European ground-based UV-measurements used for assessment of OMUVB data quality

European ground-based UV-measurements used for assessment

of OMUVB data quality

Arjan van Dijk, Peter den Outer and Harry SlaperOne year of OMI, FMI, Helsinki, Finland, June 24-27, 2008

2OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Our plan:

• Compare the OMUVB product from overpass data with UVB ground measurements

• Check for forms of bias (clouds, latitude, etc…)• Use our own AMOUR-model to estimate UVB from

OMI ozone and OMI reflectivity• Use these AMOUR UVB estimates to assess possible

attributions for the bias in the OMUVB product

3OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Ground measurements:

Location Lon Lat UV Ozone Pyranometer Sodankyla 26.63 67.64 1991-2006 1978-2006 1957-2006 Jokioinen 23.50 60.81 1995-2006 1978-2006 1957-2006 Norrkoping* 16.15 58.58 1983-2003 1983-2006 1983-2006 Bilthoven 5.18 52.10 1994-2008 1973-2008 1965-2008 Lindenberg 14.12 52.21 1995-2007 1964-2007 1981-2006 Potsdam 13.08 53.36 1995-2003 1964-2003 1937-2003 Hradec Kralove* 15.83 50.19 1996-2006 1964-2006 1953-2006 Thessaloniki* 22.97 40.52 1992-2006 1982-2006 1980-2006 Uccle 4.36 50.80 1993-2006 1973-2008 1951-2006

4OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Ratio OMUVB / ground measurement (1/2)

5OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Ratio OMUVB / ground measurement (2/2)

6OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

The effect of clouds:Ratio(OMUVB/Measured) vs CMF (1/2)

7OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

The effect of clouds:Ratio(OMUVB/Measured) vs CMF (2/2)

8OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Attempts to assess cloud correction

Other satellite,our algorithm:

“the good old times”

OMUVBproduct

Our algorithmon OMI ozone

and OLD OMI reflectivity

(gridded)

Our algorithmon OMI ozone

and NEW OMI cloud

radiative fraction(overpass)

Site: Bilthoven

9OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Cloud Modification Factor: UVB vs pyranometer

EPTOMS OMI

10OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Radiative Cloud Fraction: grid vs overpass

11OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Latitude dependence of ratio OMUVB/Measured

“AMOUR_Local” uses:our algorithm + OMI ozone

+ new cloud product as if it were CMF from pyranometer+ site-info for aerosols and

albedo!

12OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Latitude dependence of ratio OMUVB/Measured

“AMOUR_Local” shows the potential of OMI products!

13OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

Conclusions

• For Europe, OMUVB gives overestimates• Overestimation is strongest in very clouded situations• The new “cloud reflection factor” behaves as a

pyranometer CMF• OMUVB has a latitude-dependent bias • With site-info for aerosols and albedo, we have shown

major improvement of (the bias in) OMI-UVB estimates• Please, resurrect the old-style reflectivity product!• Overpass data (ozone and reflection) and gridded data

seem not in agreement

14OMIVAL-2008 E-mail: Arjan.van.Dijk@RIVM.nl

• Thank you very much for your kind permission to use the following ground measurements (collected for SCOUT-O3):

Finland:Jussi Kaurola, Anders Lindfors (Jokioinen, Sodankyla)

Greece: Alkis Bais, Andreas Kazantzidis (Thessaloniki)

Czech Republic: Michael Janouch (Hradec Kralove)

Germany: Uwe Feister (Lindenberg, Potsdam)

Sweden: Weine Josefsson (Norrkoping)

Belgium: Didier Gillotay, Hugo de Backer (Ukkel)