1. Validation of slant delays acquired by different techniques within GNSS4SWEC Benchmark campaign Current status
M. Kačmařík, J. Douša, G. Dick, F. Zus, H. Brenot, E. Pottiaux,
G. Möller, P. Václavovic, L. Morel, W. Rohm, P. Hordyniec
GNSS4SWEC 3rd Workshop, Reykjavik, March , 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:
Solution
Institution
Strategy
Software
GNSS
El. cut-off
Mapping function
Products
ZTD / gradients interval
Post-fit residuals
CNAM
Le CNAM DD
Gamit
GPS
3 °
VMF1
IGS
1h / 1h NO
GFZ
GFZ Potsdam
PPP
EPOS 8
7 °
GMF
15 min / 1h
YES and NO
GOP_F
GO Pecny
PPP, forward filter
G-Nut/Tefnut
IGS final
2.5 min / 2.5 min
YES
GOP_S
PPP, back-ward smoothing
ROB_G
ROB
Bernese 5.2
GPS+GLO
CODE final
ROB_V
TUO
1h / 3h
TUW
TU Wien
Napeos
30 min / 1h

5. Sources of STDs for validation
NWM raytracing:
PMF software (GFZ) using fields from global ERA INTERIM and global NCEP GFS model (Florian Zus, GFZ)
WUELS software using fields from ??? (P. Hordyniec and W. Rohm, WUELS)
BIRA software using fields from regional Aladin-CZ model (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: GNSS vs. WVR:
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)
bias between 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 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 main topics:
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:
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 behaviour of 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 Hugues Brenot (see his presentation in Reykjavik)
Coordinator: Hugues Brenot
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