Validation of Slant Delays Acquired by Different Techniques within GNSS4SWEC Benchmark Campaign

1. Validation of slant delays acquired by different techniques within GNSS4SWEC Benchmark campaignCurrent status M. Kačmařík, J. Douša, G. Dick, F. Zus, H. Brenot, E. Pottiaux, G. Möller, P. Václavovic, L. Morel, W. Rohm, P. Hordyniec GNSS4SWEC3rd Workshop, Reykjavik, March 8 - 10,2016

2. Enjoy your stay in Iceland!

3. Slant Delays - introduction • Slant delay represents an influence of neutral atmosphere on GNSS signal in the AZI/ELE of signal • STD = SHD + SWD Slant total delay = slant hydrostatic delay + slant wet delay • STD = ZHD*mfH + ZWD*mfW + mfG*( GN*cos(A) + GE*sin(A) ) + res – mpt • ZHD = zenith hydrostatic delay • ZWD = zenith wet delay • mfH, mfW, mfG = mapping function for dry part of delay, wet part, horizontal gradients • GN, GE = horizontal gradient for north-south, east-west direction • A = azimuth angle of observation • res= post-fit residual • mpt = multipath • SIWV (Slant Integrated Water Vapour) = k * SWD

4. Sources of STDs for validation • GNSS solutions:

5. Sources of STDs for validation • NWM raytracing: • PMF software (GFZ) using fields from global ERA INTERIMand globalNCEP GFS model (Florian Zus, GFZ) • WUELS software using fields from ??? (P. Hordyniec and W. Rohm, WUELS) • BIRA software using fields from regional Aladin-CZmodel (H. Brenot), STDs were not delivered yet for the validation • Water Vapour Radiometer (WVR) – station POTM/POTS

6. Selected stations • POTS + POTM • GOPE • LDB2 + LDB0 • WTZR + WTZS + WTZZ • KIBG • SAAL

7. Validation results – single stations • results for whole Benchmark period = 56 days • all result statistics in mm • noR version = residuals were not used in STD computation • GNSS x GNSS = GFZ solution used as a reference solution • zenith direction = all STD were mapped back to the zenith using simple 1/sin(elevation)

8. POTS GNSS vs. GNSS zenith

9. POTS GNSS vs. NWM zenith

10. POTS GNSS vs. WVR zenith

11. POTS, GNSS vs. GNSS, slant

12. POTS GNSS vs. NWM slant

13. POTS, GNSS vs. WVR, slant

14. GOPE LDB2 GNSS vs. GNSS zenith WTZR WTZZ

15. GNSS vs. NWM ERA zenith GOPE LDB2 WTZR WTZZ

16. Basic summary • GNSS vs. GNSS: • all solutions (except GOP_F) are in a very good agreement, however, GOP_F was included for specific assessment of real-time capable technique (forward Kalman filter only) • biasbetween GFZ and other solutions is usually below 2-3 mm in zenith direction (except station POTM where GFZ solution has some problem) • SDEV between GFZ and other solutions is typically between 4 and 6 mm in zenith direction (except GOP_F) while SDEV between GFZ and GFZ_noR around 3-4 mm • fractional SDEV stays almost stable with increasing elevation angle (not showed) • GNSS vs. WVR: • WVR has a positive bias around 6 mm vs. GNSS in zenith direction • SDEV values are a little bit higher than for GNSS x GNSS comparison at all elevations, especially at the lower ones • all GNSS solutions perform very similarly in terms of bias and SDEV (except for GOP_F being a little bit worse in SDEV) • all GNSS solutions without residuals (noR) perform slightly better than their versions including residuals

17. Basic summary • GNSS vs. NWM: • NWM_GFS has a bias of approximately 5 mm versus NWM_ERA in zenith direction • in terms of standard deviation the agreement between NWM_ERA and NWM_GFS is similar to agreement between NWM_XXX and all GNSS solutions • all GNSS solution perform very similarly (GOP_F is not visibly worse) • all GNSS solutions without residuals (noR) perform slightly better than their versions including residuals • NWM_WUELS solution has a significant problem (bias around 160 – 200 mm in zenith direction and standard deviation around 20 - 30 mm when compared to GNSS/NWM_ERA/NWM_GFS solutions), WUELS is working on problem elimination, results not shown in the presentation

18. Validation results – dual stations • dual stations are supposed to deliver identical/similar slants • results for whole Benchmark period = 56 days • all result statistics in mm • noR version = residuals were not used in STD computation • zenith direction = all STD were mapped back to the zenith using simple 1/sin(elevation)

19. TUW LDB0 x LDB2 GNSS vs. GNSS zenith GFZ GOP_F GOP_S

20. Paper in a preparation • M. Kačmařík, J. Douša, G. Dick, F. Zus, H. Brenot, E. Pottiaux, G. Möller, P. Václavovic, L. Morel, W. Rohm, P. Hordyniec, Validation of slant total delays from different techniques, GNSS4SWEC Special Issue • main topics: • comparison of STDs from different techniques (GNSS, NWM, WVR) for 10 stations and whole Benchmark period • evaluation of quality of GNSS STDs • evaluation of differences in GNSS STDs obtained by different software/strategies • assessment of influence of post-fit residuals on quality of GNSS STDs = using results from dual stations, comparison of GNSS vs. NWM/WVR. Call attention to the problematic information about state of the troposphere stored in residuals.

21. Extended activities (future) • Purpose - deepen the basic study • if work on any of proposed topic is done before the submission of the paper (summer 2016), it can be included in it • Google document: https://docs.google.com/document/d/1oK-2JT5E4QSoaeBXd4MxvrXsSp81Y2uB7grhkL_axvg/edit# • please join!

22. Extended activities (future) • Detailed study of GNSS post-fit residuals • Topics, thoughts: • eliminate multipath/azimuth dependent influence from residuals • ??? • Coordinator: ??? • Participant: Michal Kacmarik

23. Extended activities (future) • Detailed study of GNSS post-fit residuals • Topics, thoughts: • eliminate multipath/azimuth dependent influence from residuals • evaluate azimuth-dependency of GNSS post-fit residuals (there might a significant effect of GNSS post-fit residuals in comparison to NWM or WVR data) • ??? • Coordinator: ??? • Participant: Michal Kacmarik

24. Extended activities (future) • STD validation of specific weather events during Benchmark period Topics, thoughts: • take a closer look on a selected severe/calm weather events and evaluate behaviourof STD during those specific periods • all validation is already done at the level of individual days so it is mainly only a matter of time to work ready results • Coordinator: ??? • Participant: Michal Kacmarik

25. Extended activities (future) • Improvement of delays and gradients from NWM ray-tracing Topics, thoughts: • New methodology for NWM-raytracing of HuguesBrenot (see his presentation in Reykjavik) • Coordinator: HuguesBrenot • Participant:

26. Extended activities (future) • Evaluation of GNSS processing settings on quality of STDs Topics, thoughts: • quantify influence of GNSS processing parameters on ZTD/gradients/post-fit residuals (time interval of ZTD/gradient estimation, time interval of observations, mapping function, cut-off angle, etc.) • Coordinator: • Participant: Michal Kacmarik