# Presentation: 085262

## E-GVAP: EUMETNET GPS Water Vapour Programme

***Galina Dick (1) and ******Jan Dou******s******a (******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.

**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  

***Main product: ZTD/IWV ***
***of ~ 800 European sites in NRT***

***Product delay: < 1h 45 min***

***   ******Goal: ******prepare GPS derived ZTD/IWV for operational meteorological use ***

***UK Met******Office****** and Meteo France ******uses NRT ZTDs in their operational forecasts***

*** *****  *****Hourly transfer to UK Met ftp-server***

***Using for assimilation into NWP models***

***      ******IWV  Maps***

## E-GVAP Members 

**Contact and information points**
- Email address: _[egvap@dmi.dk](mailto:egvap@dmi.dk)_
- Web address: _[http://egvap.dmi.dk](http://egvap.dmi.dk/)_

**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**

## NRT Data Flow in E-GVAP 

***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 Met****Office****).**

## 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. 

- 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

**GFZ  ****(****~220**** sites)****:**
**Germany + EUREF**

**NGAA  ****(****~360**** sites)****:**
**Sweden, Denmark,**
**Finnland, Norway**

**E-GVAP  ****(****~800**** sites)**

**Notes:**

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***

***GFZ NRT Processing Scheme***

## IWV Monitoring (Web Page of GFZ)

***Comparison to ***
***COSMO-DE****** of****** German Weather Service (DWD)***

***Animation ******(selected  time interval)***

***Time series (last 2 or 7 days)***

***IWV****** Monitoring (Web Page ******of ******GFZ)***

## Validation: Web Page E-GVAP (1)

***Validation: ******Web Page ******E-GVAP (1******)***

***A feedback for ACs****** -****** ******Validation****** ******with****** ******HIRLAM****** ******model for each AC: Bias***

***Example GOP***** **

## Validation: Web Page E-GVAP (2)

***Validation: ******Web Page ******E-GVAP (2******)***

***A feedback for ACs****** -****** ******Validation****** ******with****** ******HIRLAM****** ******model for each AC: StdDev***

***Example GOP***** **

## PPP performance (GFZ, 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.

- 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.

***PPP performance (Example NGAA)***

## 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

*Temperature RMS Diff.*

*Wind Speed RMS Diff.*

*Pressure (hPa)*

*Forecast lead time (hours)*

*Pressure (hPa)*

*Forecast lead time (hours)*

- 23 forecasts
- June-July 2005
- Verification : radiosonde
- measurements

**BLUE=better****RED=worse**

- Without GPS ZTD data

-  WithGPS ZTD data

***Impact over Europe (Results of Meteo France, P.Poli et al.)***

***Impact of ground-based GPS measurements on forecasts***

## 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**