1. 27th IUGG General Assembly July 8-18, 2019 Montreal, Canada
Comparing atmospheric data and models at station Wettzell during CONT17
Daniel Landskron1, Johannes Böhm1, Thomas Klügel2, Torben Schüler2
1 Technische Universität Wien, Austria
2 Federal Agency for Cartography and Geodesy, Geodetic Observatory Wettzell, Germany

2. Overview (1)
Comparison between a variety of atmospheric datasets over station WETTZELL, Germany between Nov 28 and Dec 12, 2017
In situ pressure data
Radiosonde data
Numerical weather model data
GNSS estimates
VLBI estimates
Water vapor radiometer data
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

3. Overview (2) zhd: zenith hydrostatic delay in situ, NWM, Radiosonde
zwd: zenith wet delay Radiosonde, NWM, GNSS, VLBI, WVR
shd + swd: slant delay hydrostatic + wet Radiosonde, NWM (VMF3+VMF1)
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

4. Mapping function from radiosonde data?
All TU Wien troposphere mapping functions (VMF3, VMF1, GPT3, GMF) are based on ray-tracing through NWM data
Mapping functions can likewise be determined from radiosonde data
NWM
Radiosonde
mfh + mfw
globally
mfh + mfw
locally
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

5. Mapping function from radiosonde data!
Dense 2D model of atmosphere above the station
Densified through interpolation
1D ray-tracing yields zhd, zwd, mfh and mfw
b and c coefficients from VMF3 => a coefficients
Local mapping function from radiosonde data
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

6. Pre-comparison steps
All data reduced to hell = 666 m dh = 8 m ≈ dp = 1 hPa ≈ dzhd = 2.5 mm
Different temporal resolutions:
In situ: every minute
Radiosonde: twice daily at ~08:00 and ~14:00
NWM: six-hourly
GNSS: hourly
VLBI: hourly
WVR: every minute
Interpolation
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

7. Results: Zenith Hydrostatic Delay
Δzhd w.r.t. in situ
[mm]
Bias σ
VMF3
-3.0
1.8
VMF1
-0.7
1.7
NCEP
-0.4
0.9 RS
=> All solutions show very good agreement
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

8. Results: Zenith Wet Delay (1)
Δzwd w.r.t. Radiosonde
[mm]
Bias σ
VMF3
-0.8
5.4
VMF1
0.5
5.5
NCEP
-5.0
4.1
GNSS
-1.6
4.2
WVR
-6.2
12.2
VLBI
2.3
=> Generally very good agreement, except for outliers in WVR data
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

9. Results: Zenith Wet Delay (2)
Δzwd w.r.t. Radiosonde
[mm]
Bias σ
GNSSBKG
-1.6
4.2
GNSSWETT
-6.3
5.2
VLBI
2.3
4.1
=> Estimations from GNSS and VLBI are very similar
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

10. Results: Slant Hydrostatic Delay at 5°
Δshd w.r.t. Radiosonde
[mm]
Bias σ
VMF3
-27.5
18.5
VMF1
-3.3
18.1
Zenith delays from Radiosonde:
[mm]
Bias σ
VMF3
-0.5
5.5
VMF1
0.2
4.8
=> Again very good agreement, but VMF1 has smaller bias than VMF3
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

11. Results: Slant Wet Delay at 5°
Δswd w.r.t. Radiosonde
[mm]
Bias σ
VMF3
-9.0
58.3
VMF1
4.7
58.9
Zenith delays from Radiosonde:
[mm]
Bias σ
VMF3
-0.3
4.7
VMF1
1.1
1.4
=> Worse agreement, but not surprising for the slant wet delay
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

12. What limits the accuracy
Radiosondes do not ascend vertically
Radiosonde profiles only 2D
Radiosondes ascend for up to 90 min before they burst, but integrated value valid for launch time
Height reductions
Temporal interpolations with few sample values
Outliers in WVR data
=> Results are absolutely pleasant, sub-mm not necessary!
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)

13. And finally…
Feel free to use this extensive meteorological dataset by the Geodetic Observatory WETTZELL:
2019/07/ Comparing atmospheric data and models at station Wettzell during CONT17 (Landskron et al., 2019)