Browsing by Subject "SPECTRORADIOMETER"

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  • Mäkelä, Jakke Sakari; Lakkala, Kaisa; Koskela, Tapani; Karppinen, Tomi; Karhu, Juha Matti; Savastiouk, Vladimir; Suokanerva, Hanne; Kaurola, Jussi; Arola, Antti; Lindfors, Anders Vilhelm; Meinander, Outi; De Leeuw, Gerrit; Heikkilä, Anu (2016)
    The data flow involved in a long-term continuous solar spectral UV irradiance monitoring program is investigated and structured to provide an overall view on the multiphase process from data acquisition to the final products. The program employing Brewer spectrophotometers as measuring instruments is maintained by the Finnish Meteorological Institute (FMI) ever since the 1990s at two sites in Finland: Sodankyla (67 degrees N) and Jokioinen (61 degrees N). It is built upon rigorous operation routines, processing procedures, and tools for quality control (QC) and quality analysis (QA) under continuous development and evaluation. Three distinct levels of data emerge, each after certain phase in the data flow: Level 0 denoting raw data, Level 1 meaning calibrated data processed in near-real time, and Level 2 comprising of postprocessed data corrected for all distinguishable errors and known inaccuracies. The final products disseminated to the users are demonstrated to result from a process with a multitude of separate steps, each required in the production of high-quality data on solar UV radiation at the Earth's surface.
  • Heikkilä, Anu; Makelä, Jakke Sakari; Lakkala, Kaisa; Meinander, Outi; Kaurola, Jussi; Koskela, Tapani; Karhu, Juha Matti; Karppinen, Tomi; Kyro, Esko; De Leeuw, Gerrit (2016)
    The two Brewer spectrophotometers of the Finnish Meteorological Institute at Jokioinen and Sodankyla 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.