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Risultati finali
The European UV Database (EUVDB) contains measurements of ultraviolet spectral irradiance collected from more than 30 stations across Europe over the past decade. The database also holds ancillary information and auxiliary data, such as ozone column depths and cloud amount, which can help in the interpretation of the spectral data.
The EUVDB is open to all who need terrestrial UV data for scientific research.
As part of the EDUCE project, a powerful web-page interface to the database has been designed and installed. This provides user-friendly access to the spectral UV data and enables fast and efficient retrieval of spectral data in response to user-defined search criteria. Web-page facilities for the submission of spectral data are also in place. Software tools have been installed for the on-line calculation of various products from spectral UV measurements in the database.
The EUVDB has been upgraded to ensure it has sufficient power to handle the anticipated future expansion of the database. The database continues to grow. In the first two years of the EDUCE project, more than 500,000 spectra from over 20 European measuring stations were submitted to the database. The database holds more than 1,200,000 spectra from over 30 stations.
The UV climatology includes a detailed statistical description of the variation in daily, monthly and annual UV quantities across Europe, given as a function of location, season and atmospheric conditions. The relationship between clouds, atmospheric aerosols and UV radiation has been investigated over wide scales. Errors and uncertainties in UV measurements and also the variability in UV doses received at the ground have been studied using data from sites across Europe, and compared with model calculations. The model calculations incorporate ground-based and satellite (e.g. TOMS and GOME) data as input, using global radiation data to help account for cloud effects. The statistical description of the UV climate, combined with additional ancillary information, has also be used to construct synoptic maps of ground-level UV radiation.
Some measuring sites now possess a data set that covers a continuous ten-year period, thus offering the possibility that for the first time an unambiguous trend in UV irradiance may be seen. On the basis of an evaluation of the influence of atmospheric conditions on the ability to detect a trend in UV irradiance, the three most promising EDUCE sites were selected and the data from these sites evaluated for a measured trend in UV irradiance. The analysis includes the determination of the best wavelength band to adopt and an investigation of the uncertainties in the results.
The methods of reconstruction of past UVR variations since the beginning of the total ozone and pyranometer observations are examined for 3 sites in Central Europe. The climatology and long-term oscillations in the reconstructed UV data are discussed with a separation of the total ozone and cloud/aerosol effects on surface UV. New trend methodology has been applied to the reconstructed and observed UVR time series. Temporal variability of the long-term pattern has been delineated using the wavelet decomposition or smoothing by a local regression. Thus, the trend represents local rate of the changes of the smooth component extracted from the UV time series rather than a slope of the linear term of regression.
Radiative transfer models are indispensable to most tasks connected with quality control and data analysis. Within the EDUCE project, models have been refined and developed to deliver improvements in speed (necessary for on-line quality checks) and accuracy (by incorporating polarisation in the transfer calculations, for example).
The FastRT model is now available for on-line calculations of ground-level spectral irradiance at http://zardoz.nilu.no/~olaeng/fastrt/fastrt.html.
Radiative transfer models are also essential in the study of the UV radiation environment. The effects of topographical influences on the irradiance received at EDUCE measuring sites has been studied with the help of 3-dimensional calculations.
Reports are available on the reconstruction of spectra from filter radiometers, the importance of polarisation in calculations of radiance and irradiance, paremetrisation for cloud and aerosol effects and on studies of ultraviolet sky radiance and sky anisotropy.
For the data held within the European UV Database to be beneficial and useful, it is essential that they are reliable and of known quality. To this end, extensive quality control (QC) and quality assurance (QA) procedures have been developed.
Diagnostic software tools have been developed and installed at the database. They are also available for use at local sites. These tools examine all spectral data in the database and flag spectra for errors in the wavelength scale and for anomalies arising from atmospheric variability and instrumental failings.
CheckUVSpec is a quality indicator program for measured global (hemispherical) UV spectra, and is available at http://zardoz.nilu.no/~olaeng/CheckUVSpec/CheckUVSpec.html.
SHICrivm enables operators and users of solar UV-spectra to assess several aspects of the quality of measured UV-spectra, such as wavelength shifts and various spectral anomalies. The tool also provides a standardised method of calculating biologically-weighted UV doses from spectral UV-measurements, and spectra with a standard slit function. SHICrivm is available at http://www.rivm.nl/shicrivm.
A number of site audits of stations submitting UV measurements to the database have been completed. The audit covers all aspects of instrument calibration, data collection and analysis. The published results of the audit give assurance that UV radiation data are reliable and also, by recording examples of best practice, help individual stations to improve the quality of their measurements.
A document has been constructed that attempts to explain and recommend to data submitters, database users, and database managers and operators the nature of Quality Assurance as seen from the database. The report includes implications for the methods adopted at the observing sites and at the database when carrying out Quality Control procedures and preparing the resulting data and ancillary information for presentation to the potential users of the database. The introduction provides a description of the distinction between Quality Control and Quality Assurance, and sets out the general philosophy of the approach. The subsequent sections review the nature of QC as performed at the observing sites, with the ultimate goal of QA in mind, describe the nature of the relevant evidence that is conducive to achieving some degree of QA at the database, and consider the desirable goals for future QA in a database of this type.
An inventory of the quality control procedures applied at spectral UV monitoring stations in Europe has been compiled and published. This inventory gives a detailed synopsis of what's what and how in UV measurement across Europe, and enables individuals to gauge what is standard practice in UV measurement.
Spectral data within the database have been analysed and flagged according to the following criteria:
-Wavelength errors (shifts) for two wavelength regions;
-Instrument sensitivity (lowest measurable irradiance);
-Spike detection;
-Spectral distortion (due to variable conditions during the scan);
-Irradiance-scale errors.
Detailed reports for all measurement sites are available at the project web pages.
Pubblicazioni
Quality assurance of reference standards from nine European solar-ultraviolet monitoring laboratories
Autori:
GRÖBNER J (European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra (IT)), REMBGES D (European Commission, Joint Research Centre, Institute for Environment and Sustainability, Ispra (IT)), BAIS A F (Laboratory of Atmospheric Physics, Aristotle University of Thessaloniki (GR)), BLUMTHALER M (Institut für Medical Physik, Innsbruck (AT)), CABOT T (Interactions entre Rayonnement Solaire et Atmosphère, Université Joseph Fourier, Grenoble (FR)), JOSEFSSON W (Swedish Meteorological and Hydrological Institute, Norrköping (SE)), KOSKELA T (Finnish Meteorological Institute, Ozonz and Ultraviolet Research, Helsinki (FI)), THORSETH T M (Department of Physics, Norwegian University of Science and Technology, Trondheim (NO)), WEBB A R (Department of Physics, University of Manchester Institute of Science and Technology, Manchester (GB)), WESTER U (Swedish Radiation Protection Institute, Stockholm (SE))
Pubblicato in:
An article published in: Applied Optics, Vol.41, No. 21, (20 July 2002), pp.4278-4282, 2002, Pagina/e 4278-4282
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