A Norwegian Ionosphere Model Based on GPS Data

1. A Norwegian Ionosphere Model Based on GPS Data Anna B.O. Jensen Nordic Institute of Navigation Oslo, June 2008

2. Outline • Navigation in the arctic • Ionospheric activity at high latitudes • SATREFTM Ionosphere Model • Verification towards IGS GIM • Comparison with EGNOS ionosphere model • Summary

3. Navigation in the arctic (1) • Norway is located at high latitudes, from 60° to 80° N, mainly in the arctic region • GPS is used extensively as a navigational mean in the arctic • Unfortunately, GNSS performance is limited in the arctic compared to mid latitudes

4. Navigation in the arctic (2) • Much offshore activity in the Norwegian Sea • Need for reliable navigation • In the future: • Increasing activity and more traffic due to global warming and more oil and gas exploration • Increasing need for navigation

5. Ionospheric activity at high latitudes • At high latitudes characteristics of the ionospheric activity are different than at mid latitudes: • Higher ionospheric variability • Increased amount of scintillation • This does affect navigation users e.g. by: • Reduced accuracy • Poor signal tracking (loss of lock)

6. Ionospheric activity at high latitudes Feb. 28, 2008 70°N network 60°N network Trimble gpsnet software

7. SATREFTM Ionosphere Model (1) • Several ionosphere models exist, but they are generally poor for high latitudes • In 2007 the NMA therefore started development of a regional Norwegian ionosphere model based on the SATREFTM network of GNSS stations

8. SATREFTM Ionosphere Model (2) • The model is based on: • GPS data from selected SATREFTM stations • Estimation of ionospheric delays in the stations • Spatial interpolation to obtain nationwide grid model

9. Test area

10. Test data

11. Verification towards GIM (1) • Verification with respect to the Global Ionosphere Model (GIM) of the IGS • IONEX files retrieved from the IGS web site, and L1 ionosphere delays extracted for comparison with SATREFTM Ionosphere Model • 20 grid points used for verification

12. Verification towards GIM (2) • Differences, SATREFTM minus IGS GIM • 30 second sampling, 20 grid points

13. Verification towards GIM (3) • Summing up: • Mean of differences of 2 - 5 cm is basically negligible • Indicates no offset between the two models • Standard deviation of 12 – 19 cm • Occur mainly because no filtering is applied to the SATREFTM model • Lower standard deviation on the day with low ionospheric activity

14. Comparison with the EGNOS iono. model • Verification of the SATREFTM model towards the IGS GIM showed acceptable results • Therefore, the SATREFTM model is now used for a preliminary evaluation of the performance of the EGNOS ionosphere model in the arctic

15. Comparison with EGNOS iono. model • Differences, SATREFTM minus EGNOS • 16 grid points

16. Selected grid point – Feb. 28, 2008 • EGNOS: blue, GIM: green, SATREFTM: red • EGNOS model is biased

17. Test area

18. Selected grid points – Feb. 28, 2008 • EGNOS bias for upper grid point

19. Selected grid points – Feb. 2, 2008 • Another day - again EGNOS bias for same point

20. 16 grid points, Jan. 15, 2008

21. Future work • Modify model to run in real time • Lots of programming • Further investigations to decide on: • Coverage area • Grid spacing • Number of SATREFTM stations to include • Temporal update interval • Information to users – web application

22. Summary • Development of the SATREFTM Ionosphere Model has been initiated • Verification of the SATREFTM Ionosphere Model towards the IGS GIM show very good results • Comparison with EGNOS model show deviations for some grid points • Improvement expected with new EGNOS version this summer

23. Acknowledgments • Thanks to the Norwegian Space Centre for providing support for the work • Thanks to Ola Øvstedal, Norwegian University of Life Sciences in Ås, for valuable discussions during the development phase