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Douša J an (1) , Christine Hackman (2) , Sam S Leeuwen (3)

Douša J an (1) , Christine Hackman (2) , Sam S Leeuwen (3) ( 1) Research Institute of Geodesy, Topography and Cartography , Czech Republic (2) United States Naval Observatory, Washington, D.C. U.S.A. (3) Netherlands Aerospace Center, Netherlands JAN.DOUSA@PECNY.CZ

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Douša J an (1) , Christine Hackman (2) , Sam S Leeuwen (3)

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  1. Douša Jan (1),Christine Hackman(2), Sam S Leeuwen(3) (1) Research Institute of Geodesy, Topography and Cartography, Czech Republic (2) United States Naval Observatory, Washington, D.C. U.S.A. (3) Netherlands Aerospace Center, Netherlands JAN.DOUSA@PECNY.CZ GNSS4SWEC Final Workshop, February 19, 2016, Noordwijk, Netherlands Intra-/Inter-technique comparisons of tropospheric products using GOP-TropDB and developments towards the IGS Troposphere web portal

  2. Introduction • Introduction • Evaluation of GNSS Repro1/Repro2 products • Tropospheric ties andInter-technique evaluations • Preparing IGS Tropospheric Working Group web • Conclusions

  3. EUREF Repro2 vs. ERA-Interim Table: Total statistics for EUREF ACs and EUREF combined solutions – ZTD + gradients Figure: Monthly statistics for EUREF Repro2 combined solution – ZTD Bias/Sdev • Pacione R, Araszkiewicz A, Brockmann E,Dousa J, EPN Repro2: A reference GNSS tropospheric dataset over Europe., (AMTD in revision), 2017

  4. EUREF Repro2 vs. ERA-Interim Figures: Geographical visualization of ZTD total Bias (left) and Sdev (right) for all stations Bias: from -8 to 8 mm, prevailing a long-term negative value -2 mm (not understood yet) Sdev:from 5to 18 mm, strong latitudinal and seasonal dependency

  5. Improvement of EUREF Repro2/Repro1 Reference: ERA-Interim reanalysis (1996-2014), 6-hourly sampling (00, 06, 12, 18h) Figure 1: Distribution of total ZTD Bias (left) and Sdev (right) for all stations Figure 2: Distribution of total ZTD Bias/Sdev/RMS improvements for all stations degradation improvement

  6. GOP 2nd reprocessing: 7 variants • Repro2 improved repeatability of horizontal/vertical components by 50% and 25%, respectively • Low elevation angle cut-off demonstrates lower repeatability • Non-tidal atmospheric loading should be used with a priori ZHD • No effect of higher-order ionosphere effect or stacking tropo-gradients to 24 hours • DoušaJ, Václavovic P, The GOP troposphere product from the 2nd European re-processing (1996-2014), (AMTD in revision), 2017

  7. GOP Repro2: Troposphere • All results from coordinated repeatability assessments were confirmed by independent evaluation of troposphere products w.r.t. to ERA-Interim • Repro2 improved Repro1 by about 8-9% in tropospheric path delays • Low elevation angles shows improvements in both gradients & ZTDs • Stacking gradients from 6h to 24h improved tropo-coordinates decorrelations and stabilized the solutions

  8. Evaluation of GOP Repro2 gradients GO4 × GO6: tropospheric gradient modelling 6 × 24 hours Standard deviation Bias

  9. GOP Repro2: tropo horizontal gradients • GNSS tropospheric horizontal • gradients (GRD)were sensitive • to an asymmetry of GNSS signal • tracking at low-elevation angles • GRDs are compared to ERA-Interim NWM reanalysis • promising indicator for cleaning historical archive • Before • replacement • EPN CB: http://epncb.oma.be GOP reprocessing • Low elevation tracking degradation • After • replacement • Douša J, Václavovic P, The GOP troposphere product from the 2nd European re-processing (1996-2014), (AMTD in revision), 2017

  10. Monthly mean biases in N/E-gradients

  11. IGS Repro1/Repro2 comparisons • Reference: ERA-Interim reanalysis (1996-2014), 6-hourly sampling (00, 06, 12, 18h) • A small positive impact for CODE 3-day troposphere solution • Improvements of Repro2 (individual ACs) w.r.t. IGS Repro1 • GFZ after correcting gradient signs similar to CODE problem of opposed sign in horizontal gradients

