Characteristics of GPS ZTD products. Jan Douša EUREF Analysis Centre Workshop

Transcription

1 Characteristics of GPS ZTD products Jan Douša EUREF Analysis Centre Workshop March 15-16, 2006

2 Outline ZTD and PWV products Stragegy changes GPS constellation effect solution characteristics ZTD differences (NRT products, IGS & EUR products) Spectral analysis evaluation Hr DoY plots evaluation ZTD differences Summary 2

3 ZTD/PWV products used Zenith total delay (ZTD) NRT GPS products: COST-716/TOUGH: (ASI,ACRI,BKG,GFZ,GOP,IEEC,LPT,NKG,NKGS) PP GPS products: GOP, ZTD from numerical weather model Precipitable Water Vapor (PWV) PWV converted at KNMI from COST-716/TOUGH ACs ZTD PWV calculated at GOP from radiosonde profiles provided by British Atmospheric Data Centre PWV calculated at University of Wyoming 3

4 ZTD comparisons comparison NRT x post-processing 1/4 of 2005 comparison old NRT x new NRT 4

5 PWV evaluation GPS radiosondes - 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)! directly collocated sites remote comparison 5

6 PWV comparison UW GOP/BADC radobs - 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 = 0m GPS-Raobs height diff = 0m GPS-Raobs height diff = +247m GPS-Raobs height diff = +475m 6

7 ZTD differences NRT GOP HIRLAM (NWP) 7

8 ZTD comparison NRT GOP HIRLAM (NWP) - weekly Sdev and Bias - GPS ZTD from GOP near real-time - NWM Hirlam from DMI also seasonal variation in offset 8

9 ZTD hourly comparison GPS HIRLAM (NWP) - GPS ZTD from GOP near real-time - NWM HIRLAM from DMI! based on 2,5 years of comparison! Std.dev. Bias daily variation (6-hour periods?) coincides with HIRLAM update cycle 9

10 From BSW 4.2 to BSW 5.0 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. 10

11 BSW 4.2 and BSW 5.0 tropospheric model time&site variable new tropospheric model to the old one 0-5mm 11

12 Coordinate repeatability in NRT (amb-free ambig-fix solution) hour-to-hour coordinate repeatabilities improved from 10/25/25 mm to 6/6/16 mm (North/East/Up) by ambiguity resolving 12

13 Distributions of NRT ZTD PP Different variants of the processing: BOR1 GOPE 1) BSW 4.2 ( ) 2) BSW 5.0 (2004) ambiguity free 3) BSW 5.0 (2004) ambiguity fix POTS 13

14 Distributions of NRT ZTD PP Different variants of the processing: stations at boundary areas BUCU MATE 1) BSW 4.2 ( ) 2) BSW 5.0 (2004) ambiguity free 3) BSW 5.0 (2004) ambiguity fix CAGL 14

15 Distributions of NRT HIRLAM Different variants of the processing: x-scale 2,5x smaller! BOR1 GOPE 1) BSW 4.2 ( ) 2) BSW 5.0 (2004) ambiguity free 3) BSW 5.0 (2004) ambiguity fix POTS 15

16 Distributions of NRT HIRLAM Different variants of the processing: x-scale 2,5x smaller! BUCU MATE 1) BSW 4.2 ( ) 2) BSW 5.0 (2004) ambiguity free 3) BSW 5.0 (2004) ambiguity fix CAGL 16

17 Distributions of ACs NRT ZTD ACRI ASI BKG GFZ GOP IEEC LPT NKG NKGS B O R 1 G O P E H E R S P O T S W T Z R O N S A M A R 6 C A G L M A T E 17

18 # Sites HR x DoY visualization # Satellites # Observations aposteriori RMS TEC Prec. Water Vapor 18

19 ZTD differences: 19

20 ZTD differences: ambiguity free 20

21 ZTD differences: ambiguity fix 21

22 NRT PP (GPS) - hourly doy plots (various ACs) 22

23 Spectral analysis different AC s ACs ZTD differences w.r.t. GOP PostProc NGK (precise DD solution) LPT ACRI ASI 1. strong signal on repeating the GPS constellation 2. visible signal on repeating the satellites visibility at site BKG GOPE IEEC NKGS GFZ 23

24 Spectral analysis different sites at GOP GOP ZTD differences w.r.t. GOP PostProc (precise DD solution) PSDs are shifted! MALL MATE CAGL HERS ONSA POTS sites at network boundaries: MALL, MATE, CAGL, HERS are more affected GOPE BOR1 24

25 ZTD comparison: 25

26 ZTD comparison: 26

27 Spectral analysis IGS / EUR products PSDs are shifted! IGSPPP and EURBKG ZTD differences HERS EUR w.r.t. GOP PostProc MATE EUR (precise DD solution) VIS0 EUR POTS EUR HERS IGS MATE IGS BKGEUR is strongly affected compared to PPPIGS VIS0 IGS POTS IGS 27

28 Summary 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...) 28

29 Summary (continued) 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..). 29