Point spread functions for mapping artificial night sky luminance over large territories

Knowledge of the night sky radiance over a large region may be valuable information for identifying sites suitable for astronomical observations or for assessing the impact of artificial light at night on ecosystems. Measuring the sky radiance can be a complex endeavour, depending on the desired temporal and spatial resolution. Likewise, the modelling of artificial night sky radiance for multiple points of a region can represent a significant amount of computing time depending on the complexity of the model used. The use of the convolution of a point spread function with the geographical distribution of light sources has been suggested in order to model the sky radiance over large territories of hundreds of kilometres in size. We determined how the point spread function is sensitive to the main driving parameters of the artificial night sky radiance, such as the wavelength, the ground reflectance, the obstacle properties, the upward light output ratio, and the aerosol optical depth using the Illumina v2 model. The obtained functions were then used to model the artificial night sky brightness of the Mont-Mégantic International Dark Sky Reserve for winter and summer conditions. The results were compared with the New World Atlas of artificial night sky brightness, the Illumina v2 model, and in situ Sky Quality Camera measurements. We found that the New World Atlas overestimates the artificial sky brightness by 55 per cent, whereas the Illumina model underestimates it by 48 per cent. This may be due to varying atmospheric conditions and the fact that the model accounts only for public light sources.