Post on 11-Jan-2016
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
20
30
40
50
60
70
80
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
diff
eren
ce t
o B
oku
U
niv
ersi
ty (
%)
(b)
0
10
20
30
40
50
60
70
80
0 5 10 15 20 25 30 35
distance to BOKU University (km)
rela
tive
dif
fere
nce
to
Bo
ku
Un
iver
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
8
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
ne
h
om
og
en
isa
tio
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”.