International Intercomparison of Solar UVR Spectral Measurement Systems in Melbourne in 2013

Monitoring ambient solar UVR levels provides information on how much there is in both real time and historically. Quality assurance of ambient measurements of solar UVR is critical to ensuring accuracy and stability and this can be achieved by regular intercomparisons of spectral measurement systems with those of other organizations. In October and November of 2013 a solar UVR spectroradiometer from Public Health England (PHE) was brought to Melbourne for a campaign of intercomparisons with a new Bentham spectrometer of Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) and one at the Australian Bureau of Meteorology (BOM), supported by New Zealand's National Institute for Water and Atmosphere (NIWA). Given all three spectroradiometers have calibrations that are traceable to various national standards, the intercomparison provides a chance to determine measurement uncertainties and traceability that support UV measurement networks in Australia, New Zealand and the UK. UV Index measurements from all three systems were compared and ratios determined for clear sky conditions when the scans from each instrument were within 2 min of each other. While wavelengths below 305 nm showed substantial differences between the PHE unit and the two other systems, overall the intercomparison results were encouraging, with mean differences in measured UV Index between the BOM/NIWA and those of PHE and ARPANSA of <0.1% and 7.5%, respectively.