1Finnish Meteorological Institute, Climate Research, P.O. Box 503,
00101 Helsinki, Finland
2Finnish Meteorological Institute, Arctic Research Center,
Tähteläntie 62, 99600 Sodankylä, Finland
3independent researcher: Helsinki, Finland
4University of Helsinki, Department of Physics, P.O. Box 64, 00014
University of Helsinki, Helsinki, Finland
acurrently at: University of Jyväskylä, Jyväskylä, Finland
Received: 07 Dec 2015 – Discussion started: 18 Jan 2016
Abstract. The two Brewer spectrophotometers of the Finnish Meteorological Institute at Jokioinen and Sodankylä have been operated according to the highest levels of the WMO∕GAW (World Meteorological Organization∕Global Atmosphere Watch) recommendations with rigorous quality control and quality assurance. The calibration of the instruments is based on annual recalibrations of primary standard lamps in the VTT MIKES Metrology National Standards Laboratory in Finland and an exhaustive measurement program with measurements of standard and working lamps in the on-site optical laboratories. Over the years, the maintenance of the calibration has produced data sets of approximately 2000 lamp scans for both instruments. An extensive re-examination of the lamp measurements and the response of the spectrophotometers was carried out. The primary standard lamps were found to age on an average rate of 0.3 % per burn. The responsivity at wavelength 311 nm was found to exhibit both long-term and short-term changes. The overall long-term change was declining. In addition, abrupt changes of as large as 25 % were detected. The short-term changes were found to fluctuate on time frames shorter than the interval between the measurements of the primary standard lamps. This underlines the importance of the use of more frequently measured working standard lamps.
Revised: 15 Oct 2016 – Accepted: 25 Oct 2016 – Published: 22 Nov 2016
Heikkilä, A., Sakari Mäkelä, J., Lakkala, K., Meinander, O., Kaurola, J., Koskela, T., Karhu, J. M., Karppinen, T., Kyrö, E., and de Leeuw, G.: In search of traceability: two decades of calibrated Brewer UV measurements in Sodankylä and Jokioinen, Geosci. Instrum. Method. Data Syst., 5, 531-540, doi:10.5194/gi-5-531-2016, 2016.