The recent increase in the ultraviolet radiation that reaches the ground, mainly due to the decrease in stratospheric ozone, demands high quality measurements over the world. For this goal the use of broadband instruments to measure erythemal-weighted irradiance is widely extended due to their low cost and easy maintenance and use. Nevertheless considerable efforts in quality assurance and quality control (QA/QC) are requiredin order to obtain a homogenised eryhtemal radiation from different regional and national networks over whole Europe. The laboratories that provide the calibration to these networks must guarantee reliable methodologies. For this purpose, the WG4 (Quality Control) within the COST-726 European action (Long-term changes and climatology of the UV radiation over Europe) is promoting the inter-laboratory intercomparison and the adoption of common procedures. In this work the procedures for calibrating broadband radiometers adopted by the laboratory "El Arenosillo" in Huelva, Spain, are presented. The methodology used at INTA has been intercompared with the UV laboratory at PMOD/WRC (World Radiaton Centre) in Davos (Switzerland) and results are presented in this document.
QASUME is a European Commission funded project that aims to develop and test a transportable unit for providing quality assurance to UV spectroradiometric measurements conducted in Europe. The comparisons will be performed at the home sites of the instruments, thus avoiding the risk of transporting instruments to participate in intercomparison campaigns. Spectral measurements obtained at each of the stations will be compared, following detailed and objective comparison protocols, against collocated measurements performed by a thoroughly tested and validated travelling unit. The transportable unit comprises a spectroradiometer, its calibrator with a set of calibration lamps traceable to the sources of different Standards Laboratories, and devices for determining the slit function and the angular response of the local spectroradiometers. The unit will be transported by road to about 25 UV stations over a period of about two years. The spectroradiometer of the transportable unit is compared in an intercomparison campaign with six instruments to establish a relation, which would then be used as a reference for its calibration over the period of its regular operation at the European stations. Different weather patterns (from clear skies to heavy rain) were present during the campaign, allowing the performance of the spectroradiometers to be evaluated under unfavourable conditions (as may be experienced at home sites) as well as the more desirable dry conditions. Measurements in the laboratory revealed that the calibration standards of the spectroradiometers differ by up to 10%. The evaluation is completed through comparisons with the same six instruments at their homes sites.
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.