  12. GFZ Repro2 – w.r.t. ERA-Interim Bias Sdev

  13. CODE Repro2 – w.r.t. ERA-Interim Bias Sdev

  14. Comparison of CODE global tropo products CODE Repro2 ZTD results: COD × COF period 1994-2013 vs. ERA-Interim  Assessment by ERA-Interim: positive results for CO2 (blue) positive results for CF2 (red)  Small differences in midnights (sdev 1-2mm) 14

  15. DevelopingTroposheric Ties • … approximations for correcting altitude differences in ZTD comparisons … • Δ ZHD(Teke et al., 2011) • Δ ZWD (Dousa and Elias, 2014) Vertical decay parameter β, γ estimated from ERA-Interim background data set ZWD vertical reduction assessment via global ERA-Interim NWM data • ZWD vertically approximated at different altitudes compared to integrated ZWDs • Table shows r.m.s. of ZWD differences [mm] at various altitudes Dousa J, Elias M (2014), An improved model for tropospheric wet delay, GRL 41

  16. GOPE (GNSS) vs Praha-Libus(Raobs) • continuous long-term operation • 6-hour temporal resolution • >260m vertical difference • >35km horizontal distance EUREF Repro2 vs. IGRA Corrections: 1. NONE 2. ZHD only 3. ZHD+ZWD

  17. GOPE (GNSS) vs Praha-Libus (Raobs)

  18. EUREF Repro2 vsRadiosonde (IGRA) GNSS repro vs. IGRA (Integrated Global Radiosonde Archive) Impact of tropospheric ties applied in GNSS vs. Radiosonde comparisons • No corrections applied • ZHD corrections applied • ZHD+ZWD corrections applied

  19. Parameter vertical scaling / tropo-ties

  20. Hopfield-revisited, 6thpower scaling • Hopfield (1967) derived the formula for the height dependence of the zenith hydrostatic refractivity N (hi) at height hi as a function of the refractivity at the surface N (hs), surface height and the equivalent height heq: • Leeuwen & Dousa (2016) studied an optimal power scaling of zenith dry and wet tropospheric delays Van Leeuwen S, DousaJ (2016), Hopfieldrevisited: Two-6thPowerTroposphericZenithDelayProfilesforCorrecting GNSS Data, In: Proceedingsofthe NAVITEC 2016, Dec 14-16, ESTEC, Noordwijk, Netherlands

  21. Assessment models for Tropospheric Ties January July

  22. GOPE (GNSS) vs Praha-Libus(Raobs) Dousa and Elias 2014 Exponential function Original fitting and model scale heights converted from original (no fitting) Revisited Hopfield power-function Tekeet al 2011 (ZHD+ZWD) equivalent heights converted from originalempirical from surface observations

  23. GOP-TropDB and IGS interactive web service Total statistics (over all period) for selected parameters http://www.pecny.cz/GOP-TropDB/TROPO-STAT/STAT_ERA.IGS.html

  24. GOP-TropDB and IGS interactive web service Total statistics (over all period) for selected parameters http://www.pecny.cz/GOP-TropDB/TROPO-STAT/STAT_RAO.ALL.html

  25. GOP-TropDB and IGS interactive web service Comparison metadata inventory http://www.pecny.cz/GOP-TropDB/TROPO-INFO/INFO_ALL.html

  26. GOP-TropDB, comparison of tropo parameters Monthly statistics: time-series visualisation and combination http://www.pecny.cz/GOP-TropDB/TROPO-STAT/STAT_ERA.EUR.html

  27. GOP-TropDB – interactive web service Monthly statistics: time-series visualisation and combination http://www.pecny.cz/GOP-TropDB/TROPO-STAT/STAT_ERA.GOP.html

  28. GOP-TropDB – online service http://www.pecny.cz

  29. Thank you for your attention Acknowledgements: • IGS and EUREF for GNSS data, products and models • USNO for IGS final tropospheric product • ASI for EUREF combined product • CODE and GFZfor IGS AC’s Global 2nd reprocessing tropospheric products • ASI, MUT, LPT, IGN for European 2ndreprocessing tropospheric products • ECMWF for ERA-Interim re-analysis • For IGRA radiosonde dataset • GFZ for VLBI solution • CHMI for data/models provided for GNSS4SWEC WG1 Benchmark campaign Ministry of Education, Youth and Science of the Czech Republic for the support for some GOP contributions to COST ES1206 Actions (LD14102) Ministry of Education, Youth and Science of the Czech Republic for financial support for Czech-US bilateral co-operation (LH14089) 29

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