Combined global models of the ionosphere

Transcription

1 Combined global models of the ionosphere S. Todorova (1), T. Hobiger (2), H. Schuh (1) (1) Institute of Geodesy and Geophysics (IGG), Vienna University of Technology (2) Space-Time Standards Group, Kashima Space Research Center, NICT, Japan 10. October GRF 2006, Munich

2 Content Ionosphere modelling through GNSS and satellite altimetry Combined model of the ionosphere - mathematical approach Global Ionosphere Maps (GIM) developed at IGG Summary 0utlook 10. October GRF 2006, Munich 2/23

3 The ionosphere z VTEC 1000km 50km STEC STEC = M(z). VTEC ; 1TECU = e - /m October GRF 2006, Munich 3/23

4 P Modelling the ionosphere using GNSS Linear combination L4=L1-L2 TEC The geometry-free combination contains: Ionospheric refraction (TEC) Differential P1-P2 Code Biases (DCBs) influences on L4 caused by the receiver- and the satellite clock, usually in ns ( k ) k ( k Δb Δb = + ξ ξ ( F( z) E (, s)) + c Δb Δb ) k k i, 4 = + ξ4 Ii + c i 4 E V β i i k k E ( β, s ) - VTEC at the ionospheric V Δb Δb i k i = b = b i b k, 1 k,2 b i, 1 i,2 pierce point - satellite DCBs -receiver DCBs F( z k i ) ξe 0,162m/ TECU - mapping function 2 2 ξ4 = 1 f1 f2 0,647 - constant - relates the ionospheric refraction on L4 to L1 10. October GRF 2006, Munich 4/23

5 Modelling the ionosphere using satellite altimetry TOPEX/Poseidon (till Oct. 2005) and Jason1: Observations at two distinct frequencies (Ku- and C-Band) Orbit altitude km Deliver directly VTEC values Altimetry data for this study is provided by ADS Central, GFZ Potsdam October GRF 2006, Munich 5/23

6 Global Ionosphere Maps (GIM) E V ( β, s) n = max n n= 0 m= 0 ~ P nm (sinβ)( a nm cos( ms) + b nm sin ( ms)) E V ( β, s) - Vertical Total Electron Content (in TECU) β, s =UT+ λ π ~ P = nm N nm P a nm, b nm nm - geomagnetic latitude, sun-fixed longitude - normalized Legendre function with degree n and order m - unknown coefficients of the harmonic expansion (the calculated ionospheric parameters) Modified Single Layer Model F(z) = 1/cosz with sinz = sin(αz ). R/(R+H), α = and H = 506.7km 10. October GRF 2006, Munich 6/23

7 Combined model - mathematical approach Applying least-squares adjustment (Gauss-Markov model) on each set of different observations and combining the normal equations by adding the relevant N-matrices DCB DCB/SF GPS DCB/SF GPS SF GPS P GPS DCB DCB/SF GPS 0 DCB/SF GPS 0 SF GPS + SF ALT offsets/sf ALT offsets/sf ALT offsets P ALT SF ALT offsets/sf ALT offsets/sf ALT offsets 10. October GRF 2006, Munich 7/23

8 Matlab based software for developing 2-hourly GIM RINEX data ca.180 Stations Navigation message V T E C Computation Combination Estimation V T E C JASON1, TOPEX double-frequency ionospheric correction GNSS observations Combined GIM Altimetry observations 10. October GRF 2006, Munich 8/23

9 Global Ionosphere Maps developed at IGG Global VTEC and RMS VTEC maps in IONEX format, 2-hourly resolution, degree and order of the spherical expansion 15 GPS and GLONASS data (GNSS-only solution) phase levelled to code observations, sampling rate 30 sec GNSS combined with TOPEX/Poseidon and JASON1 data σ apr ALT = 0.25 TECU Satellites and receivers DCB for GPS and GLONASS Comparisons with JASON1 measurements and with GIM produced by the Analysis Centres of the IGS Ionosphere WG 10. October GRF 2006, Munich 9/23

10 Observations used, day GNSS: 181 IGS stations Altimetry: JASON1 (blue), TOPEX (red) 10. October GRF 2006, Munich 10/23

