http://arxiv.org/abs/1807.10593
Artificial light at night has affected most of the natural nocturnal landscapes worldwide and the subsequent light pollution has diverse effects on flora, fauna and human well-being. To evaluate the environmental impacts of light pollution, it is crucial to understand both the natural and artificial components of light at night under all weather conditions. The night sky brightness for clear skies is relatively well understood and a reference point for a lower limit is defined. However, no such reference point exists for cloudy skies. While some studies have examined the brightening of the night sky by clouds in urban areas, the published data on the (natural) darkening by clouds is very sparse. Knowledge of reference points for the illumination of natural nocturnal environments however, is essential for experimental design and ecological modeling to assess the impacts of light pollution. Here we use differential all-sky photometry with a commercial digital camera to set an upper limit on the illumination of overcast sites without light pollution. We investigate how clouds alter the sky brightness and color temperature at two rural sites. The spatially resolved data enables us to identify and study the nearly unpolluted parts of the sky, even in a non-ideal scenario. We observe cloud attenuation and red shift not only at zenith, but for most parts of the sky, reducing luminance and illuminance levels for overcast conditions. Our results represent a first step towards finding a reference point for cloudy skies in unlit areas within the context of ecological light pollution.
A. Jechow, F. Hölker and C. Kyba
Mon, 30 Jul 18
20/49
Comments: 16 pages, 6 figures
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