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GPS data during SOP1 & SOP2(D4B2)

Olivier Bock, LAREG IGNPierre 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

IODAMED meeting, 16 May 2014

IODAMED meeting, 16 May 2014

IODAMED meeting, 16 May 2014 2

• 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

Outline

IODAMED meeting, 16 May 2014

E-GVAPEUMETNET 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 2012

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ZTD GPS data inputAROME - France

10 000 values per 3h

15 GPS ACs with different sofware and processing procedures => ZTD dataset isinhomogeneous

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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

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sedoo.frHymex database

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Comparison of NRT ZTD data at common sitesASI – SGN, 44 common sites, different software

Mean = -3 ± 5 mm Std. = 7 mm

IGE – SGN, 50 common sites, same software

Mean = 0 ± 2 mm Std. = 7 mm

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Reprocessed networkEGVAP REPRO

773 stations(3 Analysis Centres)

970 stations(2 ACs, 21 networks)

Sardinia

HYMEX_DE

HYMEX_FR

Orphéon

15 networks

IGESGN

ASI

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Reprocessing by IGN/LAREG, FranceNetwork: 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, ItalyNetwork: - Italy: ASI1 + new stations (Sardinia) = 147 sitesProcessing:- Idem repro_LAREG

Reprocessed networkHomogenous reprocessing of 970 sites for

period 1 Sep 2012 – 31 Mar 2013

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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

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Screening of ZTD data

1st stepAnalysis of formal error for ZTD, station height, and other processing output information

1 – 99 percentiles of ZTD formal error

2nd stepComparison of GPS ZTD data to ZTD data from a NWP model, rejection of data at ± 3

BeforeAfter

mean

Std.dev.

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Conversion of ZTD to IWV

6110 d

m

RZHD k Pg

accurate to 0.06%

accurate to 0.006%

Surface pressure or NWP Analysisaccurate to 0.1-1 hPa

(0.01-0.1%)

accurate to 10-3 m s-2 (0.01%)

accurate to 2.4 %

accurate to ±3 %but k’2 = 0.047 * k3/Tm

Empirical model Tm = f(Ts) or NWP AnalysisTm = 250 ± 20 K (8% variations)

)(10

3'2

6

ZHDZTD

TkkR

IWV

mv

Principle: IWV=K(Tm)* ( ZTD – ZHD ) Requires auxiliairy data

GPS IWV uncertainty:bias ≈ 0.2-0.8 kg/m2

random ≈ 0.2-1.5 kg/m2

ZTD uncertainty + ZHD uncertainty + K(Tm) uncertainty

4-6 mm (IGS solution)

0.6-0.9 kg/m2

1 mm (0.06% k1 error)+ 1-2 mm (0.5-1 hPa Ps measurement error)+ 1-2 mm (interpolation error)

0.3-0.5 kg/m2

1-2% (k2 & k3 error)+ 1-2% (Tm error < 5K)

0.1-1.1 kg/m2

IWV=5 kg/m2 IWV=40 kg/m2

Uncertainty budget of GPS IWV

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Comparison of GPS IWV to AROME WMEDMean = 1.5 kg m-2

Std.= 1.5 kg m-2

Slope = 0.96

Correl = 0.92

16 networks, 1 month (Sep 2012)Auxiliairy data for IWV conversion: AROME WMED (surf + T) + emp. model Tm =f(Ts)

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• 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)

Next steps