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

European Projects: COST, TOUGH, E-GVAP COST-716 Action (1998-2003): "Exploitation of Ground-Based GPS for Operational Numerical Weather Prediction and Climate Applications“ 15 Institutions 7 ACs TOUGH (2003-2006): „Targeting Optimal Use of GPS Humidity Measurements in Meteorology“ 15 Institutions (Coordinator DMI) 12 ACs > 400 GPS sites E-GVAP (2006 - 2009): „The EUMETNET GPS Water Vapor Programme“ 13 Institutions 10 ACs > 800 GPS sites Operational E-GVAP Network

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.

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

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 Email address: egvap@dmi.dk Web address: http://egvap.dmi.dk

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)

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).

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.

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

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

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

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 .

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)

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

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

PPP performance (GFZ, NGAA)

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.

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

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

Validation with RS and WVR (example GOP)

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

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.

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