The ozone monitoring instrument (OMI) onboard the EOS/AURA satellite was launched on 15. July 2004. The OMI products include among other things total column ozone, total column NO2, cloud characteristics, aerosol optical thickness and single scattering albedo, SO2, UV-B, HCHO and BrO. A first validation of the products has been performed, a more thoroughly validation is now being performed. In this presentation we show comparisons of OMI retrieved ozone and ground UV with ground measured UV and ozone at Sonnblick (12.8 E, 47.05 N, 3106 m altitude).
Factors affecting changes of spectral UV irradiance at the Sonnblick Observatory are studied. Spectral UV measurements at wavelengths from 290 nm to 400 nm performed during the period from 1994 to 2003 are used in this investigation. These measurements have been performed with a Brewer ozone single spectrophotometer and with a Bentham DM 150 spectroradiometer (double monochromator). The radiative transfer model DISORT (based on the Discrete Ordinate Method) was used in the simulations. Measurements of UV-radiation at Sonnblick at 305 nm under clear sky conditions show, that the snowline may influence the irradiance by mean by 24%. Cloudiness enhances the influence of the albedo since multiple reflections between surface and lower bond of the clouds become more probable. In presence of 8/8 cloud cover, UV irradiance at 305 nm is enhanced by a factor of 1.7 when the snowline is 800 m instead of 3000 m. In addition to the snowline, clouds situated below the Sonnblick are responsible for increased albedo and consequently increased radiation. Model calculations show that average albedo is increased by 0.28 ± 0.15 due to 4/8 cloud cover or more below the top of the mountain. The influence of ozone, albedo and clouds on UV variability is evaluated separately using 10-year climatology. It was found that the effect of total ozone on short- term variability of UV irradiance at 305 nm can be more than 200% and on average 56%. Clouds can cause variability of 150% or more and on average 35%.
One aim of the project CUVRA was to improve the modeling of effects of inhomogeneous albedo fields on ground UV irradiance. For the determination of the effect of heterogeneous illumination (shading effects, inclination and orientation of the facet) on the reflectivity of a facet in a mountainous region more complex approaches (than for the calculation of the reflectivity of flat surfaces) have to be chosen. We determined the 'effective' albedo for the surroundings of the Observatory Sonnblick (3106 m) by using three different methods. The first method consisted of a combination of a 3D albedo model calculation and 1D radiative transfer calculation. By using this method and a digital elevation map, the reflectivity of the region surrounding Sonnblick Observatory was calculated. The second method was an inversion method using a 1D radiative transfer model. The routine spectral UV measurements performed at Sonnblick were used to calculate the average effective albedo. The third method was entirely experimental. An albedo measuring system was used to perform reflectivity measurements of the surrounding of Sonnblick. Overall, the results showed that the average albedo of a topographically structured surface is lower than the average albedo of a corresponding (surface with same ground characteristics) flat surface.
Albedo inversion techniques are investigated in this work. Several methods are applied to spectral irradiance data from a measurement campaign held in the German Alps during the spring of 1999. One first method is based on the comparison of measurements of absolute levels of UV irradiance with model calculations. The second method takes advantage of changes in the spectral slope of spectral UV irradiance, which is a function of the surface albedo. In the third method, the surrounding area is partitioned into snow- covered and snow-free regions, and the effective albedo estimated by applying a higher or lower reflectivity to each facet before integrating over the surroundings. We present sensitivity analysis, the differences and the correlations between the various methods as well as the results for the different locations.
Beside the sun elevation angle, the total ozone content (TOC) of the atmosphere is a main input parameter of models to predict the biologically-effective UV radiation. Therefor TOC was analysed for the domain of Central Europe. The data domain contains the area from 7 degree(s)E to 17 degree(s)E in longitude and from 45 degree(s) to 50 degree(s) in latitude. Ground based as well as satellite based measurements from EPTOMS were involved. The temporal and spatial variability of TOC was analysed using auto-correlation and fitting auto- correlation functions. It becomes evident that temporal correlation decrease rapidly within the first 9 days down to the level of 1/e. From spatial correlation functions de- correlation distances (1/e) are estimated with 180 km E-W and 145 km for S-N direction. The analysis of TOC variability per 100 km for the domain of Austria was also examined. The results show that the highest values can reach up to 18%/100 km. Day-to-day variability for a certain location may exceed this level by a few percent (25%/day). These results show that for the calculation of the biologically effective UV radiation a high spatial resolution of TOC data is necessary to ensure an appropriate quality.
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