Abstract
Abstract. A measurement campaign was performed in the region of Vienna and its surroundings from May to July 2007. Within the scope of this campaign erythemal UV was measured at six ground stations within a radius of 30 km. First, the homogeneity of the UV levels within the area of one satellite pixel was studied. Second, the ground UV was compared to ground UV retrieved by the ozone monitoring instrument (OMI) onboard the NASA EOS Aura Spacecraft. During clear-sky conditions the mean bias between erythemal UV measured by the different stations was within the measurement uncertainty of ±5%. Short term fluctuations of UV between the stations were below 3% within a radius of 20 km. For partly cloudy conditions and overcast conditions the discrepancy of instantaneous values between the stations is up to 200% or even higher. If averages of the UV index over longer time periods are compared the difference between the stations decreases strongly. The agreement is better than 20% within a distance of 10 km between the stations for 3 h averages. The comparison with OMI UV showed for clear-sky conditions higher satellite retrieved UV values by, on the average, approximately 15%. The ratio of OMI to ground measured UV lies between 0.9 and 1.5. and strongly depends on the aerosol optical depth. For partly cloudy and overcast conditions the OMI derived surface UV estimates show larger deviation from the ground-based reference data, and even bigger systematic positive bias. Here the ratio OMI to ground data lies between 0.5 and 4.5. The average difference between OMI and ground measurements is +24 to +37% for partly cloudy conditions and more than +50% for overcast conditions.
Highlights
During the last three decades global increases in UV fluxes resulting from decreasing stratospheric ozone have been an issue of public concern because of the direct linkage to human health (e.g. Scientific Committee on Problems of the environment SCOPE, 1992, 1993; United Nations Environmental Program UNEP, 1998; National Radiological Protection Board, 2002)
A more profound analysis shows that the discrepancy between Ozone Monitoring Instrument (OMI) and ground UV increases with increasing turbidity
These results confirm the overestimation of ground UV by Total Ozone Mapping Spectrometer (TOMS) and OMI which was found in previous studies (Kalliskota et al, 2000; McKenzie et al, 2001b; Fioletov et al, 2002; Chubarova et al, 2002; Cede et al, 2004; Arola et al, 2005; Kazantzidis et al, 2006; Tanskanen et al, 2007)
Summary
During the last three decades global increases in UV fluxes resulting from decreasing stratospheric ozone have been an issue of public concern because of the direct linkage to human health (e.g. Scientific Committee on Problems of the environment SCOPE, 1992, 1993; United Nations Environmental Program UNEP, 1998; National Radiological Protection Board, 2002). Ground-based measurements are sparsely located and most of the nowadays available stations are in operation for 10 or 15 years. Kaurola et al, 2000; Lindfors and Vuilleumier, 2005; Koepke et al, 2006; Rieder et al, 2008) have been performed. The results of these studies show that surface UV radiation significantly increased during the last 20 to 30 years. Near surface UV measurements, reconstruction of past UV doses as well as the development of satellite derivation techniques have been among big scientific issues within the UV community during the last years. The Aura satellite was launched to a sun-synchronous afternoon orbit
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