In search of traceability: two decades of calibrated Brewer UV measurements in Sodankylä and Jokioinen
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...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-11-01
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| Series: | Geoscientific Instrumentation, Methods and Data Systems |
| Online Access: | http://www.geosci-instrum-method-data-syst.net/5/531/2016/gi-5-531-2016.pdf |
| Summary: | 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. |
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| ISSN: | 2193-0856 2193-0864 |