vtec prediction using a recursive artificial neural networks approach in brazil: initial results...
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VTEC prediction using a recursive artificial neural networks approach in Brazil: initial
results
Engineer School - University of São Paulo
Wagner Carrupt MachadoEdvaldo Simões da Fonseca Junior
MImOSA workshop – february 26th 2013 – INPE - São José dos Campos - Brazil
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2
Presentation outline
• IBGE interest, infrastructure and needs;
• Artificial Neural Networks approach;
• Experiments and Results:• Solar activity and geomagnetic field status;• Data processing and results;
• Conclusion and future work.
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IBGE and Ionosphere
(X,Y,Z)
GNSS positioning.
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Ionospheric delay
• First-order delay - More than 99%
- Proportional to TEC
pseudorange carrier-phase
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• Since 1996;
• Actually 88 stations;
• Needs densification.
RBMC
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• Real time GNSS data stream on internet (NTRIP – Networked Transport of RTCM via Internet Protocol);
• Since 2009;
• Actually 28 stations.
RBMC-IP
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On-line PPP service
• Double or single frequency data processing;
• Global Ionospheric Maps (IONEX) applied to single frequency solutions;
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IGS Global Ionospheric Maps
• Combination of four different solutions:• CODE (Center for Orbit Determination in Europe);
• ESOC (European Space Operations Centre ESA);
• UPC (Polytechnical University of Catalonia);
• JPL (Jet Propulsion Laboratory).
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9
IBGE collaborations
• Providing GNSS data free of charge to ionosphere monitoring projects:
• Unesp - Presidente Prudente (Brazil);• INPE/EMBRACE (Brazil);• La Plata University (Argentina);• IGS – currently 9 stations (international).
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ANN approach• Architecture:• Multilayer Perceptrons;• 1 hidden layer with 16
neurons.
• samples taken from 3 previous days IGS GIM, resulting in 39 grids with 276 points (10,764 samples)
• Recursive training:• Updated daily.
• Output:• 72 hours ahead of regional ionospheric Maps (IONEX).
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Experiments• 30 ANNs trained;
• Comparison between VTECGIM and VTECANN in four cases:
• IGS GIMhigh: March 21 to April 04 2001 (Day 80 to 94)
low: June 16 to june 30 2009 (Day 167 to 181)
1) high solar activity;2) day of the geomagnetic storm;3) 3 days after the day of the geomagnetic storm;4) low solar activity.
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Solar activity status
• High solar activity:
• from 139.8 sfu to 273.5 sfu
• Low solar activity:• from 66.5 sfu
to 68.5 sfu
Solar Flux 10.7 cm (NOAA - Pentiction station)
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Geomagnetic field statusDst index (Kyoto)
• High solar activity:• Day 90 => -400nT.
• Low solar activity: • less than -50 nT.
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DifferencesIncreases as approaching to
daily VTEC maximum;High solar activity
• < 15 TECU:– 86% - geomagnetic storm;
– 88% - not disturbed days. Low solar activity:
• < 5 TECU:– 99%.
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Relative differences ()• from 0% to 20% during most
of the time in both periods;
• Day 90 (case 2) between 2 h and 5 h (Local Time) VTECGIM were pushed down due to the geomagnetic storm;
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Conclusion
• 70% to 85% of VTECGIM
was correctly mapped by the ANN;
• Vertical ionospheric delay from 0.24 m to 1.79 m can be expected in L1 observables; • Insufficient for high precision applications (ambiguity
resolution);
• The proposed approach:• auto-adaptive to seasonal and longer period variations;
• real-time GNSS positioning;
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Future work
• Mod_Ion regional ionospheric maps with spacial resolution of 2° x 4° and 1 hour frequency;
• Extend the model coverage to South America;
• Use data from the actual solar cycle maximum;
• Include solar activity and geomagnetic indices in the model.
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Acknowledgments