© crown copyright met office gps water vapour in the uk and the e-gvap project jonathan jones,...

© Crown copyright Met Office

GPS Water Vapour in the UK and the E-GVAP Project Jonathan Jones, Upper Air Team, Observations R&D, UK Met [email protected]


Contents

• How and Why

• Operational Processing System

• Collaborative Networks

• Monitoring and Validation

• Forecaster Case Studies

• E-GVAP

• Future GPSWV Developments


GNSS Constellations

Signal is ‘delayed’ by atmosphere. May remove ionospheric contribution due to dispersive nature of medium- GPS operates at dual frequency.

Signal is ‘delayed’ by atmosphere. Can remove ionospheric contribution due to dispersive nature of medium - GPS operates at dual frequency.


Technique

• Too much error in individual slant delay to resolve so we can use mapping function to we can convert into a Zenith Total Delay (ZTD)

• ZTD a combination of dry and wet delays

• From knowledge of surface pressure and temperature we can calculate dry component and resolve vertical Integrated Water Vapour quantity

• 1kg/m2 IWV = ~3-5% RH

•Dispersive, use dual GPS frequencies to resolve

Neutral Atmosphere

Non-dispersive (troposphere + stratosphere)

Non-Neutral Atmosphere (Ionosphere)


Customers

• NWP

• Shown up to 4% reduction of StdDev by assimilation of GPS ZTD data

• Forecasters

• Produce IWV field plots to assist forecasters in identifying atmospheric features/phenomena

• Climate

• Also GPS is potentially a useful tool for climate monitoring but reprocessing is necessary to ensure common processing models/standards

• Validation

• Very useful tool for validation of other remote sensing instruments (radiosonde, WVR, satellite WV etc)


Cost-Effective GPS Processing

• IESSG, Nottingham University contracted to develop and deliver operational processing servers

• Intergovernmental resource sharing agreements with mapping agencies in UK

• Agreement in place between EUREF and EUMETNET guaranteeing long term future GPS data access to Met community. Also providing positioning community with meteorological parameters


GPS Processing at METO

• 4 Servers

• 2 operational in Met Office IT halls, 1 mirror semi-operational server at IESSG, 1 development server at IESSG

• Hourly Processing Solution

• Bernese v5.0 processing software

• Double Difference Network Approach

• 30-Day sliding window PPP a-priori coordinate

• Absolute Antenna Phase Centres, IGS05 and FES2004

• Process network of ~250 stations in NRT in ~30mins

• ZTD/IWV estimates at 00, 15, 30, 45 and 59 mins


Data Providers

• 162 EUREF Sites

• 104 OSGB sites

• 86 64 RGP sites

• 20 UK scientific sites (incl. 11 Met Office)

• 19 OSi and OSNI sites

• 2 Icelandic sites

• Attempted hourly ~ 400

• Downloaded hourly ~ 275


European NRT GPS Network

http://www.knmi.nl/samenw/egvap/validation/europe.html


• ASCII files copied to E-GVAP server for dissemination and conversion to BUFR

• BUFR files then put on GTS for assimilation by National Met Services

• Plots also copied to E-GVAP server for dissemination

• Plots downloaded by E-GVAP and displayed on E-GVAP website

METO Products


RS vs. GPS Validation

IWV Comparison Camborne Feb 2008

-10

-5

0

5

10

15

20

25

30

35

31-Jan 05-Feb 10-Feb 15-Feb 20-Feb 25-Feb 01-Mar

Time (Days)

IWV

(kgm

-2) RS92 TWE

GPS IWV

Diff


WVR vs. GPS Validation


NWP Monitoring

• Data QC’d by AC and gross error check vs. model

• Site specific bias corrections also applied


Case Studies

• 28th July 2005 – Offset Dry Tongue

• Dry tongue over south west not corresponding with satellite WV

• By combination of satellite and GPS WV you can infer vertical structure

• 24th June 2005 – Cold Pool Identification

• Trough progressing over southern UK from westerly direction with associated high IWV and convective thunderstorm cells

• GPS IWV identified cold pool behind front which perpetuated instability and convection


17.30

Drier Upper AirDrier Lower Air


E-GVAP and E-GVAP II

• E-GVAP I – EUMETNET programme to take GPSWV to operations in Europe

• Ensure common standards and formats in GNSS data processing

• European network expansion

• Assist ‘developing’ countries with GPS processing and assimilation techniques

• Ensure close collaboration with geodetic community (experts)

• E-GVAP II – continuation of E-GVAP I

• Connect to EUCOS and WIS

• Continued network expansion

• Improve homogeneity and quality of GNSS products


E-GVAP Website and Server

• Website v. useful tool for analysing data/biases etc

• Compiling table of all AC’s GPS processing techniques,

• Recently added Nordic and French regional plots

• E-GVAP Server to be transitioned to more operational (backed-up) server by end of E-GVAP 1

• Server now hosting met data for EUREF community

• Server soon to be hosting other data (microwave radiometer, NWP etc)


QC via the E-GVAP Website


E-GVAP ‘Supersites’

• 14 sites identified for validation of GPS IWV

• All sites have collocated instruments, geodetically stable, same model layer etc

• Probably will include EKOFISK site in near future

• Access to data from site at Inaza Observatory, Tenerife (GPS, RS, MWR, Infrared Spectrometer)


Future GPSWV Developments

• Improved NRT Plots

• Use NWP IWV over data sparse areas (Sea)

• Produce O-B plots

• Add satellite WV to plots to give some vertical structure

• Real-Time GPS Processing (15min/5min)

• Slants/Tomography

• NWP ZTD forecasts


Questions and [email protected]

http://egvap.dmi.dk/

mailto:[email protected]




© crown copyright met office gps water vapour in the uk and the e-gvap project jonathan jones,...

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