Evaluation of the Ionospheric Scintillation Effects on GNSS Receiver

Tracking Performance over Latin America with Tracking Jitter Maps

V. Sreeja and M. AquinoNottingham Geospatial Institute, University of Nottingham

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Outline of Presentation

IntroductionData and MethodologyResultsConclusions

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Ionospheric ScintillationRapid fluctuations in the amplitude and phase of transionospheric signals caused by small scale plasma density irregularities

Basu, S. et al., J. Atmos. Terr. Phys, 2002

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Ionospheric Scintillation Effects on GNSS receivers

Significantly degrade GNSS receiver tracking performanceCode and phase tracking loop performances can be degraded

Variance of the error at DLL / PLL output (tracking jitter) increases during scintillation

Good measure of scintillation effect on the receiver

Delay Locked Loop (DLL) Phase Locked Loop (PLL)

Rapid intensity fluctuations Rapid phase fluctuations

Accurate code phase alignment Accurate phase estimation

Difficulty in acquisition Cycle slips, loss of lock, difficulty in tracking

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Data and Methodology [1] Open sky scintillation data recorded in November 2012 by PolaRxS receivers during the Fp7 CIGALA project (2010-2012)

1) Presidente Prudente (PPTE) - located close to the Equatorial Ionisation Anomaly (EIA) crest (dip lat 12.3S)

2) São José dos Campos (SJCI) - located under the EIA crest (dip lat 17.8S)

3) Porto Alegre (POAL) - located beyond the EIA crest (dip lat 20.5S)

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PolaRxS receiver signal tracking performance at GPS L1C/A evaluated by:

Tracking model of Conker et al. (2003) Variance of tracking error at the carrier tracking

loop (PLL) output

kpkp

nkf

T

LSACLnc

LSACLncnB

OSC2

]12[sin1))1(241(/1)0/(

]))1(2421(/1)0/(2

11[

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Conker, R. S. et al., Radio Sci., doi: 10.1029/2000RS002604, 2003

Oscillator noise=0.01 rad2 Thermal NoisePhase scintillation

Data and Methodology [2]

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RESULTS

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Maps of amplitude scintillation index, S4

All satellites with elevation > 30⁰

dip lat 12.3S

dip lat 17.8S

dip lat 20.5S

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Receiver PLL jitter variance Maps

dip lat 12.3S

dip lat 17.8S

dip lat 20.5S

V. Sreeja et al., Space Weather, doi: 10.1029/2011SW000707, 2011

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Receiver PLL jitter variance Maps: High latitude

Data from CHAIN kindly provided by Dr Paul Prikryl

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Application of Jitter variance Maps

Provide users with the information on the prevailing tracking conditions under scintillation (possibly in near-real time)Mitigate the effects of ionospheric scintillation on GNSS positioning through the strategy introduced by Aquino et al. [2009]

Stochastic model – assigns satellite and epoch specific weights based on the estimated tracking jitterImprovement between 17% and 38% in height accuracy was obtained by this method

Aquino et al. J. Geod., 83, doi:10.1007/s00190-009-0313-6, 2009

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ConclusionsPLL jitter variance maps for GPS L1C/A signal during 13-16 November 2012 over Presidente Prudente, São José dos Campos and Porto Alegre in BrazilJitter variances calculated using the scintillation-sensitive tracking model of Conker et al. [2003]Jitter variances calculated on all the simultaneously observed satellite-to-receiver links during 13-16 November during the local pre-midnight hours are large over Presidente Prudente and São José dos Campos This indicates the likelihood for cycle slips and degradation of measurement quality, consequently degrading positioning accuracyJitter variance maps could be useful for improving the positioning accuracy by applying weights to individual satellite to receiver links using the method of Aquino et al. [2009]

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THANKS