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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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.

IBGE and Ionosphere

(X,Y,Z)

GNSS positioning.

Ionospheric delay

• First-order delay - More than 99%

- Proportional to TEC

pseudorange carrier-phase

• Since 1996;

• Actually 88 stations;

• Needs densification.

RBMC

• Real time GNSS data stream on internet (NTRIP – Networked Transport of RTCM via Internet Protocol);

• Since 2009;

• Actually 28 stations.

RBMC-IP

On-line PPP service

• Double or single frequency data processing;

• Global Ionospheric Maps (IONEX) applied to single frequency solutions;

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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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).

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).

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.

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)

Geomagnetic field statusDst index (Kyoto)

• High solar activity:• Day 90 => -400nT.

• Low solar activity: • less than -50 nT.

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%.

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;

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;

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.

Acknowledgments