R van malderen 1 5 e pottiaux 2 5 h brenot 3 and s beirle 4
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Max Planck Institute for Chemistry. Royal Meteorological Institute of Belgium. Belgian Institute for Space Aeronomy. Solar-Terrestrial Centre of Excellence. Royal Observatory of Belgium. 1. 2. 3. 4. 5. R. Van Malderen 1,5 , E. Pottiaux 2,5 , H. Brenot 3 and S. Beirle 4.

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R van malderen 1 5 e pottiaux 2 5 h brenot 3 and s beirle 4

Max Planck Institute for Chemistry

Royal Meteorological Institute of Belgium

Belgian Institute for Space Aeronomy

Solar-Terrestrial Centre of Excellence

Royal Observatory of Belgium

1

2

3

4

5

R. Van Malderen1,5, E. Pottiaux2,5, H. Brenot3 and S. Beirle4


Introduction

ROB

What?inter-technique comparison between 4 different instruments measuring the same atmospheric variable

Which variable? integrated water vapour (IWV)

Where? world-wide, but first focus on Brussels, (50°48'N, 4°21'E, 100 m asl) as case study

When? The different instruments cover different observation periods.

Aims? • assess the quality of the different measurements: the precision - accuracy - performance of the instruments

• obtain a better monitoring and understanding of the changing water vapourcontent in the atmosphere

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Outline

ROB

  • Instruments and datasets

  • Case study: Brussels

    • Data overview

    • Scatter plots

    • Impact of cloudcover

  • World-wide data exploitation

    • Site selection

    • Scatter plot properties

  • Conclusions & Perspectives

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • CIMEL sun photometer

  • direct sun measurements @ 940nm (and @ 675 and 870 nm for aerosol correction)

  • clear sky only

  • level 2 data from the AERONET website

  • GOME/SCIAMACHY/GOME-2

  • air mass corrected differential optical absorption spectroscopy method applied to nadir measurements around 700 nm.

  • cloud cover is an issue

  • GNSS/GPS

  • International GNSS Service (IGS) database (homog. reprocessing)

  • at all weather conditions, always

  • Tsurf and psurf are needed: ZTD  IWV

  • Radiosondes(RS)

  • different types

  • launched at all weather conditions

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • different instruments = different observation periods

  • scatterplots of simultaneous IWV measurementswithrespect to the GNSS device as reference

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • biaswith GPS ranges between -0.6 mm and +0.6 mm

  • best overall agreement between GPS and CIMEL sunphotometer

  • regressionslopeclosest to 1 for all-weatherdevicesscatter plot  influence of cloudcover?

GPS-CIMEL

GPS-RS9x

GPS-GOME(2)/SCIA

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

GPS-CIMEL

  • cloudcover↗ regressionslopes↘ and correlation coefficients ↘

  • GPS measurementsincorporate contribution fromclouds in directions towards satellites

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • selection of 28 sites world-wide (NH), with focus on CIMEL-GPS co-location and based on meteo data availability (GPS)!

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • scatter plot propertiesfor the 28 co-locations, orderedwithincreasinglatitutefromleft to right

  • geographicaldependency?

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • similarinter-technique conclusions as for the Brussels case study!

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

  • althoughoriginally tracing other slants/directions, very good agreement between the ground-based (2) and in-situ (1) devices

  • The IGS database of GPS measurements and the AERONET sunphotometermeasurements are verypromising to beused for IWV trend analysis due to theirhomogeneous data reprocessing (IGS) and theirregular instrument calibration (AERONET).

  • The weather observations bias (partlyclearskyneeded) in the sunphotometer and GOME(2)/SCIAMACHY data series affects the comparisonwith all-weatherdevices, but whatis the impact on the trends?  subject of a subsequentstudy

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

Brussels (Belgium)

Calgary (Italy)

monthlymeans

monthlymeans

  • althoughoverall good agreement, small difference in trend slope between GPS and radiosonde time series (-0.15 vs. -0.45 mm/decade)

  • RS IWV < IGS IWV in earlyyears: instrumentation change for RS?

  • Large difference in IWV trends (0.16 vs. 1.29 mm/decade)

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


Instruments & datasets

Case study: Brussels

World-wide exploitation

Conclusions & perspectives

ROB

Summary: all European IGS stations starting in 1995/1996

  • ratherconsistent picture: IWV ↑ , mostsignificantly (> 0.5 mm/dec) in central Europe

  • trend difference in ZTD between 2 IGS stations (MADR, VILL) nearMadrid (both use the samemeteo station data)

  • Brussels?

WMO CIMO TECO, Brussels, 16-18 Oct. 2012


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