Jan DouJan DoušašaEUREF Analysis Centre WorkshopEUREF Analysis Centre Workshop

MarchMarch 15-1615-16, 200, 20066

Characteristics of Characteristics of GPS ZTD productsGPS ZTD products

EUREF AC Workshop, March 15-16, 2006, Padua, Italy 2

OutlineOutline

ZTD and PWV productsZTD and PWV products evaluation

Stragegy changesStragegy changes evaluation

Hr Hr ×× DoY plots DoY plots GPS constellation effect solution characteristics ZTD differences (NRT products, IGS & EUR products)

Spectral analysisSpectral analysis ZTD differences

SummarySummary

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ZTD/PWV products usedZTD/PWV products used

Zenith total delay (ZTD)Zenith total delay (ZTD) NRT GPS products: COST-716/TOUGH: NRT GPS products: COST-716/TOUGH:

(ASI,ACRI,BKG,GFZ,GOP,IEEC,LPT,NKG,NKGS)(ASI,ACRI,BKG,GFZ,GOP,IEEC,LPT,NKG,NKGS) PP GPS products: GOP, EUR@BKG, IGS@JPLPP GPS products: GOP, EUR@BKG, IGS@JPL ZTD from numerical weather model HIRLAM@DMIZTD from numerical weather model HIRLAM@DMI

Precipitable Water Vapor (PWV)Precipitable Water Vapor (PWV) PWV converted at KNMI from COST-716/TOUGH ACs’ PWV converted at KNMI from COST-716/TOUGH ACs’

ZTDZTD PWV calculated at GOP from radiosonde profiles provided PWV calculated at GOP from radiosonde profiles provided

by British Atmospheric Data Centreby British Atmospheric Data Centre PWV calculated at University of WyomingPWV calculated at University of Wyoming

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ZTD comparisonsZTD comparisons2001-2003 comparison2001-2003 comparisonNRT x post-processingNRT x post-processing

1/4 of 2005 comparison1/4 of 2005 comparisonold NRT x new NRTold NRT x new NRT

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- radiosondes from British Atmospheric Data centre (reduced profiles)- PWV converted from GPS by KNMI (the Netherlands)- ! often strong seasonal variation in the systematic error (1-3mm) !! often strong seasonal variation in the systematic error (1-3mm) !

directly collocated sitesdirectly collocated sites remote comparisonremote comparison

PWV evaluation – GPS PWV evaluation – GPS ×× radiosondes radiosondes

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- UW = PWV produced by University of Wyoming- GOP/BADC = PWV produced by GOP using data from BADC (reduced profiles)- approx 0.5mm PWV systematic error in the values- full profiles from UW, but cutted to the attitude of GPS from GOP/BADC

GPS-Raobs height diff = +247m

GPS-Raobs height diff = +475m

GPS-Raobs height diff = 0m

GPS-Raobs height diff = 0m

PWV comparison – UW PWV comparison – UW ×× GOP/BADC radobs GOP/BADC radobs

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ZTD ZTD differencesdifferences – NRT GOP – NRT GOP ×× HIRLAM (NWP)HIRLAM (NWP)

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- weekly Sdev and Bias- GPS ZTD from GOP near real-time - NWM Hirlam from DMI

also seasonal variation in offset

ZTD comparison – NRT GOP ZTD comparison – NRT GOP ×× HIRLAM (NWP) HIRLAM (NWP)

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- GPS ZTD from GOP near real-time - NWM HIRLAM from DMI! based on 2,5 years of comparison !

daily variation (6-hour periods ?)coincides with HIRLAM update cycle

Bias

Std.dev.

ZTD ZTD ’hourly’ ’hourly’ comparison comparison GPS GPS ×× HIRLAM (NWP) HIRLAM (NWP)

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• While switching from Bernese V4.2 to Bernese V5.0, in May 2005 we have created completely new system for routine analysis uniquely implemented for NRT and post-processing analysis

• Solution is clustered at most of the processing steps (80 stations takes 20min in NRT on standard PC)

• Improved NRT coordinate estimation (stacking over last 28 days using two-hour solutions/NEQs)

• Ambiguity resolved in 2-hourly sessions – used in CRD estimation

• Ambiguity fixed solution provided as an alternative ZTD product

• New troposphere modelling (piece-wise linear, continuous) using a priori ZTD with hNMF and corrected with wNMF.

From BSW 4.2 to BSW 5.0From BSW 4.2 to BSW 5.0

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BSW 4.2 and BSW 5.0 tropospheric modelBSW 4.2 and BSW 5.0 tropospheric model

time&site variable new tropospheric model to the old one 0-5mmtime&site variable new tropospheric model to the old one 0-5mm

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hour-to-hour coordinate repeatabilities improved from 10/25/25 10/25/25 mmmm to 6/6/16 mm6/6/16 mm (North/East/Up) by ambiguity resolving

Coordinate repeatability in NRTCoordinate repeatability in NRT(amb-free (amb-free ×× ambig-fix solution) ambig-fix solution)

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DDistributionistributionss of of NRT NRT ZTD ZTD ×× PP ZTD, @GOP PP ZTD, @GOPDifferent variants of the processing: 1) BSW 4.2 (2001-2003)

