Spectral UV Measurements of Global Irradiance, Solar Radiance, and Actinic Flux in New Zealand: Intercomparison between Instruments and Model Calculations

Abstract

Presented here are the results of a short but intense measurement campaign at Lauder, New Zealand, in which spectral irradiance from instruments operated by the National Institute of Water and Atmospheric Research (NIWA) and Austria/Innsbruck (ATI) were traced to different irradiance standards and compared. The observed spectral differences for global irradiance were relatively small (<5%) and were consistent with those expected from observed differences in the radiation standards used by each group. Actinic fluxes measured by both groups were also intercompared and found to agree at the 10% level. The ATI instrument had the additional capability of measuring solar direct beam irradiance and sky radiances. These provided the first series of sky radiance measurements at this pristine Network for the Detection of Atmospheric Composition Change (NDACC) site. The polarization of sky radiance results were compared with estimates from a radiative transfer model without any aerosols and was found to be up to 25% smaller. Total ozone values derived from Total Ozone Mapping Spectrometer (TOMS), Dobson measurements by NIWA, spectral direct sun measurements by ATI, and spectral global irradiance measurements by NIWA agreed generally within 2%?3%.