se citar Aguiar et al (2003), Aguiar e Camargo (2006), Camargo, Monico e Ferreira (2000), Dal Poz, Camargo e Aguiar (2008), Fonseca Junior (2002, Matsuoka e Camargo (2007), Sejas et al (2010).…”

Análise da ionosfera usando dados de receptores GPS durante um período de alta atividade solar e comparação com dados de Digissondas

“…Como exemplo de serviços gratuitos dessa natureza pode-se citar os mapas de TEC produzidos e disponibilizados regularmente pelo IGS (International GNSS Service ) desde 1998 (Feltens & Schaer, 1998;IGSCB, 2009). No Brasil diversas pesquisas nesta linha já foram desenvolvidas nosúltimos dez anos Fedrizzi, 1999;Camargo et al, 2000;Fonseca Junior, 2002;Matsuoka & Camargo, 2003Rodrigues, 2003;Veronez, 2004;Aguiar & Camargo, 2006, 2007.…”