2) BSW 5.0 (2004) ambiguity free3) BSW 5.0 (2004) ambiguity fix

BOR1 GOPE POTS

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DDistributionistributionss of of NRT NRT ZTD ZTD ×× PP ZTD, @GOP PP ZTD, @GOPDifferent variants of the processing: 1) BSW 4.2 (2001-2003)

2) BSW 5.0 (2004) ambiguity freestations at boundary areasstations at boundary areas 3) BSW 5.0 (2004) ambiguity fix

BUCU MATE CAGL

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DDistributionistributionss of of NRT NRT ZTDZTD@GOP@GOP ×× HIRLAMHIRLAMDifferent variants of the processing: 1) BSW 4.2 (2001-2003)

2) BSW 5.0 (2004) ambiguity free x-scale 2,5x x-scale 2,5x smallsmaller er !! 3) BSW 5.0 (2004) ambiguity fix

BOR1 GOPE POTS

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DDistributionistributionss of of NRT NRT ZTDZTD@GOP@GOP ×× HIRLAMHIRLAMDifferent variants of the processing: 1) BSW 4.2 (2001-2003)

2) BSW 5.0 (2004) ambiguity free x-scale 2,5x x-scale 2,5x smallesmaller r !! 3) BSW 5.0 (2004) ambiguity fix

BUCU MATE CAGL

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DDistributionistributionss of of ACs’ ACs’ NRT NRT ZTD ZTD ×× PP@GOP PP@GOP

ACRI ASI BKG GFZ GOP IEEC LPT NKG NKGSBOR1

GOPE

HERS

POTS

WTZR

ONSA

MAR6

CAGL

MATE

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HR x DoY visualizationHR x DoY visualization # Sites

# Satellites

# Observations

aposteriori RMS

TEC

Prec. Water Vapor

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ZTD differences: old-NRT@GOP ZTD differences: old-NRT@GOP ×× PP@GOP PP@GOP

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ZTD differences: new-NRT@GOP ZTD differences: new-NRT@GOP ×× PP@IGS(PPP) PP@IGS(PPP) ambiguity freeambiguity free

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ZTD differences: new-NRT@GOP ZTD differences: new-NRT@GOP ×× PP@IGS(PPP) PP@IGS(PPP) ambiguity fixambiguity fix

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NRT NRT ×× PP (GPS) - hourly PP (GPS) - hourly ×× doy plots (various ACs) doy plots (various ACs)

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NGK

LPT

ACRI

ASI

BKG

GOPE

IEEC

NKGS

GFZ

ACs’ ZTD differencesw.r.t. GOP PostProc(precise DD solution)

1. strong signal on repeating the GPS

constellation

2. visible signal on repeatingthe satellites‘

visibility at site

Spectral analysisSpectral analysisdifferent ACdifferent AC’s’s

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MALL

MATE

CAGL

HERS

ONSA

POTS

GOPE

BOR1

GOP ZTD differencesw.r.t. GOP PostProc(precise DD solution)

sites at networkboundaries: MALL,MATE, CAGL, HERSare more affected

PSDs are shiftedPSDs are shifted !!

Spectral analysisSpectral analysisdifferent sites at GOPdifferent sites at GOP

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ZTD comparison: PPP@IGS ZTD comparison: PPP@IGS ×× PP@GOP PP@GOP

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ZTD comparison: EUR@BKG ZTD comparison: EUR@BKG ×× PP@GOPPP@GOP

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IGSPPP and EURBKGZTD differences

w.r.t. GOP PostProc(precise DD solution)

BKGEUR is stronglyaffected

compared to PPPIGS

PSDs are shiftedPSDs are shifted !!

Spectral analysisSpectral analysisIGS / EUR productsIGS / EUR products

HERS EUR

MATE EUR

VIS0 EUR

POTS EUR

HERS IGS

MATE IGS

VIS0 IGS

POTS IGS

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Widely used troposphere model in BSW 4.2 (no apriori ZTD and hNMF for estimates) overestimated ZTD’s wet component

New troposphere model in BSW 5.0 (a priori ZTD with hNMF and estimates with wNMF) provides better agreement with the radiosondes and numerical weather models and is about 1-5mm lower with respect to the old model

Second order ionospere effect possibly detected in a posteriori RMS of the hourly solutions

Ambiguity resolution shows some systematic error in ZTD (?) PPP and DD approach are more or less equal when used correctly GPS useful for the numerical weather model monitoring, radiosonde

calibrations (monitoring the seasonal signal ...)

SummarySummary

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ZTD in NRT could be estimated with internal accuracy of 3-6mm and syst. error of ±1-2mm (results depends on site location and season)

ZTD evaluated by Hirlam NWM resulted in std. deviation of 8-16mm and seasonally variable positive bias up to 15mm

PWVs from GPS were compared to radiosondes (two sources) with standard deviation of 1-2mm PWV and bias of 0-2mm also seasonally variable

Though using final orbit products, the EUREF ZTD product is not of a good quality (mixing strategies etc) and is suitable neither in application for climatology, nor in evaluation of other ZTD products (NRT..).

SummarySummary (continued) (continued)