© 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 Office

© Crown copyright Met Office Contents How and Why Operational Processing System Collaborative Networks Monitoring and Validation Forecaster Case Studies E-GVAP Future GPSWV Developments

© Crown copyright Met Office 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.

© Crown copyright Met Office 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/m 2 IWV = ~3-5% RH Dispersive, use dual GPS frequencies to resolve Neutral Atmosphere Non-dispersive (troposphere + stratosphere) Non-Neutral Atmosphere (Ionosphere)

© Crown copyright Met Office 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)

© Crown copyright Met Office 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

© Crown copyright Met Office 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

© Crown copyright Met Office Data Providers 162 EUREF Sites 104 OSGB sites RGP sites 20 UK scientific sites (incl. 11 Met Office) 19 OSi and OSNI sites 2 Icelandic sites Attempted hourly ~ 400 Downloaded hourly ~ 275

© Crown copyright Met Office European NRT GPS Network

© Crown copyright Met Office 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

© Crown copyright Met Office RS vs. GPS Validation

© Crown copyright Met Office WVR vs. GPS Validation

© Crown copyright Met Office NWP Monitoring Data QC’d by AC and gross error check vs. model Site specific bias corrections also applied

© Crown copyright Met Office Case Studies 28 th 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 24 th 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

© Crown copyright Met Office Drier Upper AirDrier Lower Air

© Crown copyright Met Office

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

© Crown copyright Met Office 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)

© Crown copyright Met Office QC via the E-GVAP Website

© Crown copyright Met Office 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)

© Crown copyright Met Office 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

© Crown copyright Met Office Questions and answers