IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 1 Status of the IGS ionosphere products & future developments Manuel Hernandez-Pajares (Technical University of Catalonia, Spain) Andrzej Krankowski (University of Warmia and Mazury in Olsztyn, Poland) and

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 2 Outline Introduction IGS IONO WG activities Summary of IGS global TEC maps performance Future activities and Conclusions

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 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 worldwide observations/hour, but there is lack of stations at the South and over the Seas

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 4 Determining VTEC in a global network: main problem of lack of data in South and Seas 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. 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).

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 5 Computing Global VTEC maps: layout GPS raw data (1) Preprocessing: cycle-slips, satellite pos., antenna phase centers,… (2) STEC estimation (i.e. L1-L2 bias estimation) (3) VTEC estimation over the GPS stations (i.e. deprojecting STEC) (4) VTEC interpolation (i.e. “filling the gaps”) (5) Computing the Interfrequency Delay Code Biases Kalman Filter

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 6 VTEC global maps: the cooperative effort in IGS IGS GPS data IGS Ionosphere Analysis Centers IGS Ionosphere Validation Centers IGS Ionosphere Combination Center IGS Ionosphere 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). 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.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 7 IGS Final Ionosphere Flow-Chart GPS rec.1 GPS rec.N IGS server CODE iono. ESA iono. JPL iono. UPC iono. NRCan iono* NRCan* weights UPC weights JPL JASON TEC UWM comb. … UWM server IGS server IGS Iono. JASON obs. IGS Iono. Ext.valid. IGS Ionosphere Analysis Centers IGS Ionosphere Validation Centers IGS Ionosphere Combination Center * NRCan has stopped temporarily the ionospheric production ESA ENVISAT TEC ENVISAT obs.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 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.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 9 Example of IGS Final TEC map: UT Units: 0.1 TECUs 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. 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.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 10 The IONEX format body 1 START OF TEC MAP EPOCH OF CURRENT MAP LAT/LON1/LON2/DLON/H LAT/LON1/LON2/DLON/H LAT/LON1/LON2/DLON/H END OF TEC MAP 2 START OF TEC MAP END OF TEC MAP 1 START OF RMS MAP EPOCH OF CURRENT MAP LAT/LON1/LON2/DLON/H 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.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 11 Overall validation of VTEC maps during more than 9 years of IGS final VTEC maps

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 12 Example of comparison of IGS vs JASON: each 6 hours 01-03UT07-09UT 13-15UT19-21UT 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).

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 13 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 to end of 2007 (> observations) IGSG CODG JPLG ESAG UPCG

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 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)

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 15 Evolution of Global Electron Content during more than 9 years of IGS final VTEC maps Global Electron Content Unit (GECU) defined as 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).

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 16 Yesterday’s Ionosphere (day 173, 2004, mid- low part of Solar Cycle). 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/ ftp://cddisa.gsfc.nasa.gov/gps/products/ionex/ IGS Ionosphere WG download links at : ftp://ftp://igs-rapid.man.olsztyn.pl/rapid_iono_igs/ Comparison of recent Global Ionosphere maps

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 17 IGS IONEX usage statistics for both final(IGSG) and rapid (IGRG) VTEC maps downloads from main server only - cddis.gsfc.nasa.gov

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 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.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 19 Agreement between the International GNSS Service (IGS) and the ESA SMOS project 1.The Soil Moisture and Ocean Salinity (SMOS) mission is part of the Earth Explorer programme of the European Space Agency (ESA). 2.The launch of SMOS is currently planned for November The SMOS project requests the support of the IGS over a period of nominally 7 years (the expected operational lifetime of the SMOS spacecraft). 4.Required are global maps of Vertical Total Electron Content (VTEC).

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 20 I2 effects on subdaily differential estimation 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 (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). 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.

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 21 Mean I2 effect on receiver positions (21 months, ) 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. 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. 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: /2006JB004707, 2007

IGS Analysis Center Workshop 2008 A. Krankowski and M.Hernández-Pajares Miami Beach, 2-6 June 2008 IGS Ionospheric Working Group 22 Conclusions Long series of IGS VTEC maps offers a very good source with high both spatial and temporal resolution, to get significant spectral results. 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. 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