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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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doi:10.5194/amtd-8-487-2015
© Author(s) 2015. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
14 Jan 2015
Review status
This discussion paper has been under review for the journal Atmospheric Measurement Techniques (AMT). The revised manuscript was not accepted.
Comparing OMI UV index to ground-based measurements at two Finnish sites with focus on cloud-free and overcast conditions
M. R. A. Pitkänen1, A. Arola1, K. Lakkala2, T. Koskela3, and A. V. Lindfors1 1Finnish Meteorological Institute, P.O. Box 1627, 70211, Kuopio, Finland
2Finnish Meteorological Institute, Tähteläntie 62, 99600, Sodankylä, Finland
3Finnish Meteorological Institute, P.O. Box 503, 00101, Helsinki, Finland
Abstract. Satellite based surface UV product of the Ozone Monitoring Instrument OMI was validated using ground based UV measurements from the two Finnish sites Jokioinen and Sodankylä. The goal was to further investigate the observed positive UV bias of the OMI UV product focusing on how it may be connected to cloudiness during the overpass of the Aura satellite. A total of seven years of summer time data was used to compare OMI UV index to a reference UVI observed on the ground with Solar Light 501 broadband radiometers. Cloudiness during satellite overpass was determined with auxiliary ground based observations on sunshine duration, cloud cover and global radiation as well as the satellite based MODIS cloud cover estimates. The analysis aimed to minimize the error sources from temporal discrepancies and from the differences in the field of view of OMI and its ground based reference data. As a result, OMI UV product was seen to overestimate surface UV index by 21% in average and overcast UV index up to 56%. The study confirms that OMI UV index is overestimated compared to ground based reference, and shows, that the bias is related to cloudiness and is higher during well defined overcast conditions.

Citation: Pitkänen, M. R. A., Arola, A., Lakkala, K., Koskela, T., and Lindfors, A. V.: Comparing OMI UV index to ground-based measurements at two Finnish sites with focus on cloud-free and overcast conditions, Atmos. Meas. Tech. Discuss., 8, 487-516, doi:10.5194/amtd-8-487-2015, 2015.
M. R. A. Pitkänen et al.
M. R. A. Pitkänen et al.

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