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Status of the IGS ionosphere products & future developments

This article discusses the current status and future developments of the International GPS Service (IGS) ionosphere products, including the challenges of data collection and processing. It highlights the efforts of the IGS Ionosphere Working Group in producing global Total Electron Content (TEC) maps. The article also mentions the transition process and the combination of data from different analysis and validation centers to improve accuracy.

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Status of the IGS ionosphere products & future developments

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  1. Status of the IGS ionosphere products & future developments Andrzej Krankowski (University of Warmia and Mazury in Olsztyn, Poland) and Manuel Hernandez-Pajares (Technical University of Catalonia, Spain)

  2. Outline Introduction IGS IONO WG activities Summary of IGS global TEC maps performance Future activities and Conclusions

  3. International GPS Service, IGS IGS directly manages more than about 350 permanent GPS stations, observing some 4-12 satellites at 30 sec rate: more than 250,000 STEC worldwideobservations/hour, but there is lack of stations at the South and over the Seas

  4. Determining VTEC in a global network: main problem of lack of data in South and Seas • Lack of data in equatorial Africa and Atlantic, and in part of equatorial and southern Pacific, hamper the detection of the equatorial anomalies (June 13, 2004). • It can be seen the typical “holes” appearing in the first stage of the global maps computation (each 2 hours). This requires an optimum spatial-temporal interpolation technique to extend the estimates covering all the Ionosphere.

  5. Computing Global VTEC maps: layout Kalman Filter GPS raw data (1) Preprocessing: cycle-slips, satellite pos., antenna phase centers,… (2) STEC estimation (i.e. L1-L2 bias estimation) (5) Computing the Interfrequency Delay Code Biases (3) VTEC estimation over the GPS stations (i.e. deprojecting STEC) (4) VTEC interpolation (i.e. “filling the gaps”)

  6. VTEC global maps: the cooperative effort in IGS The IGS Ionosphere Working group started its activities in June 1998 with the main goal of a routinely producing IGS Global TEC maps (IGTEC). This is being done now with a latency of 11 days (final product) and with a latency of less than 24 hours (rapid product). IGSGPS data IGSIonosphere Analysis Centers IGSIonosphere Validation Centers IGSIonosphere IGSIonosphere CombinationCenter The IGS ionosphere product is a result of the combination of different Analysis Centers TEC maps by using weights computed from GPS data by Validation Centers, in order to get a more accurate product.

  7. IGS Final Ionosphere Flow-Chart GPSrec.1 GPSrec.N ENVISAT obs. … IGSIonosphere Analysis Centers IGSserver JASON obs. CODEiono. ESAiono. JPLiono. NRCaniono* UPCiono. NRCan*weights IGSIonosphere CombinationCenter ESAENVISAT TEC IGSserver UPCweights UWMcomb. JPLJASON TEC UWMserver IGSIonosphere Validation Centers IGS Iono. IGS Iono.Ext.valid. * NRCan has stopped temporarily the ionospheric production

  8. The transition process in IGS Ionospheric Working Group • In previous year, 2007, the IGS Ionospheric Product Coordinator (IPC) and IGS Ionospheric Working Group Chairman (IWC) duties was split between Andrzej Krankowski (from University of Warmia and Mazury in Olsztyn, Poland) and Manuel Hernandez-Pajares (from Technical University of Catalonia, Spain), respectively. • Since this year, after the transition period and after IGS Governing Board and Iono WG approval, Manuel Hernandez-Pajares passed the IGS Iono WG Chairmanship to Andrzej Krankowski as well.

  9. Example of IGS Final TEC map: 2003-347-00UT Five Analysis Centers (CODE, ESA, JPL, NRCan and UPC) and 4 Validation Centers (JPL, ESA, NRCan and UPC) have been providing maps (at 2 hours x 5 deg. x 2.5 deg in UT x Lon. x Lat.), weights and external (dual-frequency altimetry-derived) TEC data. Units: 0.1 TECUs From such maps and weights the corresponding combination center (firstly ESA, and secondly UPC since Dec.2002) and recently UWM (since January, 2008) has produced the IGS TEC maps in ionex format.

  10. The IONEX format body 1 START OF TEC MAP 2004 4 27 0 0 0 EPOCH OF CURRENT MAP 87.5-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H 123 123 123 124 125 125 126 126 126 126 126 126 125 125 125 128 125 125 125 126 126 125 124 124 124 124 124 123 123 122 122 121 120 120 119 118 118 118 118 118 117 117 116 116 115 114 114 113 113 113 114 114 114 114 115 115 115 116 116 117 117 118 119 120 120 121 121 122 123 123 123 123 123 85.0-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H 129 129 130 131 132 132 133 133 134 134 134 134 134 134 134 136 135 136 130 129 129 129 128 128 128 127 126 124 123 122 121 120 119 118 117 117 117 117 116 116 115 115 114 113 112 111 110 109 109 110 109 109 109 110 111 111 112 112 113 113 115 116 117 118 120 122 123 125 126 127 128 129 129 ... -87.5-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H 87 88 88 90 90 91 92 93 93 94 94 95 94 93 91 89 87 86 85 84 83 82 81 81 80 80 79 78 78 78 77 77 76 76 76 75 75 76 77 77 76 79 79 79 80 81 82 83 83 84 85 85 85 85 85 85 85 86 87 87 87 88 88 87 87 87 87 88 87 87 87 87 87 1 END OF TEC MAP 2 START OF TEC MAP ... ... 13 END OF TEC MAP 1 START OF RMS MAP 2004 4 27 0 0 0 EPOCH OF CURRENT MAP 87.5-180.0 180.0 5.0 450.0 LAT/LON1/LON2/DLON/H 7 7 7 7 7 7 7 7 7 7 8 8 9 9 9 6 8 8 8 6 6 7 7 7 7 6 6 6 6 6 6 6 6 6 7 7 7 6 7 6 6 7 7 7 7 8 8 9 10 9 8 8 8 8 7 7 8 8 8 8 7 7 7 7 7 6 6 7 6 7 6 6 7 ... 13 END OF RMS MAP END OF FILE The IONEX (IONosphere interEXchange) format allows to store the VTEC and its error estimates in a grid format, in consecutive values –at different longitudes- for each latitude grid point.

