Ratio spectra as a quality control tool for solar spectral UV measurements

Spectra sampled by a UV spectroradiometer throughout the day are ratioed against a reference spectrum from the same instrument, typically the spectrum obtained at noon. The resultant ratios are a useful quality control tool that allows the detection of errors in the data acquisition of the instrument and shifts in its wavelength calibration. The method was applied to measurements of two high-quality spectroradiometers during the SUSPEN 1997 UV spectroradiometer intercomparison. Thus the wavelength calibration of both instruments was found to be stable to within ¤0.01 nm. In both instruments, deficiencies were identified by this method, enabling remedial action to be taken.