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

Outline  Navigation in the arctic  Ionospheric activity at high latitudes  SATREF TM Ionosphere Model  Verification towards IGS GIM  Comparison with EGNOS ionosphere model  Summary

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

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

Ionospheric activity at high latitudes  At high latitudes characteristics of the ionospheric activity are different than at mid latitudes: wHigher ionospheric variability wIncreased amount of scintillation  This does affect navigation users e.g. by: wReduced accuracy wPoor signal tracking (loss of lock)

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

SATREF TM 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 SATREF TM network of GNSS stations

SATREF TM Ionosphere Model (2)  The model is based on: wGPS data from selected SATREF TM stations wEstimation of ionospheric delays in the stations wSpatial interpolation to obtain nationwide grid model

Test area

Test data Day of yearDateK-indexIono. activity DOY 015Jan. 15, – 4Low DOY 033Feb. 02, – 6Medium DOY 059Feb. 28, – 6Medium DOY 324Nov. 20, Medium

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 SATREF TM Ionosphere Model  20 grid points used for verification

Verification towards GIM (2) DateMean [ meter ] Std. dev. [ meter ] Jan. 15, Feb. 02, Feb. 28, Nov. 20,  Differences, SATREF TM minus IGS GIM  30 second sampling, 20 grid points

Verification towards GIM (3)  Summing up: wMean of differences of cm is basically negligible Indicates no offset between the two models wStandard deviation of 12 – 19 cm Occur mainly because no filtering is applied to the SATREF TM model Lower standard deviation on the day with low ionospheric activity

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

Comparison with EGNOS iono. model DateMean [ meter ] Std. dev. [ meter ] Samples Jan. 15, Feb. 02, Feb. 28, Nov. 20,  Differences, SATREF TM minus EGNOS  16 grid points

Selected grid point – Feb. 28, 2008  EGNOS: blue, GIM: green, SATREF TM : red  EGNOS model is biased

Test area

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

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

16 grid points, Jan. 15, 2008

Future work  Modify model to run in real time wLots of programming  Further investigations to decide on: wCoverage area wGrid spacing wNumber of SATREF TM stations to include wTemporal update interval wInformation to users – web application

Summary  Development of the SATREF TM Ionosphere Model has been initiated  Verification of the SATREF TM Ionosphere Model towards the IGS GIM show very good results  Comparison with EGNOS model show deviations for some grid points wImprovement expected with new EGNOS version this summer

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