1. Comparison of GOME-2 and OMI surface UV products
Niilo Kalakoski, Finnish Meteorological Institute

2. O3M SAF Offline UV Product
Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M SAF)
Joint effort of 10 institutes in 7 European countries, FMI is the leading entity
Part of EUMETSAT’s Polar System (EPS) ground segment
3 Metop satellites to cover some 15 years up to 2020
Metop-A was successfully launched 19 October 2006
Ozone, trace gases and aerosols from GOME-2
Offline Surface UV (OUV) Product:
Developed and processed at FMI
Contains
Daily (integrated) doses
Daily maximum dose rates
Biological weightings:
Erythemal (CIE)
DNA damage
Generalized Plant Response
SCUP-h
0.5 x 0.5 degree grid, HDF5 format
Currently demonstrational status

3. O3M SAF OUV: Inputs Inputs: Total Ozone
GOME-2 NRT Total Ozone (NTO) product
Produced by the German Aerospace Center (DLR) within the O3M SAF
Read from EUMETCast broadcasting, 2.5 hours from sensing
Used in modelling of surface UV irradiance and AVHRR channel 1 reflectance
Inputs: Surface albedo:
Static regions (no seasonal variability):
TOMS 380 nm MLER
Dynamic regions (seasonal snow or ice):
Climatology of A. Tanskanen
Inputs: Aerosols:
Currently: Global Aerosol Dataset GADS
Testing with Aerocom climatology

4. O3M SAF OUV: Cloud Optical Depth Data
Inputs: AVHRR ch. 1 (630 nm) reflectances
exploits the synergy between Metop and NOAA satellites
Data readily available from EUMETCast
At least 2 cloud observations per day obtained globally
Morning (9:30): Metop-A
Afternoon (14:30): NOAA-18
Using both morning and afternoon observations improves the daily dose integration
Currently no cloud retrieval if
solar zenith angle > 70 degrees
surface albedo > 60 %

5. O3M SAF OUV vs. OMI UV Main Differences
Total Ozone source
GOME-2 / Metop
OMI / Aura
Wavelength of cloud optical depth retrieval
AVHRR 630 nm
OMI 360 nm
Cloud observations per daily dose integration
>= 2 1
Daily dose frequency
1 per day, in 0.5 x 0.5° grid
multiple (and different) values per day, for each orbit
Surface albedo
No seasonal snow or ice: TOMS 380 nm MLER
Seasonal snow or ice: Tanskanen et al. Climatology
Tanskanen et al. climatology
Aerosols
GADS (soon: Aerocom)
None (soon: Aerocom)

6. Comparisons of OUV and OMIuv
Surface UV radiation in kJ/m2 from OMI (left) and GOME-2 (right) for February 1st 2008.
GOME-2 UV not retrieved for SZA > 70 degrees

7. OUV – OMIuv absolute difference in kJ/m2

8. (OUV-OMI)/OMI relative difference

9. Time series of the surface UV from OMI and GOME-2 compared to ground-based measurements
CIE erythemal daily dose
Jokioinen (above) and Sodankylä (below)
August 2007

10. OUV-ground standard deviation OMI-ground standard deviation
Scatterplot comparisons of OMIuv and OUV CIE erythemal daily doses
Jokioinen (above) and Sodankylä (below)
From June 1st 2007 to May 31st 2008
kJ/m2
Jokioinen
Sodankylä
OUV-OMI mean error
-0.09
-0.03
OUV-ground standard deviation
0,20
0.19
OUV-ground mean error
0.09
0.15
OMI-ground standard deviation
0.40
0.36
OMI-ground mean error
0.18

11. Thank you for your attention!