The objectives of the COST action 726 are to establish long-term changes of UV-radiation in the past, which can only be derived by modelling with good and available proxy data. To find the best available models and input data, 16 models have been tested by modelling daily doses for two years of data measured at four stations distributed over Europe. The modelled data have been compared with the measured data, using different statistical methods. Models that use Cloud Modification Factors for the UV spectral range, derived from co-located measured global irradiance, give the best results.
UV-SPRAFIMO is a completely new developed UV instrument for very fast measurements of solar spectral irradiance with high spectral resolution and arbitrary step width. It combines sophisticated filter radiometer technique with a new model based on neural networks. UV-SPRAFIMO has the following specifications:
(1) Spectral region 280 - 400 nm.
(2) Arbitrary spectral resolution and step width of the UV spectra (≥ 0.05 nm).
(3) Simultaneous measurement of all spectral channels.
(4) Up to 5 measurements per second with arbitrary averaging interval of 5 to 30 seconds.
(5) Weatherproofed, air conditioned housing and fully automatic measurement system.
(6) No moving parts.
(7) Data logger up to 64 Mbytes memory for long-term measurements at remote sites.
(8) GPS to automatically set up time and geographical position data.
(9) PC based, graphical user interface for measurement set up and monitoring and processing of data.
(10) Online calculation and visualization of integrated irradiances like UV-A, UV-B and UV-Index as well as erythemal or user defined weighted irradiance.
(11) Simultaneous total ozone column retrieval from spectral measurements.
UV-SPRAFIMO is a standalone and easy to use UV spectral radiometer; it was tested in different climate regions during field measurement campaigns in order to compare measurement performance and accuracy to high quality scanning spectral radiometers. Details of functional principles and results of the measurement campaigns are presented.
In general measurements of UV-radiation are related to horizontal surfaces, as e.g. also done for the internationally standardized and applied UV-index. In order to get more information on biologically relevant UV-exposure, there is a need for quantitative data of radiation fluxes on tilted surfaces. UV exposure of the human skin is one of the most essential issues in UV research, and therefore UV-irradiance for surface orientations typical for the human body should be known for all kinds of meteorological conditions. To measure these fluxes the new automatic system ASCARATIS (Angle SCAnning RAdiometer for determination of erythemally weighted irradiance on TIlted Surfaces) was developed and built. With three units of ASCARATIS hundreds of thousands of sets of UV-index measurements (each set consisting of measurements in 27 directions) have been made at different sites (urban, rural, mountain) during the last three years. The measurements cover the whole variability of weather conditions for all seasons. The results show large differences between UV-irradiation of horizontal surfaces (measuring standard) and inclined surfaces especially during the time of the year with lower sun elevations. The measuring data are used to fit a radiation model for inclined surfaces and to model the UV-irradiance of the human body.
Images from the Earth surface taken from satellites or airplanes need atmospheric correction including angle and aerosol effects to derive accurate surface properties. For low-flying airplanes which operates in heights between 1 and 2 km one has to distinguish between the atmosphere above and below the sensor. A critical task within the atmospheric correction is the correct consideration of the vertical distribution of aerosol particles. The atmospheric boundary layer can reach heights up to 3 km during a summer day in central Europe and it can change as much as 100% during a day. Long range transport of particles occurs normally in heights between 1 and 5 km. Both lead often to a considerable amount of particles above the airplane. It will be demonstrated that the effect of an inadequate aerosol vertical profile used within the atmospheric correction scheme on the derived surface reflectances is height dependent and wavelength dependent with much larger influences in the UV than in the long NIR wavelength range both due to decreasing Rayleigh and aerosol scatttering and increasing surface reflectance with increasing wavelength. The wavelength dependency leads to different NDVI and LAI indices. Furthermore the effect is modified by the intensity of the path radiance in relation to the surface reflected radiance with leads to a dependency on solar zenith angle and sensor zenith angle.