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 (Ͻ5%) 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%.

Measuring the influence of aerosols and albedo on sky polarization

“…The method has been validated against a well-characterized spectroradiometer with a scanning polarized radiance optics (Blumthaler et al, 2008). More than 20 ° away from overexposed pixels around the sun the agreement of П was within 0.03, which agrees with the statistical error inferred from consecutive measurements under constant conditions.…”

Technical Note: A new discrete ordinate first-order rotational Raman scattering radiative transfer model – implementation and first results

“…If not otherwise noted, all calculations were performed with 16 streams, or N = 8. Strongly peaked phase functions are handled with an improved version of the Nakajima and Tanaka (1988) correction method (Buras et al, 2011).…”

“…The solution of Eq. (5) including the RRS source term Q(τ λ ,µ i ) has been included in the new C-version of the DISORT Stamnes et al (1988)) algorithm (Buras et al, 2011). This algorithm has been adopted in the libRadtran radiative transfer package (Mayer and Kylling, 2005) to solve Eq.…”

“…The spectra for the aerosol case were measured with a Bentham DTM300 double monochromator spectroradiometer (Blumthaler et al, 2008). For these measurements the instrument was equipped with gratings with 2400 lines per mm, resulting in a slit width of 0.48 nm (FWHM).…”

“…The model is based on a recent re-write (Buras et al, 2011) of the discrete-ordinate-method radiative transfer algorithm (DIS-ORT, Stamnes et al, 1988). The main difference between this work and the discrete-ordinate model of Spurr et al (2008) is in the solution of the particular integrals for the Raman scattering gain and loss terms.…”