GPS data during SOP1 & SOP2 (D4B2) Olivier Bock, LAREG IGN Pierre Bosser, ENSG IGN Contributions from: -C. Champollion, E. Doerflinger (LDL) France -R. Pacione (E-GEOS/ASI) Italy -J. A. Sanchez Sobrino (IGN-E), A. Seco (UPN), A. Botas (Logica), C. Sanchez Tugores (Sitibsa), L. García Pellicer (ARAGEA), Spain -M. Vasconcelos (DGT), Portugal -J. Jones, D. Offiler (UKMO), UK 1 IODAMED meeting, 16 May 2014

The operational GPS network and ZTD data flow (EGVAP -> assimilation in NWP models) A reprocessed dataset for HYMEX SOP1+2 – Screening of ZTD data – Conversion of ZTD to IWV – Comparison of GPS IWV to AROME WMED Op An IODAMED meeting, 16 May Outline

E-GVAP EUMETNET EIG GPS Water Vapour Program Aim: use NRT GNSS ZTD for operational meteorology. EGVAP is a consortium of 13 National Weather Services working in close collaboration with 11 National Mapping Agencies. GNSS network is composed of public & private stations and counts ~ 1500 sites. GNSS rinex data are processed by 15 ACs in Near Real Time (NRT), i.e. latency < 1h45min. NRT ZTD disseminated by UMKO on the GTS (BUFR files) and assimilated in NWP models by UKMO, Meteo-France, DMI… May IODAMED meeting, 16 May 2014

4 ZTD GPS data input AROME - France values per 3h 15 GPS ACs with different sofware and processing procedures => ZTD dataset is inhomogeneous

IODAMED meeting, 16 May NRT_EGVAP_SGN (IGN/SGN, France) Network: - RGP (France) + reference stations (321 sites) Processing: -Bernese GPS software -Ultra-rapid IGS orbits, fixed positions, CO=10°, no gradients, ZTD values at HH+00, 15, 30, 45, 59’ NRT_EGVAP_IGE (IGN, Spain) Network: - Spain + Portugal + reference stations (288 sites) Processing: -Bernese GPS software -Ultra-rapid IGS orbits, ZTD values: HH+00, 15, 30, 45, 59’ NRT_EGVAP_ASI + NRT_EGVAP_ASI1 (E-GEOS/ASI, Italy) Network: - Italy + reference stations (164 sites) Processing: -GIPSY-OASIS II software -Ultra-rapid JPL orbits, fixed positions, ZTD values HH+00, 15, 30, 45’ NRT ZTD data archived on hymex DB

IODAMED meeting, 16 May sedoo.fr Hymex database

IODAMED meeting, 16 May Comparison of NRT ZTD data at common sites ASI – SGN, 44 common sites, different software Mean = -3 ± 5 mmStd. = 7 mm IGE – SGN, 50 common sites, same software Mean = 0 ± 2 mm Std. = 7 mm

IODAMED meeting, 16 May Reprocessed network EGVAP REPRO 773 stations (3 Analysis Centres) 970 stations (2 ACs, 21 networks) Sardinia HYMEX_DE HYMEX_FR Orphéon 15 networks IGE SGN ASI

IODAMED meeting, 16 May Reprocessing by IGN/LAREG, France Network: 823 sites -France : RGP (349 sites) + Orphéon (182 sites) -Temporary sites : Cévennes (8 sites, Géosci. Montpellier) and Corsica (5 sites, GFZ) -Spain: 14 regions (231 sites) + IGE national network (37 sites) -Portugal: RENEP (43 sites) -North Africa: UNAVCO (5 sites) Processing: -GIPSY-OASIS II software -Final JPL orbits & clocks, ZTD + gradients every 5’, VMF1, 30 h session Reprocessing by e-GEOS/ASI, Italy Network: -Italy: ASI1 + new stations (Sardinia) = 147 sites Processing: -Idem repro_LAREG Reprocessed network Homogenous reprocessing of 970 sites for period 1 Sep 2012 – 31 Mar 2013

IODAMED meeting, 16 May Comparison of NRT to post-proc. data Mean = 0.5 ± 3 mm Std. = 8 mm Mean = -0.1 ± 2 mm Std. = 6 mm Mean = 0.8 ± 2 mm Std. = 4 mm IGE SGN ASI

IODAMED meeting, 16 May Screening of ZTD data 1st step Analysis of formal error for ZTD, station height, and other processing output information 1 – 99 percentiles of ZTD formal error 2nd step Comparison of GPS ZTD data to ZTD data from a NWP model, rejection of data at ± 3  Before After mean Std.dev.

IODAMED meeting, 16 May Conversion of ZTD to IWV accurate to 0.06% accurate to 0.006% Surface pressure or NWP Analysis accurate to hPa ( %) accurate to m s- 2 (0.01%) accurate to 2.4 % accurate to ±3 % but k’ 2 = * k 3 /T m Empirical model Tm = f(Ts) or NWP Analysis T m = 250 ± 20 K (8% variations) Principle: IWV=K(T m )* ( ZTD – ZHD ) Requires auxiliairy data

GPS IWV uncertainty: bias ≈ kg/m 2 random ≈ kg/m 2 ZTD uncertainty + ZHD uncertainty + K(T m ) uncertainty 4-6 mm (IGS solution) kg/m 2 1 mm (0.06% k 1 error) mm (0.5-1 hPa Ps measurement error) mm (interpolation error) kg/m 2 1-2% (k 2 & k 3 error) + 1-2% (T m error < 5K) kg/m 2 IWV=5 kg/m 2 IWV=40 kg/m 2 Uncertainty budget of GPS IWV

IODAMED meeting, 16 May Comparison of GPS IWV to AROME WMED Mean = 1.5 kg m -2 Std.= 1.5 kg m -2 Slope = 0.96 Correl = networks, 1 month (Sep 2012) Auxiliairy data for IWV conversion: AROME WMED (surf + T) + emp. model Tm =f(Ts)

Finalise validation of reprocessed GPS ZTD dataset – ZTD data screening (improve method, 1st step) – ZTD to IWV conversion (assess auxiliairay datasets) – Validate GPS IWV data by comparison with other data (MWR…) Assimilation of reprocessed GPS ZTD data – AROME WMED reanalysis Prepare data (BUFR files) and assimilation system Test impact of assimilation, case studies – Assimilation in research models Monitoring of radiosonde humidity biases Validation of simulations (case studies) Process studies (HPE) IODAMED meeting, 16 May Next steps