gps data during sop1 & sop2 (d4b2) olivier bock, lareg ign pierre bosser, ensg ign contributions...
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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
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• 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 P
g
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
T
kkR
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