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Validation of OMI UV products: results of two ground UV measurement campaigns in Austria P. Weihs 1 , M. Blumthaler 2 , H. E. Rieder 1,3,* , A. Kreuter 2 , S. Simic 1 , W. Laube 1 , A. W. Schmalwieser 5 , J. Wagner 1 , A. Tanskanen 4 , A. Webb 6 , R. Kift 6 , G.P. Gobbi 7 , and A. Arola 4

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

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Ground UV-measurement campaignsVienna and surroundings:15. May –30. July 2007Innsbruck 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

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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
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Measurement campaign Vienna (May – July 2007)

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

TGM (178 m)16°22‘ E, 48°13‘ N

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

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Measurement campaign Vienna (May – July 2007)

Strebersdorf (175 m)16°23‘ E, 48°18‘ N

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

TGM (178 m)16°22‘ E, 48°13‘ N

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

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

Bad Vöslau (286 m)16°12‘ E, 48°57‘ N

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Methods during the measurement campaigns

  • Calibration and intercomparison of all instruments at one site
  • Installation of instruments at the sites
  • Regular service and calibration of instruments
  • Analysis of data

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

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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

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

Clear sky (sun shine duration = 100%)

Partly cloudy

Cloudy (sunshine duration = 0)

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

Clear sky

V(stat x) = Σ abs(Ri – Rmean) *100

N

R=UV(x)/UV(1)

Cloudy conditions

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Ratio of OMI UV to ground measurements

Clear skyratio: 1-1.5

Partly cloudyratio: 0.5-4

Overcastratio:0.6-4.5

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Influence aerosol optical depth on UV

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

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Conclusion Vienna Campaign (1)

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

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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

Still to be done: Study of influence of tropospheric ozone

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

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

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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

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

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

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Measurement campaign Innsbruck: step 2 Installation of instruments

Hafelekar 2280m

Lans 833m

Innsbruck 616m

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

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

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First preliminary results

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

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First preliminary results

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

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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

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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”.