Ground-level solar spectral irradiance in Glasgow: an inter-comparison of two sites

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.

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.

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%.

This study demonstrates both the limitations and the level of reliability that might be expected from these systems operating under careful scientific supervision.