Quality assurance of the Brewer spectral UV measurements in Finland

Lakkala, Kaisa; Arola, Antti; Heikkilä, Anu; Kaurola, Jussi; Koskela, Tapani; Kyrö, E.; Lindfors, Anders V.; Meinander, Outi; Tanskanen, A.; Gröbner, Julian; Hülsen, Gregor

doi:10.5194/acp-8-3369-2008

Cited by 58 publications

(78 citation statements)

References 42 publications

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“…More recent studies indicated that the measurements can be largely affected by the individual characteristics of each instrument (Gröbner et al, 2006) and that proper corrections are needed in order to keep the uncertainties within the above mentioned limits or even reduce them further (Garane et al, 2006;Karppinen et al, 2014;Lakkala et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Dead time effect on the Brewer measurements: correction and estimated uncertainties

et al. 2016

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Abstract. Brewer spectrophotometers are widely used instruments which perform spectral measurements of the direct, the scattered and the global solar UV irradiance. By processing these measurements a variety of secondary products can be derived such as the total columns of ozone (TOC), sulfur dioxide and nitrogen dioxide and aerosol optical properties. Estimating and limiting the uncertainties of the final products is of critical importance. High-quality data have a lot of applications and can provide accurate estimations of trends.The dead time is specific for each instrument and improper correction of the raw data for its effect may lead to important errors in the final products. The dead time value may change with time and, with the currently used methodology, it cannot always be determined accurately. For specific cases, such as for low ozone slant columns and high intensities of the direct solar irradiance, the error in the retrieved TOC, due to a 10 ns change in the dead time from its value in use, is found to be up to 5 %. The error in the calculation of UV irradiance can be as high as 12 % near the maximum operational limit of light intensities. While in the existing documentation it is indicated that the dead time effects are important when the error in the used value is greater than 2 ns, we found that for single-monochromator Brewers a 2 ns error in the dead time may lead to errors above the limit of 1 % in the calculation of TOC; thus the tolerance limit should be lowered. A new routine for the determination of the dead time from direct solar irradiance measurements has been created and tested and a validation of the operational algorithm has been performed.Additionally, new methods for the estimation and the validation of the dead time have been developed and are analytically described. Therefore, the present study, in addition to highlighting the importance of the dead time for the processing of Brewer data sets, also provides useful information for their quality control and re-evaluation.

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Section: Introductionmentioning

confidence: 99%

Dead time effect on the Brewer measurements: correction and estimated uncertainties

et al. 2016

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“…Using the measurements of the Brewer, the irradiance scale is transfered to working standards, which are used for the calibration of the Brewer every 6 weeks. The procedure is described in more detail in Mäkelä et al (2016) and Lakkala et al (2008).…”

Section: Uv Spectroradiometer Calibrationsmentioning

confidence: 99%

“…The second Brewer is a double monochromator with a wavelength range from 290 to 365 nm. The Brewer time series is one of the longest homogenized time series measured in the Arctic (Lakkala et al, 2003(Lakkala et al, , 2008.…”

Section: Introductionmentioning

confidence: 99%

Optical laboratory facilities at the Finnish Meteorological Institute – Arctic Research Centre

Lakkala

Suokanerva

Karhu

et al. 2016

Geosci. Instrum. Method. Data Syst.

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Abstract. This paper describes the laboratory facilities at the Finnish Meteorological Institute -Arctic Research Centre (FMI-ARC, http://fmiarc.fmi.fi). They comprise an optical laboratory, a facility for biological studies, and an office. A dark room has been built, in which an optical table and a fixed lamp test system are set up, and the electronics allow high-precision adjustment of the current. The Brewer spectroradiometer, NILU-UV multifilter radiometer, and Analytical Spectral Devices (ASD) spectroradiometer of the FMI-ARC are regularly calibrated or checked for stability in the laboratory. The facilities are ideal for responding to the needs of international multidisciplinary research, giving the possibility to calibrate and characterize the research instruments as well as handle and store samples.

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“…A review of the literature shows that the methods and algorithms differ amongst the stations maintaining spectrophotometers for measurements of solar spectral UV irradiance (Lam et al, 2002;Kazadzis et al, 2005;Garane et al, 2006, Lakkala et al, 2008Simic et al, 2008;Schneider et al, 2008;Ialongo et al, 2008;Sabburg et al, 2001;Damiani et al, 2012). The measurements with Brewer #037 and Brewer #107 spectrophotometers at Sodankylä and Jokioinen respectively have followed the WMO recommendations, with stability checks every 3-4 weeks and measurements of standard lamps in laboratory (darkroom) every 6-8 weeks.…”

Section: Introductionmentioning

confidence: 99%

In search of traceability: two decades of calibrated Brewer UV measurements in Sodankylä and Jokioinen

Heikkilä

Mäkelä

Lakkala

et al. 2016

Geosci. Instrum. Method. Data Syst.

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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.

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Quality assurance of the Brewer spectral UV measurements in Finland

Cited by 58 publications

References 42 publications

Dead time effect on the Brewer measurements: correction and estimated uncertainties

Dead time effect on the Brewer measurements: correction and estimated uncertainties

Optical laboratory facilities at the Finnish Meteorological Institute – Arctic Research Centre

In search of traceability: two decades of calibrated Brewer UV measurements in Sodankylä and Jokioinen

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