Abstract
Abstract. The quality assurance of the two Brewer spectrophotometers of the Finnish Meteorological Institute is discussed in this paper. The complete data processing chain from raw signal to high quality spectra is presented. The quality assurance includes daily maintenance, laboratory characterizations, calculation of long-term spectral responsivity, data processing and quality assessment. The cosine correction of the measurements is based on a new method, and is included in the data processing software. The results showed that the actual cosine correction factor of the two Finnish Brewers can vary between 1.08–1.13 and 1.08–1.12, respectively, depending on the sky radiance distribution and wavelength. The temperature characterization showed a linear temperature dependence between the instruments' internal temperature and the photon counts per cycle, and a temperature correction was used for correcting the measurements. The long-term spectral responsivity was calculated using the time series of several lamps using two slightly different methods. The long-term spectral responsivity was scaled to the irradiance scale of the Helsinki University of Technology (HUT) for the whole of the measurement time-periods 1990–2006 and 1995–2006 for Sodankylä and Jokioinen, respectively. Both Brewers have participated in many international spectroradiometer comparisons, and have shown good stability. The differences between the Brewers and the portable reference spectroradiometer QASUME have been within 5% during 2002–2007.
Highlights
Many spectral UV measurement programs started at the end of the 1980s, after it was recognized that the stratospheric ozone content was declining over Antarctica and over the Arctic and in mid-latitudes (Booth et al, 1992; WMO, 1990)
Since the early 90’s, spectral UV radiation has been measured with the Brewer spectrophotometers #037 and #107 at two sites in Finland
Special attention has been paid to the quality of these measurements, and a comprehensive quality assurance scheme has been developed
Summary
Many spectral UV measurement programs started at the end of the 1980s, after it was recognized that the stratospheric ozone content was declining over Antarctica and over the Arctic and in mid-latitudes (Booth et al, 1992; WMO, 1990). We present the complete data processing of the FMI’s Brewer spectrophotometers from raw signal to quality-controlled UV spectra. This includes a new way of processing the spectral responsivity time series and correcting for temperature dependence and cosine error. Previous papers about the complete data processing procedure of spectral UV measurements have been published for the SUVtype spectroradiometers of the National Science Foundation (NSF) network (Booth et al, 2001; Bernhard et al, 2004) and for the two Brewer spectrophotometers of the Aristotle University of Greece in Thessaloniki (Garane et al, 2006)
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