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Volume 11, issue 9 | Copyright
Atmos. Meas. Tech., 11, 5167-5180, 2018
https://doi.org/10.5194/amt-11-5167-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Sep 2018

Research article | 11 Sep 2018

Performance of the FMI cosine error correction method for the Brewer spectral UV measurements

Kaisa Lakkala1,2, Antti Arola2, Julian Gröbner3, Sergio Fabian León-Luis4, Alberto Redondas4, Stelios Kazadzis3,5, Tomi Karppinen1, Juha Matti Karhu1, Luca Egli3, Anu Heikkilä2,6, Tapani Koskela7,a, Antonio Serrano8, and José Manuel Vilaplana9 Kaisa Lakkala et al.
  • 1Finnish Meteorological Institute, Space and Earth Observation Centre, Sodanlylä, Finland
  • 2Finnish Meteorological Institute, Climate Research Programme, Kuopio, Finland
  • 3Physikalisches Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC), Davos Dorf, Switzerland
  • 4Izaña Atmospheric Research Center, Agencia Estatal de Meteorología, Tenerife, Spain
  • 5IERSD, National Observatory of Athens, Greece
  • 6Finnish Meteorological Institute, Climate Research Programme, Helsinki, Finland
  • 7Independent researcher
  • 8Department of Physics, University of Extremadura, 06006 Badajoz, Spain
  • 9National Institute for Aerospace Technology (INTA), El Arenosillo Observatory, Huelva, Spain
  • aformerly: Finnish Meteorological Institute, Climate Research, Helsinki, Finland

Abstract. Non-ideal angular response of a spectroradiometer is a well-known error source of spectral UV measurements and for that reason instrument specific cosine error correction is applied. In this paper, the performance of the cosine error correction method of Brewer spectral UV measurements in use at the Finnish Meteorological Institute (FMI) is studied. Ideally, the correction depends on the actual sky radiation distribution, which can change even during one spectral scan due to rapid changes in cloudiness. The FMI method has been developed to take into account the changes in the ratio of direct to diffuse sky radiation and it derives a correction coefficient for each measured wavelength. Measurements of five Brewers were corrected for the cosine error and the results were compared to the reference travelling spectroradiometer (QASUME). Measurements were performed during the RBCC-E (Regional Brewer Calibration Center – Europe) X Campaign held at El Arenosillo, Huelva (37°N, 7°W), Spain, in 2015. In addition, results of site audits of FMI's Brewers in Sodankylä (67°N, 27°E) and Jokioinen (61°N, 24°E) during 2002–2014 were studied. The results show that the spectral cosine error correction varied between 4 and 14%. After that the correction was applied to Brewer UV spectra the relative differences between the QASUME and the Brewer diminished even by 10%. The study confirms that the method, originally developed for measurements at high latitudes, can be used at mid-latitudes as well. The method is applicable to other Brewers as far as the required input parameters, i.e. total ozone, aerosol information, albedo, instrument specific angular response and slit function are available.

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The performance of the cosine error correction method for correcting spectral UV measurements of the Brewer spectroradiometer was studied. The correction depends on the sky radiation distribution, which can change during one spectral scan. The results showed that the correction varied between 4 and 14 %, and that the relative differences between the reference and the Brewer diminished by 10 %. The method is applicable to other instruments as long as the required input parameters are available.
The performance of the cosine error correction method for correcting spectral UV measurements of...
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