11 VTEC - IGG GNSS only 1 UT 3 UT 5 UT 7 UT 9 UT 11 UT 13 UT 15 UT 17 UT 19 UT 21 UT 23 UT 10. October GRF 2006, Munich 11/23

12 VTEC - IGG combined 1 UT 3 UT 5 UT 7 UT 9 UT 11 UT 13 UT 15 UT 17 UT 19 UT 21 UT 23 UT 10. October GRF 2006, Munich 12/23

13 VTEC difference IGG combined minus GNSS-only 1 UT 3 UT 5 UT 7 UT 9 UT 11 UT 13 UT 15 UT 17 UT 19 UT 21 UT 23 UT 10. October GRF 2006, Munich 13/23

14 RMS - IGG GNSS only 1 UT 3 UT 5 UT 7 UT 9 UT 11 UT 13 UT 15 UT 17 UT 19 UT 21 UT 23 UT 10. October GRF 2006, Munich 14/23

15 RMS - IGG combined 1 UT 3 UT 5 UT 7 UT 9 UT 11 UT 13 UT 15 UT 17 UT 19 UT 21 UT 23 UT 10. October GRF 2006, Munich 15/23

16 RMS difference IGG combined minus GNSS-only 1 UT 3 UT 5 UT 7 UT 9 UT 11 UT 13 UT 15 UT 17 UT 19 UT 21 UT 23 UT 10. October GRF 2006, Munich 16/23

17 Satellite DCB - IGG GNSS-only vs. CODE Bias: ns Bias:-1.08 ns 10. October GRF 2006, Munich 17/23

18 Receiver DCB -IGG GNSS-only vs. CODE Bias: 0.74 ns Bias: 0.95 ns 10. October GRF 2006, Munich 18/23

19 JASON minus IGG GNSS-only and the Ionosphere WG AC, in latitude cod CODE final esa ESA final esr ESA rapid igg IGG GNSS-only igr IGS combined rapid igs IGS combined final jpl JPL final jpr JPL rapid upc UPC final 10. October GRF 2006, Munich 19/23

20 JASON minus IGG GNSS-only and the Ionosphere WG AC, in time cod CODE final esa ESA final esr ESA rapid igg IGG GNSS-only igr IGS combined rapid igs IGS combined final jpl JPL final jpr JPL rapid upc UPC final 10. October GRF 2006, Munich 20/23

21 Summary The combined GIM from GNSS and altimetry data have an accuracy up to ~1 TECU higher than the GNSS-only solution over the seas (worst case for GNSS); The altimetry offsets might also be estimated through the combination; The method can be adopted for combination with ionospheric data from other techniques (VLBI, DORIS ); Main goals - global coverage, higher accuracy and reliability. 10. October GRF 2006, Munich 21/23

22 Outlook Optimisation of the combined model: main focus the relative weighting of the individual results from the different techniques -> VCE consideration and modelling of the technique-specific error sources (altimetry) combination with other techniques (VLBI, DORIS,...) Comparisons with external data and statistics 4D model 10. October GRF 2006, Munich 22/23

23 Thank you for your attention! The project P16136-N06 is funded by the Austrian Science Fund (FWF). Many thanks to Dr. Manuel Hernández ndez-pajares (UPC) for his assistance! 10. October GRF 2006, Munich 23/23

24 COMB - GNSS-only: Δ RMS (TECU) COMB - GNSS-only: Δ VTEC (TECU) 0,50 0,00-0,50-1,00-1,50 max min mean 15,00 max min mean 0,22 0,00 0,02 0,00-0,01 0,04 10,00 9,20 6,09-0,12 5,00 0,91 0,02 0,26 0,69 0,00-0,54-1,01-5,00-6,26-10,00-2,00-1,81-15,00-13,26 sigma apr. = 1 sigma apr. = 0,20 sigma apr. = 0,05 sigma apr. = 1 sigma apr. = 0,20 sigma apr. = 0,05 COMB GNSS-only: Δ sigma a posteriori (TECU) 0,00 0,03 0, October GRF 2006, Munich 24/23