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

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

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  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. Results:Sub-pixel variation Comparison of UV index at 6 stations Clear sky (sun shine duration = 100%) Partly cloudy Cloudy (sunshine duration = 0)

  9. => No pollution effect may be seen

  10. 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

  11. Ratio of OMI UV to ground measurements Clear skyratio: 1-1.5 Partly cloudyratio: 0.5-4 Overcastratio:0.6-4.5

  12. Influence aerosol optical depth on UV June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

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

  14. 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

  15. 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

  16. 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

  17. 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)

  18. Measurement campaign in Innsbruck: step 1: calibration and intercomparison of instruments June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

  19. 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

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

  21. First preliminary results June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

  22. First preliminary results June 2008 | Department of Water, Atmosphere and Environment | Institute of Meteorology

  23. First preliminary results

  24. First preliminary results

  25. 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

  26. 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”.

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