Validation of OMI UV products:results of two ground UVmeasurement campaigns in Austria

P. Weihs1, M. Blumthaler2, H. E. Rieder1,3,*, A. Kreuter2, S. Simic1, W.

Laube1, A. W. Schmalwieser5, J. Wagner1 , A. Tanskanen4 , A. Webb6, R. Kift6, G.P. Gobbi7, and A. Arola4

[1] {Institute for Meteorology, Department Water - Atmosphere - Environment, University of Natural Resources and Applied Life Sciences (BOKU), Vienna, Austria}[2] { Division for Biomedical Physics, Innsbruck Medical University, Innsbruck, Austria}[3] {Institute for Geography and Regional Research, University of Vienna, Vienna, Austria}[4] {Finnish Meteorological Institute, Helsinki, Finland}[5] {Institute of Medical Physics and Biostatistics, University of Veterinary Medicine, Vienna, Austria} [6] {Univ. Manchester UK}[7] {ISAC-CNR, Rome, Italy}

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

Ground UV-measurement campaigns

Vienna and surroundings:15. May –30. July 2007

Innsbruck and surroundings25. August – 18. September 200715. February – 8. March 2008

Sonnblick and surroundings22. April – 9. May 2008

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

Aims of the study

- Study representativness of OMI UV for one pixel

-Homogeneity of UV within one pixel

-Influence of aerosols

-Influence of ground pollution

-Influence of topography

-Altitude

-Shading effects

-Influence of ground albedo

-Influence of cloudiness

BOKU university (256 m) 16°19‘ E, 48° 14‘ N

Measurement campaign Vienna (May – July 2007)

Vienna Veterinary Univ. (166 m) 16°25‘ E, 48° 14‘ N

TGM (178 m)16°22‘ E, 48°13‘ N

BOKU university (256 m) 16°19‘ E, 48° 14‘ N

Measurement campaign Vienna (May – July 2007)Strebersdorf (175 m)16°23‘ E, 48°18‘ N

Grossenzersdorf (156 m)16°33‘ E, 48°12‘ N

Vienna Veterinary Univ. (166 m) 16°25‘ E, 48° 14‘ N

Bad Vöslau (286 m)16°12‘ E, 48°57‘ N

TGM (178 m)16°22‘ E, 48°13‘ N

Methods during the measurement campaigns

1. Calibration and intercomparison of all instruments at one site

2. Installation of instruments at the sites

3. Regular service and calibration of instruments

4. Analysis of data

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

Vienna campaign: instrumentation At each station UV biometers(erythemal UV)

Site BOKU: Sunphotometer (aerosol opt.depth)Fish eye camera (cloudiness)

TGM and BOKU stationPortable NOLL sun photometer(aerosol optical depth)

Meteorological data from Austrian Weather Service and from BOKU station:Global and diffuse radiation, Cloudiness, Sunshine duration

Partly cloudy

Results:Sub-pixel variation Comparison of UV index at 6 stations

Cloudy (sunshine duration = 0)

Clear sky (sun shine duration = 100%)

=> No pollution effect may be seen

(a )

0

10

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0 5 10 15 20 25 30 35

d is ta n c e to B O K U U n iv e rs ity (k m )

rela

tive

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o B

oku

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niv

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ty (

%)

(b)

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0 5 10 15 20 25 30 35

distance to BOKU University (km)

rela

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sity

(%

)

12:00 11:30-12:30 11:00-13:00 10:30-13:30 09:30-14:30

Clear sky

Cloudy conditions

Sub-pixel variation: Variability of erythemal UV as a function of distance and averaging time

V(stat x) = Σ abs(Ri – Rmean) *100

NR=UV(x)/UV(1)

Ratio of OMI UV to ground measurements

Clear skyratio: 1-1.5

Partly cloudyratio: 0.5-4

Overcastratio:0.6-4.5

UV i = -1 .9367A O D + 7 .9804

6

6 .5

7

7 .5

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8 .5

9

0 0 .2 0 .4 0 .6 0 .8

Aeroso l op tica l dep th 367 nm

UV

ind

ex

aft

er

ozo

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h

om

og

en

isa

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nInfluence aerosol optical depth on UV

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Ae rosol optical de pth 368 nm

OM

I/g

rou

nd

UV

ra

tio

SZA> = 30

SZA< 30

Results: Ratio of OMI to ground based measurements as a function of aerosol optical

depth

Average differences between stations

- Clear sky : < ±5% (no pollution effect) - Cloudy conditions: up to 60%

Sub-Pixel fluctuations

- Clear sky : < ±5% within 5 km (1 h average) - Cloudy conditions: up to 200% and even larger

- Sub-pixel variation decreases with increasing time averaging: 3 h average: variation <20% within a 10 km distance

Conclusion Vienna Campaign (1)

Conclusion Vienna Campaign (2)

Comparison with OMI UV:

- Clear sky: OMI/ground data: 1-1.5- Cloudy: OMI/ground data: 0.5-4.5

- Ratio OMI UV/ground UV measurements strongly depends on aerosol optical depth

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

Still to be done: Study of influence of tropospheric ozone

Work published in ACP disc., 8, 3693-3720, 2008.

Aims of Innsbruck campaign

- Compare ground measured UV with OMI UV

- Study sub-pixel variation

- Effect of topography - Altitude- Shading effects

- Effect of ground albedo

- Effect of cloudiness

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

•Instrumentation:Innsbruck campaign

•2(3) Bentham spectrometer(UV-irradiance and actinic flux)

• 2 UV biometers(erythemal UV)

• Photodiode array, ocean optics spectrometer(UV-irradiance)

• Velis LIDAR (Aerosol optical depth, aerosol profile, aerosol characteristics)

•Sun photometer(Aerosol optical depth)

•Fisch eye camera(cloud fraction, cloud type)

Measurement campaign in Innsbruck: step 1: calibration and intercomparison of instruments

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

Innsbruck 616m

Measurement campaign Innsbruck: step 2 Installation of instruments

Hafelekar 2280m Lans 833m

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

Measurement campaign Innsbruck: step 3, Measurements, regular service and calibration of instruments

First preliminary results

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

First preliminary results

First preliminary results

First preliminary results

NEXT STEPS

- Analysis of data of Innsbruck campaign

- Include also data of Innsbruck September campaign and of Sonnblick campaign

- Investigation of effects of- Altitude

- Ground albedo

- Combine 1-D and 3-D radiative transfer calculations with data analysis

June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

AcknowledgementThanks to

-OMI International Science Team and NASA Aura Validation Data Center (AVDC) for the satellite data used in this study.

- Institute of Meteorology and Geophysics, University of Innsbruck, Austria, for kindly providing the PFR-sunphotometer.

This work was performed in the framework of the International ESA/KNMI/NIVR OMI "Announcement of Opportunity for

Calibration and Validation of the Ozone Monitoring Instrument“. The work was funded by FFG, Austria within the scope of the

project OMI-ASAP “Validation of Ozone Monitoring Instrument (OMI) Ground UV Products” and by FWF, Austria, within the

scope of the project “Investigation of UV actinic flux in mountainous region”.