Lasse Ylianttila

Erythemally weighted radiometers in solar UV monitoring: Results from the WMO/STUK intercomparison

The first international intercomparison of erythemally weighted (EW) broadband radiometers was arranged in 1995 to improve the accuracy and comparability of the measurements carried out by solar UV monitoring networks. The intercomparison was arranged at the Radiation and Nuclear Safety Authority in Helsinki, Finland, in cooperation with the University of Innsbruck and with support from the World Meteorological Organization. Altogether 20 EW meters of six different types from 16 countries were (1) tested in the laboratory by measuring the spectral and angular responsivities and (2) calibrated in solar radiation against two reference spectroradiometers. Calibration factors (CFs) for the EW meters were determined by using simultaneously measured EW solar UV spectra as a calibration reference. The CFs averaged over solar elevations higher than 35° varied from 0.87 to 1.75, with the estimated uncertainty being ±10%. As a result of this intercomparison, for the first time the calibrations of more than 100 EW radiometers around the world are possible to trace to the same origin. The present experience indicates that the accuracy of temperature‐controlled EW radiometers is not significantly lower than the accuracy of spectroradiometers provided that strict quality assurance/quality control procedures are followed.

Heliotherapy improves vitamin D balance and atopic dermatitis

Background  Vitamin D insufficiency during winter is common in the Nordic countries. Heliotherapy (HT) may heal atopic dermatitis (AD) but its effect on vitamin D balance has not been examined.

Evaluation of a single-monochromator diode array spectroradiometer for sunbed UV-radiation measurements.

The suitability of a new technology single‐monochromator diode array spectroradiometer for UV‐radiation safety measurements, in particular for sunbed measurements, was evaluated. The linearity, cosine response, temperature response, wavelength scale, stray‐light and slit function of the spectroradiometer were determined and their effects on the measurement accuracy evaluated. The main error sources were stray‐light and nonideal cosine response, for which correction methods are presented. Without correction, the stray‐light may reduce the accuracy of the measurement excessively, particularly in the UV‐B range. The expanded uncertainty of the corrected UV measurements is estimated to be 14%, which is confirmed with the comparative measurements carried out with a well‐characterized double‐monochromator spectroradiometer. The measurement accuracy is sufficient for sunbed measurements, provided that all corrections described above have been done and the user of the instrument has a good understanding of the instruments operating principles and potential error sources. If these requirements are met, the tested spectroradiometer improves and facilitates market surveillance field measurements of sunbeds.

Narrowband ultraviolet B course improves vitamin D balance in women in winter

Background  Vitamin D insufficiency is common in winter in the Nordic countries.

Spectral irradiance measurements of tungsten lamps with filter radiometers in the spectral range 290 nm to 900 nm

A method of measuring the absolute spectral irradiance of quartz-halogen-tungsten lamps is described, based on the known responsivity of a filter radiometer, the components of which are separately characterized. The characterization is described for the wide wavelength range essential for deriving the spectrum of a lamp, from 260 nm to 950 nm. Novel methods of interpolation and measurement are implemented for the spectral responsivity of the filter radiometer. The combined standard uncertainty of spectral irradiance measurements is less than 1.4 parts in 102 from 290 nm to 320 nm (ultraviolet B) and 4 parts in 103 from 440 nm to 900 nm (visible to near-infrared). As an example, the derived spectral irradiances of two lamps measured at the Helsinki University of Technology (HUT, Finland) are presented and compared with the measurement results of the National Institute of Standards and Technology (NIST, USA) and the Physikalisch-Technische Bundesanstalt (PTB, Germany). The comparisons indicate that the HUT spectral irradiance scale is between those of the NIST and the PTB in the wavelength range 290 nm to 900 nm. The long-term reproducibility of the spectral irradiance measurements is also presented. Over a period of two years, the reproducibility appears to be better than 1 part in 102.

INCREASED UV EXPOSURE IN FINLAND IN 1993

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Comparison of narrowband ultraviolet B exposure and oral vitamin D substitution on serum 25-hydroxyvitamin D concentration.

Summary Background  A short course of narrowband ultraviolet B (NB‐UVB) exposures increases the serum 25‐hydroxyvitamin D [25(OH)D] concentration in patients with psoriasis and healthy subjects.

Determination of distance offsets of diffusers for accurate radiometric measurements

A method for the determination of the effective measurement plane of spectroradiometer diffusers at various wavelength regions is described. The method is based on the inverse-square law of the distance dependence of the measured signal. The scheme is tested with three planar and one dome-shaped spectroradiometer diffuser at four wavelength bands. The distance offsets of the diffusers determined in the UVA region are from 0 mm to 2.1 mm for the planar diffusers and 6.4 mm for the dome diffuser, whereas the corresponding values in the NIR region are from 0 mm to 7.7 mm and 8.2 mm. The uncertainties of the measured reference plane positions of the diffusers are estimated to be 0.3 mm. If the reference plane position is not properly taken into account in calibration measurements with lamps, large systematic errors may appear when measuring radiation from distant sources. We also investigate the wavelength dependence of the angular responsivity of the diffusers. A clear correlation appears between the wavelength dependences of the distance offsets and the angular responsivity curves.

Intercomparison of lamp and detector‐based UV‐irradiance scales for solar UV radiometry

The high uncertainty of calibration is the most serious factor limiting accurate measurements of the solar UV, needed for the assessment of global UV trends. In this study, the calibration of FEL-type standard lamps traceable to three primary standard laboratories were compared with a transfer uncertainty of ±1.4% (2σ). In comparison with the reference lamp, the spectral UV irradiance scales agreed within 1.5%. However, the difference between a new lamp and the present reference was 2%, which is close to the limits of total uncertainty. It was interesting to observe that one of the scales, based on a cryogenic absolute radiometer, was in good agreement with the scales based on blackbody radiation sources. Examination of the long-term stability of the lamp-based UV scale in Finland showed a significant decrease of 6% in the scale when the standard lamp was changed to a lamp directly traceable to the primary standard of the National Institute of Standards and Technology (NIST). Previously, the lamp was traceable to the NIST through the secondary standard of Optronic Laboratories Inc. The main obstacle in improving the global conformity of UV scales is the instability of halogen standard lamps. On the basis of the present study, it is strongly recommended to use detector stabilization of the standard lamps and to investigate the use of portable detector standards in the intercomparisons between primary standards laboratories.

Calibration of the broadband radiometers of the Finnish solar ultraviolet monitoring network

The present solar ultraviolet (UV) monitoring network of the Finnish Meteorological Institute consists of seven sites equipped with erythemally-weighted broadband radiometers. Two of the sites are also equipped with a Brewer spectroradiometer. The Finnish Centre for Radiation and Nuclear Safety is responsible for testing and calibration of the broadband radiometers. An Optronic 742 spectroradiometer is used as a reference instrument, and the broadband radiometers are calibrated against the Optronic 742 in solar radiation. The Optronic 742 is calibrated against 1000 W FEL lamps traceable to the NIST. The errors caused by nonideal radiometric characteristics of the Optronic 742 are numerically corrected. The uncertainty (2 σ) of solar UV measurements with the Optronic 742 is estimated to be ±8 % at 310 nm and the uncertainty of the spectroradiometric solar calibration of the Solar Light Model 501 radiometers is estimated to be 11 %.