1. E-GVAP: EUMETNET GPS Water Vapour Programme
Galina Dick (1) and Jan Dousa (2)
(1) GeoForschungsZentrum Potsdam, Germany
(2) Geodetic Observatory Pecny, Czech Republic
In collaboration with E-GVAP Team
IGS Analysis Center Workshop
Miami Beach, Florida, USA
2-6 June 2008

2. European Projects: COST, TOUGH, E-GVAP
COST-716 Action ( ):
"Exploitation of Ground-Based GPS for Operational Numerical Weather Prediction and Climate Applications“
15 Institutions
7 ACs
TOUGH ( ):
„Targeting Optimal Use of GPS Humidity Measurements in Meteorology“
15 Institutions (Coordinator DMI)
12 ACs
> 400 GPS sites
E-GVAP ( ):
„The EUMETNET GPS Water Vapor Programme“
13 Institutions
10 ACs
> 800 GPS sites
Operational E-GVAP Network

3. What is E-GVAP? EUMETNET GPS Water Vapour Programme
EUMETNET = organisation of European national meteorological offices (West European + number of East European, enlarging)
E-GVAP is a separate observing programme under EUMETNET, not all EUMETNET members are members of E-GVAP.

4. E-GVAP
Goal: prepare GPS derived ZTD/IWV for operational meteorological use
Main product: ZTD/IWV
of ~ 800 European sites in NRT
IWV Maps
Product delay: < 1h 45 min
Hourly transfer to UK Met ftp-server
Using for assimilation into NWP models
UK MetOffice and Meteo France uses NRT ZTDs in their operational forecasts

5. Email address: egvap@dmi.dk
E-GVAP Members
Danish Meteorological Institute (coordinator)
Finnish Meteorological Institute
Icelandic Meteorological Office
Irish Meteorological Service
Meteo Swiss
Norwegian Meteorological Institute
Royal Meteorological Institute of Belgium
Royal Meteorological Institute of the Netherlands
Spanish Meteorological Institute
Meteo France
Croatian Met Service
Swedish Meteorological and Hydrological Institute
UK Met Office
Contact and information points
address:
Web address:

6. NRT Data Flow in E-GVAP
BUFR
MetO
FTP
server
MetDB
GOPE
Czeck Rep.
IEEC
Spain
LPT(R)
Switzerland
METO UK
NRT Users
& mirror sites
ROB
Belgium
SGN
France
NGAA
Sweden
GFZ
Germany
Linux
Workstation
GTS Users
BKG
ASI
Italy
KNMI(1)
Netherlands
Green = nation member of E-GVAP. Blue = nation not member of E-GVAP.
(IGN, Spain is currently starting as a new producer of GNSS ZTD data)

7. Monitoring: Web Page E-GVAP
Timeliness is very important for meteorological forecasting.
Arrival statistics of NRT GPS ZTD data at dataserver (by Dave Offiler, UK MetOffice).

8. Inter comparison of ZTDs from different analysis centres processing the same site, comparison with respect to NWP and radiosonde data - helps to identify optimal processing methods and helps to reject poor data.
A set of 12 „supersites“ that all centres must processed has been introduced.

9. E-GVAP Processing Strategies
PPP approach:
GFZ (EPOS)
NGAA (GIPSY)
Network approach:
ASI (GIPSY)
BKG, GOP, KNMI, LTP, ROB, METO, SGN (Bernese)

10. Motivation for "Precise Point Positioning“ (PPP)
Comparison of different adjustment approaches
PPP
Network
Advantages
Small NEQ
Keeping CPU with increasing number of sites / parameters (e.g. ZTD every 15 min, estimation of gradients)
Investigations of site dependent effect
Correlations between
parameters of all stations are taken into account
Independence of external products (except for small networks)
Disadvantages
Correlations btw stations are ignored
Use of external products (orbits, clocks)
Large NEQ
Increasing CPU with incr. number of sites/parameters
==> Main reason for switching to PPP :
efficient operation of large networks (>100 sites) within short computation time
REQUIREMENT: GPS orbits & clocks should be given with sufficient accuracy

11. Networks used by PPP Analysis Centres
E-GVAP (~800 sites)
NGAA (~360 sites):
Sweden, Denmark,
Finnland, Norway
GFZ (~220 sites):
Germany + EUREF
USA: routine impact studies for several years now
Japan: no NRT, in preparation, interesting case studies with this very dense network
IGS global frame

12. GFZ NRT Processing Scheme
GFZ EPOS Software
Part 1 - Network orbit improvement:
Adjustment of precise orbits & clocks
Global network : ~20 IGS +German sites
Input orbits: GFZ 3h Ultra Rapid (pred.)
CPU (Linux PC): ~6 to 8 minutes
Part 2 - PPP Analysis:
Estimation of trop. parameters
Large set of parameters possible
(high sampling rate, trop. gradients)
NEW: ‚slant delays‘ estimation
CPU (Linux PC): <5 min for 220 sites .

13. IWV Monitoring (Web Page of GFZ)
Time series (last 2 or 7 days)
Animation (selected time interval)
Comparison to
COSMO-DE of German Weather Service (DWD)

14. Validation: Web Page E-GVAP (1)
A feedback for ACs - Validation with HIRLAM model for each AC: Bias
Example GOP
Example GFZ

15. Validation: Web Page E-GVAP (2)
A feedback for ACs - Validation with HIRLAM model for each AC: StdDev
Example GOP
Example GFZ

16. PPP performance (GFZ, NGAA)

17. PPP performance (Example NGAA)
Data drop-outs is decreasing due to new routines at network operational centers e.g. SWEPOS
Occasional (2-3 hours per week) bad ZTD values delivered to EGVAP (see figure).
The reason for these “hick-ups” are related to the orbit and clock analysis which sometimes fails due to data (global data) collection problems.

18. Comparison of different processing strategies
ZIMM – one of the 12 ‘supersites’

19. Validation with Radiosondes (example GFZ)
GPS derived ZTD compared to ZTD from RS for Lindenberg, March 2008

20. Validation with RS and WVR (example GOP)

21. Impact of ground-based GPS measurements on forecasts
Impact over Europe (Results of Meteo France, P.Poli et al.)
23 forecasts
June-July 2005
Verification : radiosonde
measurements
Temperature RMS Diff.
Wind Speed RMS Diff.
Pressure (hPa)
Pressure (hPa)
BLUE=better RED=worse
Forecast lead time (hours)
Forecast lead time (hours)
Without GPS ZTD data
With GPS ZTD data

22. E-GVAP and IGS
E-GVAP is very thankful for the services that IGS provides the geodetic community. They are vital to the NRT GPS ZTD product that we use in meteorology.
For weather forecasting the GPS ZTD data must be available fast, and of a quality which is both good and does not fluctuate strongly in time.
The timeliness issue is important and clearly influences ZTD data quality.

23. Conclusions/Recommendations
GPS derived ZTDs are used operationally in Europe
Due to steadily increasing number of operational GPS sites PPP strategy presents a promising outlook for future efficient GPS-meteorology. E-GVAP recommends IGS to support PPP strategy with high quality adequate products.
The 'real-time' clocks will be interesting future product for using in GPS meteorology.
For current needs E-GVAP encourages IGS to deliver clock products in ‘near-real’ time (hourly) till the ‘real-time’ IGS clocks will be available as products with sufficient quality