Characterizing changes in the noise statistics of GNSS space clocks with the dynamic Allan variance

The dynamic Allan variance (DAVAR) is a tool for the characterization of precise clocks. Monitoring anomalies of precise clocks is essential, especially when they are employed onboard the satellites of a global navigation satellite system (GNSS). When an anomaly occurs, the DAVAR changes with time, its shape depending on the type of anomaly occurred. We obtain the analytic DAVAR for a change of variance in the clock noise, an anomaly with critical effects on the clock performances. This result is helpful when the clock health is monitored by observing the DAVAR

ERROR BEHAVIOR OF ATOMIC CLOCKS ABOARD GPS SATELLITES

The signal transmission and position quality obtained by GNSS positioning directly depends on the time control. The atomic clocks aboard the satellites are responsible for this control. In this research, the satellites clock errors of GPS are studied, using data from the pseudorange, the satellite semi-major axis and the correction parameters of the satellites’ clock errors found in the RINEX navigation and observation files. From these data, the satellites’ clock errors are calculated using the IGS mathematical model for rubidium and cesium clocks, and then an adjustment technique is applied in order to estimate the new parameters of the clock corrections. For cesium atomic clocks, the periodic part of the mathematical model was adapted. The correction parameters adjusted were applied in the IGS and the adapted model; finally, the results were compared with the IGS data from the clk_30s file. The experiments carried out show an improvement of 50 cm in the cesium satellites’ clock errors. In addition, the research concludes that the satellites’ clock errors do not depend on the station where the data were collected and the equipment’s antenna

Comportamento dos relógios dos satélites GPS : correções e análises

Orientador : Prof. Dr. Luiz Danilo Damasceno FerreiraDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências da Terra, Programa de Pós-Graduação em Ciências Geodésicas. Defesa: Curitiba, 01/02/2017Inclui referências : f.61-64Resumo: A transmissão do sinal e qualidade da posição obtida no posicionamento com o GNSS depende diretamente do controle do tempo. Os responsáveis por este controle são os relógios atômicos que estão a bordo dos satélites. Nesta pesquisa é estudado o erro dos relógios dos satélites GPS, para isto são utilizados os dados de pseudodistância, semieixo maior e parâmetros de correção dos erros dos relógios dos satélites encontrados nos arquivos RINEX de navegação e observação. A partir destes dados, são calculados os erros dos relógios dos satélites, utilizando o modelo matemático do IGS, e então aplicada uma técnica de ajustamento para estimar novos parâmetros de correção dos relógios. É também realizada uma adaptação na parte periódica do modelo matemático, utilizado para relógios atômicos de Césio. São aplicados então os parâmetros de correção ajustados no modelo do IGS e no adaptado, e por fim os resultados comparados com os apresentados pelo IGS no arquivo clk_30s. Os experimentos realizados apresentaram uma melhora de 50 cm nos erros dos relógios dos satélites de Césio. Ainda a pesquisa conclui que os erros dos relógios dos satélites independem da estação de onde estão sendo coletados os dados, assim como também não dependem da antena. Palavras-chave: Erro dos relógios dos satélites, relógios atômicos, relógios GPS, efemérides transmitidas.Abstract: Signal transmission and position quality obtained by the GNSS positioning directly depends on the time control. The atomic clocks aboard of satellites are responsible for this control. In this research is studied the satellites clocks errors of GPS and to do so data from pseudorange, satellite semi-major axis and correction parameters of satellites' clocks errors founded in the RINEX navigation and observation files. From this data, the satellites clocks errors are calculated using the IGS mathematical model, and then an adjustment technique was applied in order to estimate new parameters of the clocks corrections. For Cesium atomic clocks, the periodic part of the mathematical model was adapted. The correction parameters adjusted were applied in the IGS and adapted model, finally the results were compared with IGS data from clk_30s file. The experiments carried out show an improvement of 50 cm in the Cesium satellites' clocks errors. In addition, the research concludes that the satellites' clocks errors do not depend on the station where the data was collected as well it do not depend on the equipment's antenna. Keywords: Satellites clocks errors, atomic clocks, GPS clocks, broadcast ephemerides

Characterizing changes in the noise statistics of GNSS space clocks with the dynamic Allan variance

The dynamic Allan variance (DAVAR) is a tool for the characterization of precise clocks. Monitoring anomalies of precise clocks is essential, especially when they are employed onboard the satellites of a global navigation satellite system (GNSS). When an anomaly occurs, the DAVAR changes with time, its shape depending on the type of anomaly occurred. We obtain the analytic DAVAR for a change of variance in the clock noise, an anomaly with critical effects on the clock performances. This result is helpful when the clock health is monitored by observing the DAVA