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

ROYAL METEOROLOGICAL INSTITUTE OF BELGIUM

1

ROYAL OBSERVATORY OF BELGIUM

2

BELGIAN INSTITUTE FOR SPACE AERONOMY

3

MAX PLANCK INSTITUTE FOR CHEMISTRY

4

SOLAR-TERRESTRIAL CENTRE OF

EXCELLENCE5

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

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

vapour content in the atmosphere

IntroductionIntroductionROB

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

1. Instruments and datasets

2. Case study: Brusselsi. Data overviewii. Scatter plotsiii. Impact of cloud cover

3. World-wide data exploitationi. Site selection ii. Scatter plot properties

4. Conclusions & Perspectives

OutlineOutlineROB

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

RadiosondesRadiosondes (RS)(RS)• different types• launched at all weather conditions

CIMEL sun photometerCIMEL sun photometer • direct sun measurements @ 940nm

(and @ 675 and 870 nm for aerosol correction)

• clear sky only• level 2 data from the AERONET

website

GNSS/GPS GNSS/GPS • International GNSS Service (IGS)

database (homog. reprocessing)• at all weather conditions, always

• Tsurf and psurf are needed: ZTD IWV

GOME/SCIAMACHY/GOME-2GOME/SCIAMACHY/GOME-2• air mass corrected differential

optical absorption spectroscopy method applied to nadir measurements around 700 nm.

• cloud cover is an issue

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

different instruments = different observation periods scatter plots of simultaneous IWV measurements with respect to the

GNSS device as reference

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

GPS-CIMELGPS-CIMEL GPS-RS9xGPS-RS9x

GPS-GOME(2)/SCIAGPS-GOME(2)/SCIA

bias with GPS ranges between -0.6 mm and +0.6 mm

best overall agreement between GPS and CIMEL sun photometer

regression slope closest to 1 for all-weather devices scatter plot influence of cloud cover?

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

cloud cover ↗ regression slopes ↘ and correlation coefficients ↘ GPS measurements incorporate contribution from clouds in directions

towards satellitesWMO CIMO TECO, Brussels,

16-18 Oct. 2012

GPS-CIMELGPS-CIMEL

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

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 Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

scatter plot properties for the 28 co-locations, ordered with increasing latitute from left to right

geographical dependency?WMO CIMO TECO, Brussels,

16-18 Oct. 2012

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

similar inter-technique conclusions as for the Brussels case study!

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

although originally 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 sun photometer measurements are very promising to be used for IWV trend analysis due to their homogeneous data reprocessing (IGS) and their regular instrument calibration (AERONET).

The weather observations bias (partly clear sky needed) in the sun photometer and GOME(2)/SCIAMACHY data series affects the comparison with all-weather devices, but what is the impact on the trends? subject of a subsequent study

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

Brussels (Belgium) Calgary (Italy)

monthly means monthly means

although overall 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 early years: instrumentation change for RS?

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

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectivesROB

WMO CIMO TECO, Brussels,

16-18 Oct. 2012

rather consistent picture: IWV ↑ , most significantly (> 0.5 mm/dec) in central Europe

trend difference in ZTD between 2 IGS stations (MADR, VILL) near Madrid (both use the same meteo station data)

Brussels?

Instruments Instruments & datasets& datasets

World-wide World-wide exploitationexploitation

Case study: Case study: BrusselsBrussels

Conclusions Conclusions & &

perspectivesperspectives

Summary: all European IGS stations starting in 1995/1996

ROB