  11. Overall validation of VTEC maps during more than 9 years of IGS final VTEC maps

  12. Example of comparison of IGS vs JASON: 2003-347 each 6 hours 01-03UT 07-09UT Units: approx. 10 TECUs Red: Jason-1 TEC Green: IGS final TEC JASON dual frequency altimeter provides a direct and independent VTEC below its orbit (1300 km) and over the oceans (worst case for GPS). 13-15UT 19-21UT

  13. CODG JPLG IGSG ESAG Cumulative Distribution Function of VTEC discrepancy values provided by final VTEC maps (vertical axis) regarding to the VTEC values, directly observed by the TOPEX/JASON altimeters (horizontal axis), during the period day 349 2002 to end of 2007 (>30000000 observations) UPCG

  14. Rapid vs Final IGS DCBs Rapid IGS DCBs are typically in agreement with the Final ones at the level of its repeatability(less than 0.1 ns for the Satellite DCBs and less than 1 ns for the receiver DCBs)

  15. Evolution of Global Electron Content during more than 9 years of IGS final VTEC maps Global Electron Content Unit (GECU) defined as 1032 electrons Global Electron Content evolution during the availability of IGS Ionospheric products, since 1st June 1998 (source: Final IGS VTEC maps). Global Electron Content evolution during the availability of IGS Ionospheric products, vs. Solar Flux, Ap index and Xray flux, since 1st June 1998 (source: Final IGS VTEC maps).

  16. Yesterday’s Ionosphere (day 173, 2004, mid-low part of Solar Cycle). Comparison of recent Global Ionosphere maps Spring eq. Ionosphere (day 80, 2004). Spring around the Solar Max (day 80, 2002). IGS Final Ionosphere ionex files at ftp://cddisa.gsfc.nasa.gov/gps/products/ionex/ IGS Ionosphere WG download links at : http://gage152.upc.es/~ionex3/igs_iono/igs_iono.html ftp://igs-rapid.man.olsztyn.pl/rapid_iono_igs/

  17. IGS IONEX usage statistics for both final(IGSG) and rapid (IGRG) VTEC maps downloads from main server only - cddis.gsfc.nasa.gov

  18. Future plans of IGS IWG and Conclusions The following actions may be considered: - Agreement between IGS and the ESA SMOS project, -Higher temporal resolution, e.g. 1 hour (some AAC’s already produced TEC maps with even 15-minute interval), • A simple method to apply the second order ionospheric • correction has been proposed by the Iono WG, as a result • of the action item proposed at IGS 2004 Technical meeting • held in Bern.

  19. Agreement between the International GNSS Service (IGS) and the ESA SMOS project • The Soil Moisture and Ocean Salinity (SMOS) mission is part of the Earth Explorer programme of the European Space Agency (ESA). • The launch of SMOS is currently planned for November 2008. • The SMOS project requests the support of the IGS over a period of nominally 7 years (the expected operational lifetime of the SMOS spacecraft). • Required are global maps of Vertical Total Electron Content (VTEC).

  20. I2 effects on subdaily differential estimation Coordinates (north shift of AOML): Small efect (up to ~1mm) and NO significant dependence on I2 at reference stat. The small observed effect depend on the relative I2 value, regarding to the reference station (I2-I2ref). Satellite clock effect: significant (up to +2cm) and dependent on I2 at reference station Carrier phase bias effect: significant (up to +4cm) and dependent on I2 Coordinates: A negative I2-I2ref produces an increase of range, and a corresponding increase of north (instead of southward) and up component, up to 1mm, in a northern hemisphere station.

  21. Mean I2 effect on receiver positions (21 months, 2002 -03) Results are not equivalent to those obtained by previous authors: Among I2 processing complete for all the geodetic parameters, more realistic magnetic field model (see below) and more homogeneous distribution of receivers are some of the hints to explain this. Receiver position effect: Confirming previous results with differential scenario, the dependence on the difference of I2 values wrt neighbor receivers, producing long term effects at mm level and few tenths of mm for daily repeatability effect. Hernández-Pajares, M., J.M.Juan, J.Sanz and R.Orús, Second-order ionospheric term in GPS: Implementation and impact on geodetic estimates, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B08417, doi:10.1029/2006JB004707, 2007

  22. Conclusions Future improvements are determined by the users requirements (the number of users has significantly increased during the last years). A good example is the recent interest of SMOS ESA mission on using the IGS VTEC maps, including predicted products. Long series of IGS VTEC maps offers a very good source with high both spatial and temporal resolution, to get significant spectral results. A long time series of accurate global VTEC values are available since 1998, which are freely available for scientific or technical usage, with latencies of about 12 days (final product) or >1-2 days (rapid product). Thanks to the cooperative effort developed within the IGS framework and the international scientific community this open service will hopefully continue its evolution during the next years, sensitive to both new user needs and scientific achievements. Hernández-Pajares, M., J.M.Juan, J.Sanz, R.Orús,A. Garcia-Rigo, J.Feltens A. Komjathy, S.C. Schaer, A.Krankowski, The IGS VTEC maps: A reliable source of ionospheric information since 1998, submitted to Journal of Geodesy

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