Intercomparison of indoor and outdoor spectral irradiance measurements between INTI and INMETRO

We report methodology and results for indoor and outdoor intercomparison of spectral irradiance measurements by Argentinian and Brazilian national metrology institutes traced to metrological standards following independent traceability chains. A group of standard lamps, measured between 250 and 1100 nm using characterized spectroradiometers and calibrated reference standards, resulted in a bilateral degree of equivalence (DoE) better than 0.5% in visible, 0.75% in infrared, and 3.7% in ultraviolet (UV), all within calibration uncertainties. Simultaneous measurement of UV solar spectral irradiance with both spectroradiometers traced to the same reference lamp resulted in DoE better than 5.4% and 5.9% (within uncertainties) for global and diffuse incidence in the UVA range. Total UV solar irradiance computed from integration over spectral measurements agrees within the criterion of normalized error smaller than one.