title: Ground-level solar spectral irradiance in Glasgow: an inter-comparison of two sites.
abstract: BACKGROUND
  Solar spectral radiometry presents significant challenges to produce accurate and reproducible data. To investigate the reliability of the measurements, several inter-comparisons have been set up. Although these are useful, their main drawback is that equipment must be dismantled and transported to a common site and re-calibrated.
  
  
  METHODS
  In this study, an inter-comparison has been performed of two spectroradiometers that are located 3 miles apart some 30 m above sea level. These two systems have operated using different calibration techniques. Data were compared on clear days, to minimise actual differences in ultraviolet irradiation.
  
  
  RESULTS
  There were substantial differences at some individual wavelength points, but overall the mean difference of results at 5 nm intervals on an individual scan from the two systems agreed to within 11%. If the data were used to compute the erythemal irradiance, the differences were reduced to 4%.
  
  
  CONCLUSIONS
  This study demonstrates both the limitations and the level of reliability that might be expected from these systems operating under careful scientific supervision.
authors.affiliation: The Photobiology Unit, University of Dundee, Ninewells Hospital & Medical School, Dundee DD1 9SY, Scotland, UK. H.Moseley@dundee.ac.uk
authors.forename: H
authors.initials: H
authors.lastname: Moseley
authors.forename: I
authors.initials: I
authors.lastname: Clark
authors.forename: A
authors.initials: A
authors.lastname: Pearson
authors.forename: J
authors.initials: J
authors.lastname: Smyth
authors.forename: H
authors.initials: H
authors.lastname: Oliver
authors.forename: R M
authors.initials: RM
authors.lastname: Mackie
mesh_terms: D005843:Geography; D006801:Humans; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D012606:Scotland; D012621:Seasons; D013472:Sunlight; D014466:Ultraviolet Rays