Fabrication, Calibration, and Deployment of a Custom-Built Radiometer

Abstract. A custom-built spectroradiometric system was developed to measure spectral actinic flux for atmospheric photochemistry. The radiometer incorporates a UV-enhanced fibre optic cable, a compact CCD spectrograph, and an interchangeable polytetrafluoroethylene (PTFE) receiver head. Five receiver designs (domes, cones, and flat tops) were fabricated and evaluated for angular response and wavelength-dependent efficiency using collimated UV and visible LEDs. The variable cone design showed the most uniform angular sensitivity, minimizing the need for post-processing corrections. Wavelength calibration was conducted using emission LEDs from 265 to 523 nm, and the full system response was characterized from 196 to 888 nm. The system was evaluated in a controlled atmospheric chamber and in outdoor field conditions. Under clear skies, outdoor testing validated the radiometer’s effectiveness in measuring photon fluxes with an 11.2 % uncertainty. These photon fluxes were used to calculate photolysis rate constants (J-values) with an uncertainty of 15.3 % for both NO₂ and O₃. Although not fully cosine-corrected, the radiometer demonstrated sufficient stability and repeatability for deployment in research settings, particularly where commercial instruments are unavailable. This study establishes a low-cost, customizable tool for actinic flux measurements in support of atmospheric photochemistry.