Das Projekt "OMI-ASAP Validaton of Ozone Monitoring Instrument (OMI) Ground UV Products (OMI-ASAP)" wird/wurde gefördert durch: Österreichische Forschungsförderungsgesellschaft mbH (FFG). Es wird/wurde ausgeführt durch: Universität für Bodenkultur Wien, Institut für Meteorologie.Good quality UV maps are only achievable by using satellite information and satellite data. The present project deals with the validation of the UV products retrieved with the (Ozone Monitoring Instrument) OMI instrument on board of NASA/EOS AURA satellite. The project is closely connected with the ESA project (ID 2945) Validation of OMI products over Europe with ground-based UV instruments'. It is vital for producing good quality science within the scope of the ESA project (since no money is available from ESA) and it treats the important aspects in more detail than the former one. 4 Work packages (WP) are identified within the scope of the present project. They are mentioned in chronological order dealing at the beginning with a general validation of UV maps. In the next work packages, WP 2 to 4, we go more into detail of some questions, which are vital for improving the satellite UV algorithms. In WP. 1: The UV maps over Europe will be validated using the ground-based UV network consisting of several stations. Comparisons at these locations will be performed on a routine basis by the owners of the instruments themselves. From these investigations, first statements about the accuracy of the OMI ground UV determination will be made. Austria is destined for performing more deep investigations in this domain since it combines a lot of conditions which were identified as major difficulties for an accurate ground UV retrieval: Austria is a topographically very structured area, it has on the one hand regions with relatively high pollution levels comparable to other European urban areas, and on the other hand their is huge inhomogeneity in the ground type and also in the ground albedo (especially in snow covered areas). This country is therefore ideally suited to conduct the additional detail studies mentioned in WP 2, 3 and 4. In WP 2. Data of the 12 stations of the Austrian UVB network situated at altitudes between 150 and 3000 m altitude will be compared to the OMI retrieved UV after a special quality control. In order to investigate the natural variability of the UV-index on a small geographic scale (one OMI-pixel 13x24 km2), a field campaign will be carried out. Measurements will be performed with 5 similar portable broadband detectors at 5 stations within the OMI footprint scale. In WP 3 special studies and analysis of the data will be performed to investigate UV retrieval errors due to the influence of the tropospheric gases ozone, SO2, NO2 and of aerosols. In order to investigate and analyse/specify the effect of different pollutants and aerosols on UV irradiance, ground based measurements of environmental monitoring networks as well as aerosol parameters from the aerosol monitoring network AERONET will be used as input parameters for radiative transfer simulations. To gain deeper insight an aerosol model (OPAC) will also be applied. In WP4: Using the campaigns data and also additional measurements in the Viennese area